cross-posted from: https://lemmy.ca/post/49655095
This is an Ultegra 11s chain after 1000km of wear from a 1500W mid-drive. Used to ride a Tangent back in 2016. T’was shredding till it went *clunk*.
cross-posted from: https://lemmy.ca/post/49655095
This is an Ultegra 11s chain after 1000km of wear from a 1500W mid-drive. Used to ride a Tangent back in 2016. T’was shredding till it went *clunk*.
Care to educate me about drive types and why mid drive is not your preference anymore. Am looking into ebikes.
Both mid-drives and hubs are great. The main differences come down to weight distribution and climbing ability. Climbing ability is significantly better with mid-drives because they can use the bike’s drivetrain to achieve higher speed reduction and therefore higher torque. This allows a mid-drive to exchange bike speed for torque which makes it able to climb steep inclines. Hubs generally come with a fixed gearing or no gearing at all. The highest reduction hubs come with 13:1 gearing which is much smaller than the effective gearing a mid-drive and drivetrain can achieve. The lower the gearing ratio, the larger and heavier the motor has to be to achieve equivalent torque. Which brings me to weight distribution. Mid-drives sit low, in the middle of the bike which doesn’t significantly affect handling. Hubs add 1.8kg at a minimum to one end of the bike. 1.8-2.5kg on the lower end is noticeable but it isn’t horrible. Larger hubs are more noticeable. Many hubs are in the 3-5kg range. On flat ground or low inclines, there’s no significant differences in the behaviour of a small hub compared to a mid-drive. Both feel great.
Another important difference is the ability to shed heat. Most hubs shed heat poorly and overheat if pushed hard at low speed over many minutes. Some are better than others. Mid-drives are better at that and typically have internal temp monitoring and control.
Both hubs and mid-drives have special requirements around frame mounting. Most mid-drives need special frames. Hubs require strong dropouts, and/or torque arms. Installing a hub on an aluminum frame is only safe without atorque arm in the rear. And even then you may start mangling the material when cycling the nuts at 40-50Nm as required.
Hubs generally require less maintenance as tbey don’t wear your drivetrain. Direct-drive hubs should be almost indestructible as they have no internal gears to melt.
Factory mid-drives like Bosch, etc. require authorized service to repair so DIY is no-go as far as I’m awarr. Hubs don’t. This is the main reason I’m riding small hubs (Bafang G310). I can repair any part of the system myself. If the hub goes, I can replace it with another, even different hub and get the rest of the system to play nice with it.
In the end, if I were not into bike DIY, I’d probably buy a factory bike with a mid-drive. And if I wetr into DIY, then it depends on the application.
The thing is, you don’t need 1500w for climbing. I have a mid drive I limit to 450w and it’s perfectly fine. I’ve legitimately never once felt like it needed more power as long as I’m pedaling. I feel like the only reason to have these big mid drive motors is if you are allergic to pedaling.
Oh yeah, you don’t need more than 500W for climbing if you pedal. That said, if you ran a small hub of the 2-2.5kg range at 400-500W at low speed, like when climbing, you’d overheat it and melt its gears in minutes. Ebikes.ca have a nice motor simulator that can pretty accurately estimates how long it takes for many different motors to overheat.
You’re doing something seriously wrong if you’re melting gears.
Not quite. Just ran a couple of simulations with the motor I use. If you run a Bafang G310 at its nominal power of 250W at 5% incline, it would reach 150°C in 25 minutes. Its gears are nylon which soften and lose a lot of their strength well before that - in the 65-85 range. Their teeth would strip under power well before the motor reaches 150°C. At 10% incline it overheats in 5 minutes, gears would strip in less. If you run it at 500W on 5% incline and many controllers would give it that much, it would overheat in 12 minutes. Even on flat ground, I can get mine to 85°C by riding hard at high speed with the motor at ~450W in under 45 minutes. If then started climbing a steep incline with the same power and low speed, I’d very likely strip the softened gears. A friend stripped his this way. This is what they looked like:
You can see how the stripped teeth are at the motor rotor shaft end, which is one of the hottest parts of the motor.
A beefier motor like the GMAC can withstand 5% grade at 500-700W of power without overheating. Perhaps without losing teeth too since its gears are significantly stronger even if still nylon. 10% at ~650W would kill it under 13 minutes.
So it depends on a few variables but especially small motors aren’t difficult to “melt their gears of” by which I mean soften enough to strip under load.
Oh wow. I didn’t assume nylon gears!
You need a better polymer with a higher glass transition temp.
Haha, yeah. Nylon is great because it keeps the metal bits from wearing, allows them to be softer and lighter materials like alu, prevents shavings from spreading and grinding bits, and they’re quiet. But they lose strength at not too high temps. Beefier nylon gears can have enough strength even when softer. E.g. the helical gear of Bafang BBSHD which people regularly run 1kW through. Some people used to put Delrin (Teflon) gears in their motors, but I don’t think production motors have ever done that. These gears from the pic are tiny with small, helical, teeth. The front version of this motor is 1.8-1.9kg. Whenever you see a bike with a small hub, smaller than a typical disc rotor, front or rear, it almost certainly has similar sized gears. I also have a Shengyi with similar parameters to the G310 and it has almost identical design inside.
The relevance here is that mid-drive uses the chain since the motor is near the pedals, hub drive powers the wheel directly. So in this context, they no longer need to worry about the durability of the chain versus powerful motors.