Hub motor parasitic drag

HansTrio

Member
Region
USA
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?
 

Timpo

Well-Known Member
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?
So you're asking specific coefficient of drag by having a hub motor while riding your bike?

Wouldn't that depend on the size of motor, shape, speed, and all the other factors? 🤔

Drag (physics) - Simple English Wikipedia, the free encyclopedia
 

indianajo

Well-Known Member
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

Well-Known Member
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.
 

Timpo

Well-Known Member
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.
The OP is asking about parasitic drag, not mechanical friction of motor.
 

Timpo

Well-Known Member
Ok I re-read OP's question, was this about propelling the bike while motor power is turned off? 🤔
I just noticed this part, "propelling the bike with just pedal power alone ?" So maybe it was about mechanical friction?
 

soyabean

Active Member
Region
Canada
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.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
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

Well-Known Member
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

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
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.
 

Timpo

Well-Known Member
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.
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? :confused: I'm feeling we're making up our own engineering terms.
 

RunForTheHills

Well-Known Member
Region
USA
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? :confused: 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.