TQ · HPR (Harmonic Pin-Ring)

HPR50

TQ's HPR50 is the featherweight that redefined what a 'light' e-MTB motor could be: 1.85 kg, near-silent, and built around a radical Harmonic Pin-Ring gearbox that trades outright grunt for an uncanny, ride-like naturalness. TQ claims 50 Nm and a 300 W peak; independent labs measure roughly 38 Nm and ~283 W at the wheel.

Modest and progressive low down (~38 Nm nominal torque), building meaningfully only past ~60 rpm and peaking at the lab-measured 283 W around 80-90 rpm before tapering at high cadence. Watts shown are PT Labs/BIKE rear-wheel measurements, not TQ's 300 W claim.

The verdict

TQ HPR50 was never about winning the torque war. Its single-stage Harmonic Pin-Ring transmission, three concentric precision parts replacing a conventional geartrain, makes it the quietest mainstream e-MTB motor on the market and one of the lightest at just 1.85 kg. TQ's claimed figures are 50 Nm and a 300 W peak, modest numbers in a world of 85-100 Nm full-power units, and on the bench independent labs land lower still.

Getting it onto a dyno proved awkward, the housing is too compact for a conventional torque sensor, so BIKE Magazin (PT Labs) drove it on a roller and read 283 W at the rear wheel with a measured nominal torque of about 38 Nm; Velomotion's stand test put peak output at a touch over 280 W and reached the same broad conclusion. The takeaway: at low cadence the assist is modest, you need to put in real effort, around 150 W or more, before the motor leans in. Spin it up to 80-90 rpm and it comes alive, delivering smooth, proportional support that feels less like a motor and more like simply being a stronger version of yourself.

It won't haul you up a wall the way a Bosch CX will, and the standard 360 Wh battery limits range; TQ's 160 Wh range extender lifts the system to roughly 520 Wh for longer days. Buyers should also note that the HPR50 has been superseded by the 2025 HPR60 (60 Nm claimed, 350 W peak, added cooling fins), so the HPR50 now sits as the lighter, quieter, lower-torque option in TQ's range. But for riders who want an analogue-feeling bike with a quiet, discreet boost, nothing else feels quite like it.

“Less like a motor, more like simply being a stronger version of yourself.”

Sustained power & heat

How long the headline number actually lasts under sustained climbing load.

360 Wh internal

No measured thermal de-rate data published by independent labs; no widespread owner reports of cut-outs on sustained climbs given the motor's low ~283 W ceiling.

Character

Rider input

TQ does not publish a single support ratio for the HPR50. In practice the tune is sporty and input-hungry: testers found ~100 W from the rider does little, and you need around 150 W or more before the motor delivers significant support. It rewards strong pedalling over coasting rather than multiplying a lazy input.

On the trail

Exceptionally natural and discreet, it amplifies rider effort rather than replacing it, so the bike still feels like a bike. The reward is silence and finesse; the trade is that lazy pedalling gets you little.

Noise

The quietest mainstream e-MTB motor. No directly comparable absolute dBA spec is published, but Trek's acoustic study (anechoic chamber, 21 microphones, ~225 million data points over two days) found the HPR50 measured 1.5-1.8x lower in loudness and 3-5x lower in tonality than other e-MTBs, and close to an unassisted bike. The Harmonic Pin-Ring gearbox produces a faint high-pitched hum rather than the low gear-mesh whine of conventional units, and testers consistently report tyre and chain noise drowning out the drive.

Efficiency

Manufacturer claims ~90% efficiency, and Velomotion found it notably frugal on a simulated 10% climb compared with more powerful Fazua Ride 60 and Shimano EP8 RS units.

The case for and against

Strengths

Lightest mainstream e-MTB motor at 1.85 kg
Quietest drive on the market (Trek anechoic study: 1.5-1.8x quieter than rival e-MTBs)
Uncannily natural, ride-like assist
Frugal energy use for its class
Compact, fully integrated system; optional 160 Wh range extender (~520 Wh total)

Compromises

Modest claimed power (300 W) measures ~283 W at the wheel; low ~38 Nm nominal torque
Input-hungry, you must pedal hard (~150 W+) for full assist
Standard 360 Wh battery limits range without the extender
Outclassed on steep climbs by full-power rivals; now superseded by the 60 Nm HPR60

How it stacks up

Roughly on par with the Fazua Ride 50 and clearly ahead of the aging Specialized SL 1.1, but short of the Fazua Ride 60 and Shimano EP8 RS, and far below full-power units like the Bosch Performance CX (85 Nm) or DJI Avinox (105 Nm). Against its own successor, the 2025 TQ HPR60 (60 Nm, 350 W peak) adds torque, power and cooling fins for ~70 g more weight. The HPR50's trump cards are weight and near-silence, not raw power.

OWNER INTELLIGENCE

Most owners report no problems · 2,691 posts from 332 members analysed.

40Range and the small battery (complaint of design, not defect) · typical onset: Immediate - a purchase-decision issue rather than a failure.

37Grinding / rattling noise at very low assist (sprag-clutch design characteristic) · typical onset: From new or within the first ~30-70 miles.

33Thermal derating on sustained climbs (power throttles back when hot) · typical onset: 15-40 minutes into a sustained climb for heavy riders; rarely or never for lighter riders…

✓13,000 km / 650 hours on a Trek Domane+ SLR7 HPR50 in 22 months - battery mount, display and speed sensor replaced, original motor still running (grinding…

Read the full owner report →

Sources: BIKE Magazin (PT Labs) - TQ HPR 50 laboratory and practical test (283 W, 38 Nm) · Velomotion - TQ HPR50 practice and laboratory test · Trek - e-bike motor noise acoustic study · TQ E-Bike - official HPR50 system page · TQ E-Bike - batteries & range extender · MBR - TQ HPR60 launch (60 Nm, 350 W successor).