As I run for the first time with R7, I wanted to share impressions and ask for opinion/experiences to you all.

Car: 2010 GT3, no mods just alignment, rollbar, GT2 seats and harness, and Sharky bypass.
Tires: since '15, I run quite a few sets of MPSC2. Now learning R7.
Track: COTA

1. Car balance changed on R7's vs MPSC2. More front end grip, balance shifted towards oversteer which is ok on slower corners but not a great feeling on the fast stuff... it required more delicate steering inputs and judicious use of throttle (all good, fun)

2. Pressures: overinflated on the first run due to combination of delay of session and increased ambient temps. I dialed it down and my last run was with 25 front and 23 rears, ended with 34 front and 36 rear, consistent through the session (about 72-75F ambient).

3. R7 felt more stiff on the sidewalls, I'd say higher total equivalent spring rate. It felt nice to drive.

4. Good consistent behavior (once initial pressures were dropped), getting looser at the end of the stint but no big drama.

5. Alignment for reference:
Front: Camber: -2.6 F, Toe out: 0.07deg, Caster: 9 deg, swaybar 2nd from full soft
Rear: Camber: -2.6 R, Toe in: 0.11 deg, swaybar in middle position

6. Shoulders after 4 sessions: outside ok, some roundness and wear, not "extreme" when compared to inside more square shoulder.

7. To complete the weekend view... after the 4 sessions with R7, rest of the weekend was wet/dump and switched back to MPSC2, balance was back to normal (just a bit understeery). I know them better and can lean on SC2 more, still a lot to learn on R7's.

8. May need to raise 5 to 10 mm the front ride height as the R7 are wider and just rubbing the front fenders when loaded. Nothing big but you can tell from fenders and fronts.

So the question what to do to get a better balance - suggestions?
Here are some ideas:
A. More rear wing? It's a regular 997.2 GT3. Goal, more planted, reduced oversteer on fast corners (like T10)
B. Full soft on rear swaybar? (Alternative: 3 hole from full soft on front swaybar) Pros-cons? Suggestions?
C. A bit more toe-in on rear?
D. Just play more with tire pressures?

Goal is to keep having the car with good balance on MPSC2... and have a nice platform to learn the R7's.

Comments and suggestions much appreciated!

Thanks !!!

 

get your tire temps. I'll bet you need quite a bit more camber. I run NT01 and am at over -3 in front and have pretty even temps, and generally even tire wear, although I could use a bit more in front still. At some point its a balance as braking gets affected as you lose straight line contact patch.

 

Thanks Spyrex.

Any advice from you and all on preferred settings for swaybars? Of course this is track and setup oriented but good to know if those are noted in the settings...

 

1. Use tire pressures and camber to achieve consistent temps across the width of the tire (not for handling).
2. Use sway bar adjustments to achieve desired handling through the turn.
3. Put as much rubber in the rear as you can (315's).
4. Turn off traction control and use your right foot to learn how to take T10 more aggressively. (oversteer is not necessarily something to try to avoid; learn how to exploit it).

 

^ 315 if you are talking ntO1 is not the right profile for the 997. It's too low and screws with the rake.

 

JC asked about Hoosier R7's.

Your best R7 set up is 18" wheels, 245 in front and 315 in back. The bigger the contact patch in the rear, the more it will address oversteer in high speed turns like COTA T10, the carousel, etc.

 

Based on my experience, -2.6 camber in the rear is too much. I use -2.0 and most others also seem to be in the -1.8 to -2.0 range. Inner edge wear improved from R6 to R7, but still seems to be the highest wear area on mine. Keep an eye on it.

I am currently at -2.9 in front. Temps were a little more even with less camber, and some recommend keeping to about .5 delta from front to back, but I was getting outer edge wear.

Regarding R7 sizes, I would love to get more tire in the front - and I've seen others with 245's mounted, but I've tried both profiles of 245s and neither works for me. The 245/35-18 was too wide and rubbed the front main springs while the outside edge was already proud of the fender, and the 245/40-18 was tall enough to be cut by the front edge of the fender. I opted to go with the R7 225's that have nearly the exact dimensions the the R6 245/35. Since I can't run anything wider than that in the front, I've never tried anything wider than a 315 in the rear.

Front setup specs:

Stock top strut mount position
Ride height - 90mm (when using the R7 225 or R6 245)
Camber -2.9
Total Toe 17' Out (2.4mm)
Caster 8 degrees 40'

 

Now I only used to autox my 2010 GT3, but the car was incredible on 235/19 and 315/19 Hoosier A6's

 

I don't think -2.6 is enough that's what I ran for a while and my car was still chewing the outside shoulder pretty bad on track. I went to -3.2 rear and wear is now even. Best bet is to get a pyrometer and measure temps across the outer, center and inner edges and try and get even temps then look at wear patterns.

 

I know AGO is sorting out 19's, but for those running 18" wheels on a 997.2 GT3, are you running 245/40 and 315/30 R7s? The sizes seem to be the best option, but they seem to flatten out the rake versus the original setup as delivered. If Hoosier's tire height data is accurate, I'd need to lower the front 0.3" (or raise the rear but I'd rather not do that) to keep the same rake and avoid some of the balance issues.

 

I am using 18's and when I tried the R7 245/40's the outer edges were shaved by the fender, so they didn't work. In addition to being smaller diameter, the R7 235/35's actually measure more than 1/2" wider than the R6; while others have been able to fit them between the fenders and the springs, neither I nor another local GT3 owner could.

Agree that accurate tire temps are some of the most important data to collect/interpret, and it seems too seldom taken due to run session limitations, etc. But wow; -3.2 is a ton of rear camber. Glad you found a setting that works well. Lots of variables in terms of track surface/layout/temps, suspension, driving style, etc., but for my car at -2.0 the temps have a good spread with highest temps on the inner edge, and when wear is uneven it is the inner edges that cord first.

 

When the outer edge of the 245/40 was shaved by the fender, were you running adjustable thrust arms to keep the caster in spec for high camber. Before I added the thrust arms, my caster was out of spec and 245/19 would rub. As soon as I got caster back to center of spec, things cleared up. I am running -3.0 F and -2.0 R for Nittos but would bump up the front to -3.5 for R7. I have not rotated my struts.

 

Thank you for offering ideas. I was using stock thrust arms with adjustable thrust arm bushings in the control arms that can change the effective length of the thrust arms. Stock caster spec is 8 degrees +/- 30'; IIRC my caster measured 8 degrees 40', so slightly beyond spec and could be improved. Not sure how much effect it would have on fender clearance, but it should help.

 

Interesting displays of GT3 differences here. I run Hoosiers 245/35/18 on 9" wide rims (F), 315/30/18 (R) on 12" rims with 7mm spacers (F) to move the 9" rims away from the springs and don't hit fenders anywhere, although I do occasionally hear a rim/spring rub in the paddock at full lock if I hit uneven pavement that rocks the car. I am rake even front to back (suggested by the suspension mtg'r for GT3) and my cup lip is 2 1/4" off the pavement, so I am about as low as possible. I think I could even go out to 255 (F) but would likely start throwing gravel at other cars. My buddies are running 270 (F) with fender extensions. They say the 270's are faster.

Hoosier's instructions say P-Metric radial tires (R7) require about -3 degrees of of negative camber for best performance, -2.5 degrees for the best compromise of performance and wear, and less than -2.5 will produce excessive wear. They also say their R7's usually require a stiffer suspension (higher spring rate) than their competitors tires, which I have (ExE-Tc susp.) which may account for my not hitting any fenders.. Hoosier doesn't identify any other alignment specs., so I set -3.08 (F) and -2.66 (R) -----as much as I can get.

A couple seasoned fast drivers have driven this car, say it is very netural, and doubt I can improve on the setup. I think, after one more track day, I will put the 1/2' OEM rake back in and see if my lap times change.