Hello,
I wanted to replace the tyres of my 1991 240 Estate by winter-tyres. Originally my tyres are 185x80x14. For the winter-tyres this size wasn't to find, so the garagist offered me to install tyres of the size
185x70x14. He said this was not giving any problems, except for an incorrect indication of the speed because of a reduced contour. Can anyone give me an indication of the percentage of correction to count with.Dries
If your speedometer is presently accurate, on the 185.70.14 tyres an indicated 100 km/h will actually be 94 km/h approximately. You can check my arithmetic yourself: the first number in a tyre designation is the width of the tyre (in millimetres), the second number is the aspect ratio of the sidewall height to the tyre width (it's a percentage) and the third number is the wheel diameter (in inches). A 14 inch rim is
343mm, so compare 343 + (185 x 80% x 2) = 639mm to 343 + (185 x 70% x 2) = 602mm. Answer: 94.2%.You should ensure that the spare tyre matches the other 4 tyres because the difference in the rolling diameter of the two tyre types (37mm) may be greater than your differential can cope with if you fitted a
185.80.14 spare on the rear axle.
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