Dan39

Gentlemen, I managed half day of tire testing on Monday and thought I would share the results as they were quite different to my expectations.

Obviously, they are representative of my driving for that car (stock w/ MPSC2), that day, under those conditions.

First, a video of a typical lap – almost all my clean runs were 1:32.xx. This was my first time on track in the car and I only got about 40 laps in.

I believe there is a good 0.5-1.0 seconds in the car under those conditions (stock plus 220lb passenger) and I think under optimal conditions (no passenger, proper alignment, optimal pressures, no cones limiting my line) it can do a 1:29.

For comparison, the leading Porsche 911 GT America qualified in 1:19.2 for this year's GP of Mosport.



Hot Pressures -

31.0 / 31.5
32.5 / 32.5


Temperatures -

LF - O/C/I RF – I/C/O
183 / 171 / 163 187 / 169 / 160

LR - O/C/I RR – I/C/O
180 / 182 / 188 194 / 173 / 172


Suggested Optimal Pressures –

31.0 / 32.0
32.5 / 33.0


Notes -

-neutral to slight oversteer
-ABS intervention is too aggressive
-requires more camber on the front and slightly more on the rear – maybe 2.25/1.75
-requires more downforce at the front and rear, but particularly the rear

Macca

Dan. thanks for the great data points.

How did your experience differ from expectations? Good or bad?

Yes the factory geo is too conservative. the settings you target are possible without adding shims. You may end up going a little further to find the perfect balance IMO (-2.5/-2.0).

Downforce at the rear is easily adjusted off the rear wing (tighten max 13lbft).

Try ESC+TC off as may relax ABS threshold.

P.S. I think you can drop even further maybe on the front pressures?

Dan39

You're very welcome. And I love your new avatar - gorgeous!

Of course, I was thrilled with the car overall.

I was surprised, though, that the car did not understeer more and found it to be overall pretty neutral, even to over-steer slightly, especially at high speed. That seat-of-the-pants impression turned out to be backed by the data you see above - look at the front/rear temperature differential. Not what you would expect from the factory!

On tire pressures, I was thinking 29/30 maybe 30/31 or 30/30 would be ideal with the MPSC2, but lower front pressures would cool the centre of the tires more and they were already in line or slightly cooler than the average of inside and outside - not what you want.

Also, the pressures and temperatures were broadly in line with the 32/36 and 160-220 operating window suggested by Michelin for the MPSC2.

TrackFan

You'll be faster without a passenger.

Nick

I believe RWS helps to mitigate understeer.

Dan39

Hah, getting this car to the track without a passenger is not so easy and even once you are there you run the risk of picking one up!

Macca

Dan. That's a good observation as no one yet has posted carcass temp across the contact patch. Do you have a data sheet from Michelin on the MPSC2 as Ive been hunting for one or a link to one?

I think a bit more negative camber may have further affect on the ideal pressures. One thing seems certain from my (limited) track experience with the car - and that is the chassis can handle much wider tire temp range before it becomes "an issue" than say my old aircooled 993...

Yes the avatar was from our Europe ED. Took a wrong turn and almost ended up at the leaning tower of Piza in the GT3. The next photo in the sequence a Sengalense street vendor leans over to the driver side of the car and tried to sell me a fake Rolex! I parked a few 100 meters up the road and paid one of the young hip black blokes "hangin" the vicinity 5 Euro to keep an eye on here while we played tourists for a few hours. Bit nerve racking with all our gear (we were between destinations) in the car!! Everything ended well :-)

Dan39

I only have the hard copy of the tire data sheet that I got with a new set of tires I bought earlier in the season. However, I had a look at the data sheet for the Cup tires and it's virtually identical - you can find that here:

http://www.tirerack.com/tires/tirete...nd_Feeding.pdf

Tire temps - 160 to 220
Hot Pressure - 32/36

In the video I posted, you can see I'm at or near the limit and the tire temps I posted are toward the lower end of the suggested operating window. It seems then the chassis does not work its tires very hard unlike some other sports cars! I woudl imagine that over-heating the tires would take a lot of laps or some really wild driving or both.

az audi

The Michelin book is very informative for those of us new to car and tire set up.

mdrums

How does rear steer effect the desired camber settings?

In the past 997 GT3 and Carrrera cars for an expired track guy running a store table r comp tire it seems that -2.5 front and -2 rear were god starting points with zero toe up front and -2mm toe in per side on the rear.

I would think with a new chassis and rear steer this would change typical alignment settings from past 911 cars?

Dan39

I'd like to do more testing, but from the temperatures I recorded it doesn't look like I would need to add much camber to the rear at all.

Here's the Left Rear (the last corner before the temps were taken was a long 160 km/h right-hander).

LR - Outside/Middle/Inside
180 / 182 / 188

That looks pretty much perfect to me, maybe a touch more camber.

Macca

Dan. Im with you on the data analysis. What you really need done is your initial supplied chassis settings ticked off (checked) so you know what you have to start with.

The fronts clearly can benefit from some negative but my advice would be to go no further initially than -2.15'-2.30' which is the extent of the range that can be made without adding shims. The rears don't need adjusting right now IMO other than checking consistency side to side. I would run it like that and see what you find. As you get more grip from the front and confidence in the car you may push the chassis even further and may find you need a little more -ve at the front and even start to need some at the rear.

Dan39

I think you're pretty much spot on with your less is more advice - I was thinking a full turn on the front and half a percent on the rear. I certainly don't want to upset the front / rear balance as it is perfect for me right now save a bit of high speed oversteer I think I can deal with by adding wing. I may do less though and test again and see where I'm at then.

Did your car come as advertised with - 1.30 at all four corners or did you find it was out of whack? I know prior generations of GT3 have come quite wonky from the factory.

<3mph

Sorry to hijack the thread for a quick diversion. This'll be really quick, I promise...

Just in case anyone has second thoughts about 20" wheels, just look at the possibilities: the Youabian Puma has no qualms about them, and fit even bigger tires. Why? Duh, to increase the contact patch even more, of course. It needs a bit of tweaking though, as 0-60 comes in at a mildly disappointing 5.9 sec. Cue the delivery van passing in the right lane (about 1:13 in the video). But that's totally AMAZING considering the thing is massive (who ever said lighter is better obviously never met Dr. Youabian). Hahahaha...

Dan39

Sigh.