Eric_Oz_S2

I am going to get some Hoosier R6 tires for my 944S2. These will be used for track use - which is generally in the form of timed sprints where you run 6 to 10 laps per session, with generally 4 sessions per event.

I have a set of 16 and 17 inch wheels, and was intending to run one set with Hoosiers and the other with semi R spec tyres such as the Kumho KU36 which will get me to a from the track and also for use in wet weather. Both wheels are of similar weight (D90 16" and 996 twists 17")

For both 16 and 17 inch wheels I would run 225 front and 245 rear widths (front limited by both sets only having 7 inch fronts).

I'm leaning towards the 16" for Hoosier duty and was wondering what sort of performance difference there would be to the 17". Would it be noticeable in terms of lap times? Would the 16's feel much more "squirmy" due to the slightly higher side wall? 16's of course have a slight price advantage too.

So would there be much difference in performance?

mark kibort

use the 16s for wet weather, more side wall and flex for better control in the rain. 17s for the dry. There will be no noticable lap time difference between the two all other things being equal.
For years I bounced between 18s and 17s and all I had to do was make sure the 18s in the rear were a little lighter on the pressure, or they would be more skatey on my car, due to the stiffer sidewall. otherwise, they were near identical regarding feel and lap times.

Veloce Raptor

..

Eric_Oz_S2

^Thanks Dino - very useful input.

333pg333

Eric, you guys are lucky you live in a state that allows Hoos for club events. We can't run them down here unless we want to compete against Cup and other race cars on slicks. It's a shame, a crying shame. I have 2 sets gathering dust....

Eric_Oz_S2

Yeah - one of the committee members is a big Hoos fan. The argument is that bang for buck they are better than R compounds which are usually more expensive (888's, DZ03Gs, etc). Around $1,500 a set for 16s. They are allowed on "non modern" Porsches (classified as pre 968 and pre 993) can run twin grooves without moving up a class, others move up 1 class.

Heard of this:
PORSCHE SPORT CUP

After discussions with Porsche Australia, jointly we are keen to get an interclub event going. Porsche will officially support a category called PORSCHE SPORT CUP. An interclub championship sprint format for 2011 visiting a limited number of Porsche Club track days for the shootout. Classing the cars between the states is under discussion. In the mean time we have arranged 2 track sprint days with our fellow Porsche Clubbers interstate.

August 1, 2010 – NSW Club at Eastern Creek

July 4 2010 – VIC Club at Phillip Island

How many cars do you get to your sprints? We seem to get around 40-50.

Veloce Raptor

LOL...think about it. Different wheel diameters may change your effective gear ratios, which may change much of the car's behavior arouund the track. For him to claim "there will be no noticeable lap time difference" is just plain ignorant. That is what I was parodying.








Professional Racing and Driving Coach

DanR

like everything in life.......... it depends. It depends on what tire wall you run. If you run the same wall size on both wheel sizes I agree. However you can achieve same rolling diameter (or very close) depending on tire size wall you choose. There are also then the changed characteristics of running the same size rolling dia but different wall stiffness etc etc

M758

I agree. However not sure about the "no performance differece" thing. You may not be good enough to see a difference, but the 17's should be faster in the dry if you can use it. It won't be that much, but the difference does exist.

This assumes you can match the same overall diameter in both 16 and 17 sizes.

333pg333

Sounds great. I'll be there. Yes the classes will be interesting. Perhaps it will result in a standardisation throughout OZ? Here are the results from last weekend.
http://www.natsoft.com.au/cgi-bin/re...2010.WAKE.S2.Y

I am being looked at to be bumped up into the next class based on recent results. The problem with modified turbo cars is where to put them based on the potential to bump the boost. Where did you see the blurb about Porsche Aust. doing these events?

Wish we had a committee man fond of Hoosiers, but I am loving my Nittos just the same.

kurt M

It is the tire diameter not the wheel diameter.
He also said "There will be no noticable lap time difference between the two all other things being equal."

What contact patch size gain is there between a 16 and a 17 tire of the same rolling diameter?

Veloce Raptor

So you think you can run a 17" tire on a 16" wheel? LOL.









Professional Racing and Driving Coach

kurt M

Are you trying to be obtuse?

Oddjob

For R6s:

225/50/16, 24.7" OD, 9" Tread Width, $219
245/45/16, 24.7" OD, 9.2" T.W., $234

225/45/17, 24.7" OD, 8.8" T.W., $245
245/40/17, 24.5" OD, 9.3" T.W., $253

If economics is a consideration - go with the cheaper 16s. The taller sidewall on the 16s may feel a little softer than the 17s, but it wont be significant and it wont be a noticeable performance difference. Also the 16" wheels are cheaper to replace if you bend one.

GeorgeNZ

S2's here (NZ) either run 235/40/17 and 255/40/17 on 17x9's or a square setup on 16's, either 225/25/16 or 225/45/16's. Results don't identify a clear winner but the square setup is certainly more economical as tyres can be rotated around the car to even out wear - fwiw