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Old 09-19-2018, 01:19 PM   #4719
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Originally Posted by TrqlessWonder View Post
You are also describing sort of the situation that makes me choose to do the pedal dance instead of just the 5-second method. Inside rear up>diff says wtf>brakes unloaded wheel>moves all that to the outside>outside wheel spins and slides >bind up relieved>inside rear back down and snatches hard. either a spine-wrenching wiggle, or a snap spin.
Embarrassingly I feel as tho this entire situation could have been due to no preparation. I never filled the tires up from what I was running on the track. Meaning they were all way to low for an autocross event. Which could lead to what you are describing above. I also didn't do the pedal dance like I usually do at autocross bc my OFT had some sort of error. So yep. I am an idiot.
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Old 09-19-2018, 04:51 PM   #4720
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I suppose it could be that stuff, too. just out of curiosity, where would track day pressure have put the tires cold/hot?
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Old 09-20-2018, 06:19 PM   #4721
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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.

Last edited by Turbo; 09-20-2018 at 06:30 PM.
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Old 09-20-2018, 07:40 PM   #4722
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I assume all your temps are 'outside middle inside'?

Add half a degree more camber in the front.
I'd assume left to right balance discrepancy is because of your rear camber difference, RR has more cornering grip than LR, left hand turns have more rear grip than right hand turns.
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Old 09-24-2018, 01:34 PM   #4723
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I'll let others more wise than I answer the setup questions.

For corner entry understeer, especially in slower 2nd gear corners, I've have great luck addressing it with trail-braking per Randy Pobst and Scott Mansell:
https://www.scca.com/articles/200106...t-on-understee
and
https://driver61.com/uni/trail-braking/


Quote:
Originally Posted by Turbo View Post
Could I ask for help reading my tire temps/pressure data?

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?

I have video o Run #5 if that's of value.
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Old 09-24-2018, 03:25 PM   #4724
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@Turbo is your entry understeer a result of input or car setup?
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Old 09-24-2018, 04:00 PM   #4725
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Quote:
Originally Posted by Turbo View Post
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.
Tire pressure: Donít 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 isnít rolling over to the outside enough. That would also explain why youíre having understeer- you donít 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 itís 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 youíre on the brakes turning, it will almost feel like the back is swinging around. If youíre getting on the gas too early, it will push you wide, especially with a LSD. Iím 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 donít 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 itís about right. On slicks, about 2.2 is right. Again, Iím 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.
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Old 09-24-2018, 04:06 PM   #4726
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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.
Vehicles already have this from the get go. It's called ackerman. It's the difference in steering angle between the leading/tailing wheel. The 86/BRZ has a good amount of ackerman from the start. Adding toe out is just going to increase that ackerman even more.

I know because those of us that have drifted them have added angle mods, which increase steering angle and decrease ackerman to obtain a more parallel steering effect.
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Old 09-24-2018, 04:27 PM   #4727
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Vehicles already have this from the get go. It's called ackerman. It's the difference in steering angle between the leading/tailing wheel. The 86/BRZ has a good amount of ackerman from the start. Adding toe out is just going to increase that ackerman even more.

I know because those of us that have drifted them have added angle mods, which increase steering angle and decrease ackerman to obtain a more parallel steering effect.
Fair enough; I'm very surprised you don't need some toe though.
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Old 09-24-2018, 05:30 PM   #4728
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@Turbo is your entry understeer a result of input or car setup?
I'm fairly new to this, so I would say I really don't know. But after saying that, the gears in my head are turning.


Would video help assess this? This video is of my 2 fastest laps (1:15.82 & 1:15.9) from that day, both occurring during run #5. I would also welcome constructive criticism and tips to pick up time:





The RaceChrono laps times during that day said I was very consistent in each session, which is a plus. Watching my driving, though, I do believe I need to get smoother, and be more aggressive on the brakes.

Top speed on the back straight was 172km/hr or about 108MPH.


For reference, a former National Formula Ford champion laps this same configuration in a Hayabusa-powered Radical SR3 in 1min 3 seconds.

Last edited by Turbo; 09-24-2018 at 06:03 PM.
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Old 09-24-2018, 05:36 PM   #4729
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where are you feeling understeer? Can you give us a time?
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Old 09-24-2018, 05:43 PM   #4730
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I donít 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 itís about right. On slicks, about 2.2 is right. Again, Iím 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.
It isn't enough camber, your Corvette double wishbone suspension needs much less static camber than the MacPherson Strut suspension on the 86. I've run -4 and seen/heard others with more for street tires.
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Old 09-24-2018, 05:47 PM   #4731
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Quote:
Originally Posted by Turbo View Post
I'm fairly new to this, so I would say I really don't know. But after saying that, the gears in my head are turning.


Would video help assess this? This video is of my 2 fastest laps from that day, both occurring during run #5. I would also welcome constructive criticism and tips to pick up time:



Grand Bend Technical Layout - YouTube


The RaceChrono laps times during that day said I was very consistent in each session, which is a plus. Watching my driving, though, I do believe I need to get smoother. Top speed on the back straightaway was 172km/hr or about 108MPH.
I didn't see any terminal understeer, looked like you hit the tire limits on a couple of the sweepers but nothing that makes it seem like you need to start changing your setup.

Terminal understeer has a specific sound and feel associated with it and it's easy to hit, simply enter a corner too fast and turn the wheel too much. This formula will make any car, regardless of setup, to understeer.

Here's a good example of terminal understeer, I got a point by in a corner from a car that I expected to either clear the corner before I got to it, or not give the point by. I adjusted my line by cutting inside of the car while maintaining my entry speed (which was too fast for the new line):

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Old 09-24-2018, 06:00 PM   #4732
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I didn't see any terminal understeer, looked like you hit the tire limits on a couple of the sweepers but nothing that makes it seem like you need to start changing your setup.

Terminal understeer has a specific sound and feel associated with it and it's easy to hit, simply enter a corner too fast and turn the wheel too much. This formula will make any car, regardless of setup, to understeer.

Here's a good example of terminal understeer, I got a point by in a corner from a car that I expected to either clear the corner before I got to it, or not give the point by. I adjusted my line by cutting inside of the car while maintaining my entry speed (which was too fast for the new line):

https://www.youtube.com/watch?v=8oznTngj124&t=411s
ya, I saw a hint of oversteer if anything coming out of some turns.
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