Manifold

And that's despite usually doing decent cool-down laps. The brackets appear to still be structurally sound, but a little troubling that this design made it into production. I'm told that side muffler deletes should greatly reduce heat generation in this area, which may help the rear tires also.

NMM991

Regarding Sport Cup2 tires -- any differences besides pricing on K1 (Ferrari) and N0/N1 (Porsche) tires?

Any rule of thumb for what constitutes a "heat cycle" -- I've been told that when a tire gets to 170 degrees F, that counts as a heat cycle. Would four 30 minute sessions at the track spread out over 8 hours (30 minutes every other hour) constitute 4 heat cycles?

rm21

Well I didn't make it through the weekend with the old Cup2s. The old tires were down around .2 G's of lateral grip, but the worst part was the seriously diminished braking. Not good when you are trying to learn a new track. I got frustrated enough that I did a tire change at the track after the 35th heat cycle (I had a spare set anticipating this might happen). As usual, there was a lot of tread left on the old tires. Somebody should start a business selling these heat cycled Cup2s to GT3 owners who don't track their cars!

Manifold

Was the grip low from the first session, or was it a gradual drop in grip? How was the balance of the car?

Macca

Been thinking same thing, I have two sets in garage showing 40% rubber left but can bring myself to throw them away! One set will definitely go on the car before its sold...

Joe+Manifold. Be kind and remind me please. What sway bar setting you two using? Im stock but looking to firm up rear OR soften front to reduce understeer...

orthojoe

Macca, I don't think you'll like my setup since I was trying to reduce oversteer, not understeer on my car. I was having issues with mid corner and corner exit oversteer, so I put the front bar on full stiff and rear bar on full soft. Keep in mind that my setup has significant changes from yours, so the car is probably acting differently and therefore my sway bar settings will be different. My alignment and settings:

-2.7 camber front
1.5mm toe out each side
front bar stiff
9.5 degrees caster

-2.4 camber rear
3mm toe in each side
rear bar full soft

Hardware:
RSS thrust arm bushings/caster pucks
Tarett LCA monoball ends

I think better drivers might prefer more corner exit oversteer, but that doesn't give me confidence and slows me down. However, the guy who setup my car follows advice from pro driver Johanness Van Overbeek who likes a stiff front bar because that allows you to apply power sooner out of a corner (other shops like BGB follow the same the thought as well). I would agree that the stiff front bar helps stabilize the car coming out of a corner.

If you watch this video of me driving at Sonoma, at 0:40 I enter turn 6 too hot, and past the limit the car is pretty neutral. No push, no drama, which is what I like.

Manifold

I got a proprietary setup from a race shop, with both bars in the middle, tried the car, and found it to be too loose overall. We thought the rear tires might be heat-cycled out, so I replaced them, tried the car again, and found it to be much better, but still a bit on the loose side. Changed the front bar to stiff, did one more session with that, and found the car to be pretty close to where I want it - closer to neutral, and the front end feels more responsive. I'll be trying the car again this weekend, and may try playing with the sway bars more, maybe going soft in the rear and stiff or middle in the front. Will let you know how it turns out.

Seth Thomas

Yes each of those sessions is a heat cycle. The tire heats up and cools down between those sessions.

rm21

Grip was diminished in first session and dropped over next two sessions, although I may have simply noticed it more since I was going faster as I learned the track. The problem was probably compounded because my rears had more heat cycles than the fronts and my sway bar setup is soft front, middle setting rear, so I was getting a ton of oversteer when I was powering out in corners. I might have just dealt with that, but I almost had an ice braking effect a couple of times so I just decided to change tires, since I had them. It was a good chance to practice my track-side tire changing skills. Did them in under 40 minutes.

rm21

My settings are similar to Joe's with the major exception being that I run the sway bars soft in front and neutral in the rear. My biggest struggle with the car has always been understeer, so I can't imagine running with a stiff front bar. But I'm not as fast as Joe...

Macca

Hey Guys (rm21, Manifold, Joe) thanks for the data points.

Appreciate the time Joe reiterating once again your full set up.

Not meaning to make this a clinic but hoping this will provide some data points for others.

I have reverted to factory geo recently as Ive mentioned. Our local track is shorter than typical US tracks at 1.75 miles (current configuration is below on track map in black - the track extension in grey will add almost another mile to the track and opens in 1 years time). Our track has alot of elevation. Ive posted below a data trace that shows a quickish lap. A fast lap in the 991 GT3 would be about a second quicker than this. You can see the gear shifts in Blue. You are in second gear three times each lap, 3rd a similar number of times with 4th then 5th only on the straight. One bit straight 145mph vmax. The track is run clockwise.

Moving the car back from -2.15F/-1.54R to factory geo improved overall stability on this track. The more agressive setting made the car feel a bit loose. The factory settings made only a small improvement in lap time probably within 3-4 tenths which is margin of error for tyres and ambient temps, wind etc. My lap ties were consistent with both set ups running 3-4 laps a session 915 mins) within 0.3-0.5s so Id say little driver variability. Track has big variation in elevation like some Euro tracks.

So moving to stock removed looseness at expense of accelerated front tyre shoulder wear. The reality is the tyres have been heat cycling out after 25 cycles (4 track days) and are well of by 35 as previously discussed so tyre longetivity with the factory geo is neither here nor there as the more benign settings still allow the tyre to survive 4 track days...

Im still getting a little understeer I would like to dial out. Hence my thoughts to soften front bar.

Id rather not change too many things at once and go for a completely new geo (back to -2.15F/-2R for example) as I trying to understand the chassis first.

Interested in what you guys think looking at footage and track. rm21 I note you have a wing so you are probably needing to dial out more understeer now. Also Joe your track seems very fast and quite different from mine and probably driving style too so I can see especially with the aggressive settings you need other changes. Manifold, Im not so familiar with your local (Thermal?) but you and I had almost identical settings last few months so your input of value too.

Just curious what you guys might do next.

This is from Sept on tyres with 2 track days already and back to factory setting. Noise is warped front rotors transmitting vibrations through roll cage where mic is attached.


Heres another from last year using the slightly more agressive geo settings. Of note the 964 in gulf livery is a 964 cup car.

Macca

One (or two) last things Manifold+rm21+Joe. Have any of you played with lowering the front of the car (rake)?

Do you have the car set up with driver weight when having the geo done (I typically do)?

Have any of you had an attempt at corner weight balancing this car (almost impossible to do without adjustable drop links I suspect)?

Manifold

That fits my experience. At the end of our VIR event, I thought my car felt pretty good. Beginning of the next event two weeks later, with the same tires and new setup, the car felt quite loose and slow. Putting fresh rear tires on made it much better, but still a bit loose and not as fast as before, though cold weather and needing to scrub in the rear tires may have been factors.

I could be wrong, but I'm suspecting that the 'curing' and resulting hardening of the Cup 2 tires can last hours to days after a heat cycle, which would then explain significant loss of grip between events. Driving lots of road miles may also have some effect, but I have no idea how much. Immediately prior to the two days at VIR, I was at Summit Point for two days, so four consecutive days of heat cycles, around 15-20 total cycles in those days.

Macca + Joe, PMs sent.

orthojoe

Macca, great discussion. My thoughts:
More negative camber up front might be giving you more grip up front whereas more negative camber in the rear may decrease rear grip, which would account for the car feeling more loose and better with stock geo (you've got me saying geo now instead of alignment!). I would bet that the oversteer could be dialed out with sway bar settings like mine if you were running that more aggressive geo. With stock geo, the sway bar settings will be different. In the end, I'm not convinced any geo setup is particularly faster and is just a factor of driving style and track layout. I'm going to guess that if I kept my front camber at -2.7, but dialed back the rear camber to -2.0, that I would end up wanting to stiffen my rear bar back up and to get the car to act the same way.
You make a good point about the tires heat cycling out before the tread becomes an issue, so trying to save the outer edges may be a moot point. I 100% agree with the rear tires and have therefore stopped trying to make changes to save them. However, I am certain that the front tires would last less than the 4-5 track days I get out of them without the camber settings I'm running. Especially at thunderhill which has very high speed sweepers that destroy the outer edges of the tires. This is a factor of the tracks I run at.

I watched your video and to my eyes it does appear that you have a bit of corner entry understeer. I used to have to this as well, but it seems to be dialed out with the toe out settings up front. You might want to try this if you haven't? What happened to the aim unit? I see you're running vbox. Too bad we don't run at the same track and we could share data.

I asked to have a corner balance done, but my shop has not found a need to corner balance the car since the height settings were already balanced from the factory with a 160# ballast in the driver seat.

Macca

Gents,

You have been most helpful. Thank you Manifold also for the PM.

I went to bed last night after penning the posting and had a "come to Jesus" moment. I mentally drove my local track for 30 minutes. I realized that Im chasing the wrong handling trait in my car!!

Yes I am experiencing mild corner entry under-steer in three corners on the track (see diagram below red arrows 1+2+3). Im not experiencing it in the two corner with the larger orange circles because these corners are heavily banked and decending (we run the track clockwise) and this the weight is over the front of the car and traction is plenty on the front axle.

If I think of where Im actually LOOSING time on the track its the areas where the green arrows are where the car wants to revert to corner exit oversteer and Im managing the car on partial throttle.

Sure mild under-steer on entry is not ideal but its manageable and not really costing alot of time. Adjusting the toe setting on front wheels out as Joe suggests may improve turn in and confidence/predictability here.

There are three corners where mild understeer is apparent and three corners where oversteer is apparent. After red arrow I (right hander) we enter an off camber left hand complex over a "hill". Here I have to gently squeeze the throttle and balance oversteer. In my 993 (lower hp) I can basically flat foot it here (it takes brave pills). Its easy to see on my videos this corner. Im told I should have 5kmph more speed through here by a veteran and semi pro.

Corner 2 red arrow understeer I can live with, it leads to snap oversteer (green arrow) if you dont get it right but, lets leave that for now because I think the while issue will become less pronounced with the changes Im suggesting at the end of this.

Corner 3 is the fast sweeper on the track leading to the front straight. There is tie taht can be made here getting full throttle application as early as possible after the apex 2/3-3/4 through the corner approx where first green arrow is). Hooking up the last part of the corner (second green arrow) shows Im leaving 6-7kmph on the table here. the corner is neutral camber and very wide with lots of run off. I come un under trail braking and start applying light throttle from half way building up but due to fighting oversteer Im currently unable to really get on the gas till after the apex which is too late...

So the epiphany I have had is that I dont actually need to dial out understeer on this track with this car to become faster. I actually need to improve turn in a fraction and DIAL OUT UNDERSTEER!

Funny how you get there in the end!

I must add I run 4-5 tracks a year (4 of them once a year only). For this reason I think I will leave my current alignment settings factory. I have 9 caster (haven't yet seen a factory delivered 991 GT3 with 8.5 as the factory state and i have 10 x geo (alignment :-)) sheets from members on here with before and after!). Some of these 4 tracks are clockwise, other anti, most are longer and faster and , some more technical, some with less elevation, some less traction surface and some more etc. I think for sake of the cars versatility at this stage Ill stay stock settings and make the changes below). The track Ive been discussing is where I would spend 50% of my track time after all....

So my suggested changes are:

1) some additional toe "out" (factory settings are basically neutral IIRC).

2). Adjust sway bars to reduce corner exit oversteer.

I will make these changes and report back in the New Year when Im next in NZ and on the track.

A quick questions however

1). what would you suggest for front wheel toe out settings that wont make the car darty on the road?

2). Would you often rear bar one notch or stiffen front bar 1 or 2 notches to dial out some understeer? Ill probably make the changes gradually at the track.

Thanks again for all your help guys. Please could you have a ponder on what i say above and see if what Im saying makes some sense to you. The red herring from the videos is that understeer is more easily apparent but the feeling of the car switching to oversteer (which Im countering by more conservative driving) isnt showing on best laps as its being managed by the nut behind the wheel so you really need to relive what the car is doing here to know whats happening).

P.S. Joe - Im using AIM DL + SmartyCam HD 2.0 these days. The second video was an early one using Sony camera (better quality but no overlay).

P.P.S. Manifold. I believe you could be right about those compounds changing. I fly in and out of NZ to do track work often 8-12 week gaps between using the car. Although I leave it parked up with high pressures I have definitely noticed on teh first set of tyres that when I left I had just completed a track day with good traction (25 cycles) and when I got back a few months later the next track day it was all over the place and cycled out. I think the compound could harden after prolonged latent periods of rest. You may be onto something. For those doing winter storage would suggest cycling to an old set of used tyres before laying the car up...