19" wheels

[mickthemaverick]

The short answer is Yes it will affect it. However it is the overall diameter of the inflated tyre that governs the speedo reading and if you do your sums correctly you can calculate the tyre size you will need on 18" wheels to match your existing 19" wheels as close as possible. I did it on my Subaru and the resulting ride improvement far outweighs the slight difference in reading. Now when my speedo reads 70mph, gps clocks me at 68.7 mph so in the 'safe' direction and no problem! Good luck with it.

[MattBLancs]

anybody give me a yes/no answer if i put 18"wheels on and normal tyres (,i.e not low profile) will it affect my speedo reading

Not enough information to give a yes/no answer.

Need the tyre sizes of current 19" and proposed 18"

Put them in here:
https://tiresize.com/comparison/
And if the difference (percentage on circumference) is low (max ±3% from memory) then you'll have no speedo issue.

[MattBLancs]

As an example

From website mentioned above

viewtopic.php?p=781482#p781482
I've swapped from 17" to 16" on the 308, and the new (narrower but taller sidewall) tyres are only 0.4% different in diameter, so no speedo issues.

Edited as miss remembered the new and old sizes! Now corrected

[bikesteve64]

thanks for the info when funds allow i will follow up on it thanks again