Tyres

Post by **Beach Bum** » 16 May 2006, 22:27

I am fitting a set of Porsche Boxter alloys and have been advised by my local tyre fitters to fit:
205 45 17 front
225 45 17 rear

They are 17 inch rims-fronts 7 and rear 8.5

does this make sense and have I been given good advise.

Post by **Ivorblueun** » 17 May 2006, 18:42

from what i understand yes as the tyres must be wide enough sit on the rim of the wheel correctly and as the rear wheel rims are wider so the wider tyre . A 7J rim equates to approx 180mm, which is what the tyre should be at the bead, to get a tyre to match makes it about 205 but as the rear works out to about 215mm you can see that 205 would be too narrow and vice versa if the wider tyre was fitted on the narrower rim. what confuses the issue is that tyre manufacturers use mm and rims are in inches have a look here for some anorak stuff on wheels and tyres http://www.chris-longhurst.com/carbible ... bible.html

Post by **kevtherev** » 17 May 2006, 21:44

Also these tyres would affect the speedo slightly as they are smaller overall diameter from standard

Post by **Ivorblueun** » 17 May 2006, 22:23

Yes, didn't look at that side as the speedo is run off the front hub a 50 profile tyre would be nearer the mark and would not affect the gearing greatly when fitted on the rear and from what ive seen is probably a more readily available
size so cheaper (still expensive in my book though)