20 inch wheel vs 26 inch wheel

[Ebikebert]

I just wanted to know what the pros and cons were to these different rim sizes. I noticed a lot of the higher powered bikes had 20 inch rims for performance. But I don't know what they mean by performance. Acceleration?speed?

 

[spinningmagnets]

Electric motors are at their most efficient when they run at higher RPMs. In order to get the motor RPMs down to wheel-speed, you have to have a very small drive cog to a very large wheel sprocket. Another step you can try is to have two reductions. The first (primary) reduction will be spinning very fast, and as a result many builders use a rubber-toothed belt and pulleys. The second slower reduction is almost always some type of chain and sprockets.

If someone wanted the simplicity and ease of using a single reduction from the motor to the wheel (while at the same time using the higher power of higher than normal volts), you can look for a motor that has a low Kv (RPMs per volt applied), and use a smaller wheel. Lukes deathbike is a prime example of this.

 

[John in CR]

I just wanted to know what the pros and cons were to these different rim sizes. I noticed a lot of the higher powered bikes had 20 inch rims for performance. But I don't know what they mean by performance. Acceleration?speed?

A smaller wheel on a direct drive hubmotor gives you better acceleration, better efficiency, reduced system stress, and generally decreases top speed little if any.

The compromises are in looks and the fact that a larger wheel is a smoother ride over bumpy surfaces. It generally changes the geometry of the bike, though often in a good way at higher speeds, but it can mess up how well the bike pedals by bringing pedal strike into the equation.

John

 

[iperov]

I tested, all ok on cross country on hardtail 20", if at least your seatpost is Cane Creek Thudbuster and battery in backpack, so bike is super lightweight and can handle bumps. Of course full suspension will be better.
Like this cheap solution from china.

 

[amberwolf]

Some other discussions
http://www.endless-sphere.com/forums/search.php?keywords=%22wheel+size%22&terms=all&author=&sc=1&sf=titleonly&sk=t&sd=d&sr=topics&st=0&ch=300&t=0&submit=Search

 

[dogman dan]

20" wheel with a hubmotor is roughly equivilant to a slightly lower gear. So take offs and hill performance improves. In some cases, the even more important thing about smaller wheels than 26" mtb rims is that motorcycle or scooter tires can be used for high HP and racing applications.

I'm the kook in the group here, Not as interested in speeds above 30 mph, but I do want similar "lower gear" like performance in 26" rims for dirt riding. For that, I use slower speed windings in the motors. It's not same as a small wheel, but I get some benefits when climbing hills with less than 3000w of power.

 

[etriker]

20" wheel with a hubmotor is roughly equivilant to a slightly lower gear. So take offs and hill performance improves. In some cases, the even more important thing about smaller wheels than 26" mtb rims is that motorcycle or scooter tires can be used for high HP and racing applications.

I'm the kook in the group here, Not as interested in speeds above 30 mph, but I do want similar "lower gear" like performance in 26" rims for dirt riding. For that, I use slower speed windings in the motors. It's not same as a small wheel, but I get some benefits when climbing hills with less than 3000w of power.

With all the traffic I can do my ride to work in about 20 mins in the truck.

With the ebike about 35 mins.

Ebike goes about 20mph tops.

Truck can go about 100 mph tops ?

Sometimes I get on the sidewalk and pedal around the traffic. That saves time too.

I am not so sure a faster ebike would get me from a to b much quicker around where I live and ride.

 

[neptronix]

20" always gets you more torque out of a hub. You can get higher continuous power out of a motor that way as well.

http://ebikes.ca/simulator/

Play around with the ebikes.ca simulator, you'll see what i'm talking about.
Also - folding bikes? those are notoriously flimsy, beware.

 

[veloman]

For the low power folks interested in high efficiency - a 20" wheel is definitely going to have more rolling resistance than a 26" or 700c.

You can still get 84% efficiency on a 9c hub in a 26" wheel, at cruising speed with the right voltage and winding.

I'm thinking of putting my HS3540 in a 24" wheel since I won't need it for 50mph riding. All my ebike experience has been with 26" wheels. Though I did just test ride the JuicedRiders cargo bike with 20" wheels and 8FUN geared hub.