Skip

Aha! [maybe] the front not lifting is the increased stiffness of the Konis at work for you - is it possible that you've not been able to put power down coming out of those corners before because the car was at the end of roll-center and quite unstable (gives the feeling of being unsafe to do so)? If so, adjust your line - entry and exit have now been changed dramatically - where you may have gone through a turn by the shortest arc to gain the advantage of runout - now you must attack the corner from up high, brake, turn ~sharp, then power out... or something like that. In other words - there's a loose nut behind the wheel... adjust as needed

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Skip

[quote]Originally posted by Mark Parker:
<strong>And while the subject of oversteer/stiff/loose is open. allow me to poll ya'll on the subject of tire pressure. I too am new to the autox game, having just run in my second last Sunday. I started off by following the recommendations on the SCCA site about running tire pressures of 40-43 psi, and equal at all four corners for my rwd car. I've settled at 40 psi front (85.5 na with 215/60 15 all around) and the front wheels are very well behaved. But my last run was at 39 psi rear, and it's amazing how quickly I can break the rear tires with any kind of throttle. It's hard to come out of a turn because I can't seem to hook up with the rears. I've been advised to try a 4-5 psi differential between frt/rear. Any thoughts from this group would be greatly appreciated.</strong><hr></blockquote>

You be needin' LSD my friend! No, not that kind - Limited Slip... without it, you are DIW (Dead In the Water) coming out of corners, especially without a fairly stiff suspension. The inside wheel is lifting, no traction = no go... I'm fighting the same battle now, but have learned how to drive it out rather than give up the medal. In general, you settle the car sooner, and basically try harder than if you had LSD.

If you have LSD now and this happening - well, I'm full of it

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Mark Parker

Skip; Thanks for the tip. No I don't have LSD, but I'm afraid it would be much easier to get that "other kind" than the type which bolts to the car <img src="graemlins/oops.gif" border="0" alt="[oops]" /> I can see what you mean about the inside wheel lifting, do you think going to adjustable shocks on the rear only would be helpful? The shocks all around are fairly recent by the PO, but of an oem flavor. I'm trying to have a co-worker go with me to the next autox, just to watch the car from outside and tell me what it's doing. If I can just get the rear wheels under control, I think I can actually get times that will make me competetive in my class. As it is I'm 3 to 5 seconds from trophy times.

Skip

Just because it's the rear that's lifting, does not mean that the problem actually exists there - alone. The suspension is a whole, and really must be upgraded as such. While it wouldn't really hurt to do just the rears - it certainly wouldn't be ideal. BTW, if you don't have one already, a rear stabilizer [or upgrade] can do wonders for the traction at the rear.

Having someone watch the car while on course is excellent - I've used this many times to gain an advantage in heavy braking situations. Having an instructor ride with you is even better - or even having them drive your car, so you can feel what it's doing without the concern of being in control [very enlightening sometimes].

3-5 seconds in autocross is an eternity... looking at average 60 second runs, you'd have to improve a great deal both in the driver and the car (tires and shocks mostly). Don't be discouraged by that gap though - like most things, it shrinks with age. Some gaps can't be met when running in class against a superior car, and drivers that just won't retire I am almost 2 full seconds off FTD, but can run 2nd/3rd FTD - a gap that will never close as long as the far superior cars and drivers are around... not too shabby for an old Wasser kühlte Zylinder vier ab and a hack like me though, eh

Mark Parker

Skip; A consistent 2 secs off FTD looks to me like the mark of a man who's got his autoxin' stuff together. I have wanted to have someone ride, or drive my car, but the current situation here isn't favorable to it. First of all, folks have suggested that it's best to try and find someone with the same or a similar car, and there are precious few Porsches, none with very competetive drivers. Second, the most competetive people, all the "old hands" are the SCCA officials, and they have told us that participation has jumped this year, so much that they have their hands full during the event and not much time to drive/ride. Just the same I have been hangin' out till the end of the event to help pick up cones and such, and in the process I may be earning some points that will pay off later. The thing that makes me begin to wonder about my equipment is that at the last event, my final 3 runs were all 48.xxx seconds, and it really felt as though I was getting all I could out of the car as it's set up now. I asked the chapter president, and one of the guys who is consistently near FTD (as we rode around in the truck pickin up cones ) for his recommendations, but he's a Mazda Miata guy, and could only suggest that I try @ 4psi pressure differential front to rear. BTW I do have a 14mm sway on the rear, and a set of Yokohama AVS on order. In the meantime, I'm really enjoying the ride.

Skip

[quote]Originally posted by Mark Parker:
<strong>The thing that makes me begin to wonder about my equipment is that at the last event, my final 3 runs were all 48.xxx seconds, and it really felt as though I was getting all I could out of the car as it's set up now.<hr></blockquote></strong>

I thought the same thing near the end of my first year of autocrossing - then I had two different instructors drive my car and knock 2-3 seconds off my best time of the day. One was a 924S driver, the other a 964 driver - both SCCA National competitors at the time. I rode with each of them, and learned a few things.


[quote]<strong>... but he's a Mazda Miata guy, and could only suggest that I try @ 4psi pressure differential front to rear...</strong><hr></blockquote>

That's what I would call a SWAG - but maybe the best advice to give if wanting to offer *something*. Tire pressures are very important, but the 944 has so many tire and suspension configurations that it's hard to say what - if any - differential pressures are needed. Easiest way to get a rough idea is to mark the edges of the tires with chalk or shoe polish - then watch the edges, making sure some, but not too much, tire roll is occuring. Best way to tell is with a Pyrometer and a buddy to help get *hot* temps as you come off course. Use of a Pyrometer allowed me to make a drastic change to the recommended front camber for my Kumhos - from -2.5 to -3.5 degrees. I run ~1lb differential biased to the rear with 225&245-16 Victoracers.

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Danno

"Use of a Pyrometer allowed me to make a drastic change to the recommended front camber for my Kumhos - from -2.5 to -3.5 degrees. I run ~1lb differential biased to the rear with 225&245-16 Victoracers."

Gee golly, someone who REALLY knows how to set up alignment specs for autocrossing, what a relief!!! Wonder how many people with "my car doesn't turn" or "why does my tire wear the edges so much" type of questions are running LESS than -1 degree of camber, eh?

Skip

And this was after I was emphatically told that Kumhos could never use that much camber - but Hoosiers could. Ran the tire temps for a two-day event in the same weather. Still keep an eye on them, but nothing new to see so far - except in the rain where I go back to -2.5... camber plates should be mandatory There is a limit though - I mistakenly ran -4.5 (loose strut camber bolt) and the car was very pushy... on one side only

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FormulaOne10

As for those tire pressures, I personally think they may be a bit high, but if it works for your tire there's nothing wrong with them. Remember that tire pressures do many things, but most importantly to you right now they do two things:

1. Help modululate tire roll.

2. Change the grip of the tire in a given situation.

Now obviously even these two effects are totally related as the main object of a tire is to grip the road . Generally(but not always) for a dry pavement condition you want to run as little pressure as possible while maintaining an optimal level of tire roll. However, you also need to consider the front/rear combination of tire pressures. The porsche manual recommends a 29/36 for my 84 n/a. This is to reduce oversteer. I personally run only 29 in the front and 32 in the rear in my car and it works fine. I would probably run even less if I didn't occasionaly haul a few things in the car. Of course this is a street condition where I'm not accelerating out of the sweeper into a slalom (at least not usually <img src="graemlins/burnout.gif" border="0" alt="[burnout]" /> ). Anyway, enough blabbering about these street conditions. Even for your car on the track, I don't think you need any tire above 40 psi. Especially if you have a Z-rated or performance tire with stiffer sidewalls. My rear tires (michelin pilot xgt v4 on wider fuchs, 8" I believe) will suddenly break loose on acceleration out of a turn if I run pressures near or above 40 psi. You are only combating tire roll with your higher pressures and at a point you will experience diminishing returns with tire grip. All this crap basically means is that you have to find the middle ground where your tire isn't rolling too much and you are maximizing your contact patch with optimal tire pressure. IMO 40 psi is above this level unless you are running a very flimsy tire.