AGO

I posted a similar note on the 997 GT3 forum but had limited response, so here I am in the racing experts section!

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 (NB), no mods but alignment, rollbar, GT2 seats and harness, Brembo rotors and Sharky bypass.
Tires: since '15, I run quite a few sets of MPSC2 (235/35 and 305/30 on 19's). Now learning R7 (same front size, rear 315/30). Both in 19's as both rim sets are 19's.
Track: COTA

1. Car balance changed on R7's vs MPSC2. Fronts are wider. As expected, more front end grip, balance shifted towards oversteer which is ok on slower corners but not a great maybe 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 good to drive.

4. Good consistent behavior (once initial pressures were dropped and mostly in the last run), 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 second 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 but not "extreme wear" 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 !!!

Gary R.

Certainly no "expert" but I would stiffen front sway a notch at a time and see how that plays out.. I think your pressures are fine. You could certainly get more front camber in there, but if it's a street ride you may not want that.

jdistefa

adjust your sways, rear down or front up
agree more front camber per gary

Gary R.

Matt - My logic on adj. the the front bar was that the R7's seem to have eliminated his understeer to the point of creating some oversteer, so add some spring rate to the fronts as he is 1 adj. away from full soft in the rear already. Again, i'm just a hack that drives a race car!

AGO

Good question on front or rear sway bar adjustment
The front is quite sensitive now to small steering inputs. I'd guess If go one point stiffer on the front that effect should be amplified, is that the case?
Also in theory going stiffer in front should reduce grip.
Going down one point on rear would maximize grip overall, right?

jdistefa

Oh my God just adjust the bars and see how it drives.

Gary R.

3 way Motons are nice.

Frank 993 C4S

... if you spend the time to set them up.

mmuller

Definitely agree on adjusting sways. Start here.

Per Hoosier (http://www.hoosiertire.com/images/co...s/TCTR7_A7.pdf) your starting pressures are to low and your risking a tire blowout. The rear of a GT3 is heavy and to low of a starting pressure hurts the tire (even more so if your on a track with banking). Your hot pressures are fine, although I think 38 works better.

Is the lsd stock? Stock lsd in a GT3 is good for about 3 days on track before it's junk. This won't help with cornering stability.

Setting the car up one way for both tires will compromise it for both tires. I would pick one tire for setup and deal with it on the other tire the best I can.

Gary R.

I was kidding.. but I agree!

AGO

Good stuff, I wanted to get some comments from experienced guys before wrenching. Easiest is to play with sway bars. I'll run again as is then loosen the rear if needed.
And yes, oem diff... maybe I need to take care of that ...

I know pressures are at the limit, I'm going easy on warmup until I get pressure up.

mmuller

LSD upgrade will help, not just here, but all around. I would take care of that.

Don't mess around with the pressures. Taking it easy isn't enough. I have seen to many Hoosiers wasted from under inflation

XPC5

I would go stiffer on the front bar, it will add rate in roll to reduce oversteer, and also flatten the car slightly more to help with camber related wear. If anything it will slow down the steering input as it adds more load to the front instead of allowing the rear to take as much burden.

AGO

i see your logic on stiffer front, there's a bit of a roll on the front looking at some pictures at the track.

Muller: Thanks for the pressures advice, will be careful on that

CosmosMpower

I would stiffen the front sway, soften the rear sway if it's oversteering too much. My car came with rear set at nearly full stiff front at nearly full soft and it was a handful. I'm now at one from full stiff on the front and full soft on the rear and it's very neutral.

I'd run a bit more front negative camber if you can. Around -2.8 to -3 would be better with Hoosiers. I think your starting pressures might be a tad low, try something like 25R 27F cold and bleed them off to low 30's when hot.

What lap times are you running at COTA on the R7s?