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Patientzero
Patientzero Dork
8/22/21 6:37 p.m.

I did my first autocross yesterday since 2019 and I'm pretty sure my first since I redid all my front suspension (the last two years are a blur). I need more front grip real bad but I'm not sure where to start. I guess mid corner grip is ok If I baby it into the corner but then as soon as I get back on the throttle it starts pushing wide on corner exit.

Here's what I'm working with.

2002 Mustang
3240lbs w/ driver
Eibach front sway bar
MM 1" rear sway bar

Torque Arm/Panhard bar
425lb front springs
275lb rear springs
Koni SA coilovers
Full MM front suspension with forward offset control arms
295/35-18 A052's on 10.5" wheels
0 toe
-4° camber

Tom1200
Tom1200 SuperDork
8/22/21 6:54 p.m.

Random thoughts:

Back off the front bar

Possibly more rebound in the front 

Slight drop I front tire pressure.

Next what can you do as a driver?

Trail the brakes deeper into the corner

Wind on the throttle just that bit slower.

Wind the throttle in faster & use the power to rotate the car.

My question as always is exactly under what conditions and exactly what are doing when it pushes.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
8/22/21 8:17 p.m.

I always kinda wonder where the Ackerman angle is and if it can be improved.

The Fox body guys used to find the knuckles with the best steering arm angle ('83 Continental?), then move the rack as far back as possible with bushings or good old fashioned cutting and welding, and then redrill the control arm mounting points in the crossmember to push the ball joint more forward, and also raise the roll center and get some antidive while they were in there moving things...

 

Then again they were also starting with a really, really bad suspension geometry-wise.

APEowner
APEowner SuperDork
8/22/21 8:34 p.m.

It sounds like it's a little tight in the middle and really bad on exit.  How is it on turn in?

dps214
dps214 Dork
8/22/21 8:57 p.m.

Sounds like the main thing you want is to unstick the rear end a bit. Given the car and the stick axle rear, I'm a little surprised that you can't accomplish that just through throttle application. But if not, or at least if it's not consistent and predictable, more rear swaybar (or maybe spring) would probably be where I'd start. I assume the konis are rebound only, if you have a strong enough diff, turning the rears up a bit might promote oversteer, but too much or with too weak of a diff and it might cause some wheelspin issues. On that note, it could also be a diff issue, or at least could be helped by a different diff setup. Either more lockup to loosen up the rear, or if you've got some crazy diff in it with a bunch of preload to it, it could be just not unlocking enough to turn the car in the first place.

Apexcarver
Apexcarver UltimaDork
8/22/21 9:07 p.m.

Autocrossed a 97 cobra for years and years. Still have the car.  To some degree, corner entry understeer will always be challenging. Be sure to consider your driving approach. You can't dive it in like a miata. Slower in and faster out is important. Barring all that though...

I forget numbers on alignment, but mine is set to as much caster as possible on mm cc plates. 

 

Mustangs are counterintuitive, you make the front suspension work better by not letting it work. How big is the front bar? I have a monster 35mm addco on mine coupled with non-coilover 950lb-in springs. It works pretty well and was advised by Sam Strano.

 

Also, how old are the tires?  Have you checked bumpsteer?

ShinnyGroove (Forum Supporter)
ShinnyGroove (Forum Supporter) HalfDork
8/22/21 10:03 p.m.

4 degrees of camber is a lot!  How are your tires wearing?  If it's all inside edge, I'd dial back the front camber a bit. 

dps214
dps214 Dork
8/22/21 10:16 p.m.

Not for A052s, especially on a relatively softly sprung, front heavy car. I was actually considering suggesting maybe trying a bit more for initial turn in grip. Tires look pretty evenly worn in the photo.

Patientzero
Patientzero Dork
8/22/21 11:20 p.m.

Tom: Front sway bar is not adjustable but I have a stock bar I can try out.  More front rebound and less tire pressure are both options.  

Pete: I'm using the forward offset k-member and control arms so I think that would address what you're alluding to.

Everybody else:  It has a freshly built rearend with an Eaton Truetrac that hooks up really well.  The car has 500hp so I can get the rear end to come out with throttle but it takes alot and doesn't seem helpful on a relatively tight course.  My rear sway bar is at the softest setting so I can try stiffening it up to see what happens.  I just thought I'd try to stick the front before I unstick the back if I can.  The front swaybar is 35mm and I think among the stiffest available.

On turn in the car goes into a pretty controlled 4 wheel drift and once I start powering out of the turn it pushes wide.  If I can get the front to grip more I would be able to get on the throttle sooner and carry more speed through the corner.

So far most of the recommendations I've seen are; less front tire pressure, more rear bar, less front bar.

jh36
jh36 HalfDork
8/23/21 5:35 a.m.

Based on everything I've read here, I would only stiffen the rear, to about 1/2 setting. I would run it and then increase/decrease accordingly. 
I'd leave everything else the same until knowing those results. Then I'd probably play with pressures. 
I road race, so maybe my approach is a little different, but I've found that changing more than one suspension setting at a time without testing leads to confusion for me.  

APEowner
APEowner SuperDork
8/23/21 11:22 a.m.

Tire pressure and adjustments that effect contact patch and steering angle can effect total grip but changes to spring rate, shocks and sway bars move the available grip around.  That assumes that your adjustments don't allow the suspension to move in a range that screws up geometry.

As a general rule if you've got a problem on turn in  you want to make your changes on the front of the car and if you're trying to fix a corner exit issue then you'll want to adjust the rear.

In the OP's case I'd stiffen the rear bar.  That's the textbook solution for a RWD car that pushes on exit and takes significant amount of power to rotate with the throttle.   Not knowing motion ratios this is just a gut thing but think the rear springs are a bit on the soft side as well. If you can get the balance where you want it with just the sway bar adjustment then I wouldn't mess with them.  In an autocross situation the softer springs may help on launch.

Tom1200
Tom1200 SuperDork
8/23/21 11:31 a.m.

I always go by Carroll Smith's fix the end that isn't working. With that said if adjusting the rear bar leads to improved times then so be it.

L5wolvesf
L5wolvesf HalfDork
8/23/21 12:07 p.m.

Have you done tire temp tests or have pics of the fronts?

Apexcarver
Apexcarver UltimaDork
8/23/21 12:08 p.m.

Might attempt dropping the front to 3* camber...

jh36
jh36 HalfDork
8/23/21 2:38 p.m.
Tom1200 said:

I always got by Carroll Smith's fix the end that isn't working. With that said if adjusting the rear bar leads to improved times then so be it.

And that's how I got to where I got!  I have worn those books out.  Right up there with Richard Feynman's books on physics.  They made complicated things easy to understand.

OldGray320i
OldGray320i Dork
8/23/21 8:43 p.m.

"I guess mid corner grip is ok If I baby it into the corner but then as soon as I get back on the throttle it starts pushing wide on corner exit."

"On turn in the car goes into a pretty controlled 4 wheel drift and once I start powering out of the turn it pushes wide."

I may be dumb, but I read that and think you need to let the car rotate a little more before you get on the power. 

As soon as you gas it, weight transfers off the front, so what was a good direction mid corner now pushes wide. 

If it wouldn't turn in to save its life, then doing something to the front of the car makes sense, but it's at throttle application if I read right. 

I thought a little more rake would make the rear end want to come around more easily at turn in, roll couple or something like that, change the way the car reacts.  Sway bar or spring rate do the same thing effectively, I guess, i just remember with the 320i a half inch lower in the rear and the car wouldn't try to swap ends when I turned the wheel (they're notoriously tail happy anyway).  

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
8/23/21 9:05 p.m.
OldGray320i said:

"I guess mid corner grip is ok If I baby it into the corner but then as soon as I get back on the throttle it starts pushing wide on corner exit."

"On turn in the car goes into a pretty controlled 4 wheel drift and once I start powering out of the turn it pushes wide."

I may be dumb, but I read that and think you need to let the car rotate a little more before you get on the power.

That's pretty much what the GRM article about getting the most from a 911 said: you can gain a lot of time by waiting an extra second before getting on the power.

Granted, 911s are a really special case (fingerquotes optional) but the theory still remains the same, especially if you have enough acceleration traction to be able to understeer under power instead of just blowing the tires away. 

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
8/23/21 10:28 p.m.

Rear panhard bar.  The SN95 / Fox rear is horrible for lateral location.  Unless you are super, super smooth, this IS part of your problem.  Battery relocation and anything else you can do to take weight off the front will also help.

Do those and then we can look into sway bar and tire pressure adjustments.  
 

You made massive front end suspension upgrades but still have a Quadra bind rear axle.

dps214
dps214 Dork
8/23/21 10:37 p.m.

I also thought the rear spring rates sounded kind of soft, but I also know that solid axles are weird sometimes and I don't know a ton about them. Could be a situation where trading sway bar stiffness for more spring rate would help. Keep the same overall roll stiffness but stiffen up the car a bit in front-rear weight transfer, might help throttle application loosen up the rear without making it loose all the time or asking too much of the differential.

Patientzero
Patientzero Dork
8/23/21 10:41 p.m.

In reply to AnthonyGS (Forum Supporter) :

I forgot to mention I have a torque arm/PHB.  Battery is in the back.  Weight distribution is 54/46 which is fairly good for these cars.

Patientzero
Patientzero Dork
8/23/21 10:44 p.m.

In reply to dps214 :

I've been talking to Jack Hindley at Maximum Motorsports.  He thinks my springs rates are perfect and has recommended a bigger rear sway bar to move more of my weight transfer to the rear of the car and get rid of the understeer.
I currently have the 1" x .120" and he suggested the 1.25" x .125". 

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
8/23/21 10:59 p.m.

In reply to dps214 :

Rear spring rates are actually kind of aggressive, at least with a stock rear suspension.  The solid axle Cobras had 160lb springs, and bear in mind that the spring acts on the control arm so wheel rate was closer to 100lb/in.

Something to bear in mind with solid axles (of which I am a fan) is that there are two effects to consider: the actual sprung weight is lower than the weight distribution may suggest due to the higher unsprung weight, and spring rates get "screwy" for single-wheel-bump scenarios because one-wheel bump is going to be working against TWO springs and shocks, not just one.  Philosophically, since we are dealing with cars here and not theoretical constructs, for ALL vehicles, single-wheel bump affects all four corners of the suspension, but more directly on a solid axle, assuming the chassis does not get upset, it affects both ends of the axle no matter what, because you're going to be levering the offside spring/shock against the offside contact patch.

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
8/24/21 11:20 a.m.
Patientzero said:

In reply to AnthonyGS (Forum Supporter) :

I forgot to mention I have a torque arm/PHB.  Battery is in the back.  Weight distribution is 54/46 which is fairly good for these cars.

So it's a fully built MM car then.  Did you ask them for their alignment specs?  
 

Are you running a square tire setup or really wides in the rear?  Hmmm just checked square....  

Do you have the forward offset control arms and bushing to maximize caster?  
 

A bigger rear bar will make the rear a bit more happy and may balance the car with tire pressure adjustments.  I will stay tuned.  They are suggesting a pretty dramatic rear bar change.

Tom1200
Tom1200 SuperDork
8/24/21 11:34 a.m.

Word of caution; if the car is regularly street driven keep in mind you are dialing in low speed oversteer, which at highway speeds may make the car dicey. The rear bar is adjustable (I think) so you can dial that back out between events. Again just something to be aware of. 

Patientzero
Patientzero Dork
8/24/21 4:18 p.m.

Here is what Maximum Motorsports said;

Mr. Stump,

 Assuming that the current rear swaybar on your car is set to full stiff, the front roll stiffness percentage is now 74.8%. With the rear swaybar on full soft, it is now 76.2%. With the Steeda front swaybar, OEM 1” rear swaybar and original rear springs, it was previously 73.2%. The car understeers worse than before, but it has less overall body roll. There is far too much weight transfer between the front tires in corners. This will always result in a lot of understeer. You need to have a larger percentage of the weight transfer during cornering, to happen across the rear tires.

 The spring rates on the car look perfect for the weight distribution, so the easiest way to increase weight transfer across the rear axle, while keeping the body roll low is to use a stiffer rear swaybar. If you change the rear swaybar to the MMRSB-9.1 model, on full soft the front roll stiffness percentage will be 71% and on full stiff it will be 68%. To convert your existing rear swaybar to this model, you need to purchase the MMRSB-95 and SB-012. This will make the car vastly faster to drive, as you won’t be waiting, waiting, waiting to be able to get on the throttle until after the corner ends.

 

Let me know how this works.  

 

Sincerely,

Jack Hidley

Maximum Motorsports Tech Support

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