Barbara_S

Help -
I've read the alignment specs for autocrossing a C4. Camber is not dissimilar to what I have set up. I'm about to re-align due to a pothole mishap this week and was comparing what I have to the alignment spec regarding toe.

I have 0 toe in the front, and .26in in the rear.
The AX spec says to go with 3/16" out front, and 1/16" in rear.

I guess I don't understand how toe changes really make a difference.
If I change the toe to match the recomended AX setting, while I already amused to the negative camber - what shoul I expect? Better cornering? Any difference in handling?


Thanks.

UstaB-GS549

In front, toe-out helps turn-in while toe-in enhances directional stability. Solo II can get away with lots of toe-out, but hight speed events are better with toe settings approaching zero. Toe-out will make the car twitchy in a straight line. Combined with negative camber, toe-out will wear insides of front tires pretty quickly. A lot depends on type of events, whether you trailer car and how big your tire budget is.

Rear settings need to be toe-in at maximum suspension droop. If rears ever toe-out under heavy braking, you will probably spin.

MitchAlsup

The front end of a car will naturally toe-in during turns. This is simply a function of the inside tire running a smaller radius than the outside tire. This toe scrubs off speed (requiring more throttle to maintain constant speed), and reduces the traction available for turning.

What, you say, isn't Acerman steering supposed to prevent toe-changes while turning? Well, yes it is, but Acerman only works when the slip angles on the tires are very small (and in particular, only when the slip angles of the rear tires are zero)*. Once you get useful slip angles on the tires, the Acerman no longer compensates for natural (dynamic) toe-in during cornering.

Changing the static toe to a small amount of toe-out will allow the front tires to run at toe-zero in the turn, thus preventing loss of speed while turning, and allowing the traction that was scrubbing speed off to become available to actually turn the car.
[*] ref:: “Race Car Vehicle Dynamics” by William Milliken and Doug Milliken.

Barbara_S

Well thanks guys -that really did help. I found a good racing shop to work with too. Now I'll uinderstand what I'm going to ask for.

Slalom4me

I disagree. My vote is that for conventional vehicles,
the front toe settings will move in the direction of toe-out when the
steering wheel is turned off-center.

There are links to some good articles in this thread
[a/x] when does toe out stop helping turn in and start hurting steady state? .

I agree with UstaB, but I point out this applies to the front. I would
not want to have to control a C4 with a stock rear suspension set
for '0' toe-in braking & cornering at high speeds.

The rear toe changes in the direction of toe-out as the rear rises
(ie: under braking). At some point the outer rear wheel can begin
to rear-steer the car - helpful in rotating at low speed, but creating
very unsettling oversteer at high speed.

Some discussion on camber and three levels of setting 'aggressiveness'
appear in this recent thread Camber Caster Toe C4 Autocrossing

.

larryfs

you should expect your car to handle terribly on the hiway, but rather well at auto-x.

BrianCunningham

Best of both worlds, have them set it to zero toe, mark the tie-rods with some tape, and just crank in 2-3 threads of toe-out at the event with a couple of wrenches. I do it all the time

Just remember to reset it after the event, all that toe-out will destroy your tires on the road.