Circumference and speed ?

ebike11

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Hi guys
What would be the proper calculation to determine the speed loss from larger wheels to small ones?
I measured my 26 inch wheels and with tires installed the circumference is 215cm
I then measured my 17inch wheels with tires and got 180cm.
Since there is 35cm difference Im curious to know. I didnt have a speedometer on my bike at the time so I couldnt check my top speed with the 26inch wheels.
Is there a formula to find out the difference regarding speed between 2 different wheel sizes with the same amount of power and on the same bike?
Thanks
 
Convert the tire circumference difference into a percentage, and that percentage will also be the change in speed, with RPM's being the same.
 
spinningmagnets said:
Convert the tire circumference difference into a percentage, and that percentage will also be the change in speed, with RPM's being the same.

A smaller diameter wheel will usually be able to spin up to a higher percentage of its free speed. So the difference in top speed is likely to be a little bit less than the difference in circumference.
 
spinningmagnets said:
Convert the tire circumference difference into a percentage, and that percentage will also be the change in speed, with RPM's being the same.

How would i change it into a percentage?
 
180___"X"
215 x 100 =

For the two fractions to be equal, you can multiply the cross-located numbers and they will both equal the same number. Therefore...180 x 100 = 18,000

Then, 215 x "X" must equal 18,000

"X" equals 18,000 divided by 215 = 83.7

The smaller tire circumference is 83.7% the size of the larger tire, or...16.3% smaller.

If top speed of the larger 26" tire is 30-MPH, then multiply top speed by 0.837
 
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