kadeer

Hello,
I have 7/9 x 17 now, would like set of wheels for DE and Autocross.

I don't know from the OEM website, what offsets they have. Front need ET55, and rear ET70 for an 1995 993.

What happens if I change the rims to 7.5 and 9.5 x 17, then what offsets are required.

Thanks
-Kadeer

Tom W

On a narrow bodied car, the offset on both front and rear is 55 mm (ET55). I'm pretty sure offset on 8x18 and 10x18 was posted in a recent thread on the 993 board. You could split the difference for 7.5 and 9.5's. What size tires do you plan on using that you would go to 7.5 and 9.5?

kadeer

I was planning to go to 225/45/17 in the front and 275/?/17 on the rear.

Christer

Kadeer

The tyre size rear would have to be 275/35 I guess otherwise you would get a real increase in diameter. Before going that route it may be a good idea to check which tyres are available in those sizes - i think it's quite a rare size that one....

Another option is to go to 18" inch wheels with 225/40 and 265/35. These tyre sizes would be easier to find....

Christer

mark911

I have a 993 and run 8x17 and 10x17 supercup rims. I have seen others use the stock rims 7/9. If I had to do it over again I would go with the following setup.
Wheels - Buy some cheap used 7x17 and 9x17 cup rims.
Tires - Kumho 245/45/17 on front
Kumho 275/40/17 on rear.

These sizes will give you the correct diameter that is the same as the stock tires.

Good luck

Mark S.

Tom T.

[quote]Originally posted by mark911:
<strong>I have a 993 and run 8x17 and 10x17 supercup rims. I have seen others use the stock rims 7/9. If I had to do it over again I would go with the following setup.
Wheels - Buy some cheap used 7x17 and 9x17 cup rims.
Tires - Kumho 245/45/17 on front
Kumho 275/40/17 on rear.

These sizes will give you the correct diameter that is the same as the stock tires.

Good luck

Mark S. </strong><hr></blockquote>

Hi Mark,

Those sizes sound pretty large for a 993 wheel especially the front ones. Any problems with
rubbing or sidewall rolling? What suspension setup do you have?

Tom

Christer

Mark S.

The standard size for 17" are 205/50 on front and 255/40 on rear. If you go to 245's on the front (I am not sure whether they are too wide, but if you have them then I guess they are OK), the aspect ration should be 40 - i.e. 245/40 not 245/45 - this will be too big. Likewise with the rear, standard is 255/40, the 275/40 is also bigger. 285/35 based on diameter only would be better if there is enough room width-wise. I have made some calculations below to demonstrate:

Overall diameter 205/50/17 = 63.68cms
Overall diameter 245/45/17 = 65.23cms
Overall diameter 255/40/17 = 63.58cms
Overall diameter 275/40/17 = 65.18cms

I agree that your front and rear options are close to each other but not to the standard sizes. My suggestions are below:

Overall diameter 225/45/17 = 63.43cms
Overall diameter 285/35/17 = 63.13cms

Obviously these sizes are based purely on diameter so I don't know if there would a problem with the 285 on the rear from a room-perspective.

Just my 2 cents, but both your front and rear diameters are running close to 3% over standard.

Christer

mark911

The reason I go with the sizes I listed above is because they are available. Kuhmo's do not come in a 285/35. I have no rubbing issues. I had a stock suspension with these sizes and no clearance issues at all. I now have a PSS-9 suspension and the ride is 2" lower. I still have no clearance issues although I can no longer get the thickness of my finger between the tire and the fender.

Optimal sizes are great but living in the real world you must find sizes that are close to optimal given availability.

Kumho makes the following sizes along with the diameter.
225/45/17 24.6"
245/45/17 25.3"
255/40/17 24.8"
275/40/17 25.3"
315/35/17 25.3"

Standard Pirelli PZero's are as follows
205/50/17 25.1"
255/40/17 25.2"

As you can see the Kumho 245/45/17 and 275/40/17 are very close to stock sizes in diameter.

You can fit as big as 255/40/17 on front and 315/35/17 on rear but you will have to roll the fenders. 285's will fit fine with no fender roll but you will have to find a tire manufacturer that makes a 285 in the type of tire you wish to use.

I try to go with as large a tire on the front as I can get, due to understeer.

If you wish to be conservative go with 225/45/17 up front and 255/40/17 in the rear. Do not go with 225/45/17 up front and 275/40/17 in the rear. You will get a lot of understeer if you do.

Hope this helps
Mark S.

kadeer

Thanks you guys have been very helpful
-Kadeer

Jim Michaels

Wait, Kadeer. Before you buy wide rubber for narrow rims, I agree with Tom T.: 245s are too wide for 7" or 7.5" rims. Oh, you can get them on, and you can even drive around on them, but they will just not work as well as a narrower tire. I like Mark's "conservative" recommendation; 225 fronts and 255s rear. That should provide a good front/rear balance in grip.