Pros and cons of 20'' wheeled e bikes?

[andreuther]

I'm in the process of turning my wife's mtb into an ebike for her and plan on building one for myself when finished. I have seen many 20'' wheeled ebikes on this forum, whats the deal? I get that they can be compact (especially the folding models), I would like some input on the functionality of these bikes. What are some of the advantages and disadvantages? Just curious.

 

[Ykick]

I recently built a folder with 20" wheels and noticed there's slightly quicker steering, all else being equal brakes tend to lock quicker, less leveraged to walk out of potholes or over curbs, etc.

These are relatively minor things and not truly criteria to do it or not do it, merely noticeable observations compared to my experience with 26-27" wheels.

 

[chvidgov.bc.ca]

Small bikes are nice for urban riding because they are so nimble. My Cannondale Hooligan is a good example. Low weight strong rigid small frame with cromolly fork.Turns on a dime and accelerates awesomely with a front EZEE motor on it. Big Apple tires. Disk brakes.There are many other cool 20" bikes out there. Find the one you love even if it takes a few tries....from the BMX spectrum through folders and mini-veloes..../urban.The Hooligan is my last one.

 

[dogman dan]

Other than those needing a more compact bike for taking on the train or whatever, the main reason for a smaller wheel is torque. This applies to hubmotors, not mid drives.

The smaller wheel with the hub motor in it will climb hills better, leave a stop sign better, etc. The effect is actually a lower gear. In the case of longtail cargo bikes, a 20" rim can mean the cargo deck can be lower to the ground, greatly improving handling. Only the motor wheel need be small, the other wheel can be larger if you want it that way, provided the frame is built for different size wheels.

The cons include the possibility that the wheel is more affected by large potholes, etc. For a purely pedaled bike, a very large diameter wheel may roll better, coast farther, etc. But stuff like that stops mattering much once you have a motor to take up the extra effort of riding a 20"

 

[matsh]

i also maybe want do fit 20" on my dh bike that has 26". for main reason better torque and cooler motor when cruising slow. now my top speed is 60kmh. litle affraid it will be to low and look stupid
im curious what will my New top speed be, and my commute to work is 15km how will battery consumption change ? With a average speed at 35kmh.
but to change i need 2 New rims, tires, hose and spokes. and a effort to do the job. is it Worth it. will it be much more fun to drive. if i am looking for a torque monster. i have peaks of 12kw..

 

[Miles]

It's slightly confusing to say that you have "better torque" with a smaller wheel. What you have is a lower torque requirement.

Another advantage of smaller wheels, that hasn't been mentioned, is that they are stronger for a given rim section.

 

[Ykick]

Besides looking weird, using 20" wheels with 26" frames you must be wary of pedal strike while cornering. Shorter crank arms often result.

 

[lianjuin]

Going 20" makes a lot of sense when the motor is added...

 

[USAEBIKECO]

Easier storage with 20 inch bikes. But there are not as sturdy on the roads for daily commutes IMO.

I don't pedal as much either for a workout compared to my 26 inch ebike.

 

[Chalo]

20 inch wheels ride poorly compared to larger wheels, suffer higher rolling resistance, and offer less traction. They require higher tire pressure to prevent pinch flats and rim damage.

On the other hand, they have much higher strength per weight, less rotational inertia, and a lower effective gear ratio than larger wheels.

Cranks can run out of ground clearance if small diameter wheels are retrofitted to a bike that didn't come with them originally.

 

[John in CR]

With a hubmotor, a smaller wheel means less motor stress, more efficient operation, and better hill climbing. To a hubmotor going from a 26" wheel to a 20" wheel is like cutting 23% off the total weight of you and your bike, because you've lowered the gearing by that much. It doesn't result in a 23% reduction in speed though, not even close. In fact, with some setups there may be little or no decrease in top speed, but that varies with how stressed it was with the larger wheel. Sure there are some compromises, but it mostly depends on the terrain and how you use your bike.

 

[dogman dan]

Crystal clear the motor is happier with a 20" wheel. But the whole package of rider comfort and motor needs to be considered.

For the longest rides, rider comfort may trump all. My long distance touring/ cargo bike was built with the focus 90% rider comfort, then I just upsized the motor enough to have one capable of hauling me, and all that heavy bike plus cargo. This bike is full suspension, extra long, very plush to ride, and 130 pounds without the battery. It's suspension makes it actually comfortable to ride on washboard dirt roads, at full gallop. Hopefully it will also have less problems with spokes and rims on a long ride. So far it has.

My next project will also be a cargo bike, but intended for shorter runs to the store. It's going to be less long, no suspension, and the motor will be in a 20" rear wheel.

More or less imitating the edgerunner but about a foot shorter. And on the cheap. http://www.ebikes.ca/shop/edgerunner.html

 

[andreuther]

Good info for both sides of the coin. I really like the idea of having a small ebike for short trips (10 mile range). Thanks for all the input!

 

[MadRhino]

... Sure there are some compromises, but it mostly depends on the terrain and how you use your bike.

Exactly. You can be quite comfortable on small wheels with big tires, even on rough streets. Your whole power system will sure be happier and it makes it much easier to achieve exciting performance. On the dirt you need larger diameter, not only for comfort but mostly for safety, and if you want performance with larger wheels you are playing constantly with the limits of your system. Finding the limits may be expansive. I have fried a full garbage can of motors and controllers, built a few bikes before getting to know how to tune and ride the limits reliably.