Tyre sizes and oil

[rpjg_1975]

Another one for all you experienced 944 drivers..... []

Presently fitted to my car are a set of Porsche Boxster 17" Alloys, fitted with, from memory, 225/45/17's on the front and 235/40/17's on the rear. Do I have to stick to that profile on the rears or would I be able to run 235/45/17's instead? I believe the boxsters run lower profile on the rears but do I have to on my 944?

Any advice gratefully recieved. Tyres are good at the moment but would like to know for future reference

Secondly I am going to do an basic service when I pick the car up tomorrow and am unsure of what grade of oil I need to be using? What am I better off using?

 

[mik_ok]

Fronts are the corret size, but rears should be 255/40/17. Your gearing is marginally lower as a result - the sidewalls of a 235/40 obviously being slightly shorter.

You don't have a set of four boxter front wheels on it?

 

[rpjg_1975]

Nope, I believe they are fronts and rears. I will check the sizes tomorrow as I was posting them from memory. Pick the car up tomorrow evening so I will update... I could be having a memory failure. The rears did seem pretty wide so may well have been 255's if that's what you think they should be?

 

[rpjg_1975]

Just picked the car up..... update on tyre sizes. Rears are 255/40/17's. Presumably I have to stick to that profile on the rears?

 

[mik_ok]

Good stuff. []

You can of course change the profile - but I'm not sure why you'd want to? [&:]

255/40/17 gives you the correct rolling radius and therefore it's the "correct" size. Your front 225/45 have a sidewall height of 101.25mm, your rear 255/40 a sidewall height of 102mm.

A 255/45/17 would have a sidewall height of 114.75mm and would increase your gearing by approx 4.5%.