Hub motor parasitic drag

[HansTrio]

Can anyone with a hub motor bike describe how much parasitic drag the hub motor adds to propelling the bike with just pedal power alone ?

Would it double the effort?

 

[indianajo]

There are two kinds of hub motor. Direct drive, and geared hub motor.
My Direct drive motor when pedaled unpowered felt as if I was in 2 higher sprocket ratios than I really was. I took it off after 500 miles for that reason. Also used a lot of watthours on the hills I ride on; 70 to 100 hills on my summer commute one way.
My geared hub motors don't drag at all when pedaled forwards unpowered. The motor does spin when you pull it in reverse, you can hear the whine. But nobody pedals a bike in reverse.
There is one perverted kind of geared hub motor where Grin took out the one way clutch, charged extra over the regular Mac motor, and customers ate it up. Something about recharging the battery downhill, ha ha! That one drags when pedaled unpowered.
I suppose there is some air drag from a 8" diameter motor body, but considering I sit straight up like Mary Poppins on the carrousel horse, that is negligible in my case. If you lean forwards with your hips in the air like a Tour de France rider, I suppose at 30-50 mph there would be considerable air drag from the hub motor. You see my panniers in the picture, the air drag from them is probably 5 or 10 times that of the hub motor.

 

[tomjasz]

Can anyone with a hub motor bike describe how much parasitic drag the hub motor adds to propelling the bike with just pedal power alone ?

Would it double the effort?

DD hubs suck if you need to pedal under your power, GD hubs are better, and mid drives are better yet.

 

[tomjasz]

parasitic drag

Typically that's an aeronautical term.

propelling the bike with just pedal power alone ?

And that's what was responded to.

 

[MartsEbike]

Put it this way... on my DD 1000w Hub drive bike, I can't really get out of 1st/2nd gear for long without it becoming a little overbearing. It really is a chore to ride unpowered.

 

[soyabean]

Can anyone with a hub motor bike describe how much parasitic drag the hub motor adds to propelling the bike with just pedal power alone ?

I ride my ebike without the battery all the time, it works great like my other regular MTB.

If you are not able to test drive it, focus attention to ebikes that look like a regular bike to start.

 

[tomjasz]

I ride my ebike without the battery all the tim

Which motor?

 

[AHicks]

Here's the deal. The direct drive hubs DO have inherent drag on them when unpowered. That motor thinks it's a generator when coasting, and generators take power to turn. Look into regenerative braking. It's available only on direct drive motors and one pretty special gear driven hub that has no clutch on the motor (GMAC). The reason MOST gear driven hubs AND mid drives have motors that use a clutch is to avoid this inherent drag. When the bike is coasting unpowered, this clutch releases allowing the motor to come to a stop.

Direct drive rear hubs don't coast unpowered as well as MOST geared hubs or mid drives. I think it fair to call that a fact..... -Al

 

[ElevenAD]

unlike some middrives there is no parasitic drag pedaling a non powered hub bike, you just have to deal with the extra weight of the motor and bike.

 

[AHicks]

unlike some middrives there is no parasitic drag pedaling a non powered hub bike, you just have to deal with the extra weight of the motor and bike.

Sorry, I need to disagree. After having owned 3 different direct drive "kit" bikes, and a RAD City, also (originally) equipped with a direct drive, I can tell you there IS considerable drag involved with that type of a hub motor when coasting with no power.

It's the gear driven hubs and mid drives where there's a potential question, with most being equipped with clutches to eliminate that potential for drag.

 

[RunForTheHills]

Okay sorry for being picky, but when I hear parasitic drag, my brain register is as parasitic drag, not mechanical friction from gears, pedals, chains, or any other power loss from powertrains.
Is that what we're talking about? I'm feeling we're making up our own engineering terms.

Well, if you are going to be pedantic, cogging torque from a DD motor isn't mechanical friction.

 

[RunForTheHills]

Most of the drag from a DD motor is caused from magnetic forces in the motor.

https://en.wikipedia.org/wiki/Cogging_torque

 

[RunForTheHills]

Okay so that magnetic force is called cogging torque?

Yes. Most people just call it "cogging". This is maybe a better reference on how it applies to an ebike:

https://boxercycles.com/what-is-cogging-on-ebike/

 

[ElevenAD]

Sorry, I need to disagree. After having owned 3 different direct drive "kit" bikes, and a RAD City, also (originally) equipped with a direct drive, I can tell you there IS considerable drag involved with that type of a hub motor when coasting with no power.

It's the gear driven hubs and mid drives where there's a potential question, with most being equipped with clutches to eliminate that potential for drag.

yes that is true Direct Drive motor have a ton a parasitic drag, i forget they even exist sometimes because i have never owned or ridden one but yeah im sure dealing with cogging and the additional weight of a direct drive has to be a nightmare to pedal without power!