Car Craft
Click here to find out more!

Reader Tech Questions - Ask Anything

Mustang Handling
Pastor Mark Jasa; Los Angeles, CA: Is there a bolt-on suspension for a ‘69 Mustang that will give me Ferrari-like cornering, like one g or more? Also, why are lateral acceleration stats different from track-performance values? For instance, Road & Track will state that a given Ferrari had a cornering ability of say 0.94, but at a given moment on an actual track they might generate 1.2 g according to the in-car test equipment. It sounds like a large discrepancy. Also, what suspension do you recommend I buy for my ‘69 Mustang for track-day use?

Jeff Smith: When you get a really good tech question from a pastor, you have to answer it, right? So here goes, Pastor Mark. Let's dive into the lateral acceleration question first. I think your initial question has more to do with the huge difference between instantaneous g's and average g's. The numbers you mention from the track appear to be instantaneous g's compared with average g's generated during the on-track test. Instantaneous numbers are generated with a g-meter generally near the entry to a corner; these numbers are impressive, but average g's mean much more. For example, we could pull a 1.5 g on a banked course, but that really doesn't mean as much as it might if we did it on a flat surface. The typical lateral acceleration test used to generate an average number is obtained by driving the car on a 200-foot circle and measuring the elapsed time for each lap. The formula is:

Lateral acceleration = 1.227 x [radius / [time x time]

If our car produced an 11-second lap on a 200-foot circle, it would produce this result:

Lateral acceleration (g) = 1.227 x [100 / [11 x 11]
Lateral acceleration (g) = 1.01 g

This number is far more useful in helping to determine how well the car grips the road. However, with the driver located on the left side of the car, driving counterclockwise will almost always create a higher lateral g number than driving clockwise. That's why it's best to drive in both directions and average the numbers. But keep in mind that this test does not tell the whole story of handling. Since the suspension is constantly loaded, a skidpad test only evaluates it at the maximum loaded point. A better test is a slalom, where the car is almost constantly in transition. The time required to run the slalom is also an average and is dependent almost as much on the car's components as it is on driver skill.

To maximize handling, the idea is to be able to plant the tires to generate maximum cornering force. For example, with a car entering the corner, generally the movement of the front suspension is regulated first by the shock absorbers followed by the effect of both the front springs and the front antiroll bar. The springs and front bar determine the total suspension travel, which affects how much the camber changes (either positive or negative) with suspension movement. The springs allow the suspension to deflect, while the shocks determine how quickly or slowly that movement occurs. Changing the front (and rear) suspension to come up with an ideal combination is what determines "tuning" the suspension.

The quickest and most important way you can improve the handling of your car is to improve the traction between the car and the pavement with tires. Upgrading to a 16- 17-, or 18-inch tire and wheel package from a factory 15-inch wheel will do more to improve the handling of your car than any other single change. But traction will only help to the extent that the tires are limited by the suspension. Chassis upgrades will allow the front and rear suspensions to plant the tires properly during cornering. As is the case with most '60s and early '70s cars, under load, the front suspension tends to produce what is called a positive camber gain. This is what causes the car to understeer, or plow, in an aggressive corner. Imagine your Mustang in a hard lefthand turn. Normal weight transfer pushes more weight to the front-right corner, quickly compressing the soft coil spring and shock. This allows the suspension to compress. As this happens, the camber angle of the right-front tire tends to gain positive camber, which is the outward tilt of the top of the tire. This angle is the exact opposite of what is considered ideal for best handling. What is needed is a change in geometry with a modified upper control arm that will create a negative camber gain when the suspension is compressed. This is what occurs when you use components like Global West's tubular upper control arm for the Mustang. In fact, stock early Mustang suspensions were so poor that these cars were the first candidates for the Global West negative roll design back in the mid-'80s. This is similar but actually better than the old Shelby modification, which relocated the upper control arm mounting points. The Global West arms also relocate the mounting position of the upper arms but produce a much more aggressive curve. When combined with matched front and rear springs, adjustable shocks, a front sway bar, and better tires and wheels, the result is nothing less than amazing. While you may not be able to whip up on Ferraris, you could certainly dramatically improve the Mustang's current handling prowess.

More Info
Global West Suspension Components; San Bernardino, CA; 909/890-0759; GlobalWest.net

Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!
0 comments
Car Craft