Effect of wheel size on speedo readout?

Battenhall

Finding my (electric) wheels
Nov 6, 2020
10
2
I recently laced a 250w Yose motor into my Pashley. Vintage rod brakes and Westwood rim wheel, and it is a 26 x 1 ⅜ inch quite a bigger wheel than a 26 mountain bike wheel say 26 x 1.75.
The display is a Yose Power Y02 and reads "26 inch" on the display.
This will be an incorrect speed reading presumably?
Any thoughts chaps?
Steve
 

Nealh

Esteemed Pedelecer
Aug 7, 2014
13,904
5,376
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West Sx RH
1 3/8 is smaller then 1.75 /1 3/4.
 

flecc

Member
Oct 25, 2006
48,819
26,486
I recently laced a 250w Yose motor into my Pashley. Vintage rod brakes and Westwood rim wheel, and it is a 26 x 1 ⅜ inch quite a bigger wheel than a 26 mountain bike wheel say 26 x 1.75.
The display is a Yose Power Y02 and reads "26 inch" on the display.
This will be an incorrect speed reading presumably?
Any thoughts chaps?
Steve
It will be about 4.8% fast, e.g. 15 mph will be 15.7 mph on the road, 20mph will be almost 21 mph, not a big difference and I don't think enough to worry about.
.
 
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Battenhall

Finding my (electric) wheels
Nov 6, 2020
10
2
It will be about 4.8% fast, e.g. 15 mph will be 15.7 mph on the road, 20mph will be almost 21 mph, not a big difference and I don't think enough to worry about.
.
Thanks, seems logical. Did you work it out mathematically?
 

flecc

Member
Oct 25, 2006
48,819
26,486
Thanks, seems logical. Did you work it out mathematically?
Yes, based on your tyre sizes. However tyres vary considerably as you've visually seen, so only the actual measured diameter of both is good enough for an precise answer.
.
 
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