Eunorau SPECTER-S 4.0 Review: 1,000 W, 45 Miles

83.7 lb · 26 × 4.0 Kenda tires · Bafang G510 (M620) 1,000 W mid-drive · 140 mm fork, 50 mm rear travel · SRAM NX 11-speed · 840 Wh · Class 2 default, 28 mph display limit · 300 lb payload · 16" or 18" frame · $3,799 · verified October 2, 2026

Quick Answer: The Eunorau SPECTER-S 4.0, sold as the Hunter X9, is a $3,799 full-suspension fat-tire e-bike on Bafang's 1,000 W G510 mid-drive, with SRAM NX eleven-speed gearing, a 140 mm fork, a rack and fenders, at 83.7 lb. Ridden on the throttle alone, a 180 lb rider gets about 45 miles from a charge at 15 mph on level pavement.

It replaces the 3.0 on Eunorau's US page, 4.5 lb lighter with the rack and fenders now fitted (what changed). Settle the frame by inseam first: Eunorau's printed saddle heights suit inseams up to about 30 inches (the fit section). On public roads and paths, its 1,000 W motor and throttle sit inside 4 of 51 jurisdictions' e-bike definitions on October 2, 2026 (the law section).

What's on this page

Twenty-seven sections: who the 4.0 suits, what changed from the 3.0, its motor, suspension, parts and frames, Eunorau's other bikes with a rear shock, the range and payload, your fit, the law at 20 and at 28 mph, ownership, and the verdict.

• Who the SPECTER-S 4.0 is for
• How we verified this Eunorau SPECTER-S 4.0 review
• Eunorau SPECTER-S 4.0 specifications
• SPECTER-S 4.0 or the 3.0: what changed
• The Bafang G510 mid-drive and a thumb throttle
• A 140 mm fork and 50 mm of rear travel
• Eleven SRAM gears, four-piston brakes and the display
• Two frames, the rack and the 5 Ah option
• SPECTER-S 4.0 or another Eunorau with a rear shock
• How far the SPECTER-S 4.0 goes on one charge
• What the 300 lb payload covers
• Will the SPECTER-S 4.0 fit you?
• The Mercer fit test
• What the law calls it: 1,000 W, a throttle and 20 mph
• The 28 mph display limit
• Charging and battery care
• Where Eunorau prints a figure two ways
• Recall and warning record
• Warranty, and who handles a claim
• Buying it from us
• The honest ledger
• Who should buy it
• Before you buy: the checklist
• Limitations of this review
• The source register
• Frequently asked questions
• The bottom line

Who the SPECTER-S 4.0 is for

The Moon Black as Eunorau photographed it, set on a light studio backdrop made for this card. Eunorau prints the $3,799 and the 1,000 W G510; the 45 miles come from the range section.

The SPECTER-S 4.0 is built for ground that changes under you: a logging road to a stand of timber, a two-track across a ranch, a washed-out climb to a fishing access, a gravel shoulder home. Eunorau titles it a "Hunting Fat Tire Bike" and describes "a full-suspension platform built for changing terrain" and "confident exploration beyond smooth pavement" (Eunorau's SPECTER-S 4.0 page).

Moon Black from the drive side, in Eunorau's studio photograph. Under the studio lights the finish reads blue-gray, with the rack and fenders fitted.

What sets it apart is where the motor sits: in the middle of the frame, turning the chainring, so the SRAM eleven-speed gears its power the way they gear your legs. On a long climb you shift down and the motor keeps spinning briskly while the rear wheel crawls; on the flat you shift up and it settles.

The rest of the bike matches that ground. A 140 mm fork and a rear shock keep the 4.0-inch tires on broken surfaces, four-piston brakes stop 83.7 lb plus your load, and the rack Eunorau now fits is, in its words, "a practical carrying platform for compatible bags and cargo accessories" (its feature rows).

Want the same motor with a frame you step through? Our SPECTER-ST 2.0 review covers it at $2,999. Want two hubs driving both wheels? Our DEFENDER-S 2.0 review covers the dual-motor bike at $2,799.

How we verified this Eunorau SPECTER-S 4.0 review

Every specification is Eunorau's, read from the SPECTER-S 4.0 page and its product record on October 2, 2026, and every figure that needs arithmetic is recomputed here. When two of Eunorau's own sources disagree, the conflicts table prints both figures side by side.

Both models end in a subsection that shows the formula and lists each input (range, fit). Every one of the 51 jurisdictions is screened at both of Eunorau's speeds, and each read carries its date in the Limitations. We sell the SPECTER-S 4.0, and the honest ledger sends each rider it suits less well to another of our bikes. Milad Ghobadibeygvand, BScN (Western University, 2014), wrote it; send corrections to corrections@redtailebikes.com.

Eunorau SPECTER-S 4.0 specifications

Eunorau's own figures, from the SPECTER-S 4.0 page read October 2, 2026:

The geometry table on the SPECTER-S 4.0 page, both frames:

Read from the SPECTER-S 4.0 page on October 2, 2026; the inch figures are Eunorau's. The saddle heights run from the crank axle (the fit section).

SPECTER-S 4.0 or the 3.0: what changed

Eunorau's US page for the Hunter X9 described the SPECTER-S 3.0 on August 31, 2026 and the 4.0 on October 2, 2026, at the same address. The motor family, the 1,000 W rating, the 140 mm of fork travel, the SRAM NX drivetrain and the 300 lb payload carry over; the frame sizes, the weight, the speed setting, the shock, the display and what comes in the box changed.

The 3.0 column is Eunorau's page as the Internet Archive captured it on August 31, 2026; the 4.0 column is the same page read October 2, 2026.

The motor name changed, and the motor family did not. Eunorau's 3.0 copy called it "the Bafang G510(M620) motor", and Bafang's 2021 OEM workbook files the M620 under the model codes "MM G510.750.C / MM G510.1000.C".

Want the 3.0's extras on a 4.0? Eunorau lists the 27.5 × 3 wheel set "For SPECTER-S" at $399 and its single-speed conversion kit at $199 among the 4.0's accessories (Eunorau's page).

Moon Black from the left, as Eunorau photographed it: the rotors, the side stand and the rear rack over its fender.

The Bafang G510 mid-drive and a thumb throttle

A 48 V, 1,000 W Bafang G510 sits at the bottom bracket and turns the 40-tooth chainring, so its power reaches the rear wheel through the same eleven gears as yours (Eunorau's specification). Eunorau's copy: the motor "can work with the selected gear, giving the rider more control over how power is delivered as the terrain changes".

The drive unit, chainring and crank, cropped from Eunorau's drive-side photograph of the Moon Black; the rear shock stands above them under its rocker link.

On the throttle alone, the modeled motor holds 22.6 mph up a 4% grade, 17.0 up 8% and 11.0 up 15% with 180 lb aboard (the climb table). Bafang's workbook rates the 1,000 W version at 160 N·m and 180 rpm at the chainring, and the low cogs of the 11–42T cassette let it keep turning near that speed while the wheel climbs slowly.

A thumb throttle moves the bike without pedaling, and five pedal-assist levels add power while you pedal (Eunorau's rows). A "motor cut-off shift sensor briefly interrupts motor assistance during gear changes", which Eunorau says reduces drivetrain load while you shift.

Ease your pedal pressure as you shift, and the sensor does the same for the motor.

A 140 mm fork and 50 mm of rear travel

An EXPLORER fork with 140 mm of travel on 36 mm stanchions leads, and an AO-38RC shock, 190 mm eye to eye with 50 mm of travel, works the rear wheel (Eunorau's specification). Eunorau's copy says the pair "help the wheels follow uneven terrain and reduce the impact transferred to the rider".

The 26 × 4.0 tires add their own give. Run them softer for sand, snow and loose gravel and firmer on pavement, inside the pressure printed on the sidewall; the tire table shows what the casing costs in range.

The front end, cropped from Eunorau's front three-quarter photograph: the fork, the 180 mm rotor and the Kenda tire.

Eleven SRAM gears, four-piston brakes and the display

You shift SRAM NX 1 × 11 with an NX trigger, over a PG-1130 11–42T cassette and a long-cage derailleur, on a KMC e11 Sport chain (Eunorau's specification). Eunorau's copy: "The wide gear range helps riders prepare for climbs, settle into a cruising cadence, and respond to changing gradients."

The cassette and long-cage derailleur, cropped from Eunorau's drive-side photograph.

HD-E620 four-piston hydraulic brakes stop both wheels on 180 mm rotors, which Eunorau calls "controlled stopping performance". With 83.7 lb of bike and up to 300 lb aboard, bed the pads in on a quiet road before the first steep descent.

The rest, as Eunorau lists it:

• The display: a BAFANG DP C018.CB on the bar, on the UART protocol, which Eunorau says "keeps essential riding information and assist controls within easy reach".
• The cockpit: a 700 mm aluminum riser bar with 25 mm of rise, a 90 mm stem and 130 mm dual-lock grips.
• The saddle: the Eunorau Comfort C7 on a 31.6 × 280 mm aluminum post.
• The lights: a headlight that runs on 6 to 48 V, and a rear light with a reflector.
• The rest: an aluminum rack, full aluminum fenders front and rear, platform pedals with reflectors and an adjustable kickstand.

Two frames, the rack and the 5 Ah option

The SPECTER-S 4.0 comes in a 16-inch and an 18-inch frame at the same $3,799, each in Moon Black or Army Green. Eunorau's table separates them by 51 mm of seat tube and 50 mm of saddle height; the wheelbase, reach, stack and top tube are the same.

Army Green from the front three-quarter, in Eunorau's studio photograph: the fork and headlight, the battery case in the down tube and the 4.0-inch tires.

At 83.7 lb and 79.7 inches long (Eunorau's weight row and row K), it needs a hitch rack rated above 83.7 lb per bike with trays for 4.0-inch tires. Lift the 840 Wh pack out of its lockable mount before you load the bike.

The optional 48V 5Ah pack adds 240 Wh, for 1,080 Wh in all, and Eunorau lists it beside the bike as the "EUNORAU 48V5AH Secondary Ebike Battery with Type-C Port" at $219 (Eunorau's page). Its FAQ: "The 48V 5Ah secondary battery is an optional configuration and is included only when that option is specifically offered and selected."

Moon Black from behind on its left side, photographed by Eunorau: the rack and rear light over the fender, the rear rotor and the side stand.

SPECTER-S 4.0 or another Eunorau with a rear shock

Beside five other Eunorau bikes we sell with a fork and a rear shock, the SPECTER-S 4.0 is the only one in this table on 4.0-inch tires with a 1,000 W mid-drive and eleven gears. The others run hub motors, a 500 W mid-drive, nine gears or narrower tires.

Each row comes from that model's page at Eunorau (SPECTER-S 4.0, DEFENDER, DEFENDER-S 2.0, SPECTER-ST 2.0, FAT-HS, URUS 2.0), read September 26 and October 2, 2026; Eunorau prints the FAT-HS at 77.1 lb in its specification and 79.4 lb in its geometry table. Our prices were read October 2, 2026.

Pick the SPECTER-S 4.0 for a 1,000 W mid-drive with eleven gears on 4.0-inch tires, full suspension, and a rack and fenders already on the bike.

Pick the SPECTER-ST 2.0 for the same motor family on a step-through frame, the FAT-HS for a mid-drive on 4.0 tires with a taller saddle range on its 19-inch frame, the DEFENDER-S 2.0 for a motor in each wheel, the DEFENDER for full suspension at the lowest price, and the URUS 2.0 for the lowest weight here. Our Eunorau collection holds all six.

Army Green from behind on its left side, in Eunorau's photograph: the rack and rear light, the rear rotor and the 4.0-inch rear tire.

How far the SPECTER-S 4.0 goes on one charge

From its 840 Wh pack, a 180 lb rider on the throttle covers about 45 miles at 15 mph over level pavement, 53 at 12 mph and 33 at 20 mph. Pedal easily and 15 mph stretches to 67 miles. The optional 48V 5Ah pack raises the total to 1,080 Wh, about 57 miles at 15 mph on the throttle.

Three steps to price your own ride:

1. Read your speed and how hard you pedal off the two speed tables.
2. Add about 128 Wh for each 1,000 feet of climbing, and climb in the large cogs (the gear tables).
3. Adjust for what you weigh with your gear and the day's temperature, then plan on 85% of the result, keeping the top of the 10 to 15% Eunorau's FAQ says to recharge at.

Each row prices one steady ride from Bafang's published M620 figures, the 40T chainring and SRAM 11–42T cassette Eunorau lists, measured drag of everyday riders and a cycling-power model checked on a real road. Every input is listed in the formula subsection, which follows one ride from the rear wheel back to the battery.

How far will it go at the speed I ride?

On the throttle, the speed you hold decides the range more than any other choice. The pack that lasts 45 miles at 15 mph lasts 33 at 20 mph, 26% fewer, and 20 at the 28 mph display limit Eunorau prints. Air resistance is most of the difference: the force grows with the square of your speed, so the power to hold that speed grows with the cube.

Throttle only, level pavement, a 180 lb rider at 77 °F. The planning columns keep 15% of each pack, the top of the 10 to 15% Eunorau's FAQ says to recharge at. The gear is the cog in which the motor spends least at that speed, with the chainring's rpm beside it; "both packs" adds the optional 48V 5Ah pack.

Pedal lightly and the same 840 Wh covers 67 miles at 15 mph instead of 45. On this 83.7 lb bike, 75 watts of your own (an easy effort) would hold about 8 mph with no motor at all, and 150 W about 13 mph.

Miles from the 840 Wh pack, full charge, level pavement, a 180 lb rider. "Legs alone" marks a speed your own watts already hold, so the motor adds nothing; past 100 miles the table stops counting, because stops and wind decide a ride that long. At 28 mph the 11T needs 90 rpm at the cranks, the most this model asks of a pedaling rider.

The two pedaling columns follow the watts you put in, whichever of the five assist levels you select: the level sets how much the controller adds, and the row for your speed and your effort is your range.

Army Green from the drive side, as Eunorau photographed it. Both colors carry the same 840 Wh pack in the down tube, the one every row above is priced from.

Which gear saves battery?

On level ground, a middle cog: at 15 mph the 15T costs least, and the dearest gear the motor can turn costs 21% more. On a climb, shift to the large cogs: at 8 mph up an 8% grade the 42T costs 67 Wh a mile against 120 in the 11T.

The G510 drives the chainring, so the cog you pick sets the motor's own speed. Bafang's workbook rates the 1,000 W version at 180 rpm, far above a rider's cadence, and on a light load the motor wastes least at the lower chainring speeds a 15T or 17T gives. From 20 mph up, every cog it can turn sits within 8% of the cheapest.

Level pavement, a 180 lb rider, throttle only. Each cog is named by its teeth, the 42T the largest and easiest and the 11T the smallest and hardest. A cog is left out where its chainring would have to turn faster than the motor's no-load speed.

On a hill the order flips. Holding 8 mph up an 8% grade costs 120 Wh a mile in the 11T and 67 in the 42T, so the hard gear spends 78% more on the same climb. Pedaling easily, the 36T is cheapest at 56 Wh a mile, and the 42T would ask your legs for 98 rpm.

8 mph, a 180 lb rider; each cell is the cost per mile and the miles the 840 Wh pack gives at that cost. "Past 90 rpm" marks a cog that needs more cadence than the model allows, after Hansen and colleagues, whose riders chose 72.4 rpm freely and called 90 rpm "relatively high".

How much do hills cost, and how steep a climb will it hold?

Every 1,000 feet you climb costs about 128 Wh beyond the same distance on the flat. Raising 263.7 lb (a 180 lb rider plus the 83.7 lb bike) through 1,000 feet takes 99 Wh at the wheel, and the chain, the motor and the pack's own losses add the rest.

Spent on climbing alone, the 840 Wh pack would lift that rider about 6,500 feet, and with the 5 Ah pack fitted about 8,400.

A 180 lb rider. The first two columns are the fastest steady speed the motor holds at its rated 1,000 W: on a 10% grade, 14.9 mph on the throttle and 15.8 pedaling easily. The last column spends the whole 840 Wh pack on that grade at 8 mph.

Price a hilly ride as its level miles plus its climbing. Twenty miles at 15 mph on the throttle take about 376 Wh; 2,000 feet of climbing adds about 257, for 633 Wh, inside the 714 Wh you can use while keeping Eunorau's 15%. Stops, starts and wind come on top of every steady figure here.

Eunorau's FAQ names the MAX-CARGO and the JUMBO as the models that charge from pedaling, so on the SPECTER-S 4.0 a descent puts nothing back in the pack. Our JUMBO review covers that stand-up scooter.

Does my weight change the range?

On the flat a little, and on a climb a great deal. From a 130 lb rider to Eunorau's 300 lb limit, 15 mph on the throttle falls from 49 miles to 37, while an 8% climb at 8 mph pedaling easily falls from 19 miles to 10.

You and everything you carry; the bike's own 83.7 lb sits in every row. Eunorau's payload row counts rider and cargo together, and the 300 lb row is that limit.

In Martin's power model, weight adds to what the tires and the slope cost and nothing to what the air costs, which is why the 15 mph column gives up about a quarter of its miles across the table and the climbing column about half.

Does cold weather drain the battery?

Yes, so plan from the row nearest the day's temperature. At freezing, 15 mph pedaling easily falls from 67 miles to 50, a quarter fewer. Eunorau names LG cells, "LG 3500mAh, 13S5P", so the central line is McMaster University's measured LG HG2 cell, with brackets from Samsung's data sheets and Casado and colleagues' cold tests.

The pack's usable energy against 77 °F, and the miles a full 840 Wh pack gives on level pavement for a 180 lb rider. The central figure is the HG2 at a 0.5C discharge; the brackets run from the lowest capacity Samsung's sheets print at that temperature to the highest energy measured at a gentler rate. The model sets the cells at the air temperature.

Three losses stack at 32 °F: the pack gives about 89% of its 77 °F energy, the air is 9% denser, and the tires roll 18% harder. At 95 °F the range edges up, because thinner air and warmer rubber outweigh the 1% the cells lose.

Bring the pack indoors on a cold night. Eunorau's pack lifts out of the down tube on its lockable mount, so a warm pack can start the ride.

Do the 4-inch tires cut range?

They cost range, and the model prices them at the slow end of measured fat-bike casings. Eunorau lists the "Kenda K-1151, 26 × 4.0 inches", Kenda's Juggernaut, and the sidewall in its photographs reads "30 TPI CASING WIRE BEAD". Bicycle Rolling Resistance measured the Juggernaut Pro, the slowest of its twelve fat-bike casings, and the model uses that figure; no lab or field figure for the 30 TPI wire-bead version was found.

Miles from the 840 Wh pack, level pavement, a 180 lb rider. The two upper rows are the fastest and the middle of the twelve fat-bike tires on the same drum, so a faster-rolling 26 × 4.0 casing would land between them and the row used.

Pressure and the road move your figure along these rows as much as the tread does. The model also takes the drag of a rider upright on flat bars; sit up like the cruiser riders in the same survey and 20 mph on the throttle gives 31 miles in place of 33.

Eunorau's 40 miles, as a ride

Eunorau rates the SPECTER-S 4.0 at "Up to 40 miles" on its pack, and the model finds the ride that earns it: 840 Wh over 40 miles is 21.0 Wh a mile, a steady 17.0 mph on the throttle or 20.3 mph pedaling easily, on level pavement.

Its "Up to 52 mi / 83 km combined*" adds the optional 5 Ah pack (Eunorau's specification): 1,080 Wh over 52 miles is 20.8 Wh a mile, the same kind of ride.

The steady speed on level pavement at which each figure's watt-hours, spread over its miles, match the model's cost per mile, for a 180 lb rider at 77 °F with every watt-hour used.

Planned with Eunorau's 15% kept, the 840 Wh pack gives 38 miles at 15 mph on the throttle and 57 pedaling easily. For a check from outside, Electrek's 2021 review of an earlier Spectre S, with a 48v 14ah pack, reports the display at 80% "after about three miles of rough terrain"; it prints no speed, effort or climb for those miles, so no cost per mile is drawn from it.

How the range tables are computed

To hold any speed, the rear wheel needs power flowing to it without a break. Martin and colleagues' model, checked against riders on a real road in 1998, gives it in still air:

Power at the wheel = v × [ m × g × (Crr × cos θ + sin θ) + ½ × ρ × CdA × v² ]

v is your speed, m the mass of you and the bike, g gravity, θ the slope, Crr the tires' rolling resistance (0.0126 means a drag of 1.26% of the weight on them), ρ the air's density and CdA your drag area, frontal size times shape. Tires and slope make up the first term; the air makes up the second.

From the wheel back to the pack:

1. The chain delivers 97.7% of what the motor puts in, the drivetrain figure Martin's model.
2. Your legs supply their watts first and the motor the rest; a pedaling row keeps your cadence at or below 90 rpm.
3. The gear decides how fast the motor spins: chainring rpm = wheel rpm × cog teeth ÷ 40. Bafang's 2021 OEM workbook files the M620 under "MM G510.750.C / MM G510.1000.C" and prints two no-load speeds, 150 and 190 rpm, two rated speeds, 140 and 180, and an efficiency of "≥ 80" percent without pairing the columns; the model takes the 1,000 W pair for Eunorau's 1,000 W motor.
4. The pack loses a little more inside itself, 3.4% at 15 mph, by the battery efficiency Arango, Lopez and Ceren measured on a 48 V mid-drive.

Then watt-hours per mile = pack watts ÷ mph, and miles = 840 Wh × the share of the pack's energy the temperature leaves ÷ watt-hours per mile.

One ride, worked through: 15 mph on level pavement, throttle only, a 180 lb rider. Of the 202.7 W the wheel needs, 99.3 W goes to the tires and 103.3 W to the air; at the chainring that is 207.5 W.

In the 15T, at 65 chainring rpm, the motor model (back-EMF 2.412 N·m per amp, 0.103 Ω winding resistance, 2.519 A no-load current) puts out 30.3 N·m at 76.1% efficiency and draws 272.5 W. The pack's own losses raise that to 282.0 W: at 15 mph, 18.8 Wh a mile, and 840 ÷ 18.8 is 45 miles.

Its first check, before any figure was used: it matches Martin's worked example within a tenth of a watt.

No efficiency measurement of the G510 itself was found, so the 85% at its rated point is the value, above Bafang's 80% floor, at which the model's efficiency surface comes closest to the mid-drive map Arango, Lopez and Ceren measured: within 5.2 points at its seven readings, where the floor misses by 14.2.

At the floor the 15 mph throttle ride gives 41 miles in place of 45, and Bafang's other printed pair, 150 and 140 rpm at 750 W, gives 44.

What the 300 lb payload covers

Eunorau rates the SPECTER-S 4.0 for a "Maximum payload" of "300 lb / 136 kg, including rider and cargo" (its specification). The 300 lb covers your body and all your gear; the 83.7 lb of bike is not counted in it.

Take a 200 lb hunter with a 45 lb pack on the rack and a 15 lb rifle case, 260 lb in all, inside the rating with 40 lb to spare. At 15 mph on the throttle the weight table puts a 300 lb load at about 37 miles per pack on the flat (the weight table), and the climbing rows fall faster than the flat ones.

Put your loaded pack on a bathroom scale before opening day, and keep rider, pack and anything bolted to the rack under Eunorau's 300 lb. For a load that rides behind the bike, Eunorau lists its hunting trailers and a cargo trailer among the 4.0's compatible accessories; we stock the hunting trailer at $442.80, the two-wheel hunting trailer at $394.80 and the one-wheel cargo trailer at $394.80.

Will the SPECTER-S 4.0 fit you?

Measure your barefoot inseam before you choose a frame: at Eunorau's printed saddle heights, the 18-inch frame reaches the fit formula's height for inseams up to about 30.0 inches, and the 16-inch for inseams up to about 28.2. Set a little lower, at 106% of inseam, the 18-inch serves inseams to about 30.8 inches and the 16-inch to about 29.0.

Measured on Eunorau's photograph of the 18-inch frame, its top tube stands 30.6 inches up where you straddle it at a stop. On that frame the median rider leans 27 to 28 degrees toward the grips from 5'0" to 5'4", and with a relaxed back the hands carry about a fifth of body weight.

Every row comes from the 6,068 bodies in the US Army's anthropometric survey, with the saddle 109% of inseam above the pedal axle, on the 18-inch frame as Eunorau photographed it and the 16-inch on Eunorau's printed 16-inch saddle range.

Your frame in three steps:

1. Measure your inseam barefoot. Back to a wall, slide a hardcover book up between your legs until it presses like a saddle, then measure floor to the book's top edge.
2. Find your height in both saddle tables, and check that your inseam sits inside that row's range; a longer inseam reads like the row above.
3. Check that your inseam sits inside the frame's reach, and set the saddle on arrival with the knee and heel checks near the end of this section.

Eunorau prints a rider window for the 16-inch frame, "Recommended rider height 160–190cm/5'3"–6'3"", and a dash for the 18-inch, on the SPECTER-S 4.0 page. Its frame-size guide places a 16-inch frame in its 5'2"–5'6" row and an 18-inch in its 5'6"–5'10" row.

The tables below follow inseam at Eunorau's printed saddle heights, and above about 5'2" they part from both windows.

How high should the saddle go?

A saddle 109% of your inseam above the pedal axle is the target; the 18-inch frame's printed range reaches it for 95 of 100 riders at 5'0", 69 at 5'2" and 25 at 5'4". Published practice runs from 106% to 110.4% of inseam (Ferrer-Roca et al., 2012), and 109% is the figure Peveler and colleagues measured against knee angle in trained cyclists.

Eunorau prints "Saddle height 490–610mm/19.3–24in" for the 16-inch frame and "540–660mm/21.3–26in" for the 18-inch. Those figures run from the crank axle to the saddle's top: its photograph of the 18-inch frame shows the saddle 621 mm from the crank axle, inside the 18 range, while 19.3 inches off the ground would sit below the 14.2-inch bracket plus any seat post.

Along the seat post's measured 72.1-degree line, the 18-inch range Eunorau prints puts the saddle top 34.8 to 39.3 inches off the ground, and the 16-inch range 32.9 to 37.4.

The ground-to-saddle height the 109% formula gives the median rider at each height, and how many riders of 100 at that height can set it inside the 18-inch frame's printed 34.8 to 39.3 inches, at 109% and at 106%. ANSUR II bodies, women and men pooled, on Eunorau's 170 mm cranks.

The same rows on the 16-inch frame's printed range, 32.9 to 37.4 inches off the ground.

Where the 18-inch range runs out, the saddle sits a median 0.9 inches below the formula at 5'4", 1.8 at 5'6" and 2.8 at 5'8". At 106% it still covers 64 of 100 riders at 5'4" and 19 at 5'6".

If your inseam runs past the 18-inch frame's 30.8 inches, email it to us before you order: we run it against both frames, and against the FAT-HS, whose 19-inch saddle range reaches the formula for 66 of 100 riders at 5'8".

Can I put a foot down at a stop?

On the 18-inch frame, 45 of 100 riders at 5'4" clear the top tube barefoot, 87 at 5'6" and 99 at 5'8". With no standover in Eunorau's table, the top tube's upper edge is read on its 18-inch photograph, 2 inches in front of the saddle's nose: 30.6 inches off the ground.

Of 100 riders at each height, the number who clear the 18-inch top tube, 30.6 inches up, barefoot. Shoes add a little height; a rider who falls short leans the bike over to put a foot down.

The 16-inch frame's top tube is not measured here. Eunorau's table gives the two frames the same top tube, stack and reach and a seat tube 51 mm shorter on the 16, and its photographs show the 18-inch only, so no standover is printed for the smaller frame.

Eunorau's lettered drawing from its SPECTER-S 4.0 gallery; the figure for each letter is in the geometry table. Its I line rises from the axle line to the top tube and its B line starts above the saddle's nose, so neither is the stack or reach a bike shop would measure.

Will I feel cramped, or stretched out?

Expect a trail lean: on the 18-inch frame the median rider tips 28 degrees from vertical at 5'0", 27 at 5'4" and 23 at 5'8" to reach the grips. On Eunorau's photograph the grips sit 24.3 to 25.7 inches ahead of the crank axle and 32.1 to 34.1 inches above it, through the 90 mm stem and 700 mm riser bar Eunorau lists.

The median rider's trunk angle from vertical on the 18-inch frame as Eunorau photographed it: the least lean at which a straight arm reaches the grips from the sit bones, spanned across where you might sit and grip.

On the 16-inch frame the saddle sits lower for the same rider, so the reach eases: the model puts the median rider at 27 degrees at 5'0" and 23 at 5'4". Eunorau's 16-inch table prints the same 457 mm reach and 618 mm stack as the 18-inch, so both frames use the photographed cockpit.

How much weight goes on my hands?

With a relaxed back, the median rider's hands carry about 19% of body weight on the 18-inch frame from 5'0" to 5'4", and 17% at 5'8". For comparison, ten road racers on the brake hoods put 15% of their weight on the stem (Carahalios, 2015).

The share of body weight on the grips, back relaxed, on the 18-inch frame, worked from each body's segment weights (Clauser et al., 1969); the span runs across the sit zone and the grip's length, and the weight column is the survey's median at each height.

A trunk you hold up yourself takes some of that off, so read each row as the upper figure. On the 16-inch frame the model gives 19% at 5'0" and 17% at 5'4". On a long day in the woods, padded gloves help: across 36 experienced cyclists they cut pressure over the ulnar nerve by 10 to 28% (Slane et al., 2011).

How do I set the saddle when it arrives?

The target is 25 to 35 degrees of knee bend at the bottom of the pedal stroke (Peveler et al., 2007). The heel check gets you there fastest: rest your heel on the low pedal and raise the saddle until that leg just straightens. Among 19 trained cyclists it landed 70% inside that knee range, better than either inseam formula (Peveler et al., 2005).

Hold the bike upright, open the seat-post clamp, set the height by the heel check, and close the clamp firmly before you ride. Stay inside the height range Eunorau prints for your frame.

How we computed fit

Three rules build every fit row: the saddle sits 1.09 inseams above the pedal axle, the lean is the smallest trunk angle at which a straight arm meets the grip, and the hand load is the share of upper-body weight that lean puts on the bar.

A worked case: a rider of 5'8" with a 32.6-inch inseam, the survey's median at that height. From the pedal axle, that rider's saddle sits 35.6 inches up; take off the 170 mm crank and it is 28.9 from the crank axle (LeMond's 88.3% of inseam gives 28.8).

Up this frame's 72.1-degree post from a crank axle 14.0 inches off the ground, that is a saddle top 42.0 inches up, above the 18-inch frame's printed 39.3 and the 16-inch frame's 37.4 (Eunorau's saddle-height row).

The photograph is Eunorau's Moon Black from the drive side, the first image in its gallery. Before any point was read, its scale was checked against Eunorau's table: the rear tire fits a 28.92-inch circle, and the front wheel, turned slightly on the stand, gives its center but not its size.

The scale comes from the 50.2-inch wheelbase, axle center to axle center. The total length, bracket height and the top tube Eunorau's drawing runs level from the seat post's line (its H) land within 1.4%; the seat tube reads 19.0 inches to the top of its clamp ring and 18.0 to the tube's own top, against the 18 column's 18.

The chain stay reads 19.2 inches on the photograph against 16.6 in Eunorau's table, measured where Eunorau's drawing places D, from the rear axle to the crank axle's line; both figures are printed. Eunorau's stack and reach lines sit at other points than a shop's and are not compared.

Across all 6,068 bodies, LeMond's figure plus the 170 mm crank works out to 109.0% of inseam measured from the pedal, against the 109.2 ± 0.9% measured in trained cyclists (Peveler et al., 2005).

The Mercer fit test

Each of our reviews is read against the Mercers, one family of seven, and every verdict here comes from a figure Eunorau prints or from the fit model's row at that member's height.

What the verdicts read: an 18-inch saddle range of 34.8 to 39.3 inches off the ground, 32.9 to 37.4 on the 16-inch, an 18-inch top tube 30.6 inches up, the 300 lb payload Eunorau rates, the 83.7 lb weight, and the law set out in the next section.

For the Mercers the SPECTER-S 4.0 is Ruth's bike if her inseam fits the 18-inch rows; Maya checks hers with us first, and the taller members ride Eunorau's FAT-HS or FAT-HD 1.0 Pro.

What the law calls it: 1,000 W, a throttle and 20 mph

On October 2, 2026, the SPECTER-S 4.0's printed 1,000 W, its throttle and its 20 mph Class 2 default sat inside the e-bike definitions of 4 of 51 jurisdictions. Eunorau's highlight reads "Default Class 2", and its page prints "48V / 1,000W" for the motor (Eunorau's page).

Most definitions draw a 750-watt line, and a 1,000 W motor is above it. California's asks for "an electric motor that does not exceed 750 watts of power" (Cal. Veh. Code § 312.5(a)).

Four definitions take in the 4.0 at its printed figures:

Where a 1,000 W motor with a throttle at 20 mph sits inside the definition on October 2, 2026: 4 of 51 jurisdictions, each quoted from its statute through our 51-jurisdiction rule table. Rhode Island's two horsepower is about 1,492 W; D.C., Montana and Oregon set no wattage.

New Jersey's definition leaves out any throttle bike: under P.L.2025, c.285, its low-speed electric bicycle assists only while you pedal, and a throttle makes the bike a "motorized bicycle" (our New Jersey guide). Alaska's and Kentucky's codes contain no e-bike definition.

A bike outside a state's definition is governed as some other vehicle under that state's code, which names the class. Our state guide links every state's own page; read yours before the 4.0 goes on a public road, path or trail.

The 28 mph display limit

Eunorau's specification lists a "Manufacturer-defined display limit: Up to 28 mph / approximately 45 km/h" beside the "Default Class 2" highlight (Eunorau's page).

At 28 mph with a throttle, the 4.0 sits inside none of the 51 definitions. In our 51-jurisdiction rule table, every definition that allows a throttle stops it at 20 mph; Oregon's Class 2, as quoted above, "Ceases to provide assistance once the bicycle reaches a speed of 20 miles per hour" (ORS 801.258).

On any public road, path or trail, ride at the Class 2 default. Every 20 mph figure on this page, the range tables included, sits at the default Eunorau's highlight names.

Charging and battery care

The 840 Wh pack charges through a DC2.1 port, behind a 30A BMS with 40.5 V low-voltage protection (Eunorau's electronics rows). A typical outing needs much less than a full pack: 20 miles at 12 mph on the throttle draws about 320 Wh from the cells (the speed table), a little under two-fifths of it.

Recharge with 10 to 15% left, Eunorau's general FAQ advises, and park a pack you won't use for two weeks or more "in a cool, dry place with a 70%-80% charge remaining". Eunorau puts a pack's typical life at "5-6 years", with "more than 80% of their original capacity after 500 charge cycles".

Where Eunorau prints a figure two ways

Eunorau describes the SPECTER-S 4.0 on its product page, in its product record, on a lettered geometry drawing and in its photographs. When they disagree, the last column says which figure this review works from.

The page and record were read October 2, 2026, and Eunorau's warranty, FAQ and size-guide pages the same day; the specification rows matched the September 26 read row for row.

Recall and warning record

No federal recall names Eunorau or the SPECTER-S. Searched on October 2, 2026, the CPSC's recall database held no recall with "Eunorau" in its title, description or product name field, and a control query proved each field was answering.

The full list of 10,027 recalls, June 8, 1973 to September 24, 2026, was also read word by word for "Eunorau", "SPECTER-S", "SPECTER" and "Hunter X9": none appears, and a control brand, Rad Power Bikes, returned its recall from the same list.

The same day, all 373 rows of the CPSC's product safety warning listing were read: two named the control brand, and none named Eunorau or the SPECTER-S.

Warranty, and who handles a claim

Terms by component, from Eunorau's warranty policy as read on October 2, 2026:

Issued by "Eunorau Bikes, a Nevada corporation", it covers manufacturing defects on bikes bought in the US on or after August 1, 2023 (the policy). A claim asks four things of you: proof of purchase, "Product Registration right after the purchase", an "E-bike check-up by a Eunorau specialist or dealer after the first year of use", and being the original purchaser.

Order the SPECTER-S 4.0 from us and the claim is ours to run. Email a photo and a sentence on what broke, and we deal with Eunorau until the replacement arrives at your door. For the same terms across Eunorau's other bikes, see our Eunorau brand profile.

Buying it from us

The value case in numbers. On October 2, 2026, Shop Pay on our listing split the $3,799 three ways: 12 monthly payments of $342.89, 6 of $661.15 or 3 of $1,298.12, each at 15% APR.*

*Rates from 0-36% APR. Payment options through Shop Pay Installments are subject to an eligibility check and are provided by these lending partners: affirm.com/lenders. Options depend on your purchase amount, and a down payment may be required. State notices to consumers: affirm.com/licenses.

Weighing the 4.0 against the FAT-HS, the SPECTER-ST 2.0 or a hub-drive bike? Tell us your state, your load and your terrain at support@redtailebikes.com, and we will say which of them suits the job.

The honest ledger

Green flags

• A 1,000 W Bafang G510 through eleven SRAM gears: 14.9 mph up a 10% grade on the throttle with 180 lb aboard (the climb table).
• Full suspension, rack and fenders at 83.7 lb: 4.5 lb under the 3.0's printed weight, with the rack and fenders now on the bike (what changed).
• An 840 Wh pack with LG cells: about 45 miles at 15 mph on the throttle and 67 pedaling easily for a 180 lb rider on the flat (the range tables).
• Four-piston hydraulic brakes on 180 mm rotors at both ends (the parts section).
• A 300 lb payload and trailers Eunorau lists as compatible (the payload section).
• $3,799 on October 2, 2026, the price Eunorau charges itself, on all four color-and-frame choices (buying from us).

Red flags: where it is the wrong bike, and what to do

• Your inseam is longer than about 30.8 inches: the 18-inch frame's printed saddle range sits below the 106% formula height, so read the saddle tables first, or take the FAT-HD 1.0 Pro, which reaches the formula for 88 of 100 riders at 5'10" (our FAT-HD 1.0 Pro review).
• You want full suspension and stand 5'6" to 5'8": the FAT-HS 19-inch frame reaches the formula for 90 of 100 riders at 5'6" and 66 at 5'8" (our FAT-HS review).
• You ride public bike paths in a 750-watt state: the DEFENDER carries full suspension on a 500 W hub that sits inside 48 of 51 definitions (our DEFENDER review).
• Rider and gear come to more than 300 lb: the FAT-AWD 2.0 is rated for 375 lb on two 500 W hubs (our FAT-AWD 2.0 review).
• You want to step through the frame: the SPECTER-ST 2.0 puts the same motor family on a step-through (our SPECTER-ST 2.0 review).

Who should buy it

Buy the SPECTER-S 4.0 if your inseam fits its frame and you want a 1,000 W mid-drive with eleven gears for steep, loose ground, full suspension on 4.0-inch tires, four-piston brakes, a rack and fenders, room for 300 lb and trailers, where your state's definition takes it in or on land where you have permission to ride.

Choose the FAT-HS instead for a taller saddle range on full suspension (its 19-inch saddle's listed top is 43.3 inches, by our FAT-HS review), the FAT-HD 1.0 Pro for riders near six feet, and the DEFENDER for public paths in a 750-watt state.

Hold off if your inseam runs past the 18-inch rows and you have not sent it to us: the fit tables are the number to settle before this bike ships.

Before you buy: the checklist

Eight boxes to tick: four settle the bike and frame, four cover the order and your first week of riding.

• ☐ Measure your barefoot inseam and find your row in both saddle tables and the standover table: the 18-inch frame for inseams to about 30.8 inches at 106%, the 16-inch to about 29.0.
• ☐ Read your state's e-bike definition for one thing, whether it takes in a 1,000 W motor with a throttle; start at our state guide.
• ☐ Total your weight, your gear and any second pack against the 300 lb rating, which leaves out the bike's own 83.7 lb.
• ☐ Confirm your hitch rack carries 83.7 lb per bike and its trays take 4.0-inch tires.
• ☐ Work out your longest ride at 15 mph on the throttle: the 840 Wh pack plans 38 miles for a 180 lb rider on the flat, and with the 5 Ah pack, 49.
• ☐ Decide on the 48V 5Ah pack before you order; Eunorau lists it at $219 as an option.
• ☐ Charge the pack fully before the first ride, and shift under light pedal pressure while you learn the shift sensor.
• ☐ Look the box over while the driver is still there, and photograph any damage and send it to us within 48 hours.

Limitations of this review

Twenty limits on this review, numbered and tied to the section each one qualifies.

1. The specifications are Eunorau's, from its page, record, geometry drawing and table, its photographs and its FAQ, recomputed wherever arithmetic enters. The range and fit models, the two jurisdiction screens, the recall reads and our store terms are ours, each explained below.
2. Every range row is one steady speed on one grade in still air. Stops, starts and headwinds cost more; a tailwind costs less.
3. Eunorau prints the frame size, the speed, the saddle height's starting point, the chain stay, the geometry letters, the rider window and the warranty more than one way (the conflicts table); the review uses the figure named there.
4. The screens set the printed 1,000 W, the throttle and Eunorau's 83.7 lb beside each definition at 20 mph and at 28 mph, as our rule table and the statutes stood on October 2, 2026. They read the motor, speed, throttle and weight limbs, leave age, helmet and trail rules to each state, and are not legal advice.
5. New Jersey's P.L.2025, c.285 took effect on January 19, 2026, and the screen reads its low-speed electric bicycle as pedal-assist only; our New Jersey guide sets out the fee waiver and the dates.
6. The 3.0 column of the comparison is the Internet Archive's capture of Eunorau's page on August 31, 2026; Eunorau's own page now describes the 4.0 at the same address.
7. The recall reads ran on October 2, 2026. The three brand fields each passed a control query, and the full list of 10,027 recalls was read every field, matched on whole words, with a control brand found. The warning listing's 373 rows were read the same day.
8. Our price, orderability and Shop Pay terms come from our own listing, read October 2, 2026; the payments are its plan table for $3,799 at 15% APR.
9. The motor model rests on Bafang's printed M620 figures, the 1,000 W pair of speeds at 48 V and its 160 N·m, with the efficiency at the rated point fitted to a measured mid-drive map; Eunorau's page names the G510 and its rating, and Bafang files the M620 under the G510 model codes.
10. No drum or road figure for a 30 TPI wire-bead Juggernaut was found, so the model uses the Juggernaut Pro's drum figure, the slowest of twelve fat-bike casings on Bicycle Rolling Resistance's drum, with the middle and the fastest as brackets.
11. The model's wheel is the rear tire measured on Eunorau's photograph, 28.92 inches across, and its drag area that of riders on flat bars; the front wheel is turned slightly on the stand, so its size is not read.
12. The cold rows use McMaster's measured LG HG2 cell as the central line, bracketed by Samsung's 35E data sheet and Casado et al., 2025; Eunorau names LG 3500mAh cells without a model number.
13. The two-pack column adds the optional 5 Ah pack's 240 Wh and leaves out its weight, which Eunorau's page does not print; Eunorau's page prints no charger output either, so no charge time is computed here.
14. No ride of the SPECTER-S 4.0 to empty, with its speed and load stated, was found in print, so the chain from wheel to pack is checked link by link against its sources; Electrek's 2021 display reading on an earlier Spectre S prints no speed or climb to test against.
15. The fit tables use the bodies of US Army personnel. ANSUR II measured 6,068 soldiers aged 17 to 58 in 2010 to 2012; the way inseam varies at a given height should carry over to civilians, while the exact spread may not.
16. Eunorau's saddle heights are read from the crank axle to the saddle top, because its photograph of the 18-inch frame shows the saddle 621 mm from the crank axle, inside the 18-inch range, while the same figures from the ground would sit below the bracket; if Eunorau measures from another point, every saddle row moves with it.
17. The 18-inch frame is Eunorau's photograph, held to its table on three dimensions within 1.4%; the 16-inch uses the same post angle and grip, because Eunorau's table gives the two frames the same reach, stack and top tube.
18. The standover is measured on the 18-inch frame only, 2 inches ahead of the saddle's nose; the 16-inch frame's is not measured and is not printed.
19. The grip is read on the photograph at its photographed setting, and the sit bones are placed in the saddle's rear-middle quarter; moving the bar moves the lean and the hand load, and the hand figure is an upper figure for a relaxed back.
20. Treat the saddle formula as a first setting: in 19 trained cyclists the inseam formulas put 55 to 65% inside the 25 to 35 degree knee range (Peveler et al., 2005), and the heel check in the setup section gets closer. Expiry: re-verify if Eunorau changes the motor, the pack, the speed settings, the payload, the rider window, the saddle heights or the geometry, if our price moves, or if any state's definition changes.

The source register

The tiers behind this review, and what each was used for: Eunorau's page, record, drawing, photographs and policies, the statutes, the CPSC's lists, the published measurements under both models, and our own datasets.

Frequently asked questions

Is the Eunorau SPECTER-S a good e-bike?

For steep, loose ground it gives you a 1,000 W mid-drive with eleven gears, full suspension, four-piston brakes and a rack and fenders, at 83.7 lb and $3,799. A 180 lb rider covers about 45 miles at 15 mph on the throttle from one pack; check your inseam against the fit tables before choosing a frame.

What is the difference between the SPECTER-S 4.0 and the 3.0?

The 4.0 is 4.5 lb lighter at 83.7 lb with a rack and fenders fitted, comes in 16-inch and 18-inch frames, starts in Class 2, and carries an AO-38RC shock and a DP C018.CB display. The 3.0 listed 88.2 lb, 17-inch and 19-inch frames, "Class 3", a DNM shock and a free 15 Ah second pack (what changed).

Is the Bafang G510 the same as the M620?

Yes: Bafang's 2021 OEM workbook files the M620 under the model codes "MM G510.750.C / MM G510.1000.C", and Eunorau's own 3.0 page called it "the Bafang G510(M620) motor". On the 4.0 it is the 1,000 W version, which the workbook rates at 160 N·m (the motor section).

How fast does a 1000W electric bike go?

On the SPECTER-S 4.0 the setting decides it: Class 2 by default, with a display limit Eunorau lists at up to 28 mph. On the flat the modeled motor holds that 28 mph on the throttle inside its rated 1,000 W with a 180 lb rider, and up a 10% grade it holds 14.9 mph (the climb table); the 28 mph section covers where that setting fits.

Are 1000W e-bikes legal?

On public roads and paths, a 1,000 W throttle bike at 20 mph sits inside 4 of 51 jurisdictions' e-bike definitions on October 2, 2026: D.C., Montana, Oregon and Rhode Island. Most states draw a 750-watt line, and outside a definition the state's code treats the bike as another vehicle (the law section).

Can mid-drive e-bikes have a throttle?

The SPECTER-S 4.0 does: Eunorau lists a "Thumb throttle" and five pedal-assist levels on the G510. The range tables price throttle-only riding, about 45 miles at 15 mph for a 180 lb rider on the flat (the speed table).

Are mid-drive e-bikes better for hills?

On a long climb, yes: the motor works through the gears, so in the 42T at 8 mph up an 8% grade it spends 67 Wh a mile against 120 in the 11T. On the throttle it holds 17.0 mph up 8% and 11.0 up 15% with 180 lb aboard (the gear tables).

How far can the SPECTER-S 4.0 go on a full charge?

About 45 miles at 15 mph on the throttle for a 180 lb rider on level pavement, 33 at 20 mph and 53 at 12 mph, from the 840 Wh pack. Pedaling easily, 15 mph stretches to 67 miles, and the optional 5 Ah pack adds about 12 miles at 15 mph on the throttle (the speed table).

What battery does the SPECTER-S 4.0 use?

A removable, lockable 48V 17.5Ah pack with LG cells, 840 Wh, in the down tube. Eunorau's optional second pack is a 48V 5Ah, 240 Wh, with a Type-C output, listed at $219 (the frame section).

What size SPECTER-S 4.0 should I get?

Choose by inseam: at Eunorau's printed saddle heights the 18-inch frame serves inseams to about 30.8 inches at the 106% setting and the 16-inch to about 29.0. At 5'4", 64 of 100 riders reach the 106% height on the 18-inch and 45 of 100 clear its top tube (the fit section).

How much does the SPECTER-S 4.0 weigh?

Eunorau lists it at 83.7 lb (38 kg), with the rack and full aluminum fenders on it. Your 300 lb payload sits on top of that (the specifications).

Are full-suspension e-bikes worth it?

If your rides cross ruts, roots, rock or washboard, yes: the 4.0's 140 mm fork and 50 mm of rear travel take the hits your back and wrists would. If your rides stay on smooth pavement, weigh the 83.7 lb and the price against that ground; the family table sets Eunorau's options side by side.

Do fat tire bikes need suspension?

The 4.0-inch Kenda tires cushion small bumps by themselves, and the fork and shock take the larger ones. The cost of the casing shows up in range: the model prices it at the slow end of measured fat-bike tires (the tire table).

Is the SPECTER-S 4.0 good for hunting?

Eunorau titles it a "Hunting Fat Tire Bike", and it carries the four things a hunting bike is judged on: a mid-drive for climbs, 840 Wh of range, a 300 lb payload with a rack, and trailers Eunorau lists as compatible. Keep you and what rides on the bike inside 300 lb (the payload section).

Can the SPECTER-S 4.0 pull a hunting trailer?

Eunorau lists its hunting trailers and its one-wheel cargo trailer among the 4.0's compatible accessories, and we stock all three. The climb table's speeds are for bike and rider alone, with no trailer behind (the payload section).

What warranty does the SPECTER-S 4.0 come with?

Eunorau's policy gives the frame 10 years and the battery, motor and electrical parts 24 months, for bikes bought in the US. Buy it from us and we run the claim with Eunorau for you (the warranty section).

Are Eunorau bikes good?

You can judge Eunorau by its parts, because it names them: on the SPECTER-S 4.0 a Bafang G510, SRAM NX, an AO-38RC shock, HD-E620 four-piston brakes, Kenda tires and LG cells, with a 10-year frame warranty. Our Eunorau brand profile covers the range.

The bottom line

The Eunorau SPECTER-S 4.0 is a $3,799 full-suspension fat-tire e-bike on a 1,000 W Bafang G510 mid-drive, with eleven SRAM gears, four-piston brakes, a rack and fenders and an 840 Wh pack, rated to 300 lb, at 83.7 lb, in a 16- or 18-inch frame.

On the throttle a 180 lb rider covers about 45 miles at 15 mph, 37 with the full 300 lb, and the motor holds 14.9 mph up a 10% grade. Buy it for steep, loose ground and loaded trips where your state's definition takes it in or the landowner allows it, on the frame your inseam fits.

References

Every document behind the figures and rules on this page, numbered in the order the page first leans on it, with its publisher, title, the part cited and the date we read it.

1. Eunorau. SPECTER S 4.0/Hunter X9 — product page and product record: highlights, specification rows, the geometry table and lettered drawing for both frames, the feature copy, the FAQ, the compatible accessories and the studio gallery. eunorau-ebike.com/products/specter-s-hunter; product record specter-s-hunter.json. Retrieved October 2, 2026 (the specification rows equal the September 26 read, row for row); deposit copies archived.
2. Eunorau, via the Internet Archive. SPECTER-S 3.0 / Hunter X9 product page as captured August 31, 2026: the specification and components rows, "CLASS Class 3", the free gifts and the "Bafang G510(M620) motor" copy. web.archive.org/web/20260831063423. Retrieved October 2, 2026; deposit copy archived.
3. Bafang. Workbook OEM 2021, MOTORS table, M620 column (model codes MM G510.750.C / MM G510.1000.C): rated voltage, n0, rated power, nT, maximum torque and efficiency. bafang-e.com. Retrieved September 23, 2026; deposit copy archived.
4. Eunorau. DEFENDER product page and record: one 500 W rear hub with 60 N·m, the 100 mm fork and 165 mm shock, seven speeds, 27.5 × 3.0 tires, 66 lb and the 300 lb payload. defender. Retrieved October 2, 2026; deposit copies archived.
5. Eunorau. DEFENDER-S 2.0 product page and record: two 750 W hubs, 85 N·m, the 75 mm fork and air shock, nine speeds, 26 × 4.0 tires, 89.3 lb and the 300 lb payload. defender-s. Retrieved October 2, 2026; deposit copies archived.
6. Eunorau. SPECTER-ST 2.0 product page and record: the Bafang M620 mid-drive, the 140 mm fork and DNM shock, SRAM NX 11-speed, 27.5 × 3.0 tires, 88 lb and the 300 lb payload. specter-st-1. Retrieved September 26, 2026; deposit copies archived.
7. Eunorau. FAT-HS (Hunter X8) product page and record: the Bafang M615 mid-drive, the 75 mm fork and KS shock, nine speeds, 26 × 4.0 tires, 77.1 lb in the specification and 79.4 lb in the geometry table, and the 300 lb payload. fat-hs. Retrieved September 26, 2026; deposit copies archived.
8. Eunorau. URUS 2.0 product page and record: the Bafang M600 mid-drive, the RockShox 150 mm fork and shock, SRAM NX 11-speed, 27.5 × 2.8 tires, about 61.7 lb and the 300 lb payload. urus. Retrieved September 26, 2026; deposit copies archived.
9. Eunorau. EUNORAU EBIKES FAQ: the bikes that charge from pedaling, battery life ("5-6 years"; "more than 80% of their original capacity after 500 charge cycles") and the 10-15% recharging and 70%-80% storage advice. eunorau-ebike.com/pages/faqs. Retrieved September 26 and October 2, 2026; deposit copies archived.
10. Tengattini, S. and Bigazzi, A. Y. Physical characteristics and resistance parameters of typical urban cyclists. Journal of Sports Sciences 36(20):2383–2391 (2018), Table 4 (drag area by riding position); doi 10.1080/02640414.2018.1458587. civil-reactlab.sites.olt.ubc.ca. Retrieved September 23, 2026.
11. Martin, J. C., Milliken, D. L., Cobb, J. E., McFadden, K. L. and Coggan, A. R. Validation of a Mathematical Model for Road Cycling Power. Journal of Applied Biomechanics 14(3):276–291 (1998), Eq. 14 and Appendix I; doi 10.1123/jab.14.3.276. collections.lib.utah.edu. Retrieved September 23, 2026.
12. Hansen, E. A. et al. Freely chosen cadence during ergometer cycling is dependent on pedalling history. European Journal of Applied Physiology 121(11):3041–3049 (2021), Results; doi 10.1007/s00421-021-04770-w. pubmed.ncbi.nlm.nih.gov. Retrieved September 26, 2026.
13. Kollmeyer, P. et al. LG 18650HG2 Li-ion Battery Data. Mendeley Data v2, McMaster University; doi 10.17632/b5mj79w5w9.2 (0.5C discharge files, recomputed). doi.org. Retrieved September 23, 2026.
14. Samsung SDI. Specification of Product INR18650-35E, Ver. 1.1 (July 9, 2015), § 7.5 Temperature Dependence of Discharge Capacity. enerpower.de. Retrieved September 23, 2026.
15. Casado, S. et al. Evaluation of commercial Li-Ion 18650 battery cells for deep space applications. Journal of Power Sources 638:236552 (2025), Table 3; doi 10.1016/j.jpowsour.2025.236552. doi.org. Retrieved September 23, 2026.
16. NOAA, NASA and US Air Force. U.S. Standard Atmosphere, 1976 (NOAA-S/T 76-1562), sea-level pressure and the composition of dry air. ntrs.nasa.gov. Retrieved September 23, 2026.
17. Rothhämel, M. On rolling resistance of bicycle tyres with ambient temperature in focus. International Journal of Vehicle Systems Modelling and Testing 17:67–80 (2023), Tables 1 and 4; doi 10.1504/IJVSMT.2023.132317. inderscience.com. Retrieved September 23, 2026.
18. Bicycle Rolling Resistance. Kenda Juggernaut Pro 26 × 4.00, rolling resistance on the drum, and the twelve fat-bike tires the page lists. bicyclerollingresistance.com. Retrieved September 25, 2026; deposit copy archived.
19. Electrek (Mikey G). EUNORAU Spectre S review: legally bombed (downhill), August 11, 2021: the 48v 14ah pack and the display reading "after about three miles of rough terrain". electrek.co. Retrieved October 2, 2026.
20. Arango, I., Lopez, C. and Ceren, A. Improving the Autonomy of a Mid-Drive Motor Electric Bicycle Based on System Efficiency Maps and Its Performance. World Electric Vehicle Journal 12(2):59 (2021), Eq. (40) and the efficiency maps; doi 10.3390/wevj12020059. mdpi-res.com. Retrieved September 23, 2026.
21. SRAM. CS-PG-1130-A1 cassette, specifications: cog sizes for the 11-42t. sram.com. Retrieved September 23, 2026; deposit copy archived.
22. Marsh, A. P. and Martin, P. E. Perceived exertion and the preferred cycling cadence. Medicine and Science in Sports and Exercise 30(6):942–948 (1998), Results; doi 10.1097/00005768-199806000-00025. pubmed.ncbi.nlm.nih.gov. Retrieved September 26, 2026.
23. U.S. Army Natick Soldier Research, Development and Engineering Center. 2012 Anthropometric Survey of U.S. Army Personnel (ANSUR II), public data release (4,082 men, 1,986 women). army.mil. Retrieved September 25, 2026.
24. Eunorau. Frame Size Suggestion: rider height by frame size, XS to XL. eunorau-ebike.com/pages/frame-size-suggestion. Retrieved September 26 and October 2, 2026, unchanged between the two; deposit copies archived.
25. Ferrer-Roca, V., Roig, A., Galilea, P. and García-López, J. Influence of saddle height on lower limb kinematics in well-trained cyclists: static vs. dynamic evaluation in bike fitting. Journal of Strength and Conditioning Research 26(11):3025–3029 (2012). pubmed.ncbi.nlm.nih.gov. Retrieved September 25, 2026.
26. Peveler, W., Bishop, P., Smith, J., Richardson, M. and Whitehorn, E. Comparing Methods for Setting Saddle Height in Trained Cyclists. Journal of Exercise Physiology Online 8(1):51–55 (2005). asep.org. Retrieved September 25, 2026.
27. Carahalios, A. An Analysis of the Bicycle-Rider Interface Forces in Stationary Road Cycling. MS thesis, University of Colorado (2015). scholar.colorado.edu. Retrieved September 25, 2026.
28. Clauser, C. E., McConville, J. T. and Young, J. W. Weight, Volume, and Center of Mass of Segments of the Human Body, AMRL-TR-69-70 (1969). ntrs.nasa.gov. Retrieved September 25, 2026.
29. Slane, J., Timmerman, M., Ploeg, H. L. and Thelen, D. G. The influence of glove and hand position on pressure over the ulnar nerve during cycling. Clinical Biomechanics 26(6):642–648 (2011). pubmed.ncbi.nlm.nih.gov. Retrieved September 25, 2026.
30. Peveler, W. W., Pounders, J. D. and Bishop, P. A. Effects of saddle height on anaerobic power production in cycling. Journal of Strength and Conditioning Research 21(4):1023–1027 (2007). pubmed.ncbi.nlm.nih.gov. Retrieved September 25, 2026.
31. California Legislative Information. Cal. Veh. Code § 312.5, subsection (a): the definition's "an electric motor that does not exceed 750 watts of power". leginfo.legislature.ca.gov. Read for the screen of October 2, 2026.
32. Council of the District of Columbia. D.C. Code § 50-2201.02(11A), the motorized bicycle definition's "A motor incapable of propelling the device at a speed of more than 20 miles per hour on level ground". code.dccouncil.gov. Read for the screen of October 2, 2026.
33. Montana Legislature. MCA § 61-8-102(7), the electrically assisted bicycle: "no faster than 20 miles an hour on a paved, level surface". mca.legmt.gov. Read for the screen of October 2, 2026.
34. Oregon Legislature. ORS 801.258, the electric assisted bicycle and its three classes; "May be propelled by its motor without a rider pedaling", and Class 2 "Ceases to provide assistance once the bicycle reaches a speed of 20 miles per hour". oregonlegislature.gov. Read for the screen of October 2, 2026.
35. Rhode Island General Assembly. R.I. Gen. Laws § 31-1-3(g): "an electric motor rated not more than two (2) (S.A.E.) horsepower". webserver.rilegislature.gov. Read for the screen of October 2, 2026.
36. New Jersey Legislature. P.L.2025, c.285 (S4834/A6235), the amended definitions of the low-speed electric bicycle and the motorized bicycle, signed and effective January 19, 2026. pub.njleg.gov. Read for the screen of October 2, 2026, through our 51-jurisdiction rule table.
37. Redtail eBikes editorial desk. The 51-jurisdiction rule table and its dated changes, and the two SPECTER-S 4.0 screens. Every US state and DC, each row carrying its statutory citation and source; screened October 2, 2026 on Eunorau's 1,000 W, the throttle and its 83.7 lb: at 20 mph (inside 4: D.C., Montana, Oregon, Rhode Island; outside 45; no definition in Alaska and Kentucky) and at 28 mph (inside none). First-party datasets.
38. U.S. Consumer Product Safety Commission. SaferProducts recall database. saferproducts.gov/RestWebServices/Recall. Screened October 2, 2026 for "Eunorau" on the RecallTitle, RecallDescription and ProductName fields, each proved live by a control query; and the full list of 10,027 recalls, June 8, 1973 to September 24, 2026, read for "Eunorau", "SPECTER-S", "SPECTER" and "Hunter X9" on whole words, with Rad Power Bikes as the control. Screens and the list archived.
39. U.S. Consumer Product Safety Commission. Product safety warning listing (complete CSV). cpsc.gov. Read October 2, 2026: 373 warnings, 2 naming the control brand, none naming Eunorau or the SPECTER-S.
40. Eunorau Bikes. 24-Month+ Limited Warranty: coverage periods, requirements, exclusions, the issuing entity and its scope, US purchases on or after August 1, 2023. eunorau-ebike.com/pages/warranty. Retrieved September 26 and October 2, 2026, unchanged between the two; deposit copies archived.
41. Redtail eBikes. SPECTER-S 4.0 store record (redtailebikes.com/products/eunorau-specter-s-4): the two colors and two frames, prices, orderability and the Shop Pay plan table; the three trailers; the DEFENDER, DEFENDER-S 2.0, SPECTER-ST 2.0, FAT-HS, URUS 2.0, FAT-HD 1.0 Pro and FAT-AWD 2.0 prices; and our shipping policy. Read October 2, 2026.
42. Affirm. Lending partners. affirm.com/lenders. The lenders behind Shop Pay's installment plans, named in Shopify's installment terms.
43. Redtail eBikes editorial desk. SPECTER-S 4.0 range model. The computation set out in the range section of this review: Martin et al.'s power model with Bafang's M620 figures at 48 V and 1,000 W, the 40T chainring and SRAM 11–42T cassette, the rear tire's 28.92-inch diameter measured on Eunorau's photograph and the Kenda Juggernaut Pro's drum figure; Eunorau's 40 and 52 miles mapped to a ride; run October 2, 2026. First-party computation; every input and its source in its inputs table.
44. Redtail eBikes editorial desk. SPECTER-S 4.0 fit model, two frames. Eunorau's drive-side photograph of the 18-inch frame, scaled by its 1,274 mm wheelbase and held to three of its table's dimensions within 1.4%; the seat post's axis fitted on 17 rows; Eunorau's 540–660 mm and 490–610 mm saddle heights placed from the crank axle along that axis; the standover measured on the 18-inch frame; every ANSUR II body through the saddle formula at Eunorau's 170 mm crank; October 2, 2026. First-party computation; every input and its source in its inputs table.