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Discussion Starter #1 (Edited)
I had the Cayman S aligned. Here are the specs, trying to mimic Brad's suggestions of the other day:

Left front--Camber -0.8 deg; Caster 7.5 deg; Toe 0.04 deg
Right Front--Camber -0.8 deg, Caster 7.3 deg, Toe 0.04 deg
Cross camber--0
Cross caster 0.2 deg
Cross SAI--0.2 deg
Total Toe--0.08 deg


Left Rear--Camber -1.8 deg; Toe 0.09 Deg;
Right Rear--Camber -1.8 deg; Toe 0.09 deg
Cross camber--0 deg
Total Toe--0.18 deg
Thrust Angle--0 deg

I am running the stock RE050A tires on the stock 18 inch wheels. With that in mind, and with my goal of having just a touch of understeer for safety--but not much--what would you suggest my cold and hot tire pressures (F and R) be? Also, I will be running at Road Atlanta--does that affect your answer? Would you stagger for right turns?

Thanks so much.
 

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Where are you running, and what is the weather forecast (sunny, cloudy, etc) and ambient temperatures expected to be?

brad
 

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Discussion Starter #3
Road Atlanta; Cloudy, 46 deg low, 59 deg high.
 

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2-3 pounds more than street recommendation in front, and maybe 2 lbs. more than street in the rear would be a good place to start... In the front, this should keep you from rolling over onto the sidewalls until you get used to the Cayman's proper corner entry speeds. Measure them when you come in off the track and see how much pressure you've gained. In those conditions and temps, you probably will add 3-4 lbs, maybe not that much of it's quite cloudy. Decide how they felt during the session and adjust accordingly. My guess is you'll be bleeding some air out and keeping them 34-35s front and slightly higher in the rear when they're hot. The Bridgestone's have a stiffer sidewall than the Michelins so you might be able to run a little lower in the front than that for a tad more grip, and still not see any roll-over.

brad
 

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Another good question. What's your skill level?

I just ran at Lime Rock under similar conditions (on Michellins). I started at factory recomended pressures and the car felt great. No roll over on the fronts, minimal understeer, the back was stuck like glue. I picked up 4 psi when hot.

Most importantly, make sure you give them a chance to warm up when driving in these conditions.
 

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2-3 pounds more than street recommendation in front, and maybe 2 lbs. more than street in the rear would be a good place to start... In the front, this should keep you from rolling over onto the sidewalls until you get used to the Cayman's proper corner entry speeds. Measure them when you come in off the track and see how much pressure you've gained. In those conditions and temps, you probably will add 3-4 lbs, maybe not that much of it's quite cloudy. Decide how they felt during the session and adjust accordingly. My guess is you'll be bleeding some air out and keeping them 34-35s front and slightly higher in the rear when they're hot. The Bridgestone's have a stiffer sidewall than the Michelins so you might be able to run a little lower in the front than that for a tad more grip, and still not see any roll-over.

brad
Quick:

Make sure you correct for temp if you set your cold pressures in a heated garage. Cold pressure measured first thing in the morning, out in an open parking lot before the engine has been started would probably be equivilent to 2 or 3 lbs more than factory that Beez is recommending above.

When you measure cold pressure in a heated garage, you need to correct in the following way. Add 1 PSI for each 10 degrees temp difference between the warm garage and the cold outdoors. Or, in summer, when garage is cool and outside is warm, subtract 1 PSI for each 10 degrees difference.

I really don't care much for the cold pressure method for track inflation. I'd just fill to factory recommendations and run a session noting in your head how the car feels. Check pressures IMMEDIATELY when you get in. If your pit area is far from the track-out, then pull over in a safe place and check as near track-out as you can. Don't let your instructor talk your ear off at the end of the session as your tires cool. Be consistent about where you measure and try to find a good spot to really get the best hot measurement possible.

With R tires, the hot pressure is usually ideal at 37 to 39 psi..front or rear.
With street tires, the idea pressure is usually a bit higher...into the low 40's...maybe 42? The outside tires are going to gain more air pressure when hot than the inside tires...Outside does the most work.

The magic of hot pressure is that it tells you where the tire is on the track. You just set the same pressure all around. Brilliant!

You want to look at the outside edge of the tires to see how much they roll over. Most have a little triangle or other mark to show you where the ideal roll-over point is. Theoretically, you want the tire to roll just at or just before the point of the triangle on the top of the sidewall. More air will give less roll-over. Less air will give more roll-over.

If you're over-inflated, the sidewalls will not be rolling over, which is good, but the tires will have too small a contact patch. That means grip is compromised and the tire will wear too much in the middle of the tread. In the extreme, the tire will get really hot in the contact area.

So, I'd start at factory spec for first session and gradually work your speeds up according to ability. At the end of session, immediately check outside tires first, release air as needed to get 42psi in each tire. If you need to add, make a note and add later. The important thing is to get your hot measurement as hot as you can and be consistent with that.

If 42 isn't giving the right roll-over, than reduce your target hot pressure. If they're rolling over too much, increase that target.

I've found the CS to be very easy to correct if it gets out of shape, unlike the911s I've driven. So trying to dial in understeer for safety is really not recommended. You have stability control to babysit you. It's possible to drive this car off the track, but not frikking likely if you're paying attention and not driving way over your head.

Your aim should be good grip, good tire life and decent car balance.
 

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I started my PS2s around 34 cold. The most important thing is to check your tires hot as soon as you get through with your first run and adjust them to about 40 psi. I haven't had the chance to run Road Atlanta yet, I plan on doing one this spring. I've been told RA is very hard on the breaks and not so bad on the tires. Barber's is just the opposite, hard on tires and not so on breaks.

Enjoy! I'm sure you'll have a good time.:banana:
 

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I ran close to the settings you have and still had plenty of understeer. I don't think you need to worry about that. It was only when I went to more than 2 degrees front camber that the understeer went away.

Have fun at the track!
Dave
 

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I went a little different route for push. When I purchased RE-11's for my 19's I used 245's instead of 235's for the front and kept the rear 265 size. The combination on a stock car works well for me. Hot pressures were around 38-39 in the summer on a dry track. Of course addition of more camber, bars, coil overs would help but I'd like to 'try' to keep this one somewhat stock.
 

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I ran with my 050As for couple events, really good tires IMO; I was quite happy with ~34F and 38r hot pressures. I think 0.18 total rear toe is too excessive, I would not run more than 0.06 with stock tire sizes, and certainly not more than the fronts.
 

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I ran with my 050As for couple events, really good tires IMO; I was quite happy with ~34F and 38r hot pressures. I think 0.18 total rear toe is too excessive, I would not run more than 0.06 with stock tire sizes, and certainly not more than the fronts.
I realize all this is at least partially subject to personal driving style, but I have always set up cars with more toe in rear than front. My GT3 is now set up with total toe of 0.05 front, and 0.35 rear, with excellent wear and handling results. I doubt that you need that much toe in the rear of the Cayman, but I expect his toe numbers are okay. Much less, and I would guess traction under acceleration out of corners would suffer.
 

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I'd agree, it comes to personal preference and its relative; I personally like slightly loose attitude and the CS is moderately tight, especially with stock tire setup, hence why I suggested less toe-in for the rear. In terms of acceleration, under power the initial reaction of the suspension is to gain toe, so if you start with aggressive toe-in, you compound the problem in corner exits IMHO.
 

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Also, I will be running at Road Atlanta--does that affect your answer?
Sorry, don't mean to hijack here - Be on the lookout for a guy in a blue Mini S with white stripes. He is a co-worker and will be running Road Atlanta this weekend for the first time.

He is young, fearless, and amazingly fast. Oh, and he's a real good guy, too! :)

Have fun! One of these days I will make it to a DE down there.
 

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I'd agree, it comes to personal preference and its relative; I personally like slightly loose attitude and the CS is moderately tight, especially with stock tire setup, hence why I suggested less toe-in for the rear. In terms of acceleration, under power the initial reaction of the suspension is to gain toe, so if you start with aggressive toe-in, you compound the problem in corner exits IMHO.
My experience is that, for track driving on most tires, you can't beat a lot of camber. If you drive to the track, you must have very near zero tow or your tires will be worn out before you get there. 300 miles of interstate with a lot of toe and big negative camber and a set of R-tires can be down to the cords!

So I'm a zero toe fan during track season. The car drives a little loose, but I don't need to trailer it that way.
 

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Discussion Starter #15
Thanks for all of the help. Sounds like I might have been too aggressive on the toe for these street tires. We'll see. I'll try to post a detailed report after the event. There appears to be some of the dreaded "R" word in the forecast later in the day. Hopefully, it will hold off.
 
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