Another new TQ motor: hpr40

[Calcoaster]

The basic formula for torque in rotating systems is T = P / omega
where,
T = torque [Nm]
P = power [W]
omega = angular speed [rad/s]

Forget the 250 W. We are only talking the motor mechanical peak power. The only thing that matters is the max motor power. Torque is a marketing gimmick to hide the actual peak power from the legislators. Torque without the angular speed is of no meaning. Therefore:

• TQ HPR 40 with 200 W of power is the weakest motor. Torque @60 rpm (6.28 rad/s) is 31.8 Nm
• Specialized SL 1.1, 240 W goes next; torque 38.2 Nm
• TQ HPR 50, 300 W; torque 47.8 Nm
• Specialized SL 1.2, 320 W; torque 51 Nm
• TQ HPR 60, 350 W; torque 55.7 Nm.

That's all. "Torque" is gaslighting. It would be a real parameter only if the mfg gave the reference angular speed, or RPM at the motor spindle (these are equivalent).

Yes, there has always been marketing hype involved in ratings of all kinds. That’s probably why we rarely see the actual test parameters and data. I’ve never seen TQ state the angular velocity (stated as rpm or otherwise) their torque or power specs come from.

 

[Stefan Mikes]

Very helpful, thanks. Any idea of how the Mahle X-20 drive compares (not sure what value you use for cadence on a hub drive...)

The issue with the hub-drive motor is we don't know the reference angular speed. As @mschwett was explaining, the X20 motor has a good torque when it spins fast, that is, on the flat. The steeper the climb is and the slower you ride, the slower the hub-drive motor spins, losing its torque. That's why geared hub-drive motors are poor climbers.

 

[apctjb]

The issue with the hub-drive motor is we don't know the reference angular speed. As @mschwett was explaining, the X20 motor has a good torque when it spins fast, that is, on the flat. The steeper the climb is and the slower you ride, the slower the hub-drive motor spins, losing its torque. That's why geared hub-drive motors are poor climbers.

Like choosing a cadence for mid drive could one choose a average speed for doing the calculation (say 10kmh)?

 

[Stefan Mikes]

That’s probably why we rarely see the actual test parameters and data.

I understand Specialized motors very well, especially as Specialized gives the peak power for each motor together with the marketing torque value. It is clear that Specialized uses 60 rpm as the reference (Yamaha does the same). Therefore, the listed torque values for SL motors are fair enough. When it comes to full power motors, Specialized marketing says 50, 70 and 90 Nm. However, these figures are 68, 75 and 90 Nm.

Fancy you are choosing between three differently priced e-bike models. You look at the 50, 70, and 90 Nm specifications. Which e-bike would you choose? Not the most expensive? While it turns out the weakest motor declared as 50 Nm is actually almost 70 Nm strong!

Like choosing a cadence for mid drive could one choose a average speed for doing the calculation (say 10kmh)?

There are several aspects of using a mid-drive as an excellent climber:

• If a low gearing can be used, the rider can pedal at a very high cadence even at a very low e-bike speed. That makes the mid-drive motor very efficient. Most of electrical power will be converted into the mechanical power at low losses to the heat
• For gearing ratio < 1:1 (alpine or MTB), the torque at the rear wheel will be amplified. That's why e-MTBs often have a (say) 34T chainring but a 51T "granny" cassette sprocket. The gearing here would be 34/51 = 0.667, the reciprocal being 1.5x, meaning 1.5 times amplification of the rider + motor torque on the rear wheel
• If the rider can spin the crank on climbing, often a high leg power can be delivered.

Examples:
-- The Bosch SX is a lightweight motor of derated peak power, designed for use with gravel and road e-bikes. In case the rider can pedal at the cadence of >100 rpm and a special assistance mode (SPRINT) is used, the motor will unleash its full 600 W of peak power if the rider also provides enough own leg power
-- Recently, I was riding along my friend riding a Bosch Performance e-bike. Her motor peak power was twice of what I had on my Specialized SL 1.1 motor. If we pedalled similarly, she was obviously faster than I on climbs. However, I once dramatically downshifted and mustered a cadence of 129 (it is a very high cadence). My max leg power reached 417 W, and the motor was saturated at 240 W. I just "smoked" my friend on that climb! It was as if I were lifted by an elevator up that hill!

The issue with the hub-drive motor is it hates spinning slowly. There is no relationship between your drivetrain and the motor. As your speed drops, the hub motor efficiency and torque drop as much as you can only recover by putting a very high leg power of yours (that was what @mschwett was talking about earlier).

 

[stompandgo]

Wow that is great stuff! I had a long phone call with the ‘40 Product Manager at TQ last week, trying to sort out those crazy claims of their customer services person, and one of the things I also wanted to check was whether they had addressed the derating that the HPR50 was known for. She said not only had the case design changed, to allow for greater cooling, but that also the 40 produced considerably less heat as it is rated at 200w and they had seen no derating in their testing. That would up the efficiency considerably. I’ll be looking out for Testmybike’s review of that one!

Did TQ give you any idea of what the future of the HPR50 looks like? Will there be further firmware/software improvements going forward?

 

[mschwett]

one very easy way to observe how fairly simple this is is to ride your bike up a known steady grade at fairly low speed with power pedals or cranks. below 10mph and above 5% grade you can basically disregard aerodynamic drag, and the differences between tires of the same general type are not too significant. do it when it’s not super windy.

i have very detailed topo files for the entire city i live in, and have ridden my s-works aethos, my scott addict e-ride (x20), and turbo creo up many of these hills hundreds of times. i’ve found bikecalculator.com to be quite accurate. if it tells you that it takes 250w to go up a 5% grade at 10mph, and your (human) power meter shows 150w average for that segment at 10mph average, it’s not rocket science to know the motor contributed 100w. it’s also interesting to check the power usage on your bike’s app (most allow you to very easily see wh used and time for a ride) to arrive at a rough estimate of the motor’s efficiency in this particular situation, which i have usually found to be in the 70-80% range for the three motors i’ve looked at - a bafang front hub, the specialized SL 1, and the x20. it would be a pretty major fail if the TQ HPR motors are as inefficient as that chart from the report shows - i feel like i’m missing something there, like we all were about the “drag/damage when off” issue.

as mentioned before, this all goes completely out the window at higher speeds where the collective nuance of rider position, kit, wheels, tires, frame aero, etc all contribute a ton to how much work it takes, interacting in complex ways with effective yaw angle, pavement condition, etc etc. one could spend a lifetime fooling with these parameters.

 

[apctjb]

Great appreciate all the responses and help wrapping my head around some of the concepts. I think I am getting it but let me summarize a few things to make sure.

Assuming a 70 kg rider on a 10 kg bike climbs an 8% grade at 8 mph (3.58 m/s), the total power required is approximately 250 W (ignoring wind, road conditions, etc.) If the rider supplies half and the motor provides the other half (about 125 W), and you start with a 290 Wh battery (derated by 10% for BMS/wiring losses and 65% motor efficiency, giving 170 Wh usable at the wheel), battery runtime is 170 Wh ÷ 125 W ≈ 1.4 hours. At 8 mph, this equates to 8 mph × 1.4 hr = 11 miles (17.5 km) of continuous climbing at that speed and grade.

Am I in the right ballpark, and does that range estimate correlate to what those of you with road ebikes are experiencing? This is far less range than I was thinking...

 

[mschwett]

Great appreciate all the responses and help wrapping my head around some of the concepts. I think I am getting it but let me summarize a few things to make sure.

Assuming a 70 kg rider on a 10 kg bike climbs an 8% grade at 8 mph (3.58 m/s), the total power required is approximately 250 W (ignoring wind, road conditions, etc.) If the rider supplies half and the motor provides the other half (about 125 W), and you start with a 290 Wh battery (derated by 10% for BMS/wiring losses and 65% motor efficiency, giving 170 Wh usable at the wheel), battery runtime is 170 Wh ÷ 125 W ≈ 1.4 hours. At 8 mph, this equates to 8 mph × 1.4 hr = 11 miles (17.5 km) of continuous climbing at that speed and grade.

Am I in the right ballpark, and does that range estimate correlate to what those of you with road ebikes are experiencing? This is far less range than I was thinking...

in concept, yes. for the bikes i’ve owned the overall system efficiency is closer to 80% than your 58%, so more like 1.85 hrs to toast the battery completely, which at 8mph is 15 miles straight up an 8% grade… that’s 6,300 feet of climbing, or up Mt Diablo (near san francisco) TWICE. that’s a big ride, and in practice not all that common. and of course you’d get to come down for free, so 30 miles and 6,000 feet of climbing is certainly possible. for reference, most people around here consider a road ride “hard” if there’s 100 feet of climbing per mile. this example is twice that!