Changing wheel size affects speedo reading?

[phatsix]

Is it true that changing your wheels and tyres can affect the speed displayed on your speedo?

sorry if its a shit question cheers

[thewheeldeal com au]

yes, changing the rolling diameter of your tyres will affect your speedo.

a rough but simple way to work it out is:

let's say you have a 235/40R18 tyre (645mm)
and you put on a 235/30R22 tyre (700mm)

so the difference is 700/645 = 1.085
so your speedo will be out by 8.5%
or when your speedo reads 100kph you are actually doing 108.5kph

[NORTI]

yes.

try this calculator :

Tire size calculator

[_R_J_K_]

yes.

try this calculator :

Tire size calculator

Good link!

[NZVK308]

Borrow a hand held GPS or fit one to your car... should give you acurate speed reading

[HSVenforcer]

how would you adjust tyre size in the comp for a vz. i heard rumors there is a section in the dash settings that allows the changing of tyre sizes so as to re adjust the speedo etc

[ParkwayDrv]

yes.

try this calculator :

Tire size calculator

Thats handy

[Verynice]

Another useful calculator, you can compare 5 different sizes at once

http://www.1010tires.com/tiresizecalculator.asp