balaklava wrote:you sayng 205 / 40 is to small for solara,but now ihave originals 205/ 65 so what is the deferents,so if the wheel is 15'' is ok to have 205/65 but if its 17''then its should be 215/45
please let me know because i have no experiance with this staf
and if its better for me to change from 15'' original to 17'' what deferents its gona make better driving??
thank you again
First off the numbers work like this (Width / Sidewall / Wheel Size) Remember that wheels go inside tyres.
The sidewall of the tyre is your biggest problem. On a 205/65/15 the sidewall is 65, while on the 205/40/17 the sidewall is 40. The 15 or 17 are the size of the wheel the tyre fits on. So if I have a 205/65/15 (Stock) I have and overall Diameter of 25.5 in, mean while if I have a 205/40/17 I have a diameter of smaller diameter 23.5 in. Anyway this is bad because it will mess your speedometer up by 8% and also throw off your odometer. You can get away with a few %, but 8 is alot!
The other problem is that with less distance between the rim and the concrete, due to the lesser amount of tyre, you increase the chance of bending your wheel.
There is a formula for figuring out tyre sizes width and sidewall that will tell you what is best, or you can check out the link below. It has graphical examples of what I have tried to explain here, if it hasn't entirely made sense. It also does all the math for you

.
I choose to use a 225/45/17 as it gives me a little more width, but the guys with the 215/50/17s have better protection of their wheel rims.
Check this link:
http://www.miata.net/garage/tirecalc.html
Let's just pretend I didn't grow up, or you're going to be terribly disappointed.