Do 20" bikes pull better than bigger bikes?

[Jason Scott]

I see some comments about the smaller 20" wheel bikes pulling well and I'm just wondering how they stack up against the larger bikes and the BPM bikes. Do the smaller wheels work better for an eBike or does it all cancel out in the end?

 

[flecc]

They do in the sense that they climb better for example. That's due to the mechanical advantage of the smaller wheel, and it applies whether an electric assist or a pedal only bicycle.

Offsetting that advantage is less stable handling and steering.
.

 

[Jason Scott]

Climbing performance is probably my main concern with any bike. I've had a Dahon 20" folder before and found it nimble but definitely less stable.

Thanks.

 

[trex]

they are a bit better on muddy tracks and mountainous roads. They slip less, track better and generally feel more secure.
On flat or nearly flat roads (<5%), full size bikes seem to be better.

 

[Deleted member 4366]

I see some comments about the smaller 20" wheel bikes pulling well and I'm just wondering how they stack up against the larger bikes and the BPM bikes. Do the smaller wheels work better for an eBike or does it all cancel out in the end?

The wheel size alone doesn't determine climbing torque. What matters is the winding speed of the motor and the speed that it actually turns.

You can get a 328 rpm Q100 motor for 20" wheels and a 201 rpm one for 26" ones. The 201 rpm one in a 26" wheel will pull up the hills better, but if you put the 201 rpm one in the 20" wheel, it would pull better still; however, it would max out at 12 mph on the flat.

You can get motors in a whole range of speeds. You need to know the maximum speed of the motor (or KV), the wheel size and the current it gets to be able to predict climbing potential. Obviously, a large motor like the BPM can handle more current, so has the potential for a lot more torque than a smaller motor. Motors with low maximum speeds like the 150rpm Xiongda in low-speed setting at 15 amps can climb steeper hills than a BPM with 20 amps because it can maintain efficiency at very low speeds. Naturally it'll go much slower than the BPM. In a 26" wheel, it's similar to a 201 rpm motor of the same size in a 20" wheel, i.e 12mph max.

 

[trex]

I can help you comparing the Woosh Zephyr CDN with the Woosh Sirocco CD. Both have the same motor, same controller, the Sirocco CD has a bigger battery but that does not affect the performance of the bike because both batteries have high discharge rate BMS. I tested them the same Pier Hill near their shop in Southend.
I stopped at the bottom of Pier Hill. Both set to gear 1. Both whisked me up on throttle alone up to the top without pedalling, 12mph on average. The time taken is approximately the same, although the Zephyr CDN appeared smoother and a little quicker.
I tested the CDN on some muddy tracks at Thorndon Park last Sunday, just before the heaven opened. The CDN is nice in a way that it climbed very steep grassy banks, full of cowpats. No way I'd do that with the Sirocco CD, not on wet grass. I can find the GPS coordonates of these banks for you to test your bike if you live near Brentwood.

 

[flecc]

Here's another very precise comparison. I've owned two e-bikes of the same make with identical motor, controller and batteries.

One has the hub motor in a 28" wheel. It assists to 22 mph but is a useless hill climber unassisted, on power only quickly stalling on a 7% slope after a flying start at the foot.

The other with the identical electrical setup has the motor in a 20" wheel. It assists to just over 16 mph. It's one of the best climbing e-bikes, from a standing start with power only accelerating up the same 7% hill and cresting the top at 13 mph. It also takes my 70 kilos up a 14% hill without pedalling and will even do a power only restart on a 12%.

You can see the huge difference made by the combination of the change of effective motor gearing in different wheel sizes coupled with the mechanical advantage of a smaller wheel.

 

[Deleted member 4366]

That only works if it's exactly the same motor. I take implication from OP's question that he wants to compare a smaller motor in a 20" wheel with a bigger motor like the BPM in a bigger wheel.

 

[Jason Scott]

Thanks all, really useful little discussion. I was only referencing BPM motors because I've been told they pull the best out of the bigger bikes (when also taking into account gear shift problems on chain drives).

I quite like the 20" bikes that have the battery contained in the frame. It would appear to protect it a little more from the elements but also leave the rear rack free.

 

[trex]

The Zephyr CDN has Nexus-3 hub gear, you have to listen carefully to hear the gear shift. It's not louder than turning the ignition key. It has only 3 gears but you usually only need 2: 1 (steep hill) and 3. 2 is a bit redundant to be honest. If you see a big hill, switch over to 1, you can climb any hill at up to about 13mph, no great loss against the 15mph legal limit. If you change from 3 to 1 directly on a steep hill without blipping the brake, you can hear it crunch, not as bad as with derailleur because only the gearbox suffers, the chain stays put, but you wouldn't do that normally anyway. Blipping the brake avoids the crunch altogether.

 

[Jonah]

20" bikes like the Kalkhoff Sahel Compact and the similar AVE (MH7 I think) make great all-round bikes - very stable, comfortable and great hill climbers. They are are nothing like many cheap 20" folders (powered or unpowered) that ride a bit like toy bikes (to my thinking). They are proper bikes with excellent ride quality. KTM and R&M also do similar bikes.

 

[Deleted member 4366]

20" bikes like the Kalkhoff Sahel Compact and the similar AVE (MH7 I think) make great all-round bikes - very stable, comfortable and great hill climbers. They are are nothing like many cheap 20" folders (powered or unpowered) that ride a bit like toy bikes (to my thinking). They are proper bikes with excellent ride quality. KTM and R&M also do similar bikes.

Do you know if they have different internal gearing to go at the same speed as the 26" wheel, or does the software just allow the motor to spin faster like a S-pedelec?

 

[Jonah]

I don't know for certain but I'm fairly sure the motor internal gearing is not different. It might just be the chain wheel to rear sprocket ratio that provides the speed setting. I don't think the motor spins any faster. As you may know, the wheel circumference is a software setting on the Impulse motor.

 

[RobF]

My 20" AVE MH7 climbs quite a bit better than the Rose on 29" wheels.

Both have the Bosch motor.

Peak assistance on the AVE is higher because it's derailleur geared, but acceleration and climbing is better at all assistance levels.

The Rose freewheels faster, once those cartwheels are wound up, they stay rolling.

 

[Artstu]

they are a bit better on muddy tracks and mountainous roads. They slip less, track better and generally feel more secure.

Never in my experience have smaller wheels been better than bigger wheels. Have you actually ridden a bike?

 

[Kudoscycles]

My 20" wheeled folder with a Bafang SWX motor seems to climb hills about the same as a 26" wheeled bike with a Bafang BPM motor,but if both bikes have an SWX motor the smaller wheeled bike feels more powerful.
But its not just about hill climbing ability a bigger wheeled bike feels more comfortable to ride over longer distances.But the 20" wheeled bike can be more convenient to stow,
KudosDave

 

[trex]

Never in my experience have smaller wheels been better than bigger wheels. Have you actually ridden a bike?

yes, I have, I've never dreamed up something to post. The 20" bike has lower centre of gravity. On slippery surface, it feels much more sure footed. If you have a fall, it's probably less dangerous too.
The Zephyr CDN is crank drive with Nexus-3, not a weedy motor and very well balanced. Try it, you'll see how good it is on muddy tracks.

 

[Artstu]

The 20" bike has lower centre of gravity. On slippery surface, it feels much more sure footed. If you have a fall, it's probably less dangerous too.

You'll have to get on the mountain bike forums to tell them all they need 20" wheels on their bikes.

 

[trex]

there is no need to be sarcastic Artstu. I do realize that many people buy MTB for that purpose but for a pensioner, 26" on slippery surface feels definitely more scary than 20".

 

[flecc]

Of the three e-bikes I owned together at one time, the 26" and 28" wheel ones I no longer have and the 20" wheel one does it all brilliantly and I don't feel deprived.

But of course I am a pensioner!
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