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Tracking / Autocross / HPDE / Drifting What these cars were built for!


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Old 09-24-2018, 06:06 PM   #4733
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Originally Posted by strat61caster View Post
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.
Normally, I'd agree but his temps show the outside being very cold (or at least cold, depending on ambient). It looks like he's running too much. Am I reading that right? Inside temps are hot and outside are cold?
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Old 09-24-2018, 06:23 PM   #4734
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Normally, I'd agree but his temps show the outside being very cold (or at least cold, depending on ambient). It looks like he's running too much. Am I reading that right? Inside temps are hot and outside are cold?
I can't tell much from the tire temps he posted, for a few reasons. When were the temps taken? Straight off a hot lap or after a cooldown? Directly after getting to pits or was there time in between? How were the temps checked - with a probe or surface IR sensor?

Based on what is here, I can make general assumptions. Seems to me like this is a CW, primarily right hand turn course, so the LF is taking a lot of the load and the inside tires are cooling down. Either that or the final corner before coming off the track is a right hander.

Session 1 has no reasonable data to pull from since it's apparent the car wasn't driven as hard as the later sessions. Later sessions were better. Yes, there is a general trend that the outer edges are not as hot as the rest. Answer the above then we can come to a conclusion about camber, pressures, etc.

I would expect even more heat from the tires with a 250whp 86 on 245s. I would expect maybe 160-180 or so. I believe the RS4 optimal range is around 170? I know the Rival S 1.5 is 160.

Last edited by tony_r; 09-24-2018 at 06:35 PM. Reason: changed CCW to CW :D
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Old 09-24-2018, 06:40 PM   #4735
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Tony beat me to it.

I don't really trust tire temps any more, I think you have to adjust to the outer limit, actually find what 'too much' is and then dial back otherwise you're just hoping you're in the ballpark. I've done it a few times now "pyro says we're good, no more camber" *try more camber* "oh shit look at all this grip!"

Tires do not respond linearly, that's true on many many levels.

His tire temps are inconsistent, 20 degrees hotter on one edge on one session, then 15 degrees colder on a different session, I'm not sure what's what.

I think tire pressure is another indicator that the front tire is not being used effectively, and again here's another spot where a probe pyrometer has misled me, I've swung +/-5 psi into the same set of tires, while 37 psi looked great on the probe, 32 psi was faster and felt better on that cold day, I've gone down to 27 psi on that same tire and it performed way better than 37.

Tellingly I don't think I know anybody who has the freedom to set the suspension and alignment as they please on an 86 and runs more than 2 psi different between front and rear tires.
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Old 09-24-2018, 08:25 PM   #4736
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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.
Your car has a pretty good amount of static push built into the setup. You also don't trail brake into corners, and tend to either be fully off throttle, or a minimal amount of maintenance throttle through the corners.

You can alter your driving style to match the car better, or change the setup to rotate more.

The only instance of rotation I saw was power-oversteer, which indicates to me a setup problem first, followed by a relative hesitance to get on throttle.
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Old 09-24-2018, 10:32 PM   #4737
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Originally Posted by GrandSport View Post
where are you feeling understeer? Can you give us a time?
0:37;
1:14;
1:18;
1:53;
1:55


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Originally Posted by GrandSport View Post
ya, I saw a hint of oversteer if anything coming out of some turns.
When I'm into the throttle a bit early or a bit aggressively, yes.


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Normally, I'd agree but his temps show the outside being very cold (or at least cold, depending on ambient). It looks like he's running too much. Am I reading that right? Inside temps are hot and outside are cold?
Yes, you are reading that correct. My inside edges are always equal to or (in almost all cases) greater then the outside temps.


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Originally Posted by tony_r View Post
I can't tell much from the tire temps he posted, for a few reasons. When were the temps taken? Straight off a hot lap or after a cooldown? Directly after getting to pits or was there time in between? How were the temps checked - with a probe or surface IR sensor?
Sorry, I should have given more complete background:

-> Temps taken right after leaving the track. Maybe 400 meter (1300 feet) cool down?;

-> Readings taken using a Joe's Racing tire pyrometer w/probe;

-> Temps always taken in the order: LF, RF, RR, LR THEN pressures measured in the same order.


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Originally Posted by tony_r View Post
I would expect even more heat from the tires with a 250whp 86 on 245s. I would expect maybe 160-180 or so. I believe the RS4 optimal range is around 170? I know the Rival S 1.5 is 160.
According to the Dynapack it makes 250 WHP @ 6750 RPM, although I was shifting at 6500 all day.

I'm running 255/40R17's (not 245's) on 17lb 17x9 rims.


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Originally Posted by tony_r View Post
Based on what is here, I can make general assumptions. Seems to me like this is a CW, primarily right hand turn course, so the LF is taking a lot of the load and the inside tires are cooling down. Either that or the final corner before coming off the track is a right hander.

Correct - we were running clockwise. 2nd last corner is the long right-hander at end of the straightaway, then the dog-leg left then we pit.

The start/finish line is between the dogleg and pit entrance - I normally push right until I cross the finish line, then brake hard and dive into the pits. We were running the "Technical" layout in the top left. Map isn't entirely accurate. It looks like 1 long sweeping turn to go onto the back straight - in reality it is 2 corners and the pavement between them is a bit rough.
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Last edited by Turbo; 09-24-2018 at 11:37 PM.
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Old 09-24-2018, 11:16 PM   #4738
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First- thank you ALL so much for your help and input. I really do appreciate it.


Other than the small pressure adjustment after session 3, I was running the EXACT same cold pressures I did the last 3 times I was at this track. On those days, I was seeing 34-35 psi hot all around - but running in the 1:19's/1:20's. Never saw anything near 39 psi before. But I also haven't been this fast before. I will say I was cautious getting up to speed as I was driving the car after the pedal dance on ALL runs, so no driver aids at all.

Given this car doesn't really get driven on the street, I had just left the pressures where they are when I leave the track. I figured this would (likely) give me the same hot temps next outing.


This was the first time I've ever taken tire temps as I just got the meter. I adjusted the probe depth properly too.


One thing that really struck me was how high my (hot) front pressures were. I had read on this forum that the RS3/4 like to run ~34psi hot and I was pushing 40psi! I didn't drop my pressures because the tire temps I was seeing were fairly even across the left front.


Should I try running lower hot pressures on the front? If that gives the front end more bite going into corners, it may fix what I am thinking is 'entry understeer'.

And is there a target tire temp to aim for with RS4's?


I could also take some roll-bar out of the rear (It has 4 settings and I'm on the second softest). Doing so would probably increase the outside rear temps as the rear end rolls more. But it would also likely move the car towards understeer as it rolls more and picks up grip.

Last edited by Turbo; 09-24-2018 at 11:53 PM.
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Old 09-24-2018, 11:54 PM   #4739
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I KNOW you are only supposed to adjust one thing at a time, to properly quantify the changes.

But after carefully reading all of your replies, and thinking the feedback I want to take a stab at the big picture answer-


Leave camber where it is for now;
Lower my (hot) pressures in the front to match the rear approx 34-35 psi all around;
Move the rear bar to the softest setting;
Trail brake into corners to help rotate the car which will now have more rear end grip;
Get on the power earlier -while in the corner or earlier at exit- applying lock as needed as I wind out of the corner.


A lot easier to write about then actually do -but still have to ask- Am I getting close?
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Old 09-25-2018, 01:40 AM   #4740
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Quote:
Originally Posted by Turbo View Post
I KNOW you are only supposed to adjust one thing at a time, to properly quantify the changes.

But after carefully reading all of your replies, and thinking the feedback I want to take a stab at the big picture answer-


Leave camber where it is for now;
Lower my (hot) pressures in the front to match the rear approx 34-35 psi all around;
Move the rear bar to the softest setting;
Trail brake into corners to help rotate the car which will now have more rear end grip;
Get on the power earlier -while in the corner or earlier at exit- applying lock as needed as I wind out of the corner.


A lot easier to write about then actually do -but still have to ask- Am I getting close?

If anything I think you were getting on the gas early, not late, because you weren't trail braking. Remember, when you get on the gas, you're going to push the car wider. This is especially true with closed rear diff. How much will vary from car to car, but on throttle will push the car wide (understeer). Unless you light up the rear tires or something, you're not bringing the ass end around with gas. You're doing it with brakes.

I really don't see much understeer where you're saying you have it, but it's hard to tell from video if it's subtle. It looks well sorted if anything.

Last edited by GrandSport; 09-25-2018 at 01:58 AM.
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Old 09-25-2018, 02:22 AM   #4741
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What gas cans do you all recommend to carry e85 to the track?

Any work better then the rest? Or just get whats cheap-ish?
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Old 09-25-2018, 07:13 AM   #4742
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I have 3 VP cans i got from Amazon. Remember you need at least 1 nozzle.
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What gas cans do you all recommend to carry e85 to the track?

Any work better then the rest? Or just get whats cheap-ish?
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Old 09-25-2018, 01:07 PM   #4743
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Originally Posted by Turbo View Post
I KNOW you are only supposed to adjust one thing at a time, to properly quantify the changes.

But after carefully reading all of your replies, and thinking the feedback I want to take a stab at the big picture answer-


Leave camber where it is for now;
Lower my (hot) pressures in the front to match the rear approx 34-35 psi all around;
Move the rear bar to the softest setting;
Trail brake into corners to help rotate the car which will now have more rear end grip;
Get on the power earlier -while in the corner or earlier at exit- applying lock as needed as I wind out of the corner.


A lot easier to write about then actually do -but still have to ask- Am I getting close?
Be careful with trail braking. Done properly it can help with entry rotation. Done incorrectly it will understeer. This car is not mid-engine, so the rear wont rotate that much on entry without a bit of rear rebound. Remember that the front tires have only so much available grip for braking and turning.

On tire temp reading, think of the tire mold and how it deals with heat. The inner and outer blocks of the RS4 are large and retain more heat, the middle block is small and dissipates heat faster. I'm willing to bet that the middle block was actually hotter than what was measured on the track so lowering front and maybe rear pressures does make sense.

As far as operating range for the RS4, I remember something like 160-180(?) but I don't totally remember. Would have to talk to a Hankook tire engineer since they don't publish.

I would mess with the pressures before anything, I think.
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Old 09-25-2018, 03:03 PM   #4744
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What gas cans do you all recommend to carry e85 to the track?

Any work better then the rest? Or just get whats cheap-ish?
Second on the VP cans. Doesn't matter what color, really, even though some say not to use for fuel. I ordered a 4-pack of the yellow ones off amazon.
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Old 09-27-2018, 05:05 PM   #4745
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Second on the VP cans. Doesn't matter what color, really, even though some say not to use for fuel. I ordered a 4-pack of the yellow ones off amazon.
Are you finding e85 up here?
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Old 09-27-2018, 05:25 PM   #4746
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Are you finding e85 up here?
Nope, I gave up on E85 up here. Unplugged my flex sensor and everything. Back in TX I had a trailer so I could bring along 6 jugs, but the trailer stayed home when I moved up here.
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