996 GT3 floaty/unstable feeling
Discussion
Was hoping some of you might have some advice on this subject and/or may have experienced this previously!
Yesterday at Brands Hatch the car felt extremely floaty over the straight which pitches and dips quite a lot. In addition, when travelling at speed it really felt like it wanted to follow all of the cambers in the road. Lastly, under braking the car also didn't feel very stable at all, where it is usually rock solid.
It didn't feel like this at Brands Hatch a couple of months ago where it felt completely planted all the way around the track. The only thing which has changed since then is the car has had new tyres (moved from MPS2 to Yoko AD08R).
They were driven on for 500 miles before the track day so fully bedded in. What could be causing this? Could one of the tyres be misshapen? Incorrectly fitted?
Is there also anything suspension related which might cause the car to feel this way?
Cheers all
Yesterday at Brands Hatch the car felt extremely floaty over the straight which pitches and dips quite a lot. In addition, when travelling at speed it really felt like it wanted to follow all of the cambers in the road. Lastly, under braking the car also didn't feel very stable at all, where it is usually rock solid.
It didn't feel like this at Brands Hatch a couple of months ago where it felt completely planted all the way around the track. The only thing which has changed since then is the car has had new tyres (moved from MPS2 to Yoko AD08R).
They were driven on for 500 miles before the track day so fully bedded in. What could be causing this? Could one of the tyres be misshapen? Incorrectly fitted?
Is there also anything suspension related which might cause the car to feel this way?
Cheers all
Felt like it was the rear end.
Forgot to talk about pressures. When we were running 32F 35R the car felt really skittish at the rear end when exiting clearways onto the straight. When we moved the pressures up to 32F 39R the skittishness was mostly eliminated but the other symptoms remained. Very strange.
Forgot to talk about pressures. When we were running 32F 35R the car felt really skittish at the rear end when exiting clearways onto the straight. When we moved the pressures up to 32F 39R the skittishness was mostly eliminated but the other symptoms remained. Very strange.
I would suggest rear pressures are on the high side.
Other culprit for instability under braking is the rear diff.
Do you know if still original or replaced? Std or Motorsport plates?
If still original and the car has done over 25k miles of mixed driving then diff plates likely to be worn.
Other culprit for instability under braking is the rear diff.
Do you know if still original or replaced? Std or Motorsport plates?
If still original and the car has done over 25k miles of mixed driving then diff plates likely to be worn.
Track day tyre pressures I assume were read when hot. Most tyres like MPSCs seem to go best around 30-32 all round hot on a 996 GT3.
Exceptions are Toyo for which I was reccomended 34F 38R hot by Steve Girdwood (Simply Tyres - those were the days). This transformed the handling when I was farting about at 32 all round and not feeling at all comfortable.
I have no experience of your tyre choice though but as GT3s are pretty sensitive you need to talk to someone who has that combination and knows what they are talking about.
Exceptions are Toyo for which I was reccomended 34F 38R hot by Steve Girdwood (Simply Tyres - those were the days). This transformed the handling when I was farting about at 32 all round and not feeling at all comfortable.
I have no experience of your tyre choice though but as GT3s are pretty sensitive you need to talk to someone who has that combination and knows what they are talking about.
The key thing is what has changed since last time. If it's just the tyres, then the reason is.... tyres.
911p said:
Felt like it was the rear end.
Forgot to talk about pressures. When we were running 32F 35R the car felt really skittish at the rear end when exiting clearways onto the straight. When we moved the pressures up to 32F 39R the skittishness was mostly eliminated but the other symptoms remained. Very strange.
Is that 32/35 before you started a lap? During? What were the pressures immediately you came in?Forgot to talk about pressures. When we were running 32F 35R the car felt really skittish at the rear end when exiting clearways onto the straight. When we moved the pressures up to 32F 39R the skittishness was mostly eliminated but the other symptoms remained. Very strange.
I apologise in advance for these poor descriptions!
We started with 32F 35R hot, and the car had a strange skittish feeling, almost like the tyres were skipping across the track an inch at a time. Felt almost juddery - only when coming out of clearways though which is a little bumpy.
We then moved them to 32F 39R hot and the skittish feeling was gone, but all the other symptoms remained.
nxi20 who is an absolute track veteran in his 996 GT3 (and has used these tyres before) recommended 32F 35R hot.
We started with 32F 35R hot, and the car had a strange skittish feeling, almost like the tyres were skipping across the track an inch at a time. Felt almost juddery - only when coming out of clearways though which is a little bumpy.
We then moved them to 32F 39R hot and the skittish feeling was gone, but all the other symptoms remained.
nxi20 who is an absolute track veteran in his 996 GT3 (and has used these tyres before) recommended 32F 35R hot.
Did you try dropping the pressures down?
Otherwise the answer is that the PS2 plus whatever-pressure-you-ran-them-at was disguising a problem that has now been revealed.... but if CoG has set-up the car on PS2s and you liked it, then it's the new tyres that you don't like, because nothing else has changed.
Otherwise the answer is that the PS2 plus whatever-pressure-you-ran-them-at was disguising a problem that has now been revealed.... but if CoG has set-up the car on PS2s and you liked it, then it's the new tyres that you don't like, because nothing else has changed.
Good points. The sidewalls of the AD08Rs are way stiffer than PS2s, so if the dampers were worn they would be having to work much harder now over the bumpy stuff.
The dampers performed well on the damper testing machine at CG, but Chris did mention that the dampers were due a refurb which should be done some time this year. Maybe they are worn out.
ETA: car is on 52k and I'm unaware of it having a damper rebuild at any point.
The dampers performed well on the damper testing machine at CG, but Chris did mention that the dampers were due a refurb which should be done some time this year. Maybe they are worn out.
ETA: car is on 52k and I'm unaware of it having a damper rebuild at any point.
Edited by 911p on Tuesday 11th March 16:35
My 6.2 GT3 was on original dampers when I first got it at 50k+ miles. Felt sh*t on track initially, not very confidence inspiring and pretty skittish. The diff was also knackered. Cup diff plates, Ohlins, new bushes and a lovely geo have literally transformed it to a thing of communicative beauty. I run PS2s on the OEM rims on wet days and R888s on Allegerittas on dry days.
HTH
Cheers
Slodge
HTH
Cheers
Slodge
Slippydiff said:
They'll be toast, get 'em refurbed and start again
slodge said:
My 6.2 GT3 was on original dampers when I first got it at 50k+ miles. Felt sh*t on track initially, not very confidence inspiring and pretty skittish.
Cheers for the comments. We contacted Chris at CG and he reckons the rear off-side damper might be shot (it was weaker than the others on our visit last year). He said if both rear dampers weren't acting symmetrically it could cause a load of bump steer. Going to get it booked in for a damper refurb all round Zyp said:
If you haven't spent 10 grand on it recently, that'll be your problem.
Orangecurry said:
The key thing is what has changed since last time. If it's just the tyres, then the reason is.... tyres.
+1AD08s are much more of a road tyre than a track tyre and I believe R version is very much the same. They start out with a lot of tread depth when new, 7 or 8 mm like most road tyres. Track tyres like MPSC and Toyo R888 start with much less tread depth (about 5 mm). With so much tread, the blocks will move around more. They might get better as they wear down but I think you would be better moving to a full track tyre like most other GT3 owners use for track work. The old saying of you only get what you pay for rings true when it comes to tyres for a GT3.
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