If I change the size of my cars tires, will the speedometer read incorrectly?

T

tim

New member
Yes it will, if you only go one or two rim sizes up, it wont make that big of a difference. If your car has a digitally controled speedo, they can just reprogram the computer to have the new rim size. If it is mechanical, I think you have to get a new speedometer cable.
 
I have a '92 Bonneville. I'm considering putting some bigger wheels on it with some lower profile tires. Is my speedometer going to be messed up when I do this? If it will, how can I fix it?
 
Speedometers whether they are mechanically driven or work electronically (digitally) are governed by the transmission of your car.

Therefore the diameter of your tyre, whether it's a normal tyre but over or under inflated, or a low profile tyre on a bigger wheel will have a direct correlation on your speedometer reading.

Even on normal tyres correctly inflated there's about 10% variation in the speedo reading which is why most speed cameras allow that amount of variation.

I know of no way to adjust your speedometer to allow for this, your best bet would be to get a GPS.
 
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