[cmartin]

I want to get the alignment checked on the red car. I've read the previous posts here and on pelican and all I can sum up is to get the max camber possible. Negative 1.75 up front and 1.3 rear were recommended. What about caster and toe? I am looking for a solid street/track setup, leaning towards track.

Any and all input is much appreciated!

[Noah]

I just had my car aligned on Friday -- $150 at Allen Automotive in Silver Spring on a modern Hunter rack.

I did a bunch of research too, and had it set to:

Front
Camber -1.25
Caster 6 degrees 5' (max it out)
Toe 1/32" toe-in

Rear
Camber -1.5
Toe 1/16" toe-in

FWIW, everything I've read states that on a 911, you want the rear camber to be .25-.50 more negative than the front (unless you want to create a lot of oversteer). The above specs were taken from an article written by a very experienced 911 track guru. The main variation is in how much camber you run -- when you get beyond about 1.5, uneven tire wear becomes a bigger factor.

Today I put 245's on the back (the 225's were literally bald!) and oh man, what a difference...

If you've never had the car corner balanced, do that first -- then get it aligned. You'll be amazed at how off the weights of your car are, especially if you've done suspension work such as torsion bars and shocks.

[Vicegrip]

I recommend that check with the tire manufacture if you are using peformance tires to see what they recommend as well. Some performance tires need well more than 1.25 neg.

[Chopper Dropper]

You have to accept a compromise with track and street. Slightly aggresive street will give better wear, but you will still wear the outer shoulders badly on the track.More aggresive street, getting to -ve 2 will give bad inside wear on the street but less outside shoulder on the track. Be prepared to flip your tyres on the rims as well whichever way you go. Also different tracks will bugger up all your smart calculations,even if you have a track car, unless you re set camber etc for individual tracks, then you are just plain an*l as far as DE goes and even club race!!
Dirk

[cmartin]

Thanks guys, much appreciated. It sounds like I will have to play with this a little myself, good starting points though.

[matt de maria]

Keep in mind that no one setting fits all cars.
The general theory is that maximum tire friction occurs at 0 to -1/2 negative camber. If the camber changes from that point the tire friction will decrease.
Why are typical setups more than a degree in negative camber?

Most cars will lean into a corner. If the car has -1 degree camber on the outside wheel and the body leans 1 degree over, the resultant camber on the outside wheel (for the most part) will be 0 degrees camber. If the car leans more than 1 degree, more negative camber is dialed into that wheel to compensate for body roll.

If stiffer springs are used, the car will not lean as much. (The same with sway bars) A lot of negative camber is not needed.

Caster affects the self-centering of the steering wheel. Caster also affects the negative camber of the outside front wheel as the wheel is turned. The higher the caster the more the negative camber value the outside wheel develops. Caster is good. It reduces understeer for quick sharp turns.

Theories get muddied when the 911 is lowered. Lowering is done to reduce the height of the center of gravity. Lowering the center of gravity will reduce the lateral weight transfer across the car. This means less weight gets transferred to the outside wheels. This is good. If the tire loading is reduced, the slip angle of the tire is reduced. This means that there is less of a tendency for oversteer (or understeer depending on which axle).

The drawback to lowering is that as the car is lowered the geometries of the suspensions will produce more negative camber. Sometimes it will be more than desirable. And it cannot be tuned out. Here is where you have to decide on your compromises. Lower center of gravity vs negative camber.

Toe-in is used for two purposes. Toe in aids in the self-centering of the steering wheel. Toe-in is used to compensate for the compliance of the suspension bushings. When the rubber front end bushings get old and loose, the road wheels will get pushed back and out while the car is driven. This will produce a dynamic toe-out effect. For old cars more toe-in is dialed in to compensate for this. For the tight suspension on a track car this will eat horsepower. You want 0 toe.

[Parenn911]

Wow, great stuff Matt. Nice explation of camber and caster, your post cleared some questions I had about them, and alignments in general
You never cease to amaze me .

[Cliff Claven]

I appreciate this information as I'm in the process of lowering and stiffening the suspension. It seemed when I had zero toe with my current stock suspension I was getting a disconcerting amount of bump steer on the street; is there a recommended way to deal with that?

BTW, Toyo recommends -2.0 to -5.0 for RA1s for maximum performance, and they note the following:

-The degree of negative camber required to get the most performance out of the RA1 can often lead to inside shoulder wear.

- To maximize tire life, the tire should be dismounted from the wheel and flipped (move inside shoulder to the outside) when the tire is about half way worn.

[matt de maria]

Static toe doesn't cause bump steer. You've got other issues. The definition of bump steer is a change of spindle direction when the suspension (wheel) goes through a jounce and rebound. Typically for the 911 it is due to the tie rods not being parallel to the ground when the suspension encounters a bump (assuming that there are no major problems elsewhere in the suspension). This is what the rack spacers are for when you lower the 911.