Please Give Advise!!!!!
 

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.

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.

question
 

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.

size?
 

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.

another question
 

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.

all right
 

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.:)