Review What is your hub 'freewheel' time? Rolling resistance comparison

[Carbon.]

Good day,

I would like to suggest a topic in which we could compare our hubs freewheeling time.

Freewheel time means that you raise up your wheel, accelerate it max (using e.g. a thumb throttle) and let it spin till stop, results is given in seconds.

This is quite interesting while comparing rolling resistance.

I attached the movie which shows it.

Front hub AKM Q100SX from Pro swytch set 2021.
Freewheel time is about 19 second.

I tested also a Xiongda ytw-06 old production model 2019, had 5-9 sec, new model should be better as manufacturer promised but I haven't tested it so far.

 

[Sturmey]

Ah....But you need to compare 'like with like' as regards the weight/size of the tyre and rim. A hub fitted with a large and heavy 29"tyre will have a greater 'flywheel effect' than a smaller lightweigh 16" wheel on a Brampton, so should spin for longer.

 

[AndyBike]

There appears to be a fair bit of drag on that YT vid wheel. If it was able to run free without drag factor id expect it to keep turning for considerably longer and even as it slows right down for it to end up doing 1/2 turns as the weight of the valve swings it back and forward.

 

[wheeliepete]

Too many variables, voltage and motor winding speed are going to affect results. I'm sure there will also be a difference between a brand new motor and one that has been run in for a few hundred miles even in like for like testing. Freewheels/cassettes will increase drag on a rear motor as will disc brakes.

 

[Nealh]

One has to define max speed criteria, is this the legal max speed 25kmh or the motor max winding speed. Certainly the latter isn't equal as nor will the components be

Internal gearing will make a difference as they vary a lot commonly most use to be 1:4:4 or 1:5 but now hubs have gearing up to 1:14.

 

[Nealh]

My 6/7 yo Bafang cst (1:4:4 ) freewheels for about 8 secs if I spin it by hand, but I have an old 3 or 4 yo cassette, likely bearings are a bit rougher now and I can here slight rubbing of the rotor as it rotates so not really a fair comparison.
If I use power it is much the same.

Unpowered riding is no issue, though personally I wouldn't do so carrying all the extra weight up hill .

 

[Woosh]

Too many variables, voltage and motor winding speed are going to affect results. I'm sure there will also be a difference between a brand new motor and one that has been run in for a few hundred miles even in like for like testing. Freewheels/cassettes will increase drag on a rear motor as will disc brakes.

The bike is a Woosh Gran-Camino. The hub motor is Shengyi DGW22C. The throttle is used to bring the bike to 15mph legal speed limit then the power is cut (when you hear 'go' at time = 0). It takes about 24 seconds to slow the wheel to a halt.

 

[Carbon.]

Thanks everyone for replies.
When we focus too much on details noone will be able to do a rough comparison.

Wheel size, tyre/tube weight, diameter of hub have an influence on moment of interia, this is obvious.
But this what I have seen so far is that the biggest factor comes from hub resistance.


On my movie, wheel was 26" (bare weighs 2,9kg (rim, hub, spokes) + tyre 950g + tube 130g) and was accelerated till ca. 28km/h. Ok when we compare standard solutions - not extra light extra components or dedicated for fat bike - these results can be more useful.

We can set four categories of freewheeling:
1. 5-9 sec.
2. 10-20sec.
3. 20-30 sec.
4. 30+ sec.


For a comperison I put this movie which I found on YT.

2'36"

 

[Nealh]

Again it is a front motor it has no disc rotor or gear cassette to hinder it.

 

[Carbon.]

Yes, exactly, and this is a real test not laboratory .

Woosh's bike has cassette and disc brake and destipe this it's freewheel time is longer then in my case (I hope initial speed was about general restricted 25 km/h).

 

[Woosh]

I hope initial speed was about general restricted 25 km/h

yes, it was.

 

[Sturmey]

Front wheel mxus xf07 700c 38c, schwalbe energiser tyre, runs for 85 seconds.

 

[Carbon.]

Front wheel mxus xf07 700c 38c, schwalbe energiser tyre, runs for 85 seconds.

Really?
I can purchase this model in my local market.
Would you be so polite and record a movie?
Do you know which production year it is?

 

[Nealh]

Front wheel mxus xf07 700c 38c, schwalbe energiser tyre, runs for 85 seconds.

Is that at 40mph max speed .

 

[Sturmey]

Is that at 40mph max speed .

No. Thats with about 18mph max speed and v brakes unhooked. I also have a yose 250 front that looks almost identical to xf07. That runs for over 60 seconds.
I would imagine that these might be different to akm in that they have a simpler single stage type gear reduction of 1 to 4.14.

 

[Sturmey]

Really?
I can purchase this model in my local market.
Would you be so polite and record a movie?
Do you know which production year it is?

I dont have a camera phone. I am the kind of guy that keeps things running for years. My phone is over 10 years old and that hub has over 26 thousand km clocked up.

 

[Sturmey]

P.S. I note that the mxus has straight cut gears whereas the the akm has helical gears. The straight gears (although noisier) can be more efficient in that they dont generate sideways thrust. Google 'helical vs straight gears'. But the power loss is probably very little anyway.

 

[Woosh]

The internal clutch and gearbox are disengaged when freewheeling. The test is indicative only of the state of your motor's bearings.
If it drops much below what it was when the motor was new then it may be worth to take action.

 

[Sturmey]

The internal clutch and gearbox are disengaged when freewheeling. The test is indicative only of the state of your motor's bearings.
If it drops much below what it was when the motor was new then it may be worth to take action.

I am only familiar with the mxus and bafang, but with them, the clutch is between the planetary gear triangular body/carrier and the axle. During motor freewheeling (unpowered) , the motor pinion is stationary, the whole triangular planetary gear body which is normally locked to the axle now spins and the planetary gears must also spin (load-less) as they are between the stationary motor pinion (sun gear) and the moving outer ring gear on the hub.

 

[Carbon.]

I found a good movie on YT which shows difference between gear and non geared motors hub.
Maybe it will be useful for somebody