Effect of wheel size on speedo readout?

[Battenhall]

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]

1 3/8 is smaller then 1.75 /1 3/4.

 

[flecc]

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.
.

 

[Battenhall]

1 3/8 is smaller then 1.75 /1 3/4.

Nope. The 26 x 1⅜ is visibly bigger. Talking wheel diameter / circumference. Not all 26" are the same as far as wheels are concerned.

 

[Battenhall]

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]

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.
.