AudiOn19s

In looking around continually for track wheels and tires for the 996 I keep coming back to the following question... Can you Over-Tire the 996?.

By this I mean is there a point where you're simply carrying around excess weight and rotational mass that isn't warranted on the car?...or should you go as large as you can squeeze appropriatly under the fenders of the car?

Obviously wheel and tire choice will have a roll in this decision. My #1 option right now is to go with factoy 18' wheels in 8' and 10' and run 235 / 295 sizing. However it's tempting to look into a set of custom wheels in order to squeeze more rubber under the car.

Andy

insite

temperature will be a decisive factor. for YOUR car, how much tire can you keep properly heated? it's possible to over tire a car to the point where the tires never come up to temp. that having been said, this is hard to do on a 911. you will not get to the point of too much tire on that car without some serious fender flares. if you can fit the turbo wheels under there, so be it. i think they're 9" and 11" wide.

JimB

Andy,
Like everything else, it's a matter of trade offs. I always wanted the widest, shortest, lightest, stickiest tire available. Unfortunately you can’t have all of those so it becomes a compromise. On stock wheels the fastest combination will most certainly be 285/30/18 & 245/35 or 40/18 Hoosier R6s. Choose 35s in front if you don't have PSM. They will lower your front a little more and are slightly lighter.

The 285s in back are short. Around an inch shorter than Hoosier's 295s and 315s. This is the same as putting in a shorter ring and pinion and really helps with acceleration. The 285s are also quite a bit lighter. Hoosier engineers claim that they don't have enough sidewall to properly deal with both lateral and vertical flex when accelerating out of corners but many 996 club racers use them successfully. I used this combo for several years.

FWIW, after a lot of experimenting, I raced Hoosier 315/30/18 - 245/35/18 on 9 and 11 inch rims. It’s what worked best for me on my 996 but was a tight fit. You need very stiff springs and lots of camber to make it work.
Jim

Tippy

I look at it on a very basic level, more tire equals more rotating mass.

More rotating mass absorbs more power.

I had 295s on my car and put the stock 255s back on, the car is simply more peppier. Now I know a lot of it had to do with going down 0.8" of diameter from the 295s but the the 295 tires alone were several pounds or more heavier adding to the total loss.

Being our car are low torque engines with high hp, to me, the smaller tire (within Porsches' recommendation) would be best unless traction becomes the issue.

If your car is all about looks and not performance, squeeze as much tire as you can fit.

10 GT3

You can easily over tire your wheels, but you can certainly run a lot more tire with the right set of wheels. Remember there is more here than just weight. Grip comes from contact patch. If you want more grip, you need to increase contact patch. There are several ways to do this. Just because you put a larger tire on the car does not increase contact patch or grip if it is at the same pressure. It does change the shape of the contact patch. The more narrow a tire is, the narrow and longer the contact patch will be. When you put a wider tire on, it does widen the contact patch; but it also reduces the length of the contact path. From this, the ONLY way to increase contact patch is to reduce tire pressure regardless of tire size.

This is where the major issue comes in with over tire sizing wheels. When the sidewall width increases on the same size wheel, it creates more sidewall flex. This results in slower turn-in and poorer response. The only way to restore the origin turn-in is to increase tire pressure to stiffen the sidewall of the tire, which of course reduces contact patch and grip.

You obviously have some physical issues that limit that width and size of wheels and tires that can be used. Surprisingly, a narrow body 996 and fit a lot of rubber underneath. I am running a set of 18x9.0" and 18x11.0" CCW Classic race wheels with 235/40-18 and 315/30-18 Corsas. This is very close to the limit you can run. Without monoballs, the limit is 255/35-18's on 18x9.5" wheels and 315/30-18's on 18x11.0" wheels. If you want to go bigger and don't want to go to monoballs, start looking at body work as you will be rubbing based on your offests on the inside or outside. The general rule is to figure out what size tire you want to run and maximize the wheel size for that tire. This allows you to run tighter on the wheels and lower pressure to increase contact patch, while maintaining turn-in and response (best of all worlds). For stock wheels stick with stock size tires as there is no performance advantage to go wider.

When looking at the right race setup, I would not recommend Turbo wheels. This has to do with 2 reasons: the front wheels are only 8.0" wide and the 18x11.0" rear wheels have the wrong offset for a narrow body. If you have a narrow body that is lowered, turbo rear wheels with just 295/30 rubber will rub the rear fenders in turns. GT3 wheels use a wider 18x8.5" front with a different offset 18x11.0" rear to fit a narrow body.

As far as tire temps go: even starting at a static pressure of 28 psi with my rear Corsas, they were up to 180 degrees after 10 minutes in 95+ degree heat and out of grip. I had to lower my static pressure 2 psi to get them down to a more reasonable low 170's to maintain grip. Temperatures were within 10 degrees across the tire (inside, middle and outside) with my camber at -1.9. My fronts on the other hand, would never go out of the 150's; but they were still within 10 degrees across the tire and within the recommended operating range.

Benjamin Choi

I'm running 19x12 with 315/25/19 tires - street 911, lowered, no rubbing, looks like a steamroller

Paul 996

Gonna revive this because I don't think anyone gave Andy the answer to the question he asked.

So at what point do you have too much tire on the car? I think we all have a consensus on the rears... Understanding that checking the tire surface temp is the determining factor but without doing the trial and error involved; does anyone have experience effectively running a 9" rim with a 245 or even wider? Also what fits..

Did that hurt or help?

-Paul

Lerxst

So would 245/40/18 & 315/30/18 (Azenis) fit on my stock 18" C2 rims and not rub with stock suspension?

Similar question is posted in Autocross forum, but figured there'd be more 996 readers here.