So I've been sifting through the rules of PCA SPB class to know what I need to do and what I should modify to be competitive. I got to the wheels and tire section and am a little confused and hoping for a bit of direction. It says the front wheels can be either 17 x 7 or 17 x 8.5 and the front tires can be either 235 or 255 from what I understand a 235 tire wont fit on the 17x7 rim, Would it be safe to deduce that I would need 17x8.5 rim for this? If not how would one go about being in compliance with a tire that doesn't fit on the approved rim?

 

Definitely don't try to squeeze 255 tires on the 7" rim. However one might analyze the syntax of the rule, what it is in the real world is fortunately simple:
1) Staggered configuration, like a stock setup: 7" (235) in front, 8.5" (255) in rear.
or
2) Square configuration, "stock" rear size all around: 8.5" (255) front and rear.

People generally gravitate to option (2) because the additional grip in front is a good thing given the balance of the car. Option (1) is a good way to use a pair of 7" rims as the front part a rain tire set.

That is all.

 

@trygve Oh I definitely wasn't going to try to squeeze those tires on. haha. I should be more clear, i meant using the 17x8.5 for the 235 tires. From what I read the widest tire that will fit on a 17x7 is a 225. Additionally, do 255 fit in the front or would i have to roll the fender for it to fit?

Thanks for the reply!

 

Trygve nailed it, just run 255's on the 8.5" wheels all around. Run a 5mm spacer up front, there's no need to roll the fender. Keep one pair of 7" wheels for rains.

 

Awesome sounds good! Thank you for the advice. I think I will run the square set up. I know I'll end up losing top end speed but my local track only has 1 long straight.

 

Think of top end speed as being more a function of how much speed you carry through the preceding corner...and that vmin will be higher with the square setup.

 

Here is some info that I assembled from a couple of sources:

Spec Boxster Wheel Options PCA Legal (17 x 8.5 Square Setup Only):

OEM:

Twists (996 Carrera 2) - 996.362.126.05 50mm offset (67251) – 10.27kg (22.6lbs) each.

Twists (Boxster S) - 986.362.126.05 50mm offset – 10.4kg each (22.9lbs) each.

Semi twists - 986.362.126.06 48mm offset (67259) – 9.62kg each (21.2lbs) each.

5 double-spokes (Boxster II S) - 986.362.126.07 48mm offset – 9.5kg (20.5lbs) each.

BBS - Sport Classic XRA - 993.362.126.55 50mm offset (67239) – 9.39kg (20.7lbs) each.

Tequipment "Dyno" wheels - 996.362.126.55 50mm offset -- Do not have weight data supposedly very light similar to 5-spoke.

Aftermarket:

Jongbloed spec Boxster wheels – JRWPCA17x8.5/48SPB – Reportedly around 20lbs each, have not found exact weight info online yet.

Rain Wheels (Front):

Some people advocate running the 17x7 stock fronts in the staggered setup for rain tires (as fronts).
Use 996 Carrera 2 Twists front wheels (17 x 7) - 996.362.124.00 55mm offset – 8.2kg (18.1lbs) each


.

 

..and be prepared for great turn-in with corner entry oversteer if coming in hot and very effective trail braking rotation. You'll have to do some tuning with the front GT3 bar to get it where you like.

 

I remember Chris Drake saying that running square was a second slower, depending on the track (we were at Hastings).

 

ok,....so wheel availability kinda sucks. anyone got a set of 8.5's they would part with (or two)....

 

Not sure if this helps but this seller on eBay has a few: LINK

 

Bought some of the Jongbloed wheels. Weighed a few of them, they are all 21.8 lbs each actual.

Will be stripping tires off my sets of twists. Will weigh them to see actual weight vs Porsche's published weights posted above.

 

You are assuming that your scales are accurate, unless you have checked them against a known standard.

 

LOL...no. I use an old bathroom scale in my garage. I doubt it's off by pounds, but probably +/- a few tenths.

Maybe I'll weigh the Jongbloeds on the other 2 bathroom scales in my house to see what I get. Standby.

 

The Jongbloeds were spec’d to be no lighter than the lightest existing OEM wheel when they were declared the new SPB wheel. Pretty dang close.