Help Needed, baseline settings for First autocross of the season

[drj2k1]

Now that things seem to finally be looking up here in NY and we've been given the go ahead to resume the autocross season, I'm tentatively registered for my first event in the mustang this year on Sunday. In typical fashion, I'm behind the 8 ball and the car is going in for an alignment Saturday morning at a friends shop (check out El Gato Engineering if you are in the Tri-State Area), hoping for ~ -2 degrees camber up front and going to zero the toe to prolong tire wear. Having little experience with setting up a RWD chassis (let alone a stick axle car), I was hoping to pick the collective minds of the TMO brain trust to get some baseline shock settings and tire pressures.

Car setup:
Koni Yellows with RE bumpstops up front and Ford Racing jounce kit in rear
Stock V6 PP springs (allegedly 2011 GT rear spring rate with a different front rate in the GT ballpark)
Stock V6 PP 35MM front swaybar
Stranoparts 1inch adjustable rear sway/endlinks (set to softest setting)
18x8.5 "square" Enkei's with 265/45/18 RE71R's

I was thinking of starting in the ball park of 2 turns off soft up front and 1 turn off soft in the rear for the Koni's. Not really sure where to start with tire pressure, maybe 35psi cold up front and 33 rear? From prior experience racing stock class cars on soft springs, they usually like a little more pressure than usual but without a pyrometer and baseline data we are just guessing at this point.

Any insight would be greatly appreciated as usual, thanks in advance

J

 

[Grant 302]

I think that’s higher than I’d target hot for those. I’d shoot for around 32-33 hot in the front and only higher IF rollover is a problem in that pressure range. Maybe 30-31 hot in the rear.

Cold pressures will depend on your cold temp. Always better to let the hot pressures dictate your cold pressures, not the other way around.

Are you going to be able to rotate front to rear is you have wear issues? Are you bringing a compressor or air tank to be able to adjust up if need be?

 

[xr7]

I put 3 or 4 chalk lines on the tires running from the edge of the tread up on to the sidewalls to see how close I'm getting to the sidewall. Start with your pressures up and drop a pound or two to see where the wear stops. My Pirelli's performed best with higher pressures, 36 fronts, 32 rears, my Falken's like a lower pressure, I'm at 28 all around, will try a little lower next session. I also run -2.5 camber, that's all I can get without cutting up the towers. Run 1/8" tow out. Running Falken 295/40-18's all around on Apex 18x11 wheels. May go to Bridgestone's or Rivals when these are shot. I run CAM C class, middle of the pack, keeping the fast guys honest. The S550's are tough to beat.

 

[DaveW]

We ran our 2012 in FS trim for many years. It was so floppy that anything less than full stiff on the Koni's was useless.

RE71's like about 34 psi front, 30 rear.

DaveW

 

[blacksheep-1]

I put 3 or 4 chalk lines on the tires running from the edge of the tread up on to the sidewalls to see how close I'm getting to the sidewall. Start with your pressures up and drop a pound or two to see where the wear stops. My Pirelli's performed best with higher pressures, 36 fronts, 32 rears, my Falken's like a lower pressure, I'm at 28 all around, will try a little lower next session. I also run -2.5 camber, that's all I can get without cutting up the towers. Run 1/8" tow out. Running Falken 295/40-18's all around on Apex 18x11 wheels. May go to Bridgestone's or Rivals when these are shot. I run CAM C class, middle of the pack, keeping the fast guys honest. The S550's are tough to beat.

Old drag racer trick, chalk lines on tires, but it works for us as well.

 

[302 Hi Pro]

DRJ:

Look forward to your Auto-X review and were you found the best tire & Koni settings for your Mustang.

 

[Bill Pemberton]

DaveW comes from a long time Autocrossing Family and he also sells tires ( among a ton of other items at Soloperformance.,com ).His business is based,primarily, on Autocross/Road Racing supplies and I think he is giving you hot tire pressures for the Bridgestones. Always good to get info from someone running a specific tire brand since the pressures can vary tremendously from manufacturer to manufacturer.

 

[drj2k1]

Thanks all for the insight and for sharing your experiences. We got in 7 runs each yesterday co-driving with my old man at NNJR on a low 40 second course. We started with 34psi front and 30psi rear as per DaveW's recommendation from his FS car which was just about perfect. We bled the hot tires back down to 34/30 between runs and got the water sprayer out after the 3rd run in the morning (92 degrees heat and a two drivers are not ideal conditions on the RE71R). We also used the old chalked sidewall trick and had no issues with rollover at all (want to see the chalk marks disappear? overdrive one lap in a camber challenged FWD car lol).

In the afternoon we played around with pressures and after a warm up run bled the tires down to 33psi F and 29psi R, and had our best times of the day. Not the finish we were hoping for but a fun day nonetheless, will post an update/reflection from the event in the car's build thread once I upload some pics/videos.

Thanks again,
J

 

[Bill Pemberton]

Well, thanks for clarifying, I assumed Dave was at hot temps, but it appears from your note it was cold pressures--- my bad. Glad you and your Dad had a good time and am sure things will improve as you get more seat time with sticky rubber?!

 

[drj2k1]

Well, thanks for clarifying, I assumed Dave was at hot temps, but it appears from your note it was cold times --- my bad. Glad you and your Dad had a good time and am sure things will improve as you get more seat time with sticky rubber?!

Bill,

To clarify, we started with 34psi F/ 30 psi R cold but bled them back down to 34psi/30psi hot as the temps rose after each run. Settled on 33psi hot and 29psi for the last runs in the afternoon.

Definitely need more seat time with the stickier tires to get more acclimated/comfortable with driving this thing on the edge of the limit.

 

[Bill Pemberton]

Dave has a lot of experience and great he chimed in. Glad it worked well for you guys.

 

[blacksheep-1]

Dave has a lot of experience and glad he chimed in. Glad it worked well for you guys.

So Dave runs primarily treaded tires on his stuff?..that's good because my experience is almost solely with slicks, or DOt/slicks. I try to help a smany people a sI can, but treaded tires react differently than slicks on a roadcourse or autocross track. It's good to know someone on here has some experience with treaded tires, it's something I'm a bit light on.

 

[Bill Pemberton]

DaveW runs in CamC ( SCCA Autocrossing ) , so he helps folks out with 200 TWR tires. He also sells your favorite rubber, Blacksheep , Hoosiers, hence he is a pretty well versed dude. His biggest problem is he is kind of a shy and quiet guy, but if he gives folks advice it is usually spot on.........helps he spends alot of time around both autocross and road race tracks assisting racers.

 

[blacksheep-1]

sounds like he need to look me up..

 

[Grant 302]

Bill,

To clarify, we started with 34psi F/ 30 psi R cold but bled them back down to 34psi/30psi hot as the temps rose after each run. Settled on 33psi hot and 29psi for the last runs in the afternoon.

Definitely need more seat time with the stickier tires to get more acclimated/comfortable with driving this thing on the edge of the limit.

What you really need to learn form this excercise is how to target hot temps based on the ‘cold’ ambient temps. Otherwise you don’t really know what your operating pressure should be and are just chasing your tail through the day bleeding off pressure.

See some of Rob’s posts about how to build a chart for temps vs. pressure. What hot pressures were you seeing, and what were the ambient temps? Would give you some idea where you should have started cold.

 

[DaveW]

What you really need to learn form this excercise is how to target hot temps based on the ‘cold’ ambient temps. Otherwise you don’t really know what your operating pressure should be and are just chasing your tail through the day bleeding off pressure.

See some of Rob’s posts about how to build a chart for temps vs. pressure. What hot pressures were you seeing, and what were the ambient temps? Would give you some idea where you should have started cold.

Not trying to be rude, but this is 100000% overkill for autocross. That is why I didn't specify hot or cold....check them at the same time *after*each*run* and go with it. It doesn't matter if that pressure temp corrects to 35.1 in some chart, what matters is that the car works at 34 shown on the gauge when checked at the given time and that you can repeat that.

Also, in an autocross setting, they almost always rise for a run or two and then stabilize. THe only time I do a real "cold" pressure is for ProSolo, which is 4 runs back to back to back to back with little time for bleeding in between. I usually start 2 psi lower than normal and that minimizes bleeding time for my helper.

For regular events, I set them before my first run (duh ) and then again after every run right when I get back and get out of the car, but any consistent procedure will work.

DaveW

 

[Grant 302]

Not trying to be rude, but this is 100000% overkill for autocross. That is why I didn't specify hot or cold....check them at the same time *after*each*run* and go with it. It doesn't matter if that pressure temp corrects to 35.1 in some chart, what matters is that the car works at 34 shown on the gauge when checked at the given time and that you can repeat that.

Also, in an autocross setting, they almost always rise for a run or two and then stabilize. THe only time I do a real "cold" pressure is for ProSolo, which is 4 runs back to back to back to back with little time for bleeding in between. I usually start 2 psi lower than normal and that minimizes bleeding time for my helper.

For regular events, I set them before my first run (duh ) and then again after every run right when I get back and get out of the car, but any consistent procedure will work.

DaveW

It’s not rude, but if the initial and subsequent drops are anything over 1 lb., then I simply disagree.

 

[DaveW]

Remember, we are talking 45-70 second runs....the first run is the worst with climb, but by setting the same pressure before, you spend the most time at the proper pressure. There are many times that only the fronts, or only one side will climb on early runs, so setting some arbitrary cold temp could end up making you spend more time (percentage wise) at the wrong pressure.

45-70 second runs, Not 20 minute sessions or 30 minute races.

DaveW

 

[Grant 302]

If anyone records the drops, they would quickly see what I mean. The cold starting pressures aren’t ‘arbitrary’. And this process lets the tires spend more time at the correct pressure.

 

[blacksheep-1]

something for everyone to chew on..

tire pressure mapping

I was asked on a FB page to explain how I do this so I'm sending them here. It's quite cumbersome to explain on FB. I have been fortunate enough to work with some very talented people over the years who have brought me along. They NEVER gave me the whole answer but expected me to figure it out...

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