24 inch to 20 inch

[billboat10]

Is there a way I can make this 24 wheel to a 20

 

[elliot friedman]

First, remove the tire then remove all of the spokes, find a hacksaw and remove several inches off the wheel and weld the two ends together. With a new set of spokes, lace and true the wheel for balance.

"Is there a way I can make this 24 wheel to a 20 "
What does that mean?

 

[WilliamT]

If you mean whether you can fit a 24 inch wheel on a frame designed for 20 inch, it depends on the tire width.

A 24 inch bmx wheel + tire can have a wheel diameter ranging from 547 mm to 755 mm.
A 20 inch bmx wheel + tire can have a wheel diameter ranging from 446 mm to 654 mm.

http://www.bikecalc.com/wheel_size_math

Find out what your 20 inch wheel diameter is and see if you can get the 24 inch to fit that range. Most likely you'll have to fit a very narrow tire on the 24 inch which will completely affect it's handling. I wouldn't recommend it.

 

[Ann M.]

Don't recommend this, @billboat10. It certainly won't work if you have rim brakes since the calipers won't reach the wheel. Just curious as to why you want to change out the wheel size. Depending upon your answer, there may be other solutions to the problem

 

[harryS]

If you're making a lowered chopper style bike, you'll have to watch out for the pedals striking the ground on turns. They might even hit without turning.

If the 24 is a powered wheel, you can always buy a 20" rim and respoke the motor with the appropriate sized spokes. It's not that hard to do yourself, but it might be better to have it done.

Disk brake conversion can also be part of the solution.

 

[billboat10]

I have a 20 inch wheel folding bike I also have a spare 24 inch electric wheel I wanted to know if I can use the hub on the 20 inch I know I have to get smaller spokes so it would leave the fold up bike a 20 inch with electric wheel

 

[harryS]

It's going to depend on the dropout width of the folding bike and the axle width you have on your 24" wheel. If they match, yes, you can have the motor re-spoked.

For instance, I believe a typical mountain bike has a 135mm rear axle and a 100mm front axle. Folders can vary on these dimensions, but mine were also 135/100. If the frame is steel, you can get away with spreading the frame a little bit, but I wouldn't do that with alloy.

If you want to analyze this more, hub motors are designed for a certain rpm based on the wheel size. When I was buying a motor for my folder, I was told to select the higher rpm version for the smaller 20" wheel, which has to turn faster to get the same speed. Based on that logic, your 24" motor may not have high enough rpm capability to go as fast in a 20" rim. However, not many folks ride folders fast. The small wheels and gearing make that hard. If you have one, you know what I mean. So you'll probably be OK.




.

 

[Deleted member 18083]

Bill ...
Now that you have clarified the issue...

There is no overwhelming problem in downsizing the rim size that your hub motor is attached to. The distance travelled for each revolution of the smaller wheel will be about 16-17% less than the distance per revolution of the larger wheel - not sufficient to scuttle your project.

I'm planning to convert my own small-wheel folder (Airnimal Black Rhino with Rohloff) to an ebike before I'm too much older (but no wiser).
... David

 

[billboat10]

I have checked the width both the same not to fussed about speed like you said nobody want to go fast with small wheels so when ordering spokes do you measure the exact length say if there 150 how do the spike sizes run it that size max or min spoke length there’s about 15 mm of thread is that allowed in the size overall

 

[Barry S]

Unless you've respoked a hub before or are a DIY-er with the patience of Job, I'd recommend finding a LBS that will do it for you. There are some good YouTube videos on the subject, and after watching a couple of them I had great respect for those that can do it. It's a blend of science and art.

 

[billboat10]

I’m pretty handy I use home lathes and can weld most thing I have a go at it time to strip the 2 wheels and measure for new spokes

 

[harryS]

I've used this online spoke calculator. There are others. You need the rim in hand before you can compute spoke lengths. I tend to get spokes 1-2 mm too long, which isn't a big deal on a double-wall rim unless you run out of thread on the spokes. I've asked one guy if he could cut a few extra threads, but he said his cutter was automated. Sure. One can also put a washer between the nipple and rim anyway.

http://www.ebikes.ca/tools/spoke-calc.html

I didn't find spoking hard to do after the first one. I followed a you tube video and referred to an existing e-wheel on another bike. There are, I think, some wrinkles with a 20" rim and it might get amplified with a bigger hub,

Youtube videos promote putting the spokes into the hub in an alternate pattern with half facing inward and the other half outward. The spokes touch where they cross, which adds strength. I couldn't do that. With an alternate pattern, I had extreme bending of the inside facing spokes. So I did them with all the spoke ends facing out. It's not so easy to put in them in all facing out. Some bending needed to thread them in, but they were straight after they went in.

 

[Deleted member 18083]

Bill ...
A courageous decision to do it yourself. Remember to take photos of both wheels before you start and to share your experiences with us.
... David