What are the spring rates front & rear?
600 lbs front and rear
Those are pretty high spring rates for a road work. On a track car, pretty typical.
600 lb/in front, try 500 lb/in rear, +/- 50lb/in or when the rear wheel spin on corner exit stops or greatly reduced. Rear wheel spin is likely due to excessive rear stiffness.
Dampers will have an effect on this too. What are they and where are they set?
Chassis height also has a significant effect. Begin with setting the ride height by the position of the lower front control arm. This should be about parallel to level ground with the car loaded. DO NOT lower the ride height more than this as it will cause the suspension camber curve to go the wrong way and cause the dynamic roll center to go below road level on bump causing the tire to dig reducing mechanical grip. LOWER IS NOT BETTER.
Once this is done, corner weigh the chassis to achieve near 50% cross weight similar to what it is now.
*Does this chassis have front, rear or both front&rear stability bars ("anti-roll" bars)?
No stability bars
*Good. Key to getting the chassis-suspension to work well with no bars is spring and damper rate.
The alternative is to use lower spring rates with F & R bars, this tends to do better on bumpy roads trading off independence of wheel movement and gaining load transfer from side to side wheel (left to right, right to left). At some point of lower spring rates with BIG bars tend to make an independent behave more like a solid axle suspension. There is a balance and trade off.
*What is the camber front / rear.
Front camber 3 Degrees, rear about 2.8 Degrees
*Performance radial tires tend to produce highest grip between 2 to 4 degrees of negative camber. The ideal setting depends partly on front to rear grip ratio needed. This affects understeer-oversteer balance and over all mechanical grip available.
Once the spring rates and damper rates have been some what adjusted to a workable range, optimize camber with a tire temperature gauge. The ideal would be the same tire temperature across the tire on all four corners. Typically, tire temperature across the tread is going to be about 10 to 20 degrees F higher on the inside. 10 degrees higher on the inside is OK, 20 degrees is running HOT. Temperature differences more than 20 is trouble.
*What is the toe front / rear.
No toe in the rear, front slight toe out, don't have the exact measurement, but I will be going back to the alignment shop this week.
*Toe front-rear is seriously important as it affects chassis-suspension behavior and tire wear in significant ways.
The exxe chassis-suspension does not like front toe out. Initially set the front toe to zero or slightly toe in, about 1mm or 0.040". Same with the rear. From there, the rear toe can be adjusted to toe in for rear stability or toe out for slightly improved turn-in (OK and used by autocross folks, not always OK for a track car).
Front and rear toe MUST track and be aligned together. The chassis-suspension will behave weird if the front-rear toe are NOT parallel. The rear track on the exxe is wider than the front, once this has been accounted for the toe can be set accurately. Imagine the exxe chassis-suspension placed into precision rectangle. From the center of each wheel, measure the distance from the center of each wheel hub to the inside edge of the precision rectangle. Adjust the distance from each wheel hub to the inside of the precision rectangle until they are equal side to side. Once this has been achieved, toe can be measured as the difference at the wheel rim's edge. This set up can also check for chassis-suspension condition as a bent chassis-suspesion-wheel hubs/uprights often does not line up inside a precision rectangle. If there are questions to chassis condition, there are specific chassis measurement check points in the Fiat-Bertone service manual. These are basic to getting the chassis-suspension to function properly.
Accuracy of setting toe is a must. IMO, modern optical alignment racks are NOT as accurate as they appear due to the optical alignment sensors being mounted on the wheels. This adds the tolerance of the wheels and attachment to the alignment setting. To deal with this, racer folks have been using alignment wheels and stands for quite a while now. like this:
http://xwebforums.com/forum/index.php?threads/26077/
http://xwebforums.com/forum/index.php?threads/25043/
*The Mazda rotary powered LeMons exxe has precision aerospace grade spherical bearings in the suspension along with new Fiat ball joints where used.. This makes for high precision and stable suspension alignment settings. We can dial in a chassis setting, put the car on the track to test, put the car back on the set up rig and be within 1 degree or less of set camber and 0.010" or less of the toe setting.
Precision string set up IS often more accurate than the common optical-digital alignment rack due to the direct connect to the hub. This eliminates the tolerance problem with the wheel (side to side run out) and connection between optical alignment sensor to the wheel.
*What are the tires and pressures front / rear?
Hoosier A7 - 245/40/15 all around. Tire pressure is 26 lbs cold all around.
*26 psi cold is a start, what are the tire pressures hot? Typically, 30 to 32 psi hot is OK. Hot tire psi also gives a clue as to running tire temperatures and how the chassis-suspension is behaving on a given course. The over worked tire is going to have higher pressure due to the higher heat involved from working harder than the rest. Work to correct this if this issue appears.
Bernice