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Fighting high speed understeer in carousel-like turns

Hi all,

Hoping you can help with some setup questions. I put on Goodyear 3Rs for the first time this weekend and I was getting some intense understeer in highspeed corners (as seen down below). While I could absolutely lift a bit to get the bite back, I was really struggling to get the rear to start to come around. No matter what I tried (within limits), the car would understeer. Tried a few different pressures 32 hot, 33-34 hot, and 35-36 hot. Tried lifting and induce a bit of oversteer with throttle/steering input. Nada. According to my pyrometer, temps across the tires were within a 15 degree window.

I pulled a degree out of the wing and that helped a bit, but not a whole lot. Still terminal. My understanding is this probably a roll bar adjustment given my lack of adjustable coilovers? Getting a good bit of body roll (from the entire car). What would you recommend, tightening up the rear bar? Would love if I could reduce the understeer without making the car twitchy in the rear

Thanks for reading!

 
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Boone

Professional Thread Killer
If your car is set up as in your profile pic, I see a GT350 with a rear wing and no other aero mods. If so, at high speed you have a couple of hundred pounds pushing down about 3 feet behind the rear wheel. This has to lighten the front end, and the faster the turn, the more the effect. AJ is moving into the GT350 arena, so buy whatever he tells you to for the front end, or keep taking wing angle out until you get back to the original balance. Check your lap times, and decide what you can live with.
 
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This is where a really good set of shocks could help, in the meantime, you could soften the front bar, but that's a crutch. Since you don't have a front splitter to match the wing, and it is definitely a faster corner, that (as mentioned above) that aero might be a great place to start. FWIW this is why I always recommend that guys go with aero "packages" like the IMSA or PWC approved kits that have seen a wind tunnel. Only 1 or 2 guys on here have the experience and ability, including wind tunnel access, to really establish what is going on. So... if that is a GT4 style wing, I'd look for a Gt4 style front splitter scheme before I did anything else.
 
It’s got a pretty big splitter up front and tons of ducting. It feels fairly balanced from an aero perspective, but it’s definitely overloading the springs/stuck struts. id

Here’s a close up

9363B4FB-DA87-4088-8791-BC5D60F1D505.jpeg


C0F8F2C7-9B17-4FBE-AC9E-4DA6A13D58C1.jpeg
 
Ok, I’ll bite. How did car handle on the rest of the corners? I assume this was COTA? I’d hate to mess too much with it if it handles good everywhere else but that one corner
It understeers in every high speed corner when you start to apply throttle. Puts power down fine at lower speed corners.

The biggest issue I have is I can’t get it to start to rotate in the higher speed stuff. Really hard to get any slip angle out of the rear tires.

on my old clapped out cup2s/pirellis in July/May, I could four wheel drift it. I’m actually a bit slower through the carousel on these fresh sticky tires
 
not sure I know the answer to this question but just wanted to say that I'm amazed you're still on FP springs with the aero and sticky tires you are running. I can only imagine a bunch more spring and some adjustable dampers are overdue by now.
 
not sure I know the answer to this question but just wanted to say that I'm amazed you're still on FP springs with the aero and sticky tires you are running. I can only imagine a bunch more spring and some adjustable dampers are overdue by now.

You and me both. The plan was for proper coil overs this winter, but the motor refresh wiped me out. I keep doing everything backwards as I break parts. If only I had broken the stock suspension first :)

A set of Cortext/MCS coilovers are definitely on the list for this offseason if my wife doesn't end me.
 
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You and me both. The plan was for proper coil overs this winter, but the motor refresh wiped me out. I keep doing everything backwards as I break parts. If only I had broken the stock suspension first :)

A set of Cortext/MCS coilovers are definitely on the list for this offseason if my wife doesn't end me.
either let her ride with you on a track day, or drive the car, that will usually solve the problem
 
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NC
This may be a two pronged attack. Is there a way to “flatten” the rear wing? IE make it less effective. Another thing may be to raise the rear tire pressures a couple of psi above the fronts(BS1 is probably giving me the evil eye). I know that tends to lessen grip, but if you have too much to start with, it might not hurt your lap times. Just a thought
 

Boone

Professional Thread Killer
So much for my Captain Obvious approach. Looks like you've addressed the aero already, but you could dial a little more out of the wing to see what happens. I don't think you'll get there with aero alone, though. You're into more of a mechanical grip situation now. I feel that knowing how your car responds to throttle inputs in a steady state corner is a great start to making the correct adjustments. You have the ear of people who know more than I do about suspension set up on an S550, so I'll sit back and learn with you.
 
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46038
I would take wing angle out first. Take a scientific approach: log high-speed corner speeds, etc.
In theory, your aero won't affect the slow/mid speed corners much. But >80-100mph aero has more of an effect. If you can feel the balance (bc of understeer) in a long high-speed turn, then trust your driving skills and dial out a little more wing.

I'm sure you're aware of the risk - oversteer in high-speed turns is much less forgiving and with shorter reaction time needed than is understeer.
 
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HB,

CoTA is not my home track. I'm from SoCal and have only raced CoTA 4 weekends so maybe I'm off base. But I take a different line through there. I enter more left almost on the stripes to open up the entry then head deeper right more double apex almost on the right apex strips twice. So I'm less steady state and more actively driving the complex. Maybe I'm making no sense at all.

I tend to drive a lot of tracks. Sometimes there is something about a turn that makes you think you got a set-up problem but really the car is fine and you don't have massive midcorner understeer or whatever defect. But sometimes you need to tune for that weird corner if the setup for that corner does not compromise other corners and of course if the corner you try and fix is important. Lazy people like me, even at competitive events, will just set it and forget it and just drive. But the guys consistently on the podium are willing to setup the car for every track and have identified the important corners for lowest laptime.
 
if the wing has a whickerbill, remove it, and see what happens
Wickerbill isn't removable on this wing, but I can dial a bit more out.

I would take wing angle out first. Take a scientific approach: log high-speed corner speeds, etc.
In theory, your aero won't affect the slow/mid speed corners much. But >80-100mph aero has more of an effect. If you can feel the balance (bc of understeer) in a long high-speed turn, then trust your driving skills and dial out a little more wing.

I'm sure you're aware of the risk - oversteer in high-speed turns is much less forgiving and with shorter reaction time needed than is understeer.
True that. COTA has one fairly highspeed turn (T6) that is exceptional dangerous if you lose it (scratch that, T19 is also brutal ha) but the carousel isn't too bad. I'll give it a shot.

HB,

CoTA is not my home track. I'm from SoCal and have only raced CoTA 4 weekends so maybe I'm off base. But I take a different line through there. I enter more left almost on the stripes to open up the entry then head deeper right more double apex almost on the right apex strips twice. So I'm less steady state and more actively driving the complex. Maybe I'm making no sense at all.

I tend to drive a lot of tracks. Sometimes there is something about a turn that makes you think you got a set-up problem but really the car is fine and you don't have massive midcorner understeer or whatever defect. But sometimes you need to tune for that weird corner if the setup for that corner does not compromise other corners and of course if the corner you try and fix is important. Lazy people like me, even at competitive events, will just set it and forget it and just drive. But the guys consistently on the podium are willing to setup the car for every track and have identified the important corners for lowest laptime.

I think I'm following. I have quite a few laps at COTA and I've tried the carousel everyway possible. Assuming I have the right line in my head, the line you're referring to asks more out of the car in the exit than the line in the video. The line in video allows you to attack the entry, turn in a little harder to get the rear to start to come around, and then start to get the power on hard for some slip angle in the rear. The fastest line I've ever had has the steering wheel straight before the last apex and no adjustments needed as you prep for T19.

On track out, it looks like this. Car is point towards the outside
218_1569.jpg

It's actually the same line Billy J takes in this video - though he attacks it a lot harder ha

At leas that's been my experience, with my particular driving skill, and my particular car :)
 
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