Factory Tire Set-up
 

Guys,

The tires I have on my car now are relatively new about a year with once or twice week driving on them however the sizes I have on right now are:

Front - P205/60HR15
Rear - P235/60 HR15

and I really don't like the performance feeling of the tire. I find on the drives I plan that the tires do not hold up under aggressive driving. The back end tends to feel loose and it feels like its going to come around on me. I find that this can be dangerous because all the correction has to come from me in the steering. The factory tires for my car or so the sticker states are P185/70 VR15 and rear being P215/60 VR15 and I am thinking to switch back to these as Porsche proabably intended this size tire for a certain reason. Does anyone run these factory sizes? I think that a V rating is stickier than an H rating but will the size difference affect my ride. Any and all help is appreciated.

v rating is not sticker, but speed rating. A higher profile probably won't help. Your handling is a combination of tires, tire profile, tire compound, suspension settings, spring rates, shock rates, sway bars, etc, etc.

I think more information is necessary. I'd go to someone (or a shop) who really knows 911s and ask them for the opinion and how to make it handle the way you want.

Thanks, I have corner balancing and alignment on my list but I want to make sure I have the right size tire or close to the right size tire before I go and do all the additional stuff and end up with the same problem because of the wrong tires.

Looking at your replacement tire sizes, they are incorrect (and not just width).

Here is a bit of math to ponder:

Stock:

185/70-15 (Sidewall 12.95 cm / overall height of 25.20")
215/60-15 (Sidewall 12.9 cm / overall height of 25.16")

Replacement:

205/60-15 (Sidewall 12.3 cm / overall height of 24.68")
235/60-15 (Sidewall 14.1 cm / overall height of 26.10")

Notice the wheel/tire packages are about the same overall diameter front to rear in the OEM package, and you have staggered them to make the rear wheel/tire package larger than the front (by nearly 2"). This will change how the car sits, rides, handles, and even speedometer error.

For the rears, you should have used 235/55-16's... lower profile to make up for the increased width.

Almost, I bought a cheep ’84 Carrera Targa last year to turn around and make some $$$. Problem is after I fixed the leak that was depreciating the car it ran so good that I ended up keeping it for a “beater”. I purchased new tyres before deciding to keep the car and ended up with 205-60x15s and 215-60x15s on 6&7 Phone dials. After driving my wife’s Carrera with 205-55s and 225-50s on 7&7x16s I found I was over driving the ’84’s tyres by A Lot! The backs are a little taller than stock and are probably rolling over quite a bit. Try 34-36 lbs hot in the back. The only cure if you are going to do “spirited driving” is lower profile tyres and/or bigger wheels. The overall height and difference front to rear thing is important too.

Re: Factory Tire Set-up
 

I'm in a bit of a similar dilemma, in that I'm in need of new tires to replace the Pirelli P6000's on the car now because they're flat spotted from sitting too long in on spot on a cement floor, and are now unbalancable.

While I'm going to 16 inch wheels at some point, driving the car now is miserable due to the vibration, so it's new interim tires for me. I did a little searching and found that my best choice, cost versus performance, may be a Yokohama AVS dB S2 in size 225/60-VR15 rear and 195/65 VR15 in the front. That's about 0.3 inches larger in diameter in the rear and the stock size in front, for my 15x7/8 Fuchs. Stock rear tire size 215/60-15.

Then, when I get the 16's I own refinished, I'll go for a true max performance tire.

There is little that will improve the performance of your car so much for so little money as wheels and tires

Option 1(cheapest)
using your stock 6 & 7 x15 wheels 205/50(or 55) x15 & 225/50 x15 performance tires from the manufacturer of you choice.

Option 2(retaining stock appearance)
Get a nice set of 7 & 9 x16 w/ 205/55 & 245/45 performance tires from the manufacturer of your choice.

Option 3(not only more expensive but you will need to get into the fender lips a little)
8 & 9 x17 wheels of your choice(forged is better) and 225/50 & 255/40 performance tires from the manufacturer of your choice.

Bill has good points.

Personally, I'd use the stock wheels (and stock size tires) and get a really nice set of performance rubber for them (SO3's, AVS Sports, etc...).

Thanks for the responses. How exactly do I tell what size fuchs I have on the car? Bill you listed stock 6 & 7 x15 wheels. Is the 6 and 7 number the depth of the rim, if so is this in inches?

I like the possibility of going with the option 1 you listed -

Option 1(cheapest)
using your stock 6 & 7 x15 wheels 205/50(or 55) x15 & 225/50 x15 performance tires from the manufacturer of you choice.

What advantage is their going with a 55 or over a 50 or vise versa? This is the height of the sidewall in a percentage correct?

The size 205/50-15 means the tire is 205 mm wide and the sidewall is 50% of that width in height (102.5). The "15" is the rim diameter in inches.

Lower profile, meaning shorter sidewalls, used to mean better handling as the tire was less sloppy (less likely to roll over on itself). These days, tire technology is at a point where sidewalls are much better - much stiffer - so you can find good tires with a ratio of 55, or even 60 (shop tire type and brand, not profile).

Funny thing will all these numbers and profiles... a 275/40-16 tire sounds low profile, but the tire is so wide (the "40" means the sidewall is still "110" mm) that a 195/55-16 is actually lower profile!

I checked with Tire Rack and they have your '84 listed as having 15 inch diameter wheels in 7 inch width on the front and 8 inch width on the rear. The actual wheel size is listed on the back side of each wheel along with a bit of other information.

You, and another poster, are basically correct in that the tire height specification is a percentage of the maximum width, but more specifically this is with the tire mounted on the measuring rim width as listed by the manufacturer of the tire. If a given tire is measured on a 7 inch rim, but you mount it on an 8 inch rim, the widest part of the tire will be a larger number, as much as 5 to 10mm, or possibly more.

I can't speak for Bill, but he may be giving you a tire size that would give an effectively higher numerical gear ratio, increasing performance in a very cost effective manner, it's something to consider.:)

Stock '84 Carrera was 6 & 7 x15.

options were 7 & 8 x15 or 6 & 7 x16

6,7,8 or 9 are rim bead widths, they are embossed on the back of the wheel

If you can read Australian, this is an 8x16 +23.3mm o/s 944 Fuchs, It could be used w/ some effort on the front of a 911

http://forums.pelicanparts.com/uploa...1118355790.jpg

For max performance you want numerous sometimes contradictory parameters to be present

• max width For a Carrera ~235 -245mmf ~255 -275mmr
• min sidewall height /40 - 50f 35 -45r
• min rolling radius
• sticky rubber
• max rim width 8"f 9.5 -10" r
• max rim diameter 15 -18'

I planned on going to 16's now, but it will be sometime in the future. For now I am going to go with 205/60-15's and 225/60-15's. The front is slightly shorter, about .3", than the stock 195/65's and the rears are only .3" taller than the stock 215/60-15's. These are on the 7 & 8 x15. I want to keep the stock look of the car and have found a deal on some Yokohama's that I can't pass up.

Go see Darrin at Westend and get a full corner balance, camber adjust, and alignment first. He will also check the condition of the overall suspension system, things like bushings.

I PM'ed his info to you a while back, it well worth every cent. He is booked usually two weeks out and is the only one who will touch your car. FYI bring cash or a check, credit cards are no good at his shop.

Bret,

I will call him tomorrow and get that done. I forgot I had that PM from you.

Thanks again,

Chris

Just had the alignment, corner balance, camber adjustment and the car slightly lowered and wow what a difference. The Porsche seems quite a bit different. Darrin at West End Alignment set-up the car for more performance while staying slightly on the conservative side for tire wear. Amazing what a difference.

Here are the numbers for anyone interested:

LF: 605 RF: 572
LR: 884 RR: 851

1456 on each side across the diagonal.

Total Weight with me in the car: 2,912 pounds

Next are the tires and possibly rims with a stock appearance if possible.