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kandlbarrett

Posted: Sun Jul 08, 2012 5:16 pm

Joined: Aug 04, 2011
Posts: 1343
Trade Rating: 0
Location: Swindon

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:-

355.6 + 126.75 +126.75 = 609.1 mm

The following site shows the same:-

www.tyresave.co.uk/tyresize.html

And this one shows speedo reading changes

www.miata.net/garage/tirecalc.html

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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