Tyres size affect speedometer?

[Banz]

Was told by my colleagues that I have 19" tyre so my speed is always higher than the speedometer reading unless the computer has been adjusted for 19". Is that true?

[ilogikal1]

Not if you've got the right size tyre on. More wheel, less tyre, same rolling radius.

[evest]

Not necessarily. Depends if the outer diameter of the whole wheel+tyre has changed. Ie - 18" wheel with fat tyres could be the same outer diameter as 19" wheels with skinny tyres.

[RS8055]

Yeah, as above... it depends on how large the profile of your tyre is. If you've gone up to a 19" wheel, the tyre profile should be smaller... as long as you have the the same outer diameter of the tyre, nothing will have changed.

[brillomaster]

as above wheel size isn't the important factor, its the rolling circumference of the tyres you have fitted.

 

They might be confusing the wheel speed with tyre pressure monitoring systems, which work out if a tyre is deflated by how quickly its rolling relative to the other wheels, and would need to be reset if the rolling radius changes. But again, if the tyre is correctly sized for the new larger wheel, the number of rotations a wheel does will be equal on 18s and 19s. And my zed didn't have TPMS anyways!

Edited August 25, 2016 by brillomaster

[ZMANALEX]

This site is good to compare the speed difference as well as other information relating to tyre sizing. https://tiresize.com/comparison/

[BobbyZ]

You need new colleagues

[KyleR]

Ignore all friends/mates/colleagues who drive diesel German barges

[jamez87]

I used thiswhen swapping from 18s to 19s

 

http://www.willtheyfit.com/#isPage=1

 

[Banz]

Ignore all friends/mates/colleagues who drive diesel German barges

 

Lol the one told me that does drive a diesel bmw.