Okay, so after some research and advice I have decided on my 997.1TT to go with a set of Forgestar track rims and Hoosier R6's as my track tires. As an aside, I have a Champion Build and Full Tarrett/Bilstein suspension with GT3 conversion and my car is trailered to the track. Unfortunately, while there are hundreds of threads on what slicks to run, there are scant few on actual sizes to run, especially when not running OEM wheel sizes. So i figured I would look to you guys for a bit of advice.

I am running Foregestar wheels with 18x9 +53 in the front and 18x12 +50 offset in the rear. I have decided to run Hoosier R6s as my track wheels as mentioned in the title.

My question is, based upon the rims I am running, what tire size would you guys recommend for Time Trials? Also, what alignment specs would you recommend? I know that I need to run at least a -3 camber in the rear, but don't know much more than that. As I mentioned above, I have the GT3 suspension conversion so can run quite a bit of camber as necessary as well as I have several shims to add extra negative camber. However I don't know what toe and camber specs to give to my shop to set me up!

Finally, I have read that most guys seem to recommend tire pressures of 33 front hot and 36 hot rear with the Hoosier R6's, but wanted to confirm this.

Thanks for all the help!

-Sayajin

 

So after a bit more research and several phone calls, I think I have narrowed down the tire size. What was recommend was:

Hoosier R6
245/40/18 -F
335/30/18 -R

The rolling diameter is supposed to be almost exactly the same with this setup keeping transmission and drivetrain problems at bay.

Does anyone else have experience with these sizes?

Now I just need to do some research on alignment specs and hot tire temps for R6s in this size.

-Sayajin

 

Those sizes won't work. The R6 245/40/18 is 25.7" tall and the 335/30/18 is 25.6" tall. You need a rear that is roughly 0.7-0.9" taller than the front due to your AWD system and all the PSM garbage on the car.

A 997GT3 runs the same tire sizes as a 997TT. With that said, a 245/35/18 and 315/30/18 is a popular R6 combo on the 997GT3 (you can also fit a 255/35/18 with minimal rubbing). The R6s run very wide. The above combo maintains the stock front to rear ratio but each tire is about 3/4" shorter in diameter than OEM so effectively you lower the car's CG a bit. I think you may find that you rub with a 335 in the rear.

I have the 245/35/18 and 315/30/18 R6 but for most track days I use the NT01 in a 245/40/18 and 305/35/18. These are exact 997TT/7GT3 sizes and is probably the best R compound out there for the money at just over $1K for the set. The NT01s will give you about 35 sessions per set compared to 15 or so for the R6s. On a 2.5 mile circuit, the R6 is about 1.5-2 sec faster than the NT01 in the first 6-8 (cycles) sessions and than about even with the NT01. Performance fall off rapidly as the R6 cycles out and the NT01 will be faster.

Good alignment setting works out to -3.0 camber in the front with a total toe of 0.06 and -2.25 camber rear with 0.34 total toe. I shoot for hot pressures at 33F/34R on a GT2 set up. Running this my tire wear is even across the tire and my wear is pretty much 1:1 front to rear. This is on a RWD set up.

 

First of all let me say "Thank You". This is EXACTLY the type of input I was hoping for.

With that said, do you still recommend those tire sizes even with me running a 18x9 in the front vs the norm of 18x8.5? I know that most guys with OZ also run 18x12 in the rear, so I assume those would be the same, however wouldnt having the extra .5 in the front allow/benefit from a slightly wider tire?

I have heard that most people run the NT01's except for when running TT and I think I will do the same. Save my Hoosiers for TT and run NT01 during normal DE or other non sanctioned races.

The alignment specs you outlined are very similar to what I normally run except that I have a 2.5- camber in the front vs -3. As I mentioned in my OP, I have the GT2 suspension with several shims, so I can run quite a bit of camber as necessary so these specs should be easy to attain.

I will start off with the tire temps you suggested and then take it from there. I would think that with my AWD setup, my pressures may be slightly different, however this is definitely a good starting point and in line with what I have been told before.

Once I can confirm the proper tire sizes, I can go on from there. Thanks!

-Sayajin

 

Yes, those are the correct wheel sizes. I run 18x9x12 wheels myself. The 9" front allows you to run anything from a 235 to a 265.

 

What about heat cycling do you guys pay the extra $20 per wheel to have it done at Tire Rack

 

pwr, i think those sizes are too small for the 997.
i;de run a 245 40 18 and a 305 35 18 so that the rear is a little taller than the front to keep the awd working correctly..

 

That's exactly what I'm saying. On the 997TT with AWD you need to run:

NT01 245/40/18 is 25.5" and 305/35/18 is 26.4". 0.9" delta

R6 245/35/18 is 24.8" and 315/30/18 is 25.6". 0.8" delta

The R6s are both smaller but the ratio is good. This size is very popular with the 996/997GT3 crowd. The NT01s are a better choice for the heavier TT since the load rating is higher. Those tires are the way to go for track days and DE stuff. Save the R6s for the occasional time trial when chasing the last second or two... The R6s are a pretty fragile tire for the heavy TT.

 

On the NT01 it's a waste. No difference. Some guys believe in it on the Hoosiers but opinion is split. 90% of the guys just throw them on and go. Most benefit to heat cycling will be on true slicks..

 

Why the smaller width tire with the NT01's? Obviously I realize the R6's are made differently and subsequently have a different purpose for choosing them, however one would think the sizes would be the same or at least closer.

I would like to run the widest possible width tires on the wheels without having to modify fenders and not screw up the AWD system, so I appreciate the input!

-Sayajin

 

The 305/35/18 NT01 is the only tire Nitto has that can be used with the 245/40/18 and give you a 0.9" larger rear as required by the 997TT/GT2/3 cars.

The NT01 305 runs wide and sits square on a 12" wheel. The 305/35/18 NT01 has better grip than the 315/30/18 NT01 since the 305 has a larger contact patch due to it's larger diameter. I've run them both back to back at the track. The 305 has a stiffer sidewall, higher load rating and is better hands down...

Tire width is not the end all be all when it comes to a tire. Look at Cup cars. They don't have overly wide rear tires but they DO have relatively tall tires with very stiff sidewalls. The taller the tire, the greater the contact patch.

 

So to revive this thread....

I finally got a phone call from Forgestar telling me my wheels would be in tomorrow morning. I have my R6s sitting in the shop waiting to be installed and I am headed to NOLA this weekend to test out my new setup.

With that said, I happened to be chatting with my Tuning Shop last week and the conversation of alignment came up. While I was telling him my plans (which I got from here obviously) he suggested something quite a bit different:

-2.5 Camber Front w/ .7 Toe out
-2.8 Camber Rear w/ 2.1 Toe In

When I told him that everything I had previously read said to go with a -3 in the front he suggested that he didn't advise it due to something about the axle length not being quite long enough or something to that effect. Also I told him I was quite surprised about the amount of Toe on the rear and he felt that was ideal.

Anyone else tried running anything similar or heard anything similar? I go in a few days to get my track alignment and I wanted to make sure I have all my facts straight.

Thanks!

-Sayajin

 

What are those toe settings in?? Rear to should be about 0º15' (minutes) per side for 0º30' total and front should be about 0º03' per side for 0º06' total. I'm not a fan of the front toe out club. 996/997 Cup cars don't even spec toe out. For comparison my alignment is as follows:

-3º15' (-3.25º) camber front w/ 0º04' (0.07º) total toe in
-2º25' (-2.42º) camber rear w/ 0º30' (0.50º) total toe in

I am assuming you are using split GT3 LCAs and shimming to achieve more camber. Your shop is right about being limited with how much they can shim out the front as you are limited with the length of the front axles as you widen the front track. Tarett sells spacers and longer bolts to get around this issue.

http://www.tarett.com/items/996-997-...-10-detail.htm

 

Thanks for the input. I was also surprised a bit by the settings he suggested.

You are correct, I am using GT3 LCAs as well as shims. Both which I got from Tarett. I did not know about the other spacer kit however, thats cool.

As an aside, are you saying I can not achieve a -3+ Front Camber using shims and GT3 LCAs? I need the above mentioned axle spacer kit in order to do this? I ask because this is the first time I have heard of the kit you referenced earlier.

Thanks!

-Sayajin

 

You can easily achieve -3 camber with the LCAs depending on the amount of shims. I am at -3.25º with 11mm of shims per side but I'm using the 997 Cup monoball ends which are 2mm longer than the stockers which would translate to 13mm of shims per side on the stock GT3 LCAs. There comes a point where the track will become too wide for the splines on the front driveshafts to fully engage the hubs. Anyones guess what that is though. However, if you are running 10mm of shims per side, you should have a 10mm spacer at the driveshaft to have the splined end fully engage as on a stock car, if that makes sense. PM sent....