The factory springs, bars, shocks and ride heights present a fairly well-balanced chassis.
However, to get the most performance out of your car’s suspension, especially if you have modified it, it will need to be tuned. Tuning means to adjust the spring rates and ride heights so that the car’s weight is as evenly distributed as possible over the 4 tires. This will allow each of the tires to make as much grip as they are capable of. Four tires at their max will make more grip than 2 or 3 that are overloaded with 1 (or 2) doing little work. A probe type tire pyrometer will help you fine tune alignment and tire pressures. The tire’s heat will tell you how hard it is working relative to the other three and how well the car’s suspension is using that one tire contact patch. Ideally, you should scale the car to balance corner weights and set ride heights.
Assuming your selection of spring rates and shocks are within reason, you will have to corner weight the car to try to get even weight distribution (on the diagonals). In most cases, once the easy things like moving the few movable components (like batteries, etc.) are done, corner weighting is accomplished by adjusting the ride height of each corner relative to its opposite.
One of my customers, racing a Milano in Lemons races had gone through a fairly successful first season. They liked the car and had had some success with it. The team felt it was fast and handled well. Their first winter, they decided to scale the car. The next spring, they were shocked to see that with that single change, the car had picked up 2-3 seconds a lap at their home track. It is work, but it is well worth it.
If scaling the car is not available to you, you can make some approximations that can get you close. I recently had a chance to measure up a customer’s GTV6 – a small local legend. This is a streetcar modified slightly for club track use. This car has a fairly common suspension set up. 27mm torsion bars, 27mm front sway bar, matching rear springs, 1” rear sway bar, Bilstein shocks. 5”x7” rims, lots of poly, SZ30 deDion triangle bearing kit. A typical high-end street package. With a slightly modified 3.0L, it was “famous” for kicking 5.0L Mustangs and M3s to the curb.
The car is a little lower than most, but still OK on the street. He has to be careful over big road imperfections, but in general, it does not make any extraordinary demands for road use.
On 205/50/15 tires – measures 4″ from ground to forward control arm bushing bottom (rear most bushing).
Measured from ground to the seam of the rocker panels – behind front wheel arch = 6″, just forward of rear wheel arch 7.25″
If you are running a different tire, you will have to make calculations to compensate for the new OD (radius actually) …
This set up gives a front control arm that angles up a little towards the ball joint i.e., not parallel with the ground. The owner reports no bump steer issues or any other handling anomalies.
I have driven the car (not on the track) and can confirm, the car is a real delight to drive – no funny business in the handling dept. In fact, it can probably go even lower and be ok. You will have to experiment with rear ride height to find the set up you like.
- from the ground to the bottom of the lower control arm bushing knuckle (the rearmost one) = 4″.
- to the bottom of the front jack point = 5.5″.
- to bottom of the rocker panel seam just behind the front wheel arch = 6″.
- to bottom of rear jack point = 6.25″.
- to lower edge of rocker panel just in front of the rear wheel arch = 7.25″.