mdrums

Just curious on your thoughts....I have a 09 Carrera S with the lowered Sport PASM. I have CCW wheels 9x18 and 12x18 standard GT3 fitment...these are Mooty's old wheels. I drive to and from the track and have been using R888 245-40-18 and 305-35-18

What tires and size would you use?

Thanks!

340Elise

That combo is fine, but I use the 255/35 front and either the 305/35 or 315/30 rear. I prefer the 315 rear.

Also, the 255 is .2 lbs lighter than the 245, and the 315 is 2.6 lbs lighter than the 305! It is nice to take off over 5 lbs of unsprung rotational, especially in the rear.

The 315 rear also gives you lower gearing for better acceleration.

Harold

There is no rub on the inner wheel well with removal of the spacer for 345s? And you are doing this on the standard RS rims? Thanks in advance. Am deciding whether to buy 18 inch track specific wheels or just use the standard rims with wider rubber...

Gus F

NJ-GT, Wll these set up be posible with a 997 GT3 (Non-RS and wheel sizes 8.5 and 12 X 18)?

On Pole

I just ordered 335/30-18 Hoosiers for my 07 GT3. I had my BBS E88 wheels
(12x18) made with 570 centers. They are made to work with the rear spacers. If I have a fitment problem, I will remove the spacers. or roll the fenders.

Rear camber is set to -2.5

Here are pictures with 315/30-18 R6s.

NJ-GT

No. It will require spacer removal, rolling the rear fenders, and removing the inner fender well anti-noise covers.

NJ-GT

There is rub with a 345, it requires rolling the fenders, and spacer removed with the stock 12" RS wheels.

I bought 19" custom wheels, because the widest 18" tire is 3/4" narrower than the widest 19" tire in Hoosiers, and a GT3 can use plenty of rear tire.

10 GT3

What size wheels are you running? This is really what should determine the tire size. With R888s, they have very soft sidewalls. As a result, they like to be stretched on a wheel or you will need to increase tire pressure to get them to run right. I initially started with 255/35s in front and 315/30s out back, same as my previous Corsas, on 18/9 and 18/11 wheels. With 2.5 degrees camber, I had to bump up the pressure 7 psi in front and 5 psi out back to get them to not rollover and heat up to proper temp. I switched to 235s up front and 295s out back and was able to drop my front pressures 8 psi and rear 5 psi. Less pressure = more contact patch. Despite such a pressure difference between the 2 sizes, my operating temp was within 10 degees (read from a Longacre probe type pyromater at the cord). Turn-in and feel at the limit improved a lot with the narrower sizes. I run 5 secs faster a lap on a 2 min roadcourse on the narrower R888s than the wider ones. Breakin was a lot faster with the narrower sizes and I have noticed they get up to temp in about a half a lap versus a lap and a half with the wider sizes. Here are my recommendations depending on your wheel sizes:

8.5": 235
9.0": 235-245
9.5": 245
10.0": 255-265
10.5": 265-275
11.0": 295
11.5": 305-315
12.0": 305-315
12.5": 335
13.0" 335

NJ-GT

Similar experience here with the R888, the tire wants high pressures or wide wheels. Running a wider wheel or a narrower tire allows to run them at lower pressures. Toyo won't recommend a 265 on a 9" wheel, or a 335 on a 12" wheel if the tires were 5 secs slower.

If I run the R888 under 36 psi, I get rollover. My 235/295 R888 on 8"/10" wheels require 38 psi front and 40 psi rear.

The SpecBoxster series are running very wide R888 for the wheels (225/255 tires on 7"/8.5" wheels). They are also running pressures on the 38-40 psi range. I don't think they are losing 5 secs a lap (2 minutes circuit) by not using the narrow 205/225 combination with the same spec wheels (Mooty try this, to see if you can break the high 1:30s at Laguna Seca).

But if you are running the wider tire at low pressures, and they are rolling over, well it is quite easy to see where you lost the 5 secs.

The R888, NT-01 and RA-1 like high pressures (40 psi), the MPSC and Corsa lower pressures, the slicks even lower pressures.

Too bad the 305 on 11" wheel did not work for you. This is being used in the SCCA Pro series Speed WC-GT, and Randy Pobst in his heavy Volvo has been winning races with these wheels and R888 tire sizes at all corners.

10 GT3

Read the post again, I bumped pressures. As a result, I lost grip over Corsas and slowed down in the corners. You don't gain grip by increasing tire pressure and reducing contact patch. That is simply physics. If you run a 295/30 and a 315/30 on the same with rim at the same pressure, which has a larger contact patch? Neither. The contract patch area is the same; only the shape is different. A narrower tire has a longer and narrower patch that helps at turn-in (corner entry and corner exit). A wider tires have shorter and wider contact patches that help at peak grip in a corner. Only reducing tire pressure increases contact patch and grip regardless of the width of the tire. The downside is reducing tire pressure makes a tire flex more which hinders turn in. Hence if you bump up pressure to reduce roll and improve turn-in, you lose any grip benefit.

I dialed my car initially on MPSCs (-2.5/-2.1 camber). When I switched to wider Corsas, I was able to run less pressure and still got even wear and fast times without changing suspension settings. In fact, I even dialed back the rear camber back to -1.9 with the wide rear Corsas. Different tires have different compositions and hence different setups. Running R888s wide will put you no where near the same range. Remember that Toyo specs them optimal at 5 degrees. What does Randy Pobst run for spring rates and camber? Check out the number of threads about people are amazed of the amount of rear camber those Volvos run. If you only use your car to track, that may be fine; but let's how well they were driving on the street too.

I run within 2 degrees of the same cold pressures with narrow R888s as I did with MPSCs or Corsas (27 psi front and 28 psi rear cold). That is a big difference from the 34 psi/33 psi I ran with the wider ones cold. I get hot pressures in 35-38 psi and 185-195 degrees on cord temp. I have noticed once they go above 200 degrees, the grip is gone. Narrow R888s also run real even with inside/center/outside all within 10 degrees of each other. The wider ones gave more than a 20-degree spread. If I ran 40 psi with either width I would not have any grip. You can make a wider R888 work better though by adding camber. Toyo specs them at optimal at 5 degrees.

On Pole

As you can see, the R6 is not much wider than my street 305/30-19 PZeros. I had to remove my rear spacers and roll the fenders to make my 335/30-18 R6s work.

NJ-GT

This is valid as long as there is not rollover due to the low pressures. If the tires are rolling over due to the low pressures, despite of having a larger static contact patch, you'll be riding on the outside edge of the tires carrying the bigger load, and that's slow.

So, essentially I can run motorcycle tires (very narrow) at low pressures and improve my lap times. The Spec Boxster guys will drop 5 seconds by running 205/225 R888 instead of 225/255 on the 7"/8.5". It works for you, it might not work for anybody else.

I'm running my R888 at -3.5 degrees front camber and -3.0 rear, in the Spec Boxster they run at -3.5 front and -3.0 rear as well. At 34psi I was getting rollover, with pressures at 38/40 the timer on the same test day and course dropped close to 1 second (55 secs lap), and no rollover.

I tested the Pirelli Corsa System (optimum grip at f:32psi/r:34psi) against Hoosier A6, and R888 against the same Hoosier A6. Multiple tests with both in the past 4 months. The corsa was in between 5.0-6.5 secs slower than the A6 (expected). the R888 has been in between 3.0-4.7 secs slower. So far the R888 produces better lap times due to higher levels of grip. Corsas 235/285 against R888 235/295. The A6 being 295/345 on fairly narrow wheels, will test again this weekend on a long track.

Adam S

I have been my 19' R888s at 28 psi (hot)... front and rear (little more rear)... no problems :-)

On Pole

I just installed some BFG R1 tires on my car.
265/35-18
335/30-18

No rubbing!

mdrums

Interesting thread....thanks!

1 observation I see is everyones brake calipers are perfectly red with a perfect white Porsche logo....odd to me....mine are a dark maroon and the Porsche logo is a yellowish tan color. This is of couse due to heat but just wondering if you guys use your brakes? LOL ;-)