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Fighting understeer in high speed corners

Egparson202

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A couple questions:
  1. How were the lap times relative to your prior tires? May be faster but less fun
  2. What about entry speeds into the problem corner? May be making more rear downforce.
  3. Have you checked your alignment to see if something changed? That would be a convenient explanation and it does happen.
  4. Are you confident in the ideal hot pressure for the tire? I know you tried different targets. Could it be that the happy place for that tire is higher or lower than you thought?
  5. Did you try more negative camber up front? Pyrometer readings can be tricky. Temps begin to equalize very quickly across the face of the tire. We the outer temps still hotter than the inner temps?
  6. Did the tread width change relative to the prior tires? Is it wider or narrower than the wheel width? If theyā€™re wider it could be contributing to a sub optimal contact patch.
  7. Did the ride height change front to rear due to tire diameter changes? Maybe youā€™ve lost some front downforce?

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honeybadger

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Sounds like you need some shitty cups on the back and 3Rs on the front to complete the setup. BOOM, problem solved!!! Youā€™re welcome!
This is the kind of innovative thinking we need around here

Thatā€˜s why I suggested increasing front roll stiffness. The intuitive solution to correct understeer on ā€œstreet suspensionā€ with sticky tires is to decrease front roll stiffness and/or decrease tire pressure. This usually doesnā€™t help and most the time makes it understeer more.
We discussed it before, your car is under sprung for weight, amount of aero and size of tires (just look at photos šŸ˜€). Now add NEW, stickier tires and yes, the car setup limitations become more apparent. You and your car are super fast but have long ago reached the limit of the street suspension.
Iā€™ve tried so many spring rates, sway bars, alignment settings on my previous ST/TT3 car and current TT/ST4 car. Different spring rates and setups are needed to optimize grip for all tires (Hoosier R7, A7, Pirelli, Michelin and fast street tires). To optimize your setup and have the ability to adjust for different grip level tires (especially new slicks), itā€™s time for coil-overs šŸ˜Ž.
Ahh, shit. My wifeā€™s going to murder me this off-season.

By the way, hereā€™s the outside front (driver front). Roll over looks okay to me...but maybe you see something

B80803C3-F427-4531-9E3F-8926B47A6635.jpeg




I wasn't thinking user error, just adjust the technique a bit to keep the tires cooler. It sounds like the front tires are losing grip in that particular set of corners, and that could be a heat problem that's unique to that tire on your car. I have had my front GY3R's go away in a corner in the middle of a session (four weeks ago). I got them back by switching the suspension magride setting to "Sport" (with the chassis still in "Track") but the next session out they were dead - 19 heat cycles and they were pretty much grip-free.

So, I do have a dumb question - when was the last time you were out on new tires? It sounds like it's been a while... And how were the lap times - faster on the GY's or slower?
True. Itā€™s been since Oct 2019 since Iā€™ve had freshies. The 3Rs matched the sticker Cup2, but the track was substantially more slippery this time out. And the understeer thing is new.

Dampers are the best, and most expensive of all the options to give you the changes you want. You most likely need more low speed damping in the front. Otherwise you have too much front spring relative to the rear. You would want stiffer springs all around if you are still getting un wanted body roll. Too much ARB and you will start causing some cross weight loading issues.

Things you can do;

-Take toe out of the front
-Add more toe out in the rear

-Add rear spring rate + add front ARB to trim the mid corner US/OS balance
-Lessen front spring rate + reduce rear ARB to trim mid corner US/OS balance


Also check your DMs.



*edit* we really should diagnose what phase of the corner you are experiencing or anticipating the understeer.

The turn in your video is notorious for people to wait...wait...wait.. steady maintenance throttle because of the understeer. Part of that is the line you take into it, and the other part is definitely setup.

To further clarify, in the turn in your video that is nearly all spring / ARB balance since the shocks velocities are low (low speed damping). With more low speed damping you can load the front tires and get the initial turn in response and then transitional US/OS balance when you are carrying speed through the mid corner and then power on corner exit.
The carousel can be stupid fast if your sliding the rear a bit the entire way through. Takes a ton of the stress off the front. I have video of me going through it faster on the clapped out cup2s than the brand new 3Rs and itā€™s not the tires (3Rs are a good bit faster). I just couldnā€™t get the car setup to take the corner like that.

All the above, plus easiest is to flatten the rear wing, if itā€™s totally flat.

Then to adjustable shocks, then to springs.

Unless your springs are way too stiff then start there.

I like the coil over suggestion.

Youā€™re going to get 50 different options out of 49 people.
I can try taking some wing out, hopefully that doesnā€™t bite me in the esses and t6.
 
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honeybadger

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A couple questions:
  1. How were the lap times relative to your prior tires? May be faster but less fun
  2. What about entry speeds into the problem corner? May be making more rear downforce.
  3. Have you checked your alignment to see if something changed? That would be a convenient explanation and it does happen.
  4. Are you confident in the ideal hot pressure for the tire? I know you tried different targets. Could it be that the happy place for that tire is higher or lower than you thought?
  5. Did you try more negative camber up front? Pyrometer readings can be tricky. Temps begin to equalize very quickly across the face of the tire. We the outer temps still hotter than the inner temps?
  6. Did the tread width change relative to the prior tires? Is it wider or narrower than the wheel width? If theyā€™re wider it could be contributing to a sub optimal contact patch.
  7. Did the ride height change front to rear due to tire diameter changes? Maybe youā€™ve lost some front downforce?
1. Prior tires were "old scrubs" that were closer to all weather tires than track tires. They were 2;29 on a good day. On sticker cup2s, I was seeing around 2:26-2:27, but it was a lot cooler.

2. Entry speed appears to be the same. Different way in, but the entry is the same. For the old tires, I had to slow down for the first apex. However, speeds are back to even-ish for mid/exit - notice on the second video the car rotates much better. Looking even more ahead, look at how bad the car understeers into t19 - I'm slower there than on the old tires!

3. I'll check at home, but it was the same before I left. -3.1 front, -2.2 rear, 1/16th toe in front and rear.

4. It's possible, but it does against what all the other drivers I know are running. Could be something to play with

5. Insides were actually the hotter ones, but hard to say for sure - good bit of braking right before pit in

6. The 3Rs are a good bit wider. I'd say half inch

7. Both are 30s, if anything the Cup2s might be a smidge taller

2:26 lap


Old tires, new motor lap
 

ShatterPoints

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This is the kind of innovative thinking we need around here



Ahh, shit. My wifeā€™s going to murder me this off-season.

By the way, hereā€™s the outside front (driver front). Roll over looks okay to me...but maybe you see something

B80803C3-F427-4531-9E3F-8926B47A6635.jpeg






True. Itā€™s been since Oct 2019 since Iā€™ve had freshies. The 3Rs matched the sticker Cup2, but the track was substantially more slippery this time out. And the understeer thing is new.



The carousel can be stupid fast if your sliding the rear a bit the entire way through. Takes a ton of the stress off the front. I have video of me going through it faster on the clapped out cup2s than the brand new 3Rs and itā€™s not the tires (3Rs are a good bit faster). I just couldnā€™t get the car setup to take the corner like that.



I can try taking some wing out, hopefully that doesnā€™t bite me in the esses and t6.

Can you add to the front splitter? If you had adjustable ride height for the front, you could raise the front ride height a few mm's to move your aero balance forward. Might be worth considering checking ride height with a full tank of gas. Now that I've thought that out, it could be that with a full tank of gas you would find the US/OS is more balanced. As you run through the tank it will start to to dip back toward understeer. A cheap test would be to do a session on a full tank, and then the next session with 1/2 tank and compare. That would also tell you if rear wing changes will do anything including changing your line through the essess.

*edited, I did a backwards*
 
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honeybadger

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I have to start every single session with a full tank otherwise I start to fuel starve after 20 mins. But tell me a little bit more.

Youā€™re think the front is too low?
 

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Side note: I guess I got at least one lap right. Notice the front steering angle and where the car is pointing even tho Iā€™m just exiting t18.

Now I just need to figure out what lap this was šŸ˜ƒ

0416DB61-4EDA-4A3D-9D5B-B403C2656381.jpeg
 

ShatterPoints

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I have to start every single session with a full tank otherwise I start to fuel starve after 20 mins. But tell me a little bit more.

Youā€™re think the front is too low?
Can you start at 3/4 tank? Or just run it really hard and try to get near fuel starvation? You'll need to find that line to make usable observations.

I wouldn't say the front is too low per say. Which ever aero element generates the most downforce will be sensitive to pitch angles. If you raise the front of the car and with it the front splitter you are taking the rear wing out of the airstream by some amount. This will change the balance front to rear, meaning with a higher front you will see less rear downforce. So if you cannot add to the front splitter, instead of looking for force generation by wing attack angle you can change the aero balance. Yes the force % will drop when you adjust ride height but it will be less than wing angle adjustments. All this to say is that the aero balance could be the cause of the understeer you are finding mid corner AND at high speed (basically where aero matters).
 
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Can you start at 3/4 tank? Or just run it really hard and try to get near fuel starvation? You'll need to find that line to make usable observations.

I wouldn't say the front is too low per say. Which ever aero element generates the most downforce will be sensitive to pitch angles. If you raise the front of the car and with it the front splitter you are taking the rear wing out of the airstream by some amount. This will change the balance front to rear, meaning with a higher front you will see less rear downforce. So if you cannot add to the front splitter, instead of looking for force generation by wing attack angle you can change the aero balance. Yes the force % will drop when you adjust ride height but it will be less than wing angle adjustments. All this to say is that the aero balance could be the cause of the understeer you are finding mid corner AND at high speed (basically where aero matters).
I can absolutely give it a shot. I'll try going out with a full tank and a few laps near empty and see what happens
 

Rob-17GT350

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Definitely getting a lot of body roll :)

IJ9A8887.jpg
Passengers donā€™t help šŸ˜€, but yes to my previous pointā€¦ā€¦under sprung. Need more roll stiffness. Iā€™d try full stiff on front sway bar and then with front at full stiff, change rear to full stiff. Not enough rear roll stiffness can also reduce front grip as rear squats too much. And the stickier the tires, the worse the condition becomes.
 

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It's probably safe to say that you're having problems that people with R's don't have, and that got me to thinking about spring rates. I went back through my notes from 2017 when people were figuring out the suspension parameters and there's something that might matter: the front FP springs are a tiny bit stiffer than the front R springs of the day, but the rears are quite a bit softer than the rear R springs.

That would tend toward understeer. If you've got the time and patience, it might be illuminating to swap out the FP springs for the factory springs and go for a drive. The car might balance a bit better.
 

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Passengers donā€™t help šŸ˜€, but yes to my previous pointā€¦ā€¦under sprung. Need more roll stiffness. Iā€™d try full stiff on front sway bar and then with front at full stiff, change rear to full stiff. Not enough rear roll stiffness can also reduce front grip as rear squats too much. And the stickier the tires, the worse the condition becomes.
Springs contribute to roll stiffness much more than ARB's. I wouldn't set the ARB;s to full stiff, you generally want them as soft as you can get away with. I do agree with the whole system being under sprung. With that said a bump in spring rates requires less total ARB


It's probably safe to say that you're having problems that people with R's don't have, and that got me to thinking about spring rates. I went back through my notes from 2017 when people were figuring out the suspension parameters and there's something that might matter: the front FP springs are a tiny bit stiffer than the front R springs of the day, but the rears are quite a bit softer than the rear R springs.

That would tend toward understeer. If you've got the time and patience, it might be illuminating to swap out the FP springs for the factory springs and go for a drive. The car might balance a bit better.
Definitely time to make a spring and damper change, at this point the diminishing returns of all the little hacks will cause issues when springs and dampers are changed AND the setup is not returned to baseline / zero. Because this whole exercise will have to happen again.
 

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Too much tire, not enough spring? Would have thought that would show up in excessive heat, pressure and wear, no?
 

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What's the angle on your front splitter?

If the understeer is developing at high speed, then that's a sign its aero related.
 

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Aren't the FP rear springs pretty soft even without the aero? If it was good before a little extra grip, it seems to me you have room to go in your current setup to get close to where you were. Why not throw stiffer rear springs in real quick before full send into coilovers? The BMR handling rear springs (980lb) are an excellent match to the FP front and will be a cheap and easy improvement. Start there + bumping up the rear bar? I just can't imagine the SC3R could possibly be so different from the Cup2 that the springs and bars can't help out.
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