8s or 9s on an SC - Whats the difference

na2ub · 01-13-2005, 06:03 AM

To get bigger rubber on the car, I can move the 7s up front with 225s on them and sell the 6s. What is the difference between getting 8s or 9s for the back, assuming I will be running 245s back there on both wheels. Again I am assuming 225s up front and 245s in the rear will maintain the approximate "rubber ratio" to the stock 205s / 225s. My only guess is that the 9s will fill out the tire a little better and help with sidewall rigidity. So what's the difference?

Doug

CarreraS2 · 01-13-2005, 06:48 AM

Maybe some have done it, but it sure seems like the vast majority of 911s will have rubbing with the 225s on the 7s run up front. Some get some rubbing with the 7s on front even using 205s.

A 245 fits better on a 9 than an 8. That's what the factory used: 225 on 8 and 245 on 9s.

coloradoporsche · 01-13-2005, 06:48 AM

Hi Doug,

I have the same question. I just bought 16x8s for the back of my 79SC thinking I'd use the 7s in front. But the more I read in the archives about tires, the more confused I get.

Seems many people suggest 205s in the front and 225s in the back on 7s and 8s...which are the same tires I had on the 6 and 7 wheel combination! I want to track my car and get as much rubber on the road as possible so I'd like to put 225s on the front 7s and 245s on the back 8s...but the consensus from the archives seems to be 9s are better for running 245 tires, and that 225s on front 7s may cause a "rubbing" issue on my lowered car.

I hope I just didn't waste my $ buying 8s for the back. Appreciate any comments from tire experts.

Drago · Drago's Garage

Double Edit: I stand corrected...see Wil Ferch's post below.

Edit: I run 7's and 9's with 225 and 245 with no rubbing.

Cdnone1 · 01-13-2005, 06:53 AM

I run 7&8s I have 225 on the front and 245 on the back. I had to roll the fenders on the front after I lowered the car and shreaded the drivers side front. Since then I have had no problems

na2ub · 01-13-2005, 06:58 AM

I found this chart on wheel size and fitment: http://members.rennlist.com/1976c38/index.html

1) For those who have 7s with 225s up front, what is involved with rolling the lip.

2) Is the answer to the 8/9s with 245s question that 245s fits better on the 9s? I suppose 8s and 9s will be somewhat similar in price, so just get the 9s?

Doug

Joe Bob · Joe Bob's Garage

using 45 series tires lessens the probability of rubbing when using 225s and 245s with 7s and 8s....I have been very happy with this set up.

No fender rolling required on my ride.

edward993 · 01-13-2005, 07:14 AM

FWIW, I've noticed that availability and price may sway you (it did me), with 9s being much more scarce and considerably more expensive ...if cost is a concern, of course.

Edward

coloradoporsche · 01-13-2005, 07:18 AM

I bought 8s because 9s were next to impossible to find.

MotoSook · 01-13-2005, 07:21 AM

245's (45 series) on an 8" rim for the rear is just fine. I've got 245 SO3's on the rear and the tire fits on the rim just fine.

Up front, I have 205 SO3's (50 series) on a 7" Fuch, but under track loads, I was rubbing so I rolled the lips a bit on the fenders.

coloradoporsche · 01-13-2005, 07:27 AM

As Doug asks above, how do you roll the fenders?

Martin

MotoSook · 01-13-2005, 07:38 AM

There are a number of ways...

Search for "rolling fender".

niner11 · 01-13-2005, 07:39 AM

I checked wheel enhancement yesterday for price and availability on 8's and 9's. Ballpark 825.00 for the 8's and 50.00 more for the 9's NIB. If used prices go any higher it would make sense to buy them new.

na2ub · 01-13-2005, 07:41 AM

Souk,

Assuming the same diameter rim, with only the width of the tires changed, stock 205/225 would imply 47.6% of the rubber is up front. Changing 225/245 would retain this ratio at 47.8% rubber up front. But 205/245 would decrease the up front rubber ratio to 45.5%. Wouldn't that contribute negatively to the understeer of our cars with the lightness of the front end?

Doug

scottb · 01-13-2005, 07:50 AM

Quote:

Originally posted by coloradoporsche
how do you roll the fenders?

When I put my 7s up front, I had some rubbing. I REALLY did not want to roll the fenders on my original factory paint. So, I had the camber adjusted a bit, and the rubbing went away. My car's only a weekend toy, so the extra wear on the tires due to the camber adjustment was a non-issue for me.

As to rolling fenders, there are several ways. It seems the method of choice is to use a baseball bat between the tire and the lip. Do a search for "rolling" "baseball" and I'm sure you'll come up with a bunch of hits. Also, I've heard that Tire Rack will loan (rent?) a tool that can be used to roll fenders.

MotoSook · 01-13-2005, 07:52 AM

Doug,

Check the tread width spec for the tires you plan to run.

IMO, you won't notice the difference between 47.8% or 45.5%, if those are indeed the correct values for tire contact....esp. on the street! On the track, there are many things that will determine how your car handles. FWIW, I ran my car at the track with 205/245's and I had a blast! Driver input on the track (and on the street in some cases) is more important than the 2.3% difference.

Wil Ferch · 01-13-2005, 07:54 AM

Notice that 9" is wider on both the inside and outside than 8"....unlike previously mentioned here....

As to section width of 205's with 7" front...notice that the track widens considerably using 7" ( vs 6") ...in addition to better sidewall support provided by the 7". Together...this aids in cutting unwanted understeer compared to 6". ( point?....you still get this kind of goodness ..it's not just the possible 225's front that give you this).

Wil