Tire size suggestions

This is a repost from the 308/328/Mondial section, because I didn't know which section might provide the best results:...............I recently bought a set of 355 wheels for my 87 3.2 Mondial Cab, and I need to decide on an "appropriate" tire size to go on these wheels. I'm presently struggling with the dilemma of keeping the stock height (will retain the same performance level, but will leave more fenderwell room than I like) or go with a slightly taller tire (use up some fenderwell space, thus looking better, but will lose performance from a car with already less power than I wish it had)

The replacement tire sizes I've come up with - ones that will keep the same ride height - are 225/40-18 front and 255/35-18 rear. These sizes deviate from / are taller than stock by .2" and .1" respectively (though probably imperceptible, the front tire will be very slightly taller than the front, thereby getting rid of some front rake that I really don't like - I prefer for a car to sit completely level)

Am I on the right track with all of this? Any of you with 355 (or other 18") wheels have any suggestions or comments?

 

Interesting. I never thought of it as a percentage, just as the amount of the fenderwell that was full of something (preferably of an "appropriate" size wheel and corresponding rubber - as times have changed the "appropriateness" of the wheel size vs. rubber has changed) Accordingly, I just measured my factory wheel / tire, and the distance between the top of the wheel and the wheel arch lip is filled with slightly more tire than air. On the other hand, using your formula, I should have a tire that's 2" taller to make up the same percentage difference on the car? If so, I'm afraid performance would suffer in a way that wouldn't be worth it.....anyone have any thoughts on my "logic?"

 

Agreed (in its present condition), but that "formula" changes drastically with a 2" larger diameter tire