#16: Re: Speedometer Accuracy Author: kandlbarrett, Location: SwindonPosted: Sun Jul 08, 2012 5:16 pm ---- 20% suggests you have a much bigger problem. While the calculators are not spot on thta is due to manufacturers slight differences NOT the calculator as the maths is simple.
196 / 65 / 14 tyre has the following diameter:-
Convert 14 inches to mm = 25.4 x 14 = 355.6mm
195 / 65 tyre has a wall hieght of 195 x 0.65 = 126.75mm
there are two lots of wall hieght in the overall diameter so the overall tyre / wheel combo diameter is:-
The calculator results may not be spot on but they are within a few %. If you are 20% out then either you are using the calculators incorrectly or you have another problem.
NOTE: most speedos overread by between 5 and 10% (indicated 30 = real 27) so any change the calculator gives needs to factored onto the original innacuracy. 20% still suggests another problem though!
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