2016 tire rules for street stock

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2016 tire rules for street stock

Postby sf.in.sd on Tue Jan 26, 2016 11:30 am

There was a lot of discussion on the rule proposals for 2016 and in the end the language seemed to stay the same (copied below). Before I replace whats left of the tires that I wore ragged at CVR, I wanted to be certain on what seems to be a lot of leeway...

Using stock rims on a car with front and rear widths of 235 and 265, replacements of up to 255 and 285 would be acceptable?

Modifications not allowed for Street Stock...
o) Installation of factory or aftermarket front wheels with a width
greater than the widest front wheels available from the factory for
AX, DE & TT Page 11
that model range, and rear wheels with a width greater than the
widest rear wheels available from the factory for that model
range; any increase in track (front or rear) greater than 14mm
over stock.
p) Installation of tires with a section width more than 20mm wider
than the largest tire available from the factory for that model
range.

Thanks,

Shawn
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Re: 2016 tire rules for street stock

Postby marcus981 on Tue Jan 26, 2016 1:50 pm

Shawn,

I believe you are correct on the size restrictions for SS, but make sure you don't forget about these other existing clauses for SS tires:

1. STREET STOCK CLASSES
...
...
The following modifications are specifically not allowed:
a) Any aftermarket enhancement listed in Section III that is not
mentioned in the above list of allowed modifications.
b) Tire tread wear ratings less than 140 or less than the OEM tire
tread wear for that model and year of car, whichever is lower.
c) Any tire that is not street legal
...
...
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Re: 2016 tire rules for street stock

Postby JayG on Tue Jan 26, 2016 10:57 pm

I spoke with Russell specifically about this.

Russell, please correct me if I am wrong

you can go 20 mm wider that any tire width that was available on that axle in your series of car regardless of the wheel diameter.
that means for example on a 986, in 18" the factory tires were 225 front and 265 rear and in 17" 205 front and 255 rear, you could use 245-17 front and 285-17 rear
you also can not increase the the wheel width wider that the widest wheel available for that axle
on a 986, 18" optional wheels were 8" front and 10" rear so you could use a 8x17 front and 10 x 17 rear

all of this assuming you do not increase the track by more that 14 mm per axle

so in a 981, if for instance the GT4 has wider tires and wheels than say a base 981, you can use the GT4 wheels and tires as your basis for maximum width

I had hoped that this was going to be mentioned on the registration page for the first events of 2016 so people that don't normally check for new rules would be aware of it.
I would bet that there will be a few that will have tires and/or wheels too wide for the new SS rule that want to run in SS
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Re: 2016 tire rules for street stock

Postby sf.in.sd on Wed Jan 27, 2016 7:55 am

Thanks Marcus and Jay,

Note also that I failed to mention some of the other provisions:

Allowed= Aftermarket or different factory wheels except as prohibited in
paragraph o. [previously mentioned], below. Section XIII Part K requires that the tire
must be covered by the fender. [as well as needing to have tread- >2/32 to start and >1/32 for timed runs, and not be too old]

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Re: 2016 tire rules for street stock

Postby JayG on Wed Jan 27, 2016 9:22 am

Here is a good (?) list of tire sizes for most P-cars
https://tiresize.com/tires/Porsche/
YMMV
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Re: 2016 tire rules for street stock

Postby jbrennen on Thu Jan 28, 2016 10:17 am

JayG wrote:so in a 981, if for instance the GT4 has wider tires and wheels than say a base 981, you can use the GT4 wheels and tires as your basis for maximum width


I'm not sure how this would actually be interpreted, but I would assume that at most, you could use the tire size for a different car of the same model as yours within the same SS class.

The GT4 is in SS08. The 981 S and GTS cars are in SS06. The base 981 is in SS04.

I'm sure that the tire size was at least part of the decision to put the GT4 in SS08. Letting SS06 or SS04 cars take advantage of SS08 tires just because the GT4 has the same "981" designation seems against the spirit of the rules.
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Re: 2016 tire rules for street stock

Postby Greg Phillips on Thu Jan 28, 2016 4:29 pm

jbrennen wrote:
JayG wrote:so in a 981, if for instance the GT4 has wider tires and wheels than say a base 981, you can use the GT4 wheels and tires as your basis for maximum width


I'm not sure how this would actually be interpreted, but I would assume that at most, you could use the tire size for a different car of the same model as yours within the same SS class.

The GT4 is in SS08. The 981 S and GTS cars are in SS06. The base 981 is in SS04.

I'm sure that the tire size was at least part of the decision to put the GT4 in SS08. Letting SS06 or SS04 cars take advantage of SS08 tires just because the GT4 has the same "981" designation seems against the spirit of the rules.


That ship has long sailed :surr:

The spirit of the rules for SS was to drive your car as delivered without after-marked modifications.
If you are adding wider wheels & tires and picking the stickiest tires available you should be running in a CC class IMHO
But specifically Caymans, I think the Cayman, Cayman S , Cayman R and Cayman GT4 are all different models and you should not pick and choose tires across model lines

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Re: 2016 tire rules for street stock

Postby rshon on Thu Jan 28, 2016 6:17 pm

First, let's remember what the SS rules were previous to this year: You could run ANY size rim and tire so long as it fit under the fender lips. We had some folks running the equivalent of the REAR tires and wheels on the FRONT, and sometimes even bigger tires and wheels on the rear (with sometimes interesting interpretations of "under the fender lips"), and other members with relatively stock cars (justifiably) felt that such situations were not really in the spirit of the SS classes. But the rule was originally written this way because many folks with otherwise stock cars liked to jazz their cars up with custom wheel and tire setups.

Now the revised rules call out respective limits on the front wheels/tires and rear wheels/tires based on what was available from the factory. However, every Porsche model in recent memory has had an eye-watering list of optional equipment, and wheels and tires are no exception, and/but these options could change slightly from year to year.

What the revised rules specifically say is that in SS classes you must limit yourself to wheel widths (and tire widths + a 20mm allowance) that are/were available from the factory for that Model Range. Model Ranges are specified in Section IV of the rules, but basically all 986s are in a model range, all 987s are in a model range, and all 981s are in a model range. So this means that you can use 981 Cayman GT4 width wheels and tires on a base or S 981 Cayman or Boxster, but the reality is that those cars already were available with optional wheel/tire sizes that were close to, if not the same size as, those spec'ed on the GT4.

It should also be noted that all other factory options allowed in SS classes and performance equipment swaps allowed in CC classes are also based on Model Ranges. There are also no stipulations on wheel and tire diameters in any of the rules language.

Is this as limiting as bone stock? Nope. Is it sometimes better than "fits under the fender lips"? You bet...
Last edited by rshon on Mon Feb 01, 2016 11:10 pm, edited 1 time in total.
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Re: 2016 tire rules for street stock

Postby ttweed on Fri Jan 29, 2016 11:01 am

rshon wrote:So this means that you can use 981 Cayman GT4 width wheels and tires on a base or S 981 Cayman or Boxster, but the reality is that those cars already were available with optional wheel/tire sizes that were close to, if not the same size as, those spec'ed on the GT4.

The GT4 stock wheels and tires are 8.5 x 20" with 245/35-20 tires (front) and 11 x 20" wheels with 295/30-20 tires (rear). Both the 987 Boxster and Cayman had an optional wheel set of 8.5" x 19" w/ 235/35-19 tires (front) and 10" x 19" w/ 265/35-19 (rear). The 981 series Boxster and Cayman S had the same sizes optional, but in 20" diameter. The new Boxster Spyder has front stock rims @ 8.5 x 20 and rears are 10.5 x 20 with the same 235/265 tires as a Boxster S, so the main difference with the GT4 is the 11" rear rim width and the wider stock tires.

So my understanding is that all stock 981s in SS class under the current rules could run a 265 front and 315 rear tire on 8.5"F and 11"R rims, if they can fit under the fender and are 140 treadwear or greater. A 987 can run a maximum of 255 front and 285 rear on 8.5"F and 10"R rims (with the same restrictions on fit and treadwear). Is that right, Russell?

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Re: 2016 tire rules for street stock

Postby rshon on Fri Jan 29, 2016 11:27 am

Tom, your understanding is correct, but people also need to remember the 15mm track increase limitation as well. Essentially this limits the decrease in wheel offset to 7mm below stock (7mm sticking out further), so folks will need to worry about strut interference as well as being covered with fender lips with oversized tires.

The original proposal was to stick with factory tire widths, but there was a lot of feedback from the membership to add some leeway to tire widths while keeping rim widths to those available from the factory (similar to SCCA SS rules, which allow ANY tire that will fit on the largest factory-size rims).

In reality, given all the limitations, I'm not sure that 315's will fit on the back of a 981 (either on the inside or the outside), as the GT4 pretty much has all the tire that would fit the body.

We'll see how things go the first half of this year. If people are still unhappy, folks can always submit proposals to make the rules even more stringent for next year...
Last edited by rshon on Mon Feb 01, 2016 11:10 pm, edited 2 times in total.
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Re: 2016 tire rules for street stock

Postby jbrennen on Fri Jan 29, 2016 11:49 am

I guess I missed the rules interpretation of "model range".

I probably assumed that each individual line in the SS listing by car was a model range:

SS04: 987 Boxster S (2005-2012)
987 Cayman S (2006-2012)
981 Boxster (2013-)
981 Cayman (2013-)

SS06: 987 Boxster Spyder (2010-2012)
987 Cayman R (2011-2012)
981 Boxster S/GTS (2013-)
981 Cayman S/GTS (2013-)
997 Carrera S/4S (2009-2011)
991 911 Carrera/4/Targa (2012-)


The SCCA rules are actually much more strict than what we have now -- in SCCA's Street class, you can't under any circumstances run a wheel wider than what you could have ordered from the factory on your exact car for that particular axle. (For instance, if 8 inch was the maximum front wheel width for your car, but 8.5 inch was available the next model year, you're still stuck with 8 inch because you couldn't have ordered 8.5 inch at the time.)
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Re: 2016 tire rules for street stock

Postby ttweed on Fri Jan 29, 2016 5:48 pm

rshon wrote:Tom, your understanding is correct, but people also need to remember the 15mm track increase limitation as well. Essentially this limits the decrease in wheel offset to 7mm below stock (7mm sticking out further), so folks will need to worry about strut interference as well as being covered with fender lips with oversized tires.

I think 305 would be the largest size you could physically fit on the rear of a GT4. James G-W could not get a 265 to fit on the front of his, without camber and caster changes that would take you out of SS class. Besides that, you have to find a good tire to run that comes in the sizes you need. There aren't many choices for the GT4 with 20" wheels, so changing to 19" rims will be necessary. If you have CC brakes, even 19"s will be tough to fit. Using 18"s would require mods that would also take you out of SS class. In 19" the best tire would probably be the RE-71R, and the widest they make right now is a 285. Maxing out the widths probably won't happen. Most people will probably just use the stock Michelin Sport Cup 2 tires, which are good, they're just not the fastest and they're expensive to replace.

rshon wrote:We'll see how things go the first half of this year. If people are still unhappy, folks can always submit proposals to make the rules even more stringent for next year...
All you would have to do is add "Except GT4" to the line of the Model Series that says "All 981".

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Re: 2016 tire rules for street stock

Postby Greg Phillips on Sat Jan 30, 2016 12:07 am

"Is this as limiting as bone stock? Nope. Is it a whole lot better than "fits under the fender lips"? You bet..."

I am not so sure, you just posted that the rules allow tires larger than will fit on the models in question. Not very limiting  :bowdown:

The track ruling and fitting under fender lips are rules that predate Street Stock.

The present interpretation of model ranges may need adjustment. Because the GT4 or GT3 had larger tires should not allow a base 991 or 981 Cayman to add tires to match them.

I would think the model ranges should be Boxster, Boxster S, Boxster R, Cayman, Cayman S, Cayman R and GT4, or at least limit the tires to the optional sizes for a Boxster or Boxster S etc.

Again, if you are buying tires and wheels to autocross or go to the track, you should be running in a CC class IMHO

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Re: 2016 tire rules for street stock

Postby jbrennen on Sat Jan 30, 2016 2:32 am

Greg Phillips wrote:Again, if you are buying tires and wheels to autocross or go to the track, you should be running in a CC class IMHO


The SS rules should reflect the reality of car ownership, which is that tires are consumables and that most owners aren't particularly interested in doing the research to figure out what tire models were available for factory delivery on their car. They will buy the tire that gets good reviews, or the tire that's on sale, or the tire that's available for immediate delivery (rather than waiting two weeks on a back-ordered tire).

Once you accept the idea that car owners don't place any particular value on sticking with the factory tire model, and that replacing tires is not viewed as a "modification" by most people, you have a little bit of a problem enforcing your quoted sentence above... How do you determine if an owner bought tires "to autocross"? The guy who buys the Bridgestone RE-71R because he read about it on an autocross forum is sent to CC class, but the guy who bought the same tire because it had the highest dry traction rating on Tire Rack's website gets to run SS? (It does have the highest dry traction rating there, by the way...)
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Re: 2016 tire rules for street stock

Postby JayG on Sat Jan 30, 2016 1:37 pm

to force people to move from SS to CC is grossly unfair

To be competitive in a CC class generally requires much more than throwing on some maybe wider and stickier tires.

I have no problem with someone putting on the best tire combination they can find on a SS car. That is something anyone can easily do at a reasonable (?) cost. Making suspension mods, etc is far more expensive.

For example a 04 Boxster S runs in SS02 and at minimum is CC06. In no way just by changing tires to the "best" allowed tire under the rules would it be competitive in CC06 or higher without extensive other mods and upgrades

I could argue that cars with a PDK in SS should be bumped up a class from non PDK cars.
Again, I'll use SS02 as an example. It includes all 986 S, all 987.1 and 987.2 Boxster and Cayman base models) as well as all NA 993
The 987 with a PDK, especially 987.2 is several seconds faster than a 986S. Does the driver play into it, sure, but 2-3 seconds in an AX and 8 seconds or so on a track is a huge difference
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