Will increasing tyre size mess up speedo readings?
jgoater,
Apr 8, 5:28pm
I want to remove my 14inch alloys from my Subaru and put on 17inch ones. Will this mean my actual speed will be higher than the speedometer shows?
pandai,
Apr 8, 5:32pm
Depends on the size of the tyres. For instance, 195/65/14 is roughly the same circumference as 225/40/17. But the wider tyres may not fit on the car, and will alter the handling.
tintop,
Apr 8, 5:34pm
Yup - if the new setup has a greater circumference than the old.
Measure the rolling radius of the two sized wheel/tyre setups.
Divide the larger by the smaller to get the multiplier number . It will be 1.xxx
Multiply your speedo reading by that number with the new wheels to get your actual road speed.
Mine is on 215-45-17. You don't want to increase the rolling circumference, otherwise you will knock the crap out of performance. And the speedo reading.
Your 14" tyres should stand about 24.12" high. My 215's should stand at 24.73", but in fact measure 23.75. If you keep at about that height, the effect on the speedo will be minimal.
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