Its not about finding the tyre, i'm going to buy brand new. i have 225/40/18 on the car just now, i saw a mazda rx8 with 225/45/18 and it got me thinking!!!
I'm not too bothered about the speedo being out as the car came out the factory with 17" wheels on it so it's probably already out!!
my theory is that the extra rubber would
a) make ride softer
b) act as rim protector
c) might actually improve looks?!!
Its just a suggestion and i thought maybe someone here would have tried it!
Sorry mate but I would not go anywhere near a suggestion such as putting different profile tyres on the rear of a performance car, regardless of make/model. To do this safely you would need to change the wheel size to compensate - this means having different size rims on the front and rear
As Hurdy has said, the rolling circumference will change and therefore you will have uneven tyre circumferences running on the front and rear. In theory changing tyres (all 4) to a higher profile will give you a softer ride but it would look seriously naff and result in poorer handling. If you are worried about rim protection, buy a tyre of the correct 40 aspect ratio that gives you this - there are several brands available - my Dunlop's have this and the tyres perform adequately for me.
Your speedo should be accurate on your current 18" wheels with the 40 profile but as far as not worrying if the speedo is out, then consider getting done by the law, failing an MOT and/or not being covered by your insurance should you have a bump
Personally, I find the ride with my own 18" Monzas very good - do you feel your's are too harsh ?
Performance tyres always have a trade off as they are designed to improve handling and grip, give more traction and braking power. On the downside, they often result in increased road noise, a harsher ride and have less resistance to aquaplaning due to the amount of rubber on the road. VW have taken all these issues into considering the optimim suspension and tyre settings for the GTI. No doubt Mazda have done the same for their car and feel that a 45 profile gives the best balance for the RX8.
My advice would be to do some proper research and speak to a professional tyre supplier before committing to any such changes.
Cass
