My 4th weekend in my Cup car was the Rose Cup and things went pretty well (3rd & 4th overall in PCA). But, I’m not convinced the car was handling as well as the faster Cups. Here is the Sunday afternoon Rose Cup (GT2) race situation:

Tires - the new S9A’s and the SB whatever they are fronts - 6 heat cycles.
Very hot afternoon – 85+
Portland is flat and almost all right hand corners
One tight decreasing radius left hander (T6)
Bump - 20 clicks front, 25 rear, rebound 0

LR tire pressure 32 when I came off of the track, 29-30 on the other 3 tires.

Handling – pushing BAD into the left hander, loose everywhere else – the car was a handful. I was 3 – 3.5 seconds slower than Saturday morning when it was cooler and the tires were new. The fastest Cup cars maintained times consistent with what they were running through the weekend, but I’m not sure about the age of their tires.

So what happened?

Did the tires drop off that much after only 6 heat cycles?
Were my pressures too high?
Is there such thing as ABS induced push, even after you let off the brake pedal? It seemed like it, but do I really have to slow down to a crawl to go through that corner?
Are you making set-up changes through the day as the track heats up and gets slippery?

Any help appreciated.
Thanks,
Mark

 

"pushing BAD into the left hander, loose everywhere else "

Sounds like corner balance was off. Are you sure your scales were level, sway bars disconnected, TIRES ALL SET TO EXACTLY 30 PSI (makes a difference!).

32 PSI on the LR is too high, should cause oversteer on right turns.

 

I for sure had oversteer on the rights!

I will double check the corner balance, I had the car set-up at a Porsche race prep shop.

If the air temp is swinging 30 degrees from morning sessions to late afternoon, and you've run a mid day track sesssion, your tires are still warm when you head out for your afternoon race. I was quessing where to set pressures. How can you calculate where to set them to end up at exactly 30?

 

Do double check the corner weights, I have seen shops screw things up too often.

There IS a way to calculate pressure rise due to different ambient temperatures. But I forgot where I read it.... make sure you check your pressures at the end of each session and bleed them down to 30 in the pits if needed. Then you have a good base setting. If you came in at 60 degrees and the hot temps were ok, and now in the next session it's 70 degrees, you probably don't have to let much air out of your tires but I usually let a few pounds out when it gets much warmer from one session to the next (or for example the sun comes out while it was cloudy before, higher track temps). Don't worry about the starting pressures after the initial session as the tires are still a little warm, just let a pound or two out if it's much warmer than the previous session. Also see if you can get a helper in the pits to check your pressures after 5-10 minutes if the session is long enough, he may need to bleed a pound or two off if it's hotter or you are pushing harder. I always seem to bleed off air, never seem to need to add any during the day.

Good luck!

 

Mark,
I could tell you but I'd have to kill you

Seriously, you will get stagger on the individual tire pressures depending on the track & conditions. Best way to get a quick handle on it is put somebody @ the wall to get pressures & temps. Come in mid-session during practices & qualifying to get them checked/adjusted. We take pressures & temps every session. Mid to late session on practices & qualifying. Also, after each race to see how close we were. Cool down laps & waiting until you are back at the garage will skew your numbers. Becomes more of a guessing game at that point.

If you can get some good temp data, you can usually identify early in the weekend if set-up changes will be needed based on tire temps being out of whack.

Good luck & congrats on your results

 

To go really fast at Portland, you need lots of down force and different camber setting on the left and right sides of the car. The right set up will make a big difference in times. Tire temps and pressures will help you know what changes to make in camber.

 

Mark in addition to all that's been said above, two other thoughts come to mind. You didn't mention where your sway bars were set and they have a huge impact on your car's performance. And probably the biggest contributing factor IMHO is your slicks had 6 heat cycles on them (so the race was the 7th?). Michelin Cup's grip drops off dramatically after 3-4 cycles, though they're still good for practice for another 6 or so. I'll bet you a white Ford dually those faster competitors were on fresher slicks....So where were your bars set?

 

Thanks all for the feedback.

The race was the 6th heat cycle and the bars are both set one off of stiff.