Hi folks,

I’ve changed my 17” alloys for 18”s and understand they’ll be an error on the speedo because of the increased diameter of the wheel + tyre.

Is there a way of changing the settings of the car to allow for the wheel size? I assume so as the car had various options for wheel sizes when sold.

Thanks
Andy 2012 (62) FL2 TD4 XS

you need to check the 'rolling-circumference' of your old and new tyre, to see the difference.

The sidewall of the tyre has a lower profile as the wheel gets larger in size so should not make much if any different to the speedo.

Doesn't the rolling-circumference remain the same?

The wheel size may be bigger, but wheel + tyre is the same isn't it, as the side wall is narrower. Steve

2008 TD4 HSE Auto, Zermatt Silver

You’re absolutely right. Error of 0.7% which I reckon I can handle...
Thanks all 2012 (62) FL2 TD4 XS

Assuming you've gone from a 235/65/17" to a 235/60/18", then there's a 2mm increase in diameter, which will make the speedometer more accurate, as they're calibrated about 3% fast as standard.

However things like DSC would normally need to know the wheel size as part of the programme parameters, as tyre side wall flexing becomes an important consideration when such systems are active.
I suspect the vehicle will know the factory tyre size, but I'm not sure if it can be changed, or if it would make much difference if it were left with the factory setup. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Exactly what Nodge68 explained. When I had the 18” wheels with 235/60/18 fitted, the speedo was virtually 100% accurate according to the GPS. The wheel/tyre combo size can be edited in the CCF if you want to but I suspect that would then give the over read error of the speedo as expected! (Now Sold). 2008 Freelander 2 (Nazca Sand) SE TD4 Auto. Statutory write off & on WOVR for hail damage but still road legal.
171037Km as of 09/05/22
Superchips Bluefin Flash
Nanocom Evo II (also sold)

The overall diameter is the same as you use a larger rim you use a lower profile tyre.

https://tiresize.com/tyre-size-calculator/

I went from the standard 235/60R18 to 255/60R18. The speedo is still under, about 2kph, as referenced against my GPS.

If you use 245/70R17 it would be pretty close to on par.


P.S. 17 inch rims are what everyone wants. Not poodle rims! Procrastination, mankind's greatest labour saving device!

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