Comment on Do you need to adjust your speedometer if you change the size of your tires?
Successful_Try543@feddit.org 3 weeks agoAfaIk, the speedometer is allowed to be overestimating your velocity by 10 %. On my car, it’s pretty accurate when using 15" the factory default summer tires, but it’s off by 10 % when using the factory default 14" winter tires.
Kecessa@sh.itjust.works 3 weeks ago
I don’t it because the 14" and 15" tires should have a different second number to their measurement to compensate, the manufacturer wouldn’t recommend installing tires that will make your speedo different depending on your wheel size.
First number is width
Second number is height of the sidewall as a % of the width
Third number is wheel size
So for example my summer tires are 255/45R20, my winter tires are 255/55R18, increasing the sidewalk height from 45% to 55% of the 255mm width compensates for the wheels being 2" smaller
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Successful_Try543@feddit.org 3 weeks ago
I know, but still the circumference differs. It’s 195/60R15 vs. 185/65R14
Comparison