Stealing the headlines today is Trek’s all-new Fuel EXe. It is a 140mm eMTB with the $12,999.99 XTR-equipped 9.9 model weighing a claimed 17.47 kg (38.51 lb) in a size medium. It rocks a 360 Wh battery powering a mid-drive motor with a peak power of 300 Watts and a maximum torque of 50 Nm. Those stats align it with other lightweight mid-level assist eMTBs on the market such as the Orbea Rise and the Turbo Levo SL. However, unlike the aforementioned, the new Fuel EXe doesn’t even look like an eBike, at least not upon first glance of the drive-side, anyway.

trek fuel exe with tq-hpr50 motor

Product Manager, Daniel Theil, tells us the TQ-HPR50 makes it possible to make eBikes that look, sound and ride like regular bikes. All you need to know about the all-new Trek Fuel EXe is right here.

That’s because the Trek Fuel EXe runs a new eBike motor from a little-known electrical engineering company based in Bavaria, Germany. That company is TQ, and their new eBike motor is the TQ-HPR50. Together with its 360 Wh battery, it weighs just 3.9 kg, and boasts a torque density of 82Nm/dm³; apparently the highest torque density of any eBike motor on the market.

The TQ-HPR50 motor is so different to the common eBike motors that we saw fit to give you guys an in-depth look at its Harmonic Pin Ring Transmission, and a breakdown of all the ways in which it is seemingly better than anything that has come before it. It launches with the Trek Fuel EXe, but we expect other eBikes to be sporting it in the future.

The TQ-HPR50: A new lightweight eBike Motor

tq-hpr50 ebike motor with control unit remote batteries

TQ produce and assemble all parts for the TQ-HPR50 drive unit, battery, display, remote and sensors predominantly in Germany and Europe

The TQ-HPR50 delivers a peak power of 300 Watts and a maximum torque of 50Nm, as compared to the 500 Watts and 85Nm/90Nm torque offered by the full-powered eBike motors out there such as the Shimano EP8 and Bosch Performance Line CX.

non drive side view of trek fuel exe and tq-hpr50 motor

Compact with narrow q-factor

The TQ-HPR50 motor has one of the smallest footprints of any eBike motor on the market. It doesn’t seem quite as small as the Fazua Ride 50 Evation Motor, but like that one, the TQ-HPR50 is small enough to fit directly behind the chainring. From the drive-side of the Fuel EXe, you can’t even tell there’s a motor in there; it’s only when you look to the non-drive side that you see any evidence of that.

size comparison tq-hpr50 motor compact tiny footprint

In fact, it is so compact that it boasts a Q-Factor of just 135mm. Putting that into context; the Q-Factor of the Shimano EP8 motor on the Orbea Rise is 177mm, while the Turbo Levo SL 1.1 motor has a Q-Factor of 181mm. Trek spec E*thirteen E*spec cranks across all models for now, so the bike’s Q-Factor is only millimeters narrower than that of the Trek Rail. However, as and when narrower Q-Factor cranks become available, Trek will be free to run a much narrower Q-Factor than most other eBikes, making for a bike that, again, will feel more natural to pedal.

tq 360wh battery

High energy density

The motor itself weighs 1.85 kg, while the 360 Wh battery weighs a claimed 1.83 kg. TQ tell us that is the highest energy density of any eBike battery on the market.

Not only is the TQ-HPR50 motor tiny, it is also packs the highest torque density of any eBike motor on the market today, while also being quieter than most of them, too.

tq-hpr50 ebike motor internals harmonic pin ring exploded view

No other eBike motor runs the Harmonic Pin Ring System (HPR) built into the TQ-HPR50 motor; it is a technology patented by TQ.

Details from TQ

So, how exactly do TQ achieve all that inside a tiny footprint? The answer lies in their patented Harmonic Pin Ring Technology. 

We hopped on a call with TQ Product Manager, Daniel Theil, to learn more about the TQ-HPR50 motor and how it differs to the higher power eMTB motors we’re all a little more familiar with. He has a background in mechanical engineering, and has been working on the TQ-HPR50 since the beginning. Here’s what we learned.

danie theil tq-hpr50 product manager

Product Manager, Daniel Theil, gave us a more in-depth explanation of the Harmonic Ping Ring Transmission

Central to any eBike motor is the mechanism it relies upon to achieve the appropriate reduction ratio. What’s that when it’s at home? Well, every eBike motor has an electric motor that spins at a much higher RPM than the rider’s pedaling cadence. The reduction ratio refers to that ratio between the RPM of the electric motor, and the RPM of the rider pedaling. What makes the TQ-HPR50 stand out is the mechanism it relies upon to achieve that reduction ratio. That’s where the Harmonic Pin Ring Technology comes in.

trek fuel exe tqhpr50 motor exploded view internal parts

The Harmonic Ping Ring technology allowed TQ to build an eBike motor that is nested around the bottom bracket of the bike, allowing it to integrate seamlessly

Most other eBike motors on the market use planetary cogs (save for the Brose offering that uses a belt drive) to achieve the desired reduction ratio. They use several steps of cogs that engage with one another to reach it. Meanwhile, the Harmonic Ping Ring requires just one step, and that is executed by the how an inner spline ring interfaces with and drives an outer spline ring.

The smaller inner spline has fewer teeth than the outer circular spline. It is not simply the difference in the number of teeth that achieves the reduction ratio, but also the difference in how fast each spline is spinning. Yes, it’s complicated. We aren’t mechanical engineers, so we’ll leave it at that. This animation sheds some light on how those splines work together to achieve the desired reduction ratio. 

Because the TQ-HPR50 can achieve the required reduction ratio in one step, without the use of lots of moving parts, the whole motor can be constructed concentric to the bottom bracket. It’s neat, right?

All about that reduction ratio (for silence)

There’s more. 

The reduction ratio of the TQ-HPR50 motor is 17.5, much lower than the reduction ratio used by other commercially available eMTB motors. On the Levo SL 1.1 motor, this is around 50. So on that bike, the electric motor spins 50 times as fast as the rider’s pedaling cadence. At the same rider cadence, the electric motor inside the SL 1.1 is spinning 3x faster than the electric motor inside the TQ-HPR50 would be. Despite these marked differences, the TQ-HPR50 motor is still optimized for a rider cadence of 60-80 RPM.

tq-hpr50 motor splines harmonic pin ring transmission

Another view of the splines of the Harmonic Pin Ring Transmission

Why did TQ opt for such a low reduction ratio? In the pursuit of silence, actually. Now, they aren’t claiming their motor is completely silent, but they are claiming it is a lot quieter than the SL 1.1, and the motors seen on popular full-assist e-mountain bikes.

tq-hpr50 electric motor concentric to bb

On most other eBike motors, the stator (above) and other components are positioned offset from the bottom bracket, giving them that classic oval shape. On the TQ-HPR50, these parts sit concentric to the bike’s bottom bracket allowing for a nested motor construction.

Another benefit of that low reduction ratio is that the motor can fully support a rider cadence of up to 140 RPM. Obviously, no one actually pedals that fast over any measurable distance. But, Daniel tells us that their data from testing showed them that, on some super technical steep climbs, riders were putting in half pedal strokes that approached that cadence.

tq-hpr50 magnesium motor casings

The TQ-HPR50 motor stator sat inside the lightweight magnesium casing

For those familiar with traditional Harmonic Drive Systems that are used in aerospace, medical and robotics applications, the TQ-HPR50 uses a mechanism that is actually quite different to those. While the TQ-HPR50 does share the same high precision and direct engagement of traditional Harmonic Drive Systems, it does not share their low efficiency.

tq-hpr50 highest torque density ebike motor

The process by which the copper wire within the stator is packaged allows TQ to produce a motor that has the highest torque density on the market; the wrapping you see here ensures they can pack a lot of copper wire into a very small space.

Those feature an inner spline that flexes in order to push the teeth into the outer circular spline. It is the flexing of that inner spline where energy is lost. With eBikes being a battery-powered application, this lack of efficiency simply isn’t workable. The TQ-HPR50 motor overcomes that issue with use of an inner spline actuator that sits offset of center, so no parts are required to flex. Daniel tells us it is this mechanism, as well as TQ’s special tooth profile, that really improves the HPR50’s efficiency over traditional Harmonic Drive Systems.

trek fuel exe 360 wh battery removal downtube

The main battery on the new Trek Fuel EXe lightweight eMTB has a 360 Wh capacity; there is an optional 160 Wh Range Extender available.

No battery required

Back to (e)bikes.

Daniel Theil tells us that, if you do want to ride the Fuel EXe (or any future bike that may have the TQ-HPR50 motor) in its analogue configuration, i.e., without the battery, it will pedal much like a regular trail bike. That’s thanks to its drag-free internals and integrated freewheel. Of course, all eBike motors have that integrated freewheel that decouples the axle from the gearing, but in some cases there are still some parts moving inside the motor even when the system is switched off. That unnecessary rotating mass and friction creates drag, and means that more of the precious Watts you are producing at the pedals are lost by the time your efforts are translated to the chainring.

tq-hpr50 motor assembly

The TQ-HPR50 motor is hand assembled in Inning, Germany. Underneath the cooling lid seen here is TQ’s patented Torque Sensor which is said to be much smaller than torque sensors seen on other eBike motors. This is another reason why TQ can produce a motor with such a small footprint.

The TQ-HPR50 motor is different in that the simplicity of the Harmonic Pin Ring Transmission means the integrated freewheel completely decouples the axle from all the other motor internals, resulting in virtually no drag. The only drag in the TQ system comes from the seals (2-3 Watts); they could be removed of course to deliver zero drag, but they are obviously extremely important in keeping water and contaminants out of the transmission.

The robots at the TQ factory are collaborative ones, in that they work alongside people in the production line to speed up assembly; here you can see the robot assembling the output drive shaft that attaches to the motor’s chainring.

Is it waterproof?

In fact, TQ went above and beyond with the waterproof rating of their HPR50 motor. Most eBike motors have a waterproof rating up to IP64 – that means they are protected from total dust ingress, and protected from water spray from any direction. The TQ motor has a rating of IP67, which means you could actually submerge the motor up to a depth of 1 meter for up to 30 minutes. The Levo SL 1.1 motor boasts that same IP rating, too.

tq-hpr50 360 wh main battery 160 wh range extender

Obviously, I hope no rider will ever have that misfortune, but that IP rating does sound rather appealing to this rider who is familiar with the deluges of Scottish winter. Also, can’t help but be reminded of Danny MacAskill’s watery excursion in “Wee Day Out”. The batteries also boast the IP Rating of 67, while the display and the remote get a rating of 66, the rating for “strong hose water”. 

tq-hpr50 remote and display unit

Tyler has a review of the new Trek Fuel EXe in the works, so you’ll not have to wait too long for details on how the TQ-HPR50 motor actually rides. In the meantime, check out our launch coverage of the EXe here, including full details on geometry, model specs, pricing and availability.

We’re at Eurobike this week keeping an eye out for any other new eBikes rocking the TQ-HPR50 motor. Stay tuned.

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Rob Haskins
Rob Haskins
8 days ago

Wow if it’s Really silent and waterproof, RELIABLE , smooth and powerful enough it might be the Ducks guts for me .I’m nearly back to my birth weight at 61kg so midpowered motor is all I need. Silence is golden. E=Mtb².

Rob Haskins
Rob Haskins
3 days ago
Reply to  Rob Haskins

I bought one as it was instantly available in Mark Renshaws shop Bathurst Australia EXe 9.7 model shimano gears, Fox suspension $11k au. It’s impressive even with motor off, seriously try it. It’s truly a very good mtb and a Emtb. Very good balance of weight, power and geometry. Power delivery and traction from a standstill on a very steep slope surprising .Well done Trek and TQ. E=Mtb²

8 days ago

It’s nice to see ebike manufacturers work not only on torque/power but also size/weight/noise/efficiency. Value oriented ebikes are mostly about having biggest battery capacity/torque/power but without torque sensor, and big/heavy/noisy drivetrain I think it’s missing a lot of the pleasure of cycling. of course there is a market for 28 mph e mopeds that are not about pedalling but just being lightweight emotorcycles that don’t require registration/insurance or motorcycle license, and will output maximum power by just ghost pedalling, and have very low cost per mile, but I think many people want something as close to a non electric bike as possible, that just multiplies your strength/stamina

Joren Miner
Joren Miner
7 days ago
Reply to  geemy

Wait, how is the “Harmonic Pin Drive” patented??? It’s also known more commonly as a Cycloidial Drive, which is commonly used in industrial motors. This is nothing new. It’s been around for 100 years (sometime in 1920s, exact date disputed).

Ryan Webb
Ryan Webb
7 days ago
Reply to  Joren Miner

It would probably be covered as “end use application”, in that the system had not been used for electric vehicles.

7 days ago
Reply to  Ryan Webb

Given the US Supreme Court’s decision that a driveshaft isn’t covered under patent law because it relies on fundamental laws of physics, this patent is arguably void.

Of course any and all logic would tell you that’s bunk, but such is the state of US politics.

6 days ago
Reply to  C365

What engineering part does not rely on the fundamentals of physics?

6 days ago
Reply to  Ryan Webb

A company called Freeflow already have a harmonic drive ebike motor. I’d be surprised if a new market use could enable a patent anyway.

6 days ago
Reply to  Joren Miner

TQ have a Patent issued in 2017 for the “Pin ring” version of the harmonic drive. It is a different implementation compared to the common Cycloidal Drive.

6 days ago

Similar harmonic ring drive system to the or from Freeflow in Scotland.