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Wheel and tyre tips

 Tyre aspect ratio 
Fitting tyres with a smaller aspect ratio (sidewall height) is an effective way to improve the handling of your car (especially quicker steering response and tighter cornering) - due to less flex in the tyre sidewalls (see diagram).



 Bigger wheels - Part 1: Rolling radius / Wheel and tyre choice... 
If you decide to purchase wheels which have a bigger diameter than your current wheels, then make sure the rolling radius (distance between the centre of the wheel and the edge of the tyre tread) is as close as possible to your current wheels and tyres.  This is achieved by fitting tyres with a smaller aspect ratio (sidewall height).  Failure of this will result in incorrect speedo and odometer readings, and the risk of your tyres hitting the wheel arch when travelling over an uneven road surface.

If you decide to purchase wheels that are wider than your current wheels, then make sure the width of the tyres are suitable (see table).  Then make sure the tyres (and wheels!) don't rub against the inside wheel arch.  This may require fitting wheels with a more negative (ie. less positive) offset - which will increase/widen the track.

Wheel & Tyre Widths
Wheel
Width
Thinnest
Tyre
Widest
Tyre
5"
5.5"
6"
6.5"
7"
7.5"
8"
8.5"
9"
9.5"
10"
175
195
195
195
195
195
205
215
225
235
255
195
205
225
235
245
245
255
255
275
285
295

 Bigger wheels - Part 2: Stepping up 
An alternative, and arguably simpler method to choosing bigger wheel and tyre combinations is 'Stepping up'. Whenever the wheel diameter increases by 1" add 20mm to the tyre width, and subtract 10% from the aspect ratio. This formula helps compensate for the increases in wheel width that usually accompany diameter increases.

Last updated: 23 Feb 2004 - 7:03pm GMT