I think I expressed myself a little poorly. What I meant was that the purely vertical motion of the car is measured as the distance between the wishbone pickup point and the ground. When calculating body roll I use the half track width in combination with the vertical motion.

/Peter

But after the A-arm is perpendicular to the strut axis, the strut continues to compress and moves inward.

If you read my post, the maximum negative camber relative to the chassis and maximum track width will occur at different positions of the A-arm. The main complication is that the sine of the negative camber relative to the chassis times the radius of the wheel/tire assembly will be added to the track width when measured relative to the chassis. This means that the A-arm may not be parallel to the ground when maximum track width is achieved, because the contact patch of the tire will be further out due to the camber.

I am not an expert but I do not think this is right. I believe the max neg camber and max track width have to be at the same point. I just do not understand how they could not be if the top of the strut is fixed and as close to the center of the car as possable?

If this is the case I belive I wish to set my stock suspension at the point where my A arm is perpendicular to the strut under the compression of a full on turn.

I / we have so far taken two approaches as to how to discover this. One is using the lean angle of the car and how it effects the angle of the a arm relative to the strut. This required an assumption as to how far the car leans in a full on turn.

The other is a measured approach as graphed by Peter. This requires an assumption as to how far my suspension will compress in a full on turn. Both methods seem to be ariving at close to the same point.

I should put something on the shocks to gage how far it compresses with a full on turn. With that I could use the strut angle as a base to work from I think.

Flieger, appreciate your help with my education. :)

???

Because the top of the strut is inclined toward the centerline of the car, the A-arm will not necessarily be level to the road surface when it is perpendicular to the strut. The maximum effective control arm length as viewed by the strut will occur when the A-arm is some degrees above horizontal.

Now, you may have a point if the car rolls 4 degrees and the A-arm is 4 degrees above horizontal, then the A-arm will be level to the road surface. However, the maximum track (hub-chassis-hub distance) width occurs when the lower ball joint, A-arm pivot point, and a point on the bottom of the chassis centerline are co-linear (the chassis thinks the A-arm is level to the ground).

The maximum effective track width, corrected for roll, will occur sometime between the peak track width A-arm position and the maximum negative camber position. If you have a large enough wheel/tire diameter, the negative camber may push the contact patch out enough to more than compensate for the loss of track width due to the A-arm not being level. This should happen when your tire radius is larger than the length of the A-arm.

Here is a good picture from the 911 performance handbook showing the effects of body roll and suspension movement on camber

.http://forums.pelicanparts.com/uploa...1235381670.jpg

I think that image is exaggerated to make the cornering force directions/vectors and expected effects easier to see.

http://forums.pelicanparts.com/uploa...1235543102.jpg
http://forums.pelicanparts.com/uploa...1235543134.jpg

Since I didn't get too much of an answer, I simply tried it out for today's track day. I added 0.6 deg negative camber to the rears - the car now has -0.8 in front, and -1.8 in the rear (previous was -1.2 in the rear, fronts are as negative as they will go).

While my butt-O-meter is an instrument of dubious accuracy, I did not perceive significantly increased grip - on corner entry. However, by mid-corner things seemed a bit more steady and controllable, and overall just felt better. Looking at the tire tread, it seems that it is wearing a bit more evenly - not just the outside edge is melted.

So, overall, I now do think 0.5 deg of negative camber is significant.

And Keith, since you always ask about camber stagger front to rear, my (bone stock) car sure feels better with 1 deg of stagger than with 0.5 deg of stagger. YMMV.

What tires are you running?

Try max front and rear (apx -1 front, -2.33 rear if near euro height) and see if it helps.

I am running at -1 front and - 2.5 rear (my max's) with 19/25mm torsion bars and 22/21 sways (from an 86 or newer). At the track, my rear seems to be good on temps across the tires (10deg range w inner highest) and mostly even wear. My front shows ware on the outside of the tires.

I set my front so the center line of the A arm pivot is .75 inch lower than the CL of the ball joint. My hope is this puts me so the A arm is at a 90 deg angle to the strut at max cornering for the most neg camber possible on my car. However I am at a very flat part of the camber curve with little gain.

With the way our cars twist about the rear suspension and lift a front tire, I almost think we need the same camber front and rear to corner at our fastest.

Very non-track-oriented Bridgestone RE760's. Car tbars & sways like yours.

I am at max front negative camber ... and I think the rear is close to maxed out as well. I am about 10mm below the actual (factory manual) ride height, and due to our roads I'm a-gonna keep it that way (my daily use freeway entrance ramp was showing its grid of rebar mesh - usually placed 3-4" below the concrete surface - on about a 15 sq ft patch since the end of winter - no joke. Last week they finally fixed it).

subbity sub

I mostly concentrate on understanding how our cars work thinking I can set it up to meet my goals. Maybe another approach is to accept the basic limitations and choose tires and settings that work the best with what we have.

I recall back in the 70's reading about a couple of different tires on a 911. One was a hot tire of the day but it did not work well on a 911's suspension and others did.

It might mean picking tires that can be flipped when one side starts to wear (front push). The Dunlop Star Spec is an example of a tire that can be flipped. Or just picking tires that are designed to work with less than perfect neg camber settings. I wonder about the Bridgestone RE-11 that has a stiff outer sidewall and softer inner. Thus sticky tires, tires that work well with less than ideal camber, and tires that can be extended by flipping on the rim.

Another thought is put back in the 50 lbs of spare, jack and tools and even run a full tank to get some weight on the front tires in the hope of getting them to bite better.

You probably already know this but there is more neg camber in our cars without sending a bunch.

On the rear the lower slot can be elongated for more camber. Some have re-profile the concentric bolts for more adjustment.

On the front, I think there is more camber by trimming the side off the inside part of the upper strut mounts and elongating the strut top holes so the shock body can approach the side of the fender. One member here found he could elongate and weld up the ball joint hole for another .75 deg. There could be another 1.5 deg doing both.


However, I am currently leaning toward fixing my suspention.

In front I am leaning toward rasing the spendle and decambering the front strut. I would like to see -2 deg camber and about .5 to .75 camber gain with compression. Thinking 22mm front trosion bars might reduce sway about 1 to 1.5 deg and the total of the three might get me close to what is ideal. Most report 22's as being pretty streetable.

In the rear I am thinking of 30 or 31mm bars as they will keep the car from twisting (lifting a front tire) about the rear which eats up front camber further. With my LSD and 205/245 stager I think I can keep the car lively yet ballanced. If my numbers are right, 31's rear torsion bars still deflect more or are softer relitive to 22mm fronts over the same bump so the ride should not be any stiffer and the front will still be stiffer than the rear to continue to transfer weight to the inside rear tire in a corner, just not so much. I would then ballance with 22 or 21 front sways and 20 or 18 rear swaybars.

On the track my rear tires run 200-210 deg just fine but the front around 180. My goal is to get the fronts closer to 200 so the rubber compound better approaches its best hold level.

Could be off base and may change my plan but that is where I am currently.

I always have a full tank & spare installed for a DE. I have no problems turning in anywhere, and understeer is not a huge problem for me. I also am a pretty crappy driver, and I like what understeer I've got just fine.

The rear tires carry 50% more load than the fronts. I bet their rated load capacity is at most 10% higher, so they are much more 'overworked' than the fronts. I see no reason to make the difference greater. Not that I think I could actually tell the difference, but I need all the help I can get.