996 GT3 floaty/unstable feeling

[911p]

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

[911p]

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.

[911p]

Yes - we've checked all the obvious.

[911p]

With regards to pressures, I think the problem lies elsewhere. Felt even worse when they were lower.

Rear diff was rebuilt last year with Guards LSD plates. Car was also fully sorted at Center Gravity a few months ago!

[911p]

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.

[911p]

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.

Edited by 911p on Tuesday 11th March 16:35

[911p]

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.

[911p]

That's the problem, it's not primarily a track car and full on semi-slicks bring many compromises.

AD08Rs are very highly praised for 996 GT3s on US forums like Rennlist. I always agree with 'you get what you pay for' - these are more expensive than the MPS2s which come standard on the car!

I don't believe that 3mm of extra tread was cause this much trouble, especially taking into account the tread pattern these tyres have

[911p]

Definitely

We trust Chris will find all of the causes anyway (if it is more than just the dampers), he'll be able to feel what it's doing on those test drives he does!

[911p]

Orangecurry said:

Without even having seen the car, I would still say that the dampers, although critical, do not work as hard on the very-smooth track, and unless they all failed wouldn't cause a general 'floaty' feeling.

Have you driven Brands? The straight and the corner that leads onto it pitch and dip quite a lot!

Orangecurry said:

But it's amazing how much extra heat will be generated in that extra 3mm, no matter how few 'blocks' there are in the tread pattern - heat = expansion = floaty.

I do hear what you're saying

But then I'd question why nobody else has ever mentioned problems like these, with these tyres or other with the same tread depth such as MPS2 or MPSS.

As you can see I'd like to believe it's not the tyres that just cost £1k causing all the problems Do appreciate the responses though.

[911p]

If you are correct though, I'm still questioning why there's absolutely nothing else to be found online about the feel of any car being adversely affected by these tyres.

It certainly is a strange one!

[911p]

They would have had near enough the full 8mm of tread at the start of the day, as I say they only had a few hundred miles on them so were pretty much new. I don't think it really improved throughout the day, although I don't think they would have worn down much over the course of the day.

[911p]

This is why I'm stumped. Plenty in the US using AD08s on their GT3s without any issues.

Rennlist - Yokohama AD-08 R
Rennlist - Texas World Speedway Sept 29th

[911p]

Orangecurry said:

Ask them what pressures they run when they go round their ovals.

[911p]

It is the first time we've moved away from PS2s. I must emphasise that all of these feelings were only apparent over the bumpy parts of the track, on the smooth parts the car felt fine other than being a little more unstable than usual under braking.