Quote:
Originally Posted by Turbo
Could I ask for help reading my tire temps/pressure data?
I'm relatively new to tracking, but I've driven this particular track 4 times now, logging over 400 miles on it at speed.
I would characterize my car as having corner entry understeer, although now that I think about it, I remember it being more pronounced in left turns. If you watch video of me on track, it does appear that my steering input is leading turn-in by a good bit. At least to me. Mid-corner I would say understeer-to-neutral, and pretty neutral at exit (unless I get on it hard).
Questions:
1) are my hot pressures to high in the later runs? How about my tire temps? I'm running and was told they like to be at 35psi hot and I'm way passed that up front - but the inside-to-outside temp measurements seem to say they're not overfilled?
2) any tips to reduce the corner entry understeer? I think because of this feeling there are a few corners I turn into too slow (as the car doesn't feel like it's reacting). I think I start on a tighter line than I could otherwise take if it would turn-in faster.
3) I wouldn't mind a bit MORE looseness in the back. There is a rather tight S bend on the front straightaway and I could definitely take a better line there if the rear end came around a bit more. Anything I can do to make that happen?
4) the rear temps seem to say I'm running too much camber, but I'm not running that much. Thoughts?
Car details & setup:
- 2013 FR-S. 250.8 RWHP boosted;
- HKS Hipermax SP coilovers ~26mm drop;
- Camber -3.0 LF & RF with 0 toe; -1.6 LR & -2.6 RR with 1/32 total toe-in;
- 255/40R17 RS4 tires on 720 Form 9" wheels;
Data notes:
- temps listed in order of measurement. All presented as outside/middle/inside;
- "shock" is Ft/Rr HKS 'click' setting with 30 being full hard;
- any changes to tire pressures listed after temp data with a ---> in front;
- data from my first 5 sessions of the day. Approx 72 deg F that day;
- obviously session one is just tires coming up to temp;
- track data from racechrono;
- A former national FF champion runs 1 min 3 seconds in his Radical SR3 w/Hayabusa. My best is 1:15.82
Run 1/
1:18 fastest lap
shock: 23/18
LF 125/123/129 34.1 psi
RF 123/117/110 34.3 psi
RR 115/126/134 33.1 psi
LR 110/123/127 32.3 psi
15 min brk
Run 2/
1:17.29 fastest / 1:16.43 optimal
shock: 23/18
LF 139/141/143 37.1 psi
RF 121/126/135 36.7 psi
RR 124/135/144 33.6 psi
LR 129/140/144 33.9 psi
15 min brk
Run 3/
1:17.09 fastest / 1:15.70 optimal
shock: 25/20
LF 147/153/152 38.3 psi
RF 140/132/124 37.5 psi
RR 127/143/147 35.4 psi
LR 136/143/145 34.6 psi
--> increased RF tire pressure by 0.8 hot psi
--> decreased RR tire pressure 0.7 hot psi
15 min brk
Run 4/
1:16.07 fastest / 1:14.98 optimal
shock: 25/20
LF 156/159/155 39.5 psi
RF 129/134/151 39.2 psi
RR 128/145/153 34.9 psi
LR 137/148/151 34.8 psi
15 min brk
Run 5/
1:15.82 fastest / 1:14.30 optimal
shock: 25/21
LF 154/156/160 39.6 psi
RF 130/140/151 39.2 psi
RR 124/139/142 34.7 psi
LR 132/139/140 34.7 psi
I have video o Run #5 if that's of value.
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Tire pressure: Don’t overthink it: You ideally want your tire pressure to be constant all the way across. If the middle is too hot, then take air out. If the outers are (equally) hot, take a little air out. If the outside is hot, more (negative) camber. If the inside is hot, less negative camber.
Your temps seem to vary a lot, but on the last three sessions, your insides are way hotter than outsides (except LF). That means you need less (negative) camber because the tire isn’t rolling over to the outside enough. That would also explain why you’re having understeer- you don’t have a flat tire turning in.
Also, your lack of toe out is likely causing understeer. You need some toe out or the two front tires will have the same radii, and obviously, the inner one needs a shorter one. You can also try softening the front if anything is adjustable. If it’s too stiff, you may not be getting weight on the front on the brakes.
Keep in mind, the car will turn on harder on the brakes and push wide on the gas. When you’re on the brakes turning, it will almost feel like the back is swinging around. If you’re getting on the gas too early, it will push you wide, especially with a LSD. I’m really shocked these cars have LSD. You may just be getting greedy with gas. With LSD, I find myself turning in a little sharper and going wider on exit. LSD just wants to straighten the car out and force the front wheels straight. It's a strange feeling when you go back and forth from open and closed diffs.
I don’t have an 86 yet, but -2.6 is a lot of camber for street tires. Race cars on slicks run about that. I run -1.5 on my C7 with 315s up front and semi-slicks and it’s about right. On slicks, about 2.2 is right. Again, I’m not familiar with the platform, but -2.6 sounds like a lot for a soft street tire and a light car with stiff suspension, and your tire temps seem to reflect it.