Does sidewall change with tire width?

[thepeel]

I'm looking to put some 17x7 wheels with a 45mm offset on my P5. I'm trying to decide if I should go with 205/40 17s, 215/40 17s or something else. What's gonna work with the best with no rubbing. In my quest I came up with a couple of questions about using different size tires on the same wheel.

Say I have a 17"x7" wheel and I put 205/40 17s on it. The height of the sidewall and the width of the tread will be X.

If I were to move up to a 215/40 17 on the same wheel, wouldn't the sidewall actually be a little taller than before since A) 40% of 215 is greater than 40% of 205 and B) tire is wider and I'm squeezing it into the same wheel, so naturally it has to flex somewhere.

Am I totally missing something or does this sounds about right?

Also, if our cars have a stock 50mm offset, anything less (48, 45, etc.) will actually pull the wheel in towards the center of the car correct?

Thanks,

-peel

[turbolife]

No, you're right.

Sidewall height numbers are aspect ratio, so yes, a 215 will have a taller sidewall than a 205.

[thepeel]

Thanks for the reply.

So as for my other question, if I'm getting 17x7s with a 45mm offset, would I be better with 205/40 17s or 215/40 17s? My main concern is that I don't want to rub. I guess the easiest solution there is to keep the stock rims.

Thanks,

-peel

[bidi]

Here's my favorite tire size calculator...

http://www.miata.net/garage/tirecalc.html

It's perfect if you want to change your wheels, but still make sure your speedometer is accurate, or if you want to know how much it'll be off.