Fighting understeer - looking for ideas
 

Hi all,

I am trying to dial my 944T for D.E.s and track days.
I installed coilovers F+R (350 front, 275 rear assisted by the original torsion bars) and beefed up the sway bars (F:27mm R:19mm currently on the middle setting) which helped a lot in reducing body roll and made the car more responsive.
I also changed the front tires to match the rear (225/50/16), but still have the original 7" phone dial wheels.
In addition, I added a strut bar and increase the front wheels camber to -2.25 angle.

Even after all these changes, I still feel that the car has a understeer tendency (most turns are 2-3 gear turns).

The two next setting I was considering are:
1. increase the stiffness of the rear springs
2. lift the rear a bit using the coil overs so that more weight will be on the front wheels.

Any thoughts or suggestions are welcomed...

I'd run -3.0 to -3.4 degrees of front camber, and get some wider wheels and tires. 225s are weak sauce. Throw some 9-10" wheels up front and tell me how it feels

Before making any spring or rake changes start with a stiffer setting on rear bar or go back to the smaller front bar.

What are your other alignment values?

other alignment numbers
 

Caster -2
Toe 0 both F & R
Rear Camber -0.5

Only adjust one setting at a time.

http://www.rapid-racer.com/suspension-tuning.php

Anti-Roll/ Sway Bar Adjustment Effects on Handling.

Lets have a look at the way we can adjust understeer and oversteer handling characteristics with the adjustment of anti-roll bars, also what effect the actual settings will have on the car if the stiffness is set too high.

Understeer.

• Reduce front or increase rear anti-roll/sway bar settings.

Oversteer.

• Increase front or reduce rear anti-roll/sway bar settings.

Anti-Roll/Sway Bar Setting-Effect-
Too Much Anti-Roll/Sway Bar: General.

• Lack of feel with sudden response.
• Prone to slide or skate rather then taking a set.
• Darting over one wheel or diagonal bumps.

Too Much Anti-Roll/Sway Bar: Front.

• Increased oversteer tendencies.

Too Much Anti-Roll Bar/Sway: Rear.

• Increased corner exit oversteer, hard to put power down with excessive sliding.

Thanks for the link Bob.
That was an interesting read.

I guess it depends how deep you want to go down this rabbit hole. I would start with the cheapest and easiest stuff first. Moving the rear sway bar to one hole stiffer is the most obvious first step. Next you could put a touch of toe-out on the front. After that I'd start double checking your suspension bushings to make sure you're not losing the alignment in corners. If you still have your old front sway bar, you could swap that back on. After that, it's into buying more parts again. Wider wheels all around would definitely help, but then you're buying tires again and making sure you can make them fit.

You didn't mention how experienced a driver you are, so I'm not going to make any assumptions, but before making any adjustments to you car, I would take stock of your technique. For example, could you be overloading the front tires by turning too abruptly into the corners? I thought I had an understeer issue which was mysteriously only manifesting in a particular corner, when an instructor recommended I be a little more patient in that corner and delay my turn-in slightly, based on his observation from the side of the track. That simple adjustment made a big difference. I can also provoke power oversteer if I mash the throttle too abruptly on corner exit, which tells me my car is pretty well balanced. It's odd to me that a car that comes with a staggered set-up from the factory that you've converted to a square set-up (which I also have, by the way), would understeer.

https://cimg6.ibsrv.net/gimg/rennlis...4e09190ffa.jpg
Here is my alignment specs on the car. Any suggestions?
This thread is interesting. When I had my 968.....it was a stock suspension and roll bars, OMG, was it ever so neutral!

Then comes my 951 with the following suspension upgrades, all of it was new and has less than 5K miles on it:

Koni adjustable shocks and struts
MO30 sway bars (I think this is the front)
KLA Strut brace
KLA Monoball Strut mount
968 MO30 adjustable sway bars

I have to say that it is not neutral, it defintely pushes. I was thinking of increasing the stiffness setting on the rear bar a while back, but since I almost never drive the car, I didn't. But it's still something that I want to do. I did rebuild the front control arms a while back and had the car aligned. I don't know nothing about alignment settings, but it was done by Chicago Performance and Tuning, I posted the as-left readings.

That looks like a pretty nice street alignment. You could go more aggressive if you were making it into a track car with more camber, again a bit of front toe-out, less rear toe-in. The problem with going aggressive is tire wear from street driving. If you are only occasionally tracking it, I'd leave that alignment alone, stiffen the rear sway, and soften the front dampers. That might be enough to give you the feel you're looking.

Cloud9 is right about driving style, if you really attack the front of the car at turn-in, you can make just about any setup understeer. Next time you're at the track, try to get as many laps as you can and really try to feel when and why the steering wheel gets light. Think about the different phases of the corner and how the car is loaded that brings out the understeer. For example does the car just skate when you turn the wheel? Does it turn in nicely, but then pushes out wide as the car settles in for mid corner? Does it plow when you put the power down coming out of the corner? Does it change through the session as the tires heat up and pressure up?

Front:
Ground Control 300
Camber Plates
M030 28.5
8” 225 Square
Rear:
Torsion 126
Ground Control 250
M030 19
8” 225

My settings vary depending on what I’m doing.

After all that, my Wife’s STI smokes it around the track.

I basically gave up. Okay, I might add a little more spring to the rear at some point, but shopping for bigger sway bars was the breaking point for me. Before you say it, I hate Tarrets. I‘ll never sell it, but I finally recognized that it’s a 30 year old car with little aftermarket support anymore, built for understeer with the most untuner friendly rear suspension ever created by man. So, I went out and bought a Cayman. You can’t turn back time.

I guess you could go 30mm torsion in the rear. This is probably the best thing you could do. I could find anyone who wanted to do it for a reasonable price. I was quoted around 30 hours at two different local Porsche shops, which is more like 4k after parts and alignment. I don't dare try it myself. My wife had a cow, and said let’s just get a newer car.

I will agree with Cloud9…68 however, that changing how you run a corner helps. My instructor recommended rolling through the turn rather than brake late and power out like a Corvette. It helped. “Carry” the motion rather than slowing and creating it. Stock cars turn this way. It takes some planning.

These cars are very adjustable, which is one reason they are still being raced today. I would need to see your data, but it sounds like you are not very smooth through the corners and your instructor is trying to straighten out the upset in your car while cornering. I will brake hard going into a corner (usually trail braking through the corner) , late apex and roll into the throttle when reaching apex. This is not a corvette and the car needs to finessed, if you can find a Mazda to chase through a corner it will be a good learning experience as they have similar handling characteristics.

You are not carrying nearly enough tire for your car.

To Yoramw, can you describe in which stage of the corner it understeers? Entry? At apex under neutral throttle? Exit? Are you trail braking when you experience understeer?
Even with really stiff springs all around, my car will understeer when I go WOT after the apex because the front gets light. I'm OK with that as I can anticipate and adjust my line accordingly and not lift.

I'm also a firm believer of focusing on the end of the car that is loosing grip to achieve balance, rather than adjusting the opposite end for less grip. Adjusting the opposite end may yield balance but reduces overall cornering ability. So, in your case, you could consider in the front: more aggressive negative camber; reduce spring rate; switching back to the stock sway bar. Or adjusting your driving style depending on when the understeer occurs.

Also what tires and pressures are you running? With some tires, a 3-4 psi change makes a big difference in grip.

Put the car on scales, until you know the weight each corner is carrying, everything else is moot.

A properly corner balanced car is the base you should be starting from.

T