Front tyres

G

goon

Senior member
 Swansea
Mine are ready for renewal and I've only just noticed that they are 225/45 not 225/40 as I previously thought. The 45 profile is a fair bit more expensive than the 40 and not as much choice,can I fit 40 instead and are there any drawbacks to this. (not much knowledge of tyres they are just black things that touch the floor right :( )
 
Yep, 45 is the correct but your car won't spontaneously combust if you fit tyres with 40 profile. The sidewalls will be thinner and that might might not look good though. 225/45/18 means that the sidewall is 45% of 225mm, 101.30mm, whereas 225/40/18 measn that the sidewall is 40% of 225mm so 90mm. A total diameter difference of 22.6mm. Your speedo wont be affected as it works off one of the rear wheels if i remember correctly.
 
goon said:
What I don't get is the profile difference on the same diameter wheels all round?
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Same diameter, but different width.

45% of 225 is about the same as 40% of 255, so the overall circumference/rolling radius/diameter is almost the same.
 
OK I understand that now the wider the tyre the higher the sidewall to keep same diameter.
 
goon said:
OK I understand that now the wider the tyre the higher the sidewall to keep same diameter.
Click to expand...
Almost...the wider the tyre, the LOWER the sidewall ratio needs to be to maintain the same/similar diameter!
 
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