What's my wheel diameter?

[EmSeeDee]

I know it seems a silly question, but looking around 'tinterweb it's not that easy.

Really the question is "what wheel diameter should I program into the controller of my new GSM kit"?

The manual for the 800S LCD says that I can choose between 16/18/20/22/24/26/700C/28/29, although the beast itself offers 27 instead of 700C.

On the other hand if I look up the tyre size (40-622) on the Schwalbe website it says that my wheel diameter is 2220mm, which equates to a diameter of 27.82 inches - so the nearest would be 28, and indeed Schwalbe classify it as a 28 inch tyre.

So - is the 800S set up to use nominal or actual wheel diameter?

Mike

 

[anotherkiwi]

Choose 28"

 

[willywombat]

your wheel diameter is not 2200mm ( 2.2 metres!)

 

[Cyclezee]

your wheel diameter is not 2200mm ( 2.2 metres!)

Maybe its' a Penny Farthing..... unless Mike meant circumference

 

[EmSeeDee]

Maybe its' a Penny Farthing..... unless Mike meant circumference

Indeed I did mean circumference. Don't think you could fit a chain drive kit to a penny farthing cos it didn't have a chain

 

[RobF]

700c, 28" and 29" are all the same size, so that's the setting to use.

It will give a fairly accurate speed reading, but the circumference of tyres varies a little depending on the sidewall and tread depth.

If you want greater accuracy you could get a trip computer which will enable you to set the circumference of the tyre in millimetres.

 

[willywombat]

"700c, 28" and 29" are all the same size"
only the same rim size ....and i believe it's the approx diameter including the tyre that the kit wants to know . A 622 rim with a racing tyre will have a different total diameter to that with a bigger touring tyre and again with a 29er MTB tyre ...hence the three different choices , the difference in circumference between a big 29er mtb tyre and a racing tyre will be more than a" little"

 

[anotherkiwi]

I repeat (sorry)

You wrote 40-622 so choose 28" in the LCD

 

[EmSeeDee]

I repeat (sorry)

You wrote 40-622 so choose 28" in the LCD

I have done, and the distances for my regular journeys now seem about right - so the answer seems to be to use the actual rolling diameter.