Alignment Philosophy Question

2

23racer

New member
I am going out with my Cougar this weekend, so I double checked my alignment to make sure it was according to target. In doing this something started to bother me and this is where I need some help in understanding what other people are doing and why.

The car has an extremely long wheel base, a huge big lump of a motor mounted high up and forward on the car. The car really wants to be a huge lawn dart and just go straight. The original builders were running almost a 1/4" of toe out in the front and - 4 degrees of camber. In the rear they were at 3/8" toe out and -2 degrees of camber. In their notes the driver was always mentioning understeer on corner entry and exit.

The second owner added a big splitter and dam to the front, raised the rear wing about 2" and went to an extreme 5/8" toe out in the front and -5 degrees of camber. At the rear he brought the car back to almost 0 toe and left the camber at -2 degrees.

The car handles very well now and points in to the corners very well. In the super high speed stuff you can balance the car on the throttle like a RWD car. You still have some power on push and the slower the corner, the worse it is.

I can live with the handling as the car is just great to drive, but it is tearing the front tires off the car. I can take an RA1 from a 4/32 to a slick in 15 laps. I want to pull the front toe in somewhat to extend the tire life, but my experince with FWD cars is limited and I really don't want to increase the push any more than it already has.

So the question is, directionally, as I pull the front toe in do I have to increase the rear roll stiffness to compensate. Will this make the car more or less sluggish to turn in. Or if I pull the front toe in will the increased straightline speed compensate for the slower corner entry? I hope that steady state cornering speeds would be the same no matter what I do as they are dependent on spring rates and aero, but I am concrened about transitional characteristics.

Any thoughts from you FWD guys?

Eric
 
Perhaps a bit too much front camber.

Does the car have any sway bars and what does it have for a diff?

You definitely do not run radical toe-out in the rear on a FWD car unless you like "dirt tracking".
 
The car is running a 3/4" Speedway bar on the front with a sway arm setting of 7.5" (its all adjustable). The rear bar is a 1.5" Speedway Bar with an in car adjustable control set at Position 3 right now, though I have tried lowering it to 1 and raising it to 5 with the expected results in steady state and transition.

The car is an ex WC car and nothing is remotely close to stock. The suspension was designed using inputs from Ford, Bill Mitchell and Multimatic. The spring rates seem a bit odd to me at 700 front and 450 rear, but the car in steady state is incredible, its just in the transitions where I am concerned. The car really works well, its just eating front tires and I would need to get at least an hour out of a set. That is why I was asking the more general question regarding effects of toe in and turn in. I just don't emotionally like the 5/8" toe out at the front.

It is also running a complete Quaife dog box and diff set up.

Eric
 
Is that a typical quaife type diff, or some sort of racing spec clutch type?

IMO the quaife style diffs are great for street cars, and ineffective for race cars. Welded or aggressive clutch style really has a positive impact on the throttle on characteristics of the car, and can have significant braking benefits as well.
 
If the front sway bar does not provide any locating function for the front supension, try disconnecting it.

I am not familiar with the Contour rear suspension so I will ask you--where are the springs located (inboard or outboard). Your rates might not be that far off if those springs are outboard (e.g., an outboard coil over) so that they are near equal to the effective rate. If inboard, you probably could use some more rear spring.
 
Never be satisfied with how a car handles. Try throwing more rear spring at it. Typically FWD cars like heavier springs in the rear than in the front.
 
If it's lke you say and a custom set-up and not strictly based on the oe suspension. You might try more ackerman and less toe out. I'm basing this off of Smith's "Engineer to Win." Toe out is a way to get more ackerman, but with scrub down the straighs. Being FWD, you will need a tiny amount of toe out to compensate for bearing slack.
 
I can't imagine that much toe is a good thing on the straights- its got to scrub speed off. Its also very simple to play with between sessions. Bring the toe gradually back to a more reasonable number, and monitor lap speeds, rpm at the end of the longest straight, feel through the corners.....That much toe is definitely compensating for something if its needed to make the car rotate.
 
"Camber thrust" happens with that much camber. "Zero scrub"( or reduced camber thrust) is around 4mm toe out, at -4 camber with a 22 in tires.
To understand this concept. ride a bike. The bike makes lateral force by tilting the tire, as much as turning the tire.
To reduce the front tire wear, make the rear do more by toeing out the rear. The result of this, is the rear tire rolls outside of the front tire, reducing the dynamic loading. Lower the dynamic loading and the front tire can turn harder.
This whole concept and application is in my book. Reducing the front tire load is a large part of going faster with FWD.
Toe out the front 4mm, toe out the rear 5-15mm. try it and get back to me.
Welding th diff can reduce the front tire wear also by spreading the load , and it makes more lateral grip for some reason.MM
 
This past weekend, we pulled the front toe out back to 1/2" and left the rear toe out at 1/4". The car handled fantastically well and we had minimal tire wear after a 1 Hour Race. The tire temps were great, but the day was very cold, in the low 50's. The pressure rise in the tires was only 6 lbs in the front and 4 lbs in the rear.

I kept the advice about zero scrub in mind when I was trying to decide on the new settings and I am glad I did as things were just great once the tires got warm.

Those rear tires sure take a long time to warm up, :eclipsee_steering::blink: when its that cold out. A few very high speed rear step outs in the first few laps. Like full lock at over 100 mph. Wow, I have to learn a whole new warm up lap method.

Thanks for the help. It was very valuable. About the book, which one are you talking about, Flying Lizard?

Eric
 
Adjust toe to about 1/8" out and get as much front caster as you can. If you can increase Ackerman, try it. I wouldn't mess with springs, bars. or shocks just yet.
 
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