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-   -   924S - Track Tire Pressures (http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/129600-924s-track-tire-pressures.html)

Bruce Ayling 09-29-2003 05:31 PM

924S - Track Tire Pressures
 
All,

I have a 1987 924S that I will be tracking for the first time at the PCA Drivers Ed event at Carolina Motorsports Park (Kershaw, SC) this coming weekend. I'm hoping for some input as to a good baseline air pressure for the tires. I will be driving to and from the event so basically I'll set it cold before I leave and pray that it's "in the ballpark".

The chassis is as follows:

- 17" Cup wheels with Kumho Ecsta's
- Weltmeister Bars & Springs (lowered)
- Koni Adjustables at all 4 corners
- Strut Tower Brace

As I say, this will be it's first time on the track (and mine as well) so any and all thoughts/recommendations would be most appreciated.

http://forums.pelicanparts.com/uploa...1064885347.jpg

944 boy 09-29-2003 07:35 PM

Are they 712's or MX's?
I ran my 712's harder than the MX's. About 38-40 cold for the 712 auto-x. So about 36 for the track is a good guess but you may want to run them lower.

-Greg

vital-transform 09-29-2003 08:58 PM

That car looks great!
Hey what size rims are you using? 6" or 7"

924Sman 09-30-2003 02:29 AM

With this you and the cars first track event the tire temp is not going to be an issue because you won't be going all that fast and they are street tires. That said a good temp to start is around 36 to 38 cold and take the temp immediately after the session if all is good you should see 40 to 42 psi. At the tires hottest point check and adjust air accordingly so that you have even pressures at the end of your runs....The second you get on pit out have someone check the pressures do not wait till you get back to the paddock or after your cool down! Have a ball!!!! Sman

Z-man 09-30-2003 05:29 AM

Like they said, 36-38 is a good starting point.

While a tire pyrometer can tell you exactly how well dialed in your alignment and tire temps are, a good seat of the pants way to check is to pay attention to the outer edges of the tires: you want the scuffing to end near the edge of the tread. If the scuffing is over the tread, then you're under-pressured. Not all the way to the edge of the tread, and then you have too much pressure.

Whenever you make adjustments in pressure, only go up or down 2 psi max.

Also: stay with a constant pressure all around for now. Later, when you begin to understand the dynamics of your car, you can vary the front to rear to help balance the car.

Tire pressures vary greatly from car to car and driver to driver: some people like to run the tires at higher temps, others lower. After some experience you'll get a feeling for what works for you. Log your temps in your track log book (everyone should have one of these!!) and pay careful attention to what feels best for you.

Oh, one more thing: a warning: this stuff is pretty addictive, so be prepared!! :)

Have fun!
-Z.

Bruce Ayling 09-30-2003 06:31 AM

My thanks to all who replied! I have crewed on an SCCA GT-3 car so have a good sense of vehicle dynamics and the effects various changes can have on a cars handling characteristics. What I was mostly looking for was a baseline pressure from which to begin tuning and there seems to be a strong consensus on that.

As "sman" stated, since this is my first time actually in the driver's seat I probably won't be that fast - so long as the car is reasonably balanced my focus will be more on improving my skills rather than its set-up. As the addiction continues (and my driving skills hopefully improve) I'll begin to focus on tuning the chassis.

I'll post after the event to let everyone know what I learned and how things go. Thanks again to all!!!! SmileWavy

Bruce Ayling 09-30-2003 06:47 AM

Quote:

Originally posted by vital-transform
That car looks great!
Hey what size rims are you using? 6" or 7"

"Vital" - Thank you!

They're 17x7's all around.

924Sman 09-30-2003 07:39 AM

Bruce, That's the attitude I love to see! So many starting out in DE want to race and go fast but with the 924S speed is in the corners and momentum. Your approach will serve you very well as it has me!! This attitude will make you much faster and a much better driver! Good Luck at your event and someday I hope to see you chasing me around the track!! lol......Sman

drew1 09-30-2003 05:03 PM

Bruce,

Have fun, let us know what pressures & settings on the Konis work best.

drew1

KilnRed83SC 10-01-2003 07:20 PM

Bruce,

Great looking car. I'll be running CMP this weekend as well. I run 3-4 lbs over stock which works out to 32F/36R. But then I've got the motor on the back end, so your mileage may vary.

Brian
Kiln Red 83 Targa.

Bruce Ayling 10-06-2003 03:11 PM

As promised - the results!

What can I say other than that the entire experience was amazing?! As stated before I've crewed a fair amount, but this was my first time in the drivers seat and words can't describe what a blast I had!

I started out running 36psi cold all around on Kumho Ecsta 712's and found things a bit slippery. I dropped pressure to 32psi and that seemed to be a reasonble point. By the time I got off the track, talked over my last run with the instructor, and got the car parked it was too late to get a meaningful hot pressure reading so I don't know what kind of heat expansion was going on.

I was very fortunate to have a great group of folks in my group (Green - newbies) and a number of other 924/944 drivers on track to compare myself with. My knowledge/skills/track awareness improved exponentially and by the time the weekend was over the differnce in my driving was night and day - I passed most people (in my group) and was only passed by a couple - two late model 996's and a fellow named Keith who had a beautiful 944S with a 968 engine. My last run out I was allowed to Solo which was amazing up until my rather, um... dramatic ...spin...

Humble pie - the spin - aka how NOT to take "the Kink". Last run of the day - track hot - tires hot - getting slippery - Keith in the afforementioned 944S gaining more rapidly than my ego wanted to let him - still not sure what exactly happened but next thing I know I'm at red line in 4th - turning in to the corner and - spin, spin, spin - most exciting... :eek:

Anyway, my thanks to everyone for their advice and good wishes. I have to have an old football injury taken care of (knee surgery) so it'll be a while before I get to do this again, but the addiction has undeniably taken hold!!

Brian - it was a pleasure to meet you! Hope you did well and look forward to seeing you again in the future!

924Sman 10-07-2003 03:56 AM

Bruce, Welcome to the 360 Club!! Sounds like you are a new track junkie! YOUR HOOKED NOW!.........Too bad you could not have checked pressure while hot to give you more of an idea of how tire temps can fluctuate and fast at that. Really need to get all 4 pronto!.....As far as the "spin" try to recall what you were doing prior to the spin as this is very helpful in your process of being a racer. This will help you correct any driving errors in the next run. You are in a place where learning the feel of the car is crucial so you can make or avoid future errors. In short recall the feel and speed you were doing and what you were doing in braking when the spin occurred. I think you unweighted the car by improper gas/braking as a result the back end came out. As stated you at redline in 4th and I will bet all that you lifted off the gas at the wrong time or you were on the brakes during cornering. But great to see you had a blast!! Last note....remember you are driving a "momentum" car and your best time will be created in the corners so be smooth and deliberate!! I hope to see you on the "grid" along side my 87 924S one day! Sman

Z-man 10-07-2003 05:12 AM

Sounds like another track addict has joined the ranks!

Welcome!!!

-Z-man.

924Sman 10-07-2003 05:22 AM

Zman... Right you are! Now we just need to keep him from the "Red Mist" syndrome!!!......for those not up on the lingo...refraining from trying to race with cars that pass you that are much faster than you in DE events. Sman

Z-man 10-07-2003 08:06 AM

Quote:

Originally posted by 924Sman
Zman... Right you are! Now we just need to keep him from the "Red Mist" syndrome!!!......for those not up on the lingo...refraining from trying to race with cars that pass you that are much faster than you in DE events. Sman
Beware the red mist!
Yes: courtesy and politeness go a lot further than racing during a DE.

-Z.

KilnRed83SC 10-07-2003 08:49 AM

Bruce,

If you get a chance, you should come down to the PCA Club race at CMP on November 7,8 & 9. I'll be there, probably working grid. The Kink usually claims a couple of racers over the weekend, especially when they try it 2 wide. So it can bite the best.

Glad you enjoyed the weekend. I hope you'll become a regular.

Brian

Bruce Ayling 10-07-2003 01:44 PM

924Sman/ZMan/Brian,

Hooked and hopelessly addicted are apt descriptions!

Most of the spin is still a blur but my best guess is that both Brian and 924Sman are right - I probably early apexed (went wide), pinched in to "compensate", and performed the cardinal sin of lifting off the throttle. For those who have not been to CMP the "kink" is a truly more of a right hand kink than a corner, It comes at the end of a long straight and if done right is taken at full throttle. The consequences are rather spectacular if it is not "done right"... :D

As Z-Man pointed out courtesy and respect at a Drivers Ed are paramount. I can see where "red-mist" could happen, but I don't think it was a factor in my spin. By the time it occured Keith had gotten to within a few car lengths of me and I'd already made up my mind to wave him past at the next straight. I screwed up is pretty much the root cause... :o

Brian - I may be in a wheel chair come November, but I'll try to make it if I can.

Thanks for the good wishes, advice, and input from everyone!


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