Tire selection help.

[G-daddy]

I am running 17x7s, and I put an order for 215/50/17s (last day for GB). These work, but should I have gone with 215/45/17s instead?

I just checked a tire calculator, and the difference in diameter between the two are 16mm, which is actually quite an amount. Too much sidewall? Any pros and cons I should have noted? Which one would you have chosen?

[pacmann33]

That size is fine. Your speedo will read about 1.6% slower than the actual speed you are travelling. 215/45/17 would read 1.8% faster than you are actually going. The speedo probably reads a tiny bit optimistic anyway, so 215/50/17 is the tire size is that I would use if I were set on a 215 width tire.

Personally on my 17x7 rims I will be getting 225/45/17 tires which will make the speedo read on 0.4% faster than I am actually traveling.

I'm not very sure as to why most people use the 215/45/17 tires rather than 215/50 17.

With the 04-09 mazda3 GT's the OEM rim width was 6.5 which is too narrow to use 225/45/17 so I reckon that may be the reason for all the 215/45 and 215/50 tires.

[pacmann33]

Also, you are within the typical +/-2-3 percent that most people recommend. I like to stick within 2 percent + or - so you are good to go!

[G-daddy]

Cool, thanks for your expertise, pacmann33. Looks like I'm good to go.

[6strings]

I just bought rx-8 rims. so they are 18x8. whats the widest i can go? like 225/40/18