Very specific Porsche wheel sizing question

[KRAM36]

Originally Posted by geetee

225 35 19 will fit a 9 wide fine. Very slight stretch but it's within specs.

You'll potentially have 2 issues with a 235. The diameter is about 25.5 which will make a slow car slower. You're going the wrong way in diameter.
Depending on the height of your car and offset, with a 235 can/will rub when you turn. At almost full lock, it can/will rub on the wheel liner.

225 is not recommended for a 9" wheel, 235 is the minimum recommended. Will it fit, yes, is it dangerous, yes and looks amateur to me. A 225/40/18 tire has a 25.08" diameter and a 235/35/19 tire has a 25.47" diameter. The 235 tire will work fine if he gets the wheel spacer correct, plenty of people here running 235 front tires.

Going 235 front 275 rear tires gives almost an identical rotation speed of 492/km front 491/km rear, which will feel much more stable then his old setup of 500/km front 495/km, less twitchy feeling, along with the extra tire patch to the road. There is less sidewall height, which means less tire flex, but at the cost of a rougher ride.

As for the car not being as quick off the line. I wouldn't worry about that unless he is running 1/4 mile drags all day and you would go by the rear tire size, not the front when calculating this and we are looking at 0.8% difference there. The car would actually be faster on the top end. Personally I bought my Boxster for the way it handles, not because it was a drag monster, which it isn't. Enhancing the handling would be way more important than the 1/4 mile time when dealing with the wheel and tire setups. There are more pros vs cons on his new setup if done correct. If he wants to have a faster 1/4 mile time, much better places to put your money to give the engine more power to do that job with this car.