What is the most optimal configuration for a hub drive bike?

Posted by InfluenceEfficient77@reddit | ebikes | View on Reddit | 8 comments

Trying to get a bike for a friend who is living in an apartment, currently I have a direct hub drive 1500 watts with a 52 volt 20 amp hour battery, which is great for me, but it might be a bit outdated. Also I charge it in the yard and they don't have the option. So they need to buy something that's either UL rated or adjacent and comes from a reputable manufacturer I think we settled on getting a mountain bike frame with fat tires, just need to figure out the power and the battery rating to get We wanted to get a rad power bike since they're going out of business and probably can get a good deal on a used one, but even with those bikes the batteries have fires, and I'm not sure I trust them as a company. Are the geared hub motors anymore efficient than the direct drive ones? Some of the bikes we tested are rated for 750 watts, but somehow they go up to 2 kilowatts without burning out the motor. Is a 750 watt geared hub motor at 52 volts capable of going 35 mph in traffic? Can they really The advertised 50- 60 miles on a 15 amp hour 52 volt battery? Are there any specific brands, sales, clearance items, or use bikes that you would recommend for under $1,000?

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8 Comments

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bradland@reddit

Honestly direct drive hubs are some of the most reliable builds you can get. Geared hubs can be more efficient, but the difference isn't all that meaningful. What matters a lot more is how fast you ride. Geared hubs have planetary gears that wear out and a one-way clutch bearing that will eventually slip. You can use similar batteries and controllers in each, so "all other things being equal" the DD hub will be more reliable. The key is to get a DD hub that is designed for your target speeds. Motors have a rating called Kv. Kv tells you how many RPM you get per volt of input. For maximum efficiency, you want to operate a motor at around 80% of max RPM. A lot of people buy DD hubs that are wound (as in stator windings/turns) to hit 45 mph, but they don't buy a battery & controller powerful enough to support those speeds, so they operate at lower efficiency. They'd be better off with a motor wound for 35 mph, which would be in its sweet spot at 28 mph. The real key to reliability is in the battery and controller. [EM3ev](https://em3ev.com) still makes good quality batteries AFAIK. Their King Shark 52v 20Ah battery is good for up to 40A (right around 2kW). Combine that with a Grin Baserunner L10 that's good for 40A, and you've got a setup that should last a long while.

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InfluenceEfficient77@reddit (OP)

Thanks, so what's a good dd wattage for direct drive motor to hit 35 on a flat consistently? I assume that wattage would be for a 48 volt battery so put in a 52 volt in there will give it a little boost

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bradland@reddit

35 mph consistently is unrealistic unless you're going to put an absolutely massive battery on there. Consumption at that speed will be around 55 Wh/mi for most bicycles, and you'd be drawing around 40A at the battery. You need around 1600W of motor power and 2000W of battery power (continuous) to maintain 35 mph, and you need a battery that can sustain voltage under that current draw deep into the discharge curve. In terms of terminal velocity, battery voltage and Kv have to be able to support the top speed. Higher voltages will drive more current, so 52V is where you want to be if you're going for speed.

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SwiftUnban@reddit

Yeah this is so true, hub windings will basically be your gear ratio (and unfortunately, doesn’t change). You wanna go with a setup where you’re cruising speed is around where the hub tops out at. If you get a hub winding that tops out at around 40mph but never plan on taking it past 20mph on the bike trails you lose so much torque and efficiency compared to having a lower winding gear ratio (my brain is skipping hard on the right word, yaknow what I mean lol) Same idea as starting your car out in 3th gear if you can do that without stalling, engines have a certain RPM range that is just much more power efficient. But because we can’t change our motor Kv like a car transmission you gotta pick one. Also just a side note: voltage sag becomes an issue too as your battery depletes. If you ride in traffic at exactly 35mph get a hub for around 40mph You’ll lose an extra few mph as your battery drains, so you could find yourself suddenly getting passed by cars again at high speeds because you aren’t keeping up with traffic. My last bike topped out at exactly 60 KPH on a full charge, which is great on our 60kph limit roads but under 40% I could only get to about 54-57 depending on the road conditions. Those extra few kph is the difference between keeping up with traffic and having cars aggressively whiz by you

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Lordly_Lobster@reddit

50-60 miles on a 15 amp-hour battery is most likely going to involve a lot of pedaling. I'd venture that range is at the lowest level of assist riding below 20 mph. And I don't think a 750 watt motor can push a bike to 35 mph. Speed, range and low price are kind of mutually exclusive. A reliable 52V 25 amp-hour triangle battery will run about $600 and that leaves $400 for the bike and motor so you'll have to compromise on something.

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InfluenceEfficient77@reddit (OP)

Can you please link to this reliable $600 battery?

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serialband@reddit

If you're replacing the BMS that often, you're getting the wrong BMS. 35mph isn't very likely with the typical 52V 750W motor. 50-60 miles on 15A 52V battery is when you set your motor to not actually run at full power. That's when you put the bike on the lowest setting. It's more like 15-20 miles if you go at full power. Those are always marketing miles. Under $1000 aren't going to be all that powerful or great. You're going to have to do more work on them. At the very least, you'll need to replace the tires and brakes quite a bit early than you normally would.

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stormdelta@reddit

> Are the geared hub motors anymore efficient than the direct drive ones? Some of the bikes we tested are rated for 750 watts, but somehow they go up to 2 kilowatts without burning out the motor. Geared hubs are more efficient and lighter, but they are _much_ easier to burn out and you'll eventually need to service or replace the internal gearing no matter what. A direct hub is just a motor built into a wheel. They're less efficient, heavier, and produce minor drag when coasting, but in exchange there's almost nothing to go wrong with them (as long as the wheel is built properly), ultra-low maintenance, they can handle a ton of abuse, and with higher end controller setups can do (ideally variable) regen braking that massively reduces brake maintenance and slightly offsets the efficiency loss.