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Discussion Starter #1
Hey guys,

I drove my first autocross on 295s yesterday. The grip is unbelievable! You just crank the wheel and keep your foot in it and it just grips and grips! It actually took a couple runs to find the limit - I forgot how quickly r-comps let go :)

There is still a lot of time to be extracted. I think I was overdriving the car a little, but even when I made an effort to slow down for the really tight and slow corners, understeer reared its ugly head. I was running 36 psi front /37 rear, still understeer.

My setup:

Front:
-375 springs w/ Bilstein HD
-Steeda Tubular 1 1/4" hollow sway
-Bumpsteered
-MM fwd. offset LCA
-3* neg. camber

Rear:
-250lb springs w/ bilstein hd
-PHB
-stock swaybar
-MM LCAs

Weight: 3545 w/ driver, F: 60%, R: 40%

I have the stock front swaybar that I can swap in, but I've swapped it a few times on street tires, but really like the response of the Steeda bar.

My Ideas:
-softer front springs
-adding a thicker rear swaybar.
-I'm running the stock diff, could an Auburn or Torsen help?
-Would converting to a PM3L help?

I would say most of my push is mid-corner to exit, it feels good through slaloms.

I'd appreciate any input. I just know there is A LOT of time left in these tires.

A couple pictures:
Image 1
Image 2
Image 3
Image 4
Image 5
 

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You might try lowering your air pressures. On 275 hoosiers I recently found that front 28/29 and rear 24/25 cold were good starting points. I Probably would not reduce front spring rate. I posted in the following thread with a similar question and you might find some of the info helpful as well.

http://forums.corral.net/forums/road-racing-auto-x/1238850-can-i-have-too-much-roll-stiffness-help-me-reduce-understeer-please-2.html

I'd begin with air pressure; it's free. Make one change at a time so you can determine its effect.
 

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Discussion Starter #3
You might try lowering your air pressures. On 275 hoosiers I recently found that front 28/29 and rear 24/25 cold were good starting points. I Probably would not reduce front spring rate. I posted in the following thread with a similar question and you might find some of the info helpful as well.

http://forums.corral.net/forums/road-racing-auto-x/1238850-can-i-have-too-much-roll-stiffness-help-me-reduce-understeer-please-2.html

I'd begin with air pressure; it's free. Make one change at a time so you can determine its effect.
Yeah, I really think I could have dropped the pressures more, but not having r-comps for like 6 years, I forgot to bring some shoe polish for testing...I'm defintely going to try more. I don't think I'll be able to drop them a ton though because I've got 295s on a 9" rim. I'll take a look at the link.
 

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I wouldn't touch the front end if I were you. Your issue is more on exit and so with the shift in weight to the back, you need more rear swaybar. You have plenty of traction to spare (that is why it understeers) and it will help the front end do more work. The cobra rear swaybar might be the biggest available though in stock style attachment. You might have to consider something like MM's adjustable swaybar.
 

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Discussion Starter #5
I wouldn't touch the front end if I were you. Your issue is more on exit and so with the shift in weight to the back, you need more rear swaybar. You have plenty of traction to spare (that is why it understeers) and it will help the front end do more work. The cobra rear swaybar might be the biggest available though in stock style attachment. You might have to consider something like MM's adjustable swaybar.
Thanks for the input. You know, they always say to work on the end of the car that you're having issues with, but I'm think it might be more of a rear balance issue. Obviously, these car in slow speed stuff are going to understeer. But, I guess by making it easier for the rear to rotate, it will help reduce understeer by increasing the rear roll resistance.

Follow up question....I'm running a stock traction lock. Would I benefit by using the F150 spring DIY or getting a different diff? It may be that my traction lock is just not optimal with the Hoosiers. Do you think a Torsen would "fix" my slow speed understeer or would it make it worse?
 

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But, I guess by making it easier for the rear to rotate, it will help reduce understeer by increasing the rear roll resistance
Sort of. Increasing the rear roll stiffness while leaving the front roll stiffness alone (or reducing it) makes the rear tires take a larger share of the lateral load transfer. That makes them operate at slightly larger slip angles, and as this is happening the fronts are running with less lateral load transfer and operate at slightly lower slip angles. This kind of shift in the relative slip angles is the definition of reduced understeer, and as a whole the car will rotate more readily.

If you have adjustable shocks/struts, playing with different damping settings front vs rear can also affect corner exit behavior.


FWIW, the extra grip you get from the Hoosiers is going to make the car roll slightly more, meaning that your front tires will lose that much more camber. I'd start by setting slightly more static negative camber before doing anything else.


Norm
 

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Discussion Starter #7 (Edited)
Sort of. Increasing the rear roll stiffness while leaving the front roll stiffness alone (or reducing it) makes the rear tires take a larger share of the lateral load transfer. That makes them operate at slightly larger slip angles, and as this is happening the fronts are running with less lateral load transfer and operate at slightly lower slip angles. This kind of shift in the relative slip angles is the definition of reduced understeer, and as a whole the car will rotate more readily.
This is good news. I probably need a little more rear bar to help with the relative slip angles.

If you have adjustable shocks/struts, playing with different damping settings front vs rear can also affect corner exit behavior.
I've got Bilsteins, adjustments here would be nice. I'd like to get ASTs, but since money doesn't grow on trees, I'll have to wait a bit. I've still got my Steeda rear adjustable swaybar, it isn't the best, but I think I'll install it and see how it feels, I've already spent the money on it...

FWIW, the extra grip you get from the Hoosiers is going to make the car roll slightly more, meaning that your front tires will lose that much more camber. I'd start by setting slightly more static negative camber before doing anything else.
I've already dialed in 3 degrees, I'm not sure I want or can get much more.

Thanks
 

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Pressure sounds very high all the way around. I would guess 30-34 front, 24-27 rear.

DaveW
 

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Discussion Starter #9
Pressure sounds very high all the way around. I would guess 30-34 front, 24-27 rear.

DaveW
Thanks for advice. I agree, I think they were too high from what I've heard...I guess, I need to bring something to mark the edges (shoe polish) to dial in the right amount of air pressure.

I'm going to play with the pressures and add my Steeda adj. rear swaybar that has been sitting in a box for a few years...
 

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I dont know about Hoosier A6's, but R6's (roadrace compound) the sweet spot is 39-40psi hot, and adjust cold temps accordingly to get to hot temps to that psi.

 

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I am not sure I ever paid attention to how different the R6's are with pressure.

A6 pressures have tended towards the cold numbers shown on that sheet. And if you got an A6 to 200 degrees, it would be so greasy that the car would slide away on the slightest slope because it had so little traction. Rough rule of thumb of A6 is if it is uncomfortable to put your hand on it, it is too hot.

Very interesting how different the numbers are. I wonder what you are supposed to do if you run R6 at an autocross?

EDIT: Here is the current care and feeding guide on the A6/R6, which shows lower pressures:

http://hoosiertire.com/pdfs/tctR6_A6.pdf

Shows 110-140 degrees for Temp.

DaveW
 

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My setup:

Front:
-375 springs w/ Bilstein HD
-Steeda Tubular 1 1/4" hollow sway
-Bumpsteered
-MM fwd. offset LCA
-3* neg. camber

Rear:
-250lb springs w/ bilstein hd
-PHB
-stock swaybar
-MM LCAs
I would assume ur using coil-overs. If so i would swap out the rears for a higher then front spring rate if you were an IRS car but looking like your running a SRA so i guess you could still go higher rate in the rear. also IDK but I think the 375lb rate up front is too high for the valving of the off the shelf HD bilsteins. you might have to get their revalved sports, stage 2's or Stage 3's. they all have a spring rate range in which they work with.

my best and most noticable upgrade was the MM k-member. world of a difference. I always understeered now its more like i cant keep my rear straight.
 

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Discussion Starter #13
I would assume ur using coil-overs. If so i would swap out the rears for a higher then front spring rate. also IDK but I think the 375lb rate up front is too high for the valving of the off the shelf HD bilsteins. you might have to get their revalved sports, stage 2's or Stage 3's. they all have a spring rate range in which they work with.

my best and most noticable upgrade was the MM k-member. world of a difference. I always understeered now its more like i cant keep my rear straight.
Thanks for the comment. I can't dothe K-member, but I may look at getting drop spindles, they should help in a similar way.

I do have coilovers and yes, 375 is sort of the outer limit. I like the set up on the street, but I think I am going need to go to a 2 way shock.
 

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A K-Member is lighter, so the center of gravity will be moved further back (same effect as putting a 25lbs ballast in the trunk)

Drop spindles will just lower the center of gravity a little bit.
 

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A K-Member is lighter, so the center of gravity will be moved further back (same effect as putting a 25lbs ballast in the trunk)

Drop spindles will just lower the center of gravity a little bit.
Not really. Compared to a stock car, that would be correct. In reality you need to think of the fact that he would be able to raise the suspension after putting drop spindles on so the camber curve and roll center position will change to the better.
 

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Not really. Compared to a stock car, that would be correct. In reality you need to think of the fact that he would be able to raise the suspension after putting drop spindles on so the camber curve and roll center position will change to the better.
With drop spindles, the suspension is lower in relation to the tire. How can you raise the suspension and not put the tire into the fender? Drop spindles are a way to lower the center of gravity without changing stock geometrics

Stock height on left; drop spindle on right
 

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Your technical points are correct, but we are discussing a car that has already had the front springs changed which I assume have lowered the car. When running drop spindles the total ride height drop can be achieved with the spindles. Allowing longer springs to be installed in the front. Then he would have stock geometry with the lower ride height and most likely a better camber curve and roll center height then what he currently has.
 

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Your technical points are correct, but we are discussing a car that has already had the front springs changed which I assume have lowered the car. When running drop spindles the total ride height drop can be achieved with the spindles. Allowing longer springs to be installed in the front. Then he would have stock geometry with the lower ride height and most likely a better camber curve and roll center height then what he currently has.
So we are talking about the same thing, but he's going BACK to stock geometry...
 

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Follow up question....I'm running a stock traction lock. Would I benefit by using the F150 spring DIY or getting a different diff? It may be that my traction lock is just not optimal with the Hoosiers. Do you think a Torsen would "fix" my slow speed understeer or would it make it worse?
If you do anything to the S spring you might want to yank it out. Good luck getting a truck spring in there and if you do it will increase understeer when coasting in. Haven't had a S spring in my rear for years.

As stated you need to lower pressures and maybe increase rear bar. I assume you are running the Cobra in your signature so you either need the add on Steeda bar or the adjustable MM unit.

I'm not a super technical guy on tires but I set my 315s at 30f and 27 rear cold then go have fun. If it pushes I slow down.

Are those front springs coil overs?
 

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Discussion Starter #20
As stated you need to lower pressures and maybe increase rear bar. I assume you are running the Cobra in your signature so you either need the add on Steeda bar or the adjustable MM unit.

Are those front springs coil overs?
Front springs are coilovers, I plan to lower the pressures and see what happens. I also have a Steeda bar up front (1.25") and I need to find my rear Steeda bar and see if I can tune out a little of the slower corner massive understeer.

Other than that, I think I really need better shocks and much stiffer springs...
 
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