Please Give Advise!!!!!

[Stuart]

Need to buy new wheels for my porsche boxter rims(7x17 and 8,5x17). On the front i'm thinking of 205/40/17 but for the rear I really need advice!!!! I've porsche alloy arms and 944 turbo brakes on the rear. What is the tyre to buy? 205/215/225 or 235? Can i go also with 205's on the rear because I can buy a set of Toyo's for a very good price. Come on everybothy, tell me what your are thinking or what your experiences are. Greetings from Holland.

[NYBugman1972]

I run a 245-45-17 tire in the rear of my car. I have 5x130 drums, a 1" spacer, 1 1/4" wider fiberglass fenders.

I would not run a 205-40-17 tire in the rear because that is way below the diameter tire that the transmission is geared for (165-15). Look for a rear tire close to that diameter for best results. Search the web for a tire diameter calculator to help you.

[Stuart]

Correct me if I'm wrong but if a 165/65/15 is the standard tyre for the back with a diameter/circumf. of 595,5mm/1870mm rhan the 205/40/17 is very close to this tyre with 595,8mm/1871mm, or I'm thinking wrong????
Come on help me!!!

8.5" = 215.9mm so a tire 215 or 225 would fit the width or even a 235 and pick your choice of profile (40/50/60) for aspect ratio.

If you run a 7" wheel in front with a 205 then do not run a 205 in the rear with a 8.5" wheel because the tire will appear smaller on the wider wheel.

The original tires, 165SR15 were 165/78R15.

[Stuart]

Thanks Superman. Alright, supose I go with a 215 or a 225 size tyre, what is the correct ratio (40/45/50?) for that size?

The aspect ratio (sidewall height) of the 205/40 is 82mm and the 225/40 is 90mm so, in my opinion, that would be a good match but I prefer the tires to look the same. If you'd like the rear tires to look larger than the front then go with the 225/60 or 235/50.

[Stuart]

is the tyre size not it importent when you look at the gearing. I mean is it not possible to buy a to big or to small tyre so the gearing is total of. Sorry for al my questions but with a subject as tyres i'm a real "nerd". How does a 215/50/17 tyre sounds?

Yes, the wheel/tire size is some what important for gearing and keeping the speedometer correct.

A 215/50 has an aspect ratio of 107.5mm. The original tire, 165/78R15 has an overall diameter of 638.4mm and it is favorable to be close to that number. The 205/40R17 is 595.8mm, a 42.6mm difference. That's a bit over 1-1/2" difference, a bit much but not too bad.

[Stuart]

what would be in your opinion the best combo of tyre sizes for the setup mentioned above? I've looked at al the members rides but many various tire sizes. I know by know that I need to buy wider fenders as the 8,5 boxers won't fit the fenders. I don't want to go al out on the back just a decent widder look. Thanks for al the reply's till now and greets from Holland.

Originally posted by Superman
205/40 is 82mm and the 225/40 is 90mm so, in my opinion, that would be a good match