Cheburator

I think you may want to rephrase this... There is no way you can adjust for dynamic camber while your wheels are pointing in a straight line... Unless you add caster... Clearly Porshe and BMW, to name a few, have wasted all those years and resources in adding caster to their race cars... What next... Double wishbone suspensions don't need any camber?

Van

Just to make sure I'm on the same page...

By "static camber", you mean the camber settings while the car is stationary on the alignment rack?

By "dynamic camber", you mean the actual angle relationship to the paved surface while cornering, which will change based on the body roll of the car?

Of course, "body roll", is the effect on the car due to the difference in height of the car's center of mass and the suspension's roll centers. And this will change the angle of the tire to the pavement due to a relative movement of the upper strut mounts.

So, let's take caster out of the equation for a moment. You have a car with -3 degrees of camber at rest (static camber). Under full cornering load, that car may be leaning enough that the outside wheel will have zero dynamic camber - meaning the wheel is perfectly perpendicular to the road. And, of course, the inside wheel will have a dynamic camber of -6 degrees. (We actually see this all the time at Lime Rock, which has all right-hand corners but one - the inside edge of the front right wheel always wears a lot... so people will run less negative camber on this wheel to make the contact patch larger for the right hand turns, even though it will reduce performance in the lefthander a little bit.)

Now, with caster added into the equation, let's pretend that the caster is 90 degrees - meaning the strut is horizontal with the road. If you turn the steering wheel, instead of changing the direction (heading) of the car, you'd be creating negative camber on one wheel and positive camber on the other wheel.

And if the caster is zero, turning the steering wheel has no affect on camber, but only direction (heading).

So, yes, it follows that if you are running 9 degrees of caster, and turn the wheel for one degree of direction (heading) change, you'll gain 1/10th of a degree of camber change.

If you turn the front wheels for a 5 degree direction (heading) change while you have 9 degrees of caster, then the outside wheel's negative camber would increase by 1/2 degree and the inside wheel's negative camber would decrease by 1/2 degree.

At my caster setting of 4.5 degrees, it would be half that amount, or 1/4 degree.

Like everything in the racing world, the perfect setup is a tradeoff or compromise. If you have power steering and don't notice any reduction in steering feel, setting the car to max caster may allow you to run less negative static camber by 1/2 degree.

This is where tuning, testing and data collection come into play. It's all about fast lap times, managing equipment wear and driver comfort level. Lots of times there isn't "one best" set up - if there were, there would be no need for race engineers!

rlets

My front settings are -3 degrees camber and 3.6 degrees caster, zero toe. I find the steering effort with a manual rack to be high and I get tired in the car. I'm running 255/40/17 NT-01 tires and have more wear occurring on the outside of the tread. It's not badly uneven, but with 8 days on the tires they're definitely going to cord at the outside edge first.

I'm thinking that I'll increase camber and reduce caster at my next alignment; say -3.5 degrees camber and 3.0 degrees caster. My hope is that this evens out the tire wear and reduces steering effort. Make sense? Other suggestions?

Thanks,
Rich

FullThrottle64

Have you profiled your tire temperatures? What are they telling you wrt camber and pressure?

rlets

I've been playing with a pyrometer and adjusting pressures. I've found that 36 PSI hot gets me generally even tread temperature inside, center and outside. Lower pressures increase steering effort dramatically and higher pressures raise the center tire temp relative to the edges.

I've stiffened my anti-roll bars slightly front and rear for my next days out on track. This with 450 lb front springs and 31mm torsion bars in the rear. We'll see how it does.

Rich

Van

Rich, I think you're going to find you're about at the minimum caster angle right now... But I think it's a good idea to increase your front camber to -3.5. What is your rear camber?

Your car looks pretty low in that picture, are you running extended control arm pins? I ask, because, without the extended pins, you'll get more body roll when the car is lower. The distance between the roll center and the center of gravity increases, so the force from cornering has a larger moment - more leverage - to lean the car over.

rlets

front: camber -3.0/-3.0, caster 3.6/3.6, zero toe
rear: camber -2.8/-2.8, toe .03/.03

The car seems very low to me as well, setup that way by a race shop. And no, the pins are not extended. I did rebuild the ball joints recently but honestly didn't know about the longer pin kit. Dang! I have been thinking about raising the car up a half inch. Good idea?

The other complication here is the LS1 engine. (don't hate me...) It's a bit heavier which is also affecting the center of gravity. But I did it without adding spacers between the subframe and body like many of these conversions have.

Thanks for your thoughts, Guys.

Rich

Van

On both my 944s, one with Toyos in SP1 and one with Hoosiers in SP2, I'm running -3.5* camber in the front, -3* camber in the rear; 4.5*-5* caster; each wheel toed out 1/32" in the front, and each wheel toed in 1/16" in the rear. For the toe settings, I use the SmartStrings and ruler at the front and rear of my 15" rims. So, for the rear wheels, the measurement from the string to the front of the rim is 1/16" larger than the back of the rim. I guess some trig could tell us the angles...

Ride height is so the front control arms are level with the ground to a wee little bit of pointing up at the ends.