I'm planning some custom e-bike builds and the options for the custom builder (because reasons, long story) are basically: Mahle X20 or something like a TongSheng TSDZ2B. These builds will be totally legal in the UK so if the TongSheng it will be the 250W one and set up as pedal assist only.

The Mahle says it will do a torque of 55Nm, and that's at the wheel. Now if I have a 650B wheel (radius, including tyre = 0.332m) that's only giving me 18N at the tyre. I make that only enough to hold the weight of 100kg of bike+rider+luggage on a 2% slope. Is this enough? Both bikes will be kind of city bikes, for quite hilly cities, and the riders are not especially strong.

https://bristolculture.wordpress.com...north-bristol/

The TongSheng will give me 80Nm and if I have a 38/50 gear that goes up to 105Nm at the wheel. Nearly twice as much as the Mahle.

But this is all just math. Does anyone have any experience of riding either of these systems and what do you reckon?

I had a 36V, 350w DIY conversion that was decently powered and a ton of fun, but way overshadowed by a BBS02. A mid-drive working in conjunction with a suitable drivetrain is superior to a small hub system IMO. I have eschewed TongSheng because their reliability is questionable (based on web reports) although maybe they've overcome their "teething" problems.

I’d go with the TongSheng for a hilly city – the extra torque really shows on steeper streets, you feel it right away. The Mahle is smooth and quiet, but 18 N at the tyre won’t help much on really steep bits, you might be pedalling hard just to keep pace. With the TongSheng 250 W+38/50 gearing you’re pushing over 100 Nm at the wheel, so hills feel way easier.

I have two TSDZ2 kits running. I had converted over a dozen bikes with hub motors and one with a powerful BBS02 mid drive before I did the Tongshengs, The TSDZ2 was my first torque sensor bike and to be honest, it required too much pedal pressure from an old guy like me to get any assist out of it, I hated it.

There's a solution where we install 3rd party firmware that redistributes the assist for weaker pedaling and also can boost the output (optional). I would have thrown my TSDZ2 away without it. It made the bike enjoyable enough that I did a bike for my wife. Hers is run in cadence mode, but it still senses torque and makes for an effortless pedaling experience, We've put 3000 miles on both bikes in two years. Still use other ebikes too. Maybe 1000 miles on those.

For locale where bikes are limited to 25 km/hour and no throttle, the TSDZ2's are nice. I think they are easy to install, don't need big batteries, and used to be inexpensive for us in the USA, Well, I see they re still being shipped to the USA for $260USD.

As for reliability, every creak and pop from my pedals is scary. It's all been loose fasteners so far. One of the clutches on my wife's motor started slipping 1000 miles ago, The classic fix on youtube was to replace it, but I just cleaned the bearing and relubed her clutch and now it's at 3000 miles. I bought a spare motor though, worried about a huge trade war.

Edit: I would not think the TSDZ2 has much torque.