Why are direct drive hub motors considered best for commuting?

Hasaf

New Member
In a different thread, there was a bit of a consensus that a direct drive rear hub was best for commuting. However, there was little discussion of why that is so.

I have a mid-drive motor on my DIY commuter, driving a NuVinci N380. I happen to think that IGH transmissions are best for commuting. That nearly precludes a rear direct drive. Yes, I know there is an exception, a direct-drive with a five-speed IGH. I have one here in my office, it was DOA and the support from the Canadian vendor was a form of, "you buy, now go away."

Ignoring that exception, most direct-drive rear motors call for a standard exposed gear arrangement, which I don't consider ideal. In addition, the motor can not use the gearing. My TDSZ2 definitely calls for use of the gearing when starting and riding against strong winds.

In comparison with a geared motor, the direct-drive has more drag when out of use, and is significantly heavier. My first commuter, yes also DIY, used a geared front hub, as I didn't want to remove the IGH and belt drive. It was actually well balanced and hen riding to work in snow and ice (yes, studded tyres) it had a bit of a two-wheel-drive effect that worked well.

So, no IGH, and no running the motor through the gears, and heavier than the geared drive,why is the direct drive considered a better choice, I just don't see it
 
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fooferdoggie

Well-Known Member
I think the argument is that they are most efficient at their highest rpms. I don't really know how that relates I do a ton of starting and stopping on my commute. I guess if your commute is flat and not many stops it would be ok. I much rather had a mid drive it lets me spin and keep my heart rate up.
 
D

Deleted member 4210

Guest
They aren't best for commuting.

Here is why:
1) Direct drives are heavier than geared drives.
2) Their acceleration is not nearly as strong or responsive as internally geared hubs, since there are no gears internally to leverage the power of the magnetic field generated by the coils.
3) They tend to be more for cargo ebikes, where the magnetic field and no gears are more 'forgiving' under heavy loads. There is really no benefit here for commuters other than POSSIBLY over many years, your maintenance (albeit negligible) could be a little lower.
4) They are typically a lot lower in terms of delivered torque, despite some of their higher watt ratings. Typically around 45 nm for a 750 watt direct drive, versus easily 65 NM for 750 geared drive, and not unusual to see up to 90 nm on geared drives, such as those made by Das Kit. Torque is what gives you the power you feel, and its what you want and need for going up hills.

Direct drive motors are cheaper than internally geared drives, and its why you have seen them many times on the Rad models over the past several years. Though Rad has gone to geared drives on some.

As far as efficiency goes, your mid drive will be superior to both geared and hub drive motors, due to the fact that the motor itself is a) not limited to the rpm of the rear wheel speed, and can be spun at speeds around 4000 rpm, being able to achieve a 'sweet spot' of efficiency combined with high torque - not uncommon to reach 70 to 80 nm of torque depending upon brand b) also leverages your drive train in terms of the gears at your hub, whereas the rear hub drive is going direct to the wheel, and there is no additional benefit from the bikes own gears, other than what is achieved from your own human input. Thus you'll see smaller batteries (36 volts and below 500 watthours) on most mid drives, while being able to achieve much longer range due to the efficiency, versus that of the hub drives. Hub drives can achieve the higher ranges via the flexibility of higher voltages and much greater amphour capacity batteries, and often the OEM's including hub drives on their ebikes, will use non-proprietary (Re-entention is one for example) casings, so you have much greater choice of battery size and availability of sources. The mid drive manufacturers typically use proprietary battery formats, locking you out of everything but what the mid drive manufacturer offers. While they are growing their available sizes as market demand and competition dictates, their proprietary batteries easily fetch more than 70% of the price of a comparably sized non propreitary battery. Also, you can generally choose what battery brand cells, and density you wish from a host of Top Tier Grade A quality battery cell suppliers with the hub drive offerings, including Samsung, Panasonic, LG, and Sanyo.

For commuting you made a good choice.

P.S. Wasn't sure if you were conflating direct drive hub (just the gears) with a direct drive motor at the hub. So I only commented on the motor itself. If you are talking about a direct drive hub, and referencing gears versus bearings (i.e. CVT style such as with your Enviola), those CVT's are actually less efficient than direct drive hubs that have gears. Thats because there is nominal 'slippage' with the internal bearings utilized to provide the seamless ratio changes.