rickw51

I have an 89 C4 with 17 x 7 inch front rims with 215/45/17 tires on presently. I would like to use Michelin Pilot ps2's which only come in 225/55/17. Has any one tried this size and or this tire?

robmug

I'm running 205/50x 17 on the front, so 225 sounds a little wide for the rim...I do recall however that a few C4 owners run wider front tyres to reduce understeer...

garrett376

225/45 is fine for the front on a 7x17 rim - I run this on both my cabrio and race car with no problem (note they are 92's with the different steering stops), matched to 255/40 rears. 225/55 is too big of a tire, though... unless you go to a larger rear tire, you're likely going to have ABS and PDAS issues.

Computamedic

According to all the information I can find on the Net, the MINIMUM rim size for a 225/45 is 7.5J. The tyre is too big for a 7J wheel and will run the risk of running off the rim under cornering.

I know that one of the Smart Groupers recently had to abandon plans to fit 225/45 tyres because the car had 7J rims. The maximum size tyre that can be (safely) fitted to a 7J rim is a 215/45.

As Garrett said, the 225/55 tyre is the wrong aspect ratio - there is a 8.64% difference between it and the 215 already fitted - the maximum diffrence allowed is 2.5%.

Hope that helps.

Regards

Dave

rickw51

Thanks for the replies. Food for thought.

Devils_son

I very much doubt that 7J is not wide enough for a 225 tyre. The 964 small body came with 8J on the rear, with a 255 tyre, which is the same ratio...

Computamedic

I'm afraid you are being too general in your comment. The suitability of a tyre to a rim is determined by a number of factors, but mostly it is in the aspect ratio of the tyre. The smaller the aspect ratio, the smaller the range of rim widths suitable. This is because the shorter sidewall of the lower aspect ratio tyre cannot bend as much as the taller sidewall.

If you look at the rim width calculator (here ) you will see that the range of rims suitable for a 255/50 tyre on a 17" rim is 7J to 8.5J but the range for the lower aspect 225/45 tyre is 7.5J to 9J. There seems to be a major difference once the aspect ratio drops below 50%

Making assumptions in this area is very dangerous - it pays to check the facts.

Regards

Dave

Tom W

Not to start any flame wars, but a 7" rim is perfectly acceptable for most 225/45 tires. If you look at the specs on the tire rack or Michelin sites, Michelin says the 225/45x17 PS2 may be used on 7-8.5" rims.

I have used 225/45's (MPSC) on my 7" rims at the track for years without issue.

Rather than using a generic calculator, it helps to check the manufacturer's web site or other sources for information specific to the tire in question. Note that the original post has a typo as PS2's come in 225/45 and not 225/55 x 17 (at least according to Tire Rack).

garrett376

The only issue I have is that I can't get my 225/45 17 kumho's to wear out on the fronts before they're heat cycled out!

Tom W

You could probably get them to wear more by driving too fast in slow turns so the car pushes like a pig and you scrub the rubber off the tires. Not that I have any experience with such driving, of course...

Devils_son

The thing is: Porsche OE 17" for the 964 was 8J with 255/40/17 tyres. According to the same calculator, these rims are too small. So I still beg to differ...