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WHEEL WIDTH

Use this forum to ask questions, clarifications, and issues about current rules

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PAUL LARSON
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WHEEL WIDTH

Post by PAUL LARSON » Mon Oct 13, 2008 11:35 am

I just looked at a 2005 Carrera 997 S wheel width for a stock
set up. The stock size is 8" and 11"
I did the math and that would works out to
203 in the fronts and 279 in the rears.
Porsche has never sold this car with those little size tires.
All modern Carrera's come with 235 in the fronts and 295
in the rears. I never knew that these numbers were so off!!!
The stock size should be 9 1/4" and 11 3/4". I sugest you change all the sizes back
to mm. If you do not want to do this, then I suggest you put the 25.4 nuber
in the tire width modifications. I can bet that there are over 90 percent of the cars
that had no idea about this problem.

Why dosen't the stock car sizes match up?
Paul

Zone7Rep(Larry Sharp)
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Location: Livermore Ca

Re: WHEEL WIDTH

Post by Zone7Rep(Larry Sharp) » Mon Oct 13, 2008 9:43 pm

Paul the rules are for the rim sizes your thinking of Tire size. you can run any tire size that fits with out rubbing.
1993 RS America
Grand Prix White
Car #6

1974 911 Carrera (resides in Australia)
Light Yellow

1974 914-6 GT (resides in San Luis obispo)

1987 944 turbo (location unknown)

1979 911SC(Hummers have it)

1972 911T (location unknown)

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PAUL LARSON
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Re: WHEEL WIDTH

Post by PAUL LARSON » Wed Oct 15, 2008 9:30 am

Thaks Larry,
I will look into my rim sizes.
Paul

Zone7Rep(Larry Sharp)
Posts: 389
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Location: Livermore Ca

Re: WHEEL WIDTH

Post by Zone7Rep(Larry Sharp) » Wed Oct 15, 2008 10:29 am

since you have a c4s you would be our in house expert Paul for all the 996 guys out there
1993 RS America
Grand Prix White
Car #6

1974 911 Carrera (resides in Australia)
Light Yellow

1974 914-6 GT (resides in San Luis obispo)

1987 944 turbo (location unknown)

1979 911SC(Hummers have it)

1972 911T (location unknown)

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PAUL LARSON
Posts: 190
Joined: Mon Aug 14, 2006 3:30 pm
Location: SAN CARLOS
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Re: WHEEL WIDTH

Post by PAUL LARSON » Tue Nov 04, 2008 10:25 pm

Sorry larry,
I only have a 997 C2S. My brother has the
C4S and he does not track his car. Wish I could
be more help.
Paul

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David Leong
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Re: WHEEL WIDTH

Post by David Leong » Wed Nov 05, 2008 12:08 am

There has been a long misunderstanding that the base wheel sizes equates to stock. It does not.

The base wheel size is simply the wheel width that the rules committee chose to use as the basis for base points. Sometimes it was stock, but other times, it was not.
David Leong

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itacud
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Re: WHEEL WIDTH

Post by itacud » Fri Nov 28, 2008 3:28 am

I think the initial question is a little misleading. Tire widths never equal rim widths, on any make of car, but I'm guessing Paul's question stems from the notion that maybe points should be based off of tire width, and not wheel width? I'm not certain...

Regarding the last point made about the arbitrary nature of base wheel widths listed in the vehicle databse: I think that the intent of the base wheel width table is to specify what wheel width is the minimum size one gets with a base speced version of a specific Porsche model, so that one does not have to go out and buy a special set of wheels just to be competive in a stock car competing against other similar cars. As such, one would expect the wheel width database to reflect the actual wheel widths that came with the car listed. For the water cooled 911s, that generally means narrow body cars have 10" rear wheels and wide body 911s have 11" rear wheels.

Since each model of Porsche has base points awarded based on the perceived performance of a stock car, and the wide body cars already have higher base points awarded for some perceived performance benefit, it would make sense that no additional points should be awarded for stock wheels. To do so just contradicts the notion of having model specific base points as indicators of performance potential. To use an specific example, the 996 C4S has higher base points than a 996 C4, even though the C4S is the heavier of the two cars. The C4S then gets additional points for it's stock rear wheel. No other 996 or 997 widebody 911 has it's rear wheel listed smaller than the true rear wheel width, so it is logical to assume this particular exception to be a mistake. There is no reason for it to be intentional.

It seems that there is some amount of resistance to making corrections to current mistakes in the vehicle database. It's possible, however, that making these small corrections is all that is needed to create a truly functional system.
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johntavernetti
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Re: WHEEL WIDTH

Post by johntavernetti » Tue Dec 02, 2008 4:24 pm

Paul,
Take a look at your rims. Near the tire-valve, stamped into the metal of your factory wheels are two numbers: the wheel width (in inches) and the wheel offset (in mm). Your option XRR Carrera Sport wheels are 8.5 inches wide in front and 11.5 inches wide in back. Thus, they are 0.5 inches wider (both front and back) than the "base" wheel width for your car. That is because your optional Carrera Sport wheels are wider than any the other stock wheels Porsche offered for the 997.1 (all the other 19s were 8" and 11"). In order to properly classify your car, if you want to run those wheels for TT, you would need to input the correct wheel widths into your current car classification in the points system (which I believe would add 20 points to your car since you currently show 8" and 11" in the system).

In general, I agree with the idea that points should be assigned based on wheel width rather than tire width, since actual tire widths can vary greatly by manufacturer from what is stamped on the sidewall and because a wider wheel can generally make a given tire perform better. Running a 295 rear tire on a 11" wide wheel will not perform as well as the exact same tire on an 11.5" wheel (since the wider wheel will tend to spread the sidewalls out more... thus making the tire more stable under lateral loading and also slightly increase the tire's contact patch).

Given that tires have a much shorter useful life than wheels, it makes sense to use wheels rather than tires to regulate the combination of the two.
Having wheel width be the determinant of points also allows newer competitors to focus on picking whichever tire works best on their stock wheels, rather than trying to justfy an expensive wheel upgrade to make the most of a regulated tire width.
John

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PAUL LARSON
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Re: WHEEL WIDTH

Post by PAUL LARSON » Thu Dec 04, 2008 2:32 pm

Hi John,
You are right. I just went outside and I saw the 11.5 and the 8.5 markings. I
never knew that they were stamped on to the wheels. I will have to look at the
points better for next year. Thanks for pointing that out to me. I have learned alot
from bringing up this thread.
Paul

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