Ideal Wheel Size for Track/AutoX for the Boxster
 

I went to my first AutoX on Sunday with the PCA Chesapeake Region and boy... did I have fun!!! I have the OEM 18" wheels and I was considering getting a set of R-compound rated tires and maybe a used set of wheels so that I don't damage mine.
I have seen many different Boxsters on track with 17 and 18 inch wheels. I know that by changing to 17" wheels the tire profile will increase, so is this better for track/AutoX??? What are your thoughts??
Thanks
LRR

For high performance driving you want a lower profile (in the 45-55 range) because the sidewalls will flex less and allow you a better, more precise manuverability.

My autocross/track wheels/tires are 225/45/17 in the front and 255/50/17 in the rear.

well if your street tires are heading down the final stretch I would not get the r-comps anytime soon. Race what you got and make your mistakes on the old set.
Once the courses start to look repetitive to you invest in new tires. You don't want to make all your mistakes on new tires because then your stuck with chewed up tires for the rest of the season. Those Rcomps, particularly in hot summer, are easily shreded on a poor surface.

Do a search on the Rennlist Autocross/competition forum for optimal Boxster sizing.
http://forums.rennlist.com/rennforums/forumdisplay.php?f=85

and if you haven't already, you should join your local PCA. Here in Jersey one of the big dealers give a 10% discount to PCA members which comes in real handy when you do your pre-autox/track annual service/alignment/brake flush/oil change/etc.

Luis,

I think we spoke on Sunday briefly. I was in a non S yellow boxster that was well, quite quick ;)

1) 17" wheels, and their tires, will be cheaper than 18" wheels and tires. Could be as much as $50-70 per tire cost difference. Plus, you can pick up 17" rims for $600-1000 vs twice that or more for 18"s.
2) What size tire do you want to run. What brand tire do you want to run.
3) While the side profile may be taller on a, for example 255/40-17 vs a 265/35-18, you will find the overall circumference is very close. Then again, I can't say I call a 40 series tire a balloon ;)

You will find that, say a Khumo XXX comes in 225 and 255 in 17", but a Yokohama or Toyo might make a 235/255 combo. Small differences but something to consider.

Looking back, I wish I went 245's all around because I would prefer to get the rear of the car to rotate more. However, some shops don't want to squeeze a 245 on a 7.5" wide rim. So, in my case I am running 225/275-18s (stock is 225/265) but notice a touch more understeer than I desire.

Its all good fun but remember the best improvement to make is SEAT TIME. Once you learn to drive well, then the other enhancements can make you even quicker.

just a very general statement as I has exactly the same thoughts after my first autocrosses:

It's not the car, the tires, or the suspension, it's the driver
As long as you can easily find someone at the same event that does the same Auto-X course in the same car 5 sec faster or a lap at the track event 15 ~ 30 sec faster than you, don't bother investing in expensive new hardware.

When your driving skills are finally honed enough (after a few years) that you reach the limit of what your car can provide, then think of stickier tires, bigger rims, PSS9 suspension, chip tuning etc. (or a GT3 RS ;) )

I am not trying to be arrogant here, as I myself am still at the beginning of this learning curve. I rather invest all the money I save by NOT buying rims/tires etc. to buy me more seat time at Auto-X and DE/TT events - Buttonwillow here I come :D

what kind of PSI should be run on 17s? track and/or daily

don't get me wrong, I agree with most of you and to be honest, I finished first in my class on my first ever autocross, that's pretty good!!! I am not trying to be any faster, I just don't want to damage my original wheels. That is why I am askign about weather to get 17 or 18 inch wheels since I will be looking for a used set on ebay.

Why are recomending to use 17" wheels if you are using 18"??? Are there any advantage of the 17" wheels other than the broader availability of tires and wheels??? In other words, the tire profile offered by the 17" wheel setup provide better performance than the 18" wheels??? It seems that the 17" wheel setup will absorb better the track/Autocross bumps, but I don't know if overall the low profile of the 18 will be better. There are some pretty good deals on ebay, so please help me out!!!! thanks, again, I am just looking for a used spare set of wheels that I can use for track/autocross so that my original wheels don't get damaged! Thanks!!!

I am running 18"s because when I bought the car last fall, that's what it had. I don't want to sell them because they are correct for the option codes the car has and I appreciate originality ;)

While I did PM you, let me share some of those thoughts here too:

The 255-40-17 that was the standard size for rears on the 17" rim has a nearly identical OVERALL DIAMETER as the 265-35-18 that is the OEM rear 18" tire size.

So, going from 17 to 18", you will likely be keeping the same outside diameter, which means gearing remains unaffected.

The trade off of going "down" to 17"s will be a slightly taller side profile. Depending upon your driving skill, you may or may not notice the slight, if perceptible, change in turn/cornering response due to the oh, approx 1/2" (10mm) difference in sidewall heights when comparing the two tires.

Ultimately, for AX or Track useage, you would want to search out the [i]lightest[/] weight rim/tire combo possible. It is possible that you could reduce unsprung corner weight by 10lbs/corner.. thus a 40 lb saving on the car. That may be a more noticable change than wheel diameter.

This is a great suggestion that I hadn't even thought to bring up. If you really are going to get into track days especially then go for the lightest you can, while still be structurally sound.

I run 245/35/18 V710s on 18 x 7.5" CCW front wheels and 285/30/18 V710s on 18 x 9" CCW rear wheels. The benefit to the 285s for me is that with two drivers they don't overheat nearly as easily as the 245s. They also give the car a bit more stability in fast transitions over the 245s. The 245s can be a little dicey at times.

On the open track I would definitely want the larger rear tires again from a heat management standpoint and a stability standpoint.

A Boxster can fit an 8.5" front wheel up front and a 10" wheel in the back. I think this wheel size, using the same tire sizes I'm using, would work quite well on the track. The 245 is slightly pinched on the front wheel. Hoosiers are less so.

Racer_d is wise... Seat time is always your best performance investment.

The Boxter Spec racing series is currently running 225/255 17's on all cars. This is what I am currently running on my track set with Michelin PS2's. It's a good compromise between traction and unsprung weight. Fore/aft balance is also pretty good. If you are running a 987s you might want a little more width on the rears due to higher HP and weight.

What are the best wheels for 225 & 255 combination then? Suspect the original 17" fronts may be a bit narrow ?

You are concerned about the fronts - correct?
The 225 fit just fine on the stock 17" rims