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Handling Tuning Table

Tuning a car for optimum handling is far from an exact science. Guides such as this one below are useful for summarizing the impact that certain components have on a car. However, it does not provide specific solutions considering the car, driver, and track conditions, or degree of change needed.

We expect to develop a more sophisicated set of scenarios with suggestions to try under certain conditions, not as exact solutions, but rather as examples of how to go about analysing and problem solving, and the possible options to try.

Until then, this table summarizes the basic purposes of suspension components and their effects on the car's handling.

Suspension Components and Handling Effects

Component

Function

Optimum

Too Little

Too Much

Springs

Maintains tire contact with the road surface over bumps and dips. Also, provides resistance to body roll.

As stiff as possible without the car bouncing off of the tops bumps.

The spring bottoms outs (the coils slam into each other under full compression). Too much body roll, sluggish steering response.

Too stiff won't allow the tire to comply to the road. The car will bounce off of bumps losing traction.

Shocks

To dampen the oscillations of the srping after traveling over bumps and dips.

Stiff enough to minimize oscillation to just one cycle.

If the shock is too soft, the car body will continue to bounce several times after a bump or dip, and will make the body very "sloshy" during braking, accelerating, and cornering. This will have an erratic effect on weight transfer and tire traction.

If bump is too stiff, it will prevent the spring from doing its job over a road bump. If rebound is too stiff it will prevent the tire from dropping to fill a dip. Overall if the shock is too stiff, it prevents the springs from working, and the car will be very difficult to control over bumpy surfaces.

Anti-roll Bar

Should be stiff enough to minimize body roll, balance roll coupling between the front and rear for equal front and rear tire grip in corners, and not cause wheels to lift off the ground during cornering.

The optimum setting is just enough stiffness to minimize camber change caused by body roll during cornering. This will allow the tires to stay as flat as possible for maximum contact patch.

Overall, as the body rolls, it changes the suspension geometry allowing the tire to tilt too much and reduce the contact patch size. Too soft a resistance on one end of the car compared to the other can cause the opposite end of the car to lose traction prematurely (also subject to springs, shocks, and tire pressure adjustments).

Overall, may cause an inside wheel to lift off the road surface during cornering. Excessive stiffness at one end of the car compared to the other end will cause the stiff end to lose traction before the opposite end (also subject to springs, shocks, and tire pressure adjustments).

Tire Pressure

Keeps the tire contact patch firmness on the road surface even across the width of the tire.

Just enough so that the surface temperature is even across the width.

The tire width will take on a concave shape, and the center will not be providing maximum possible traction. (The center temperature reading will be low)

The tire width will take on a convex shape, and the edges will not be providing maximum possible traction. (The center temperature reading will be high)

Camber

Adjusts the vertical angle of the wheel (the amount of tilt towards or away from the body). Some amount of negative camber which tilts the top of the wheel into the body is the norm for high performance cornering.

Maintains a flat tire contact patch during cornering to maximize grip for highest possible cornering speed. For street driving more than 1 degree negative camber will prematurely wear out the inside treads. For racing it's common to use as much as 3 degrees on a road course.

The deflection of the tire during corning will lift the inside edge of the tire off the track reducing the contact patch size.

The outside edge of the tire is prevented from reaching the track surface even under cornering, which reduces the tire contact patch. Also limits the contact patch available during accelerating and braking. Straight line driving will be less stable.

Front Wheel Toe

To stabilize the car in straight line driving, and to help steering responsiveness.

Viewed from the top of the car, toe is the amount of angle the wheel has relative to the front-to-back centerline of the car. It is measured by the difference in the distance between the front edges of the wheel rims versus the rear of the wheel rims. If the front edges are wider than the back edges, the toe is "out." If the front edges are closer together than back edges, the toe is "in." The units are length (inches, mm, etc.) rather than degrees.

For racing, front toe-out is preferred to increase steering responsiveness and help minimize understeer. However, this may make the car unstable in straight lines during street driving.

Optimally the front is a balance between straight line stability (acheived with toe-in) versus quick steering response (acheived with toe-out).

Sluggish steering response. Increased understeer.

Very nervous in straight line driving. The car will want to wander and is easily led by road surface features like seems, cracks, etc. Can also cause rapid tire wear.

Typical range is 1/8" to 1/4" total toe out. 1/4" can be extreme for the street.

Rear Wheel Toe

See Front Wheel Toe section above.

For most street and track applications, rear toe-in is preferred to stabilize straight line driving.

The rear of the car will be less stable in straight line driving.

Tire wear will be accelerated.

Typically the factory settings are suitable.

Coil Over Height

To adjust the height of each corner independently, thereby relocating the center of gravity and manipulating weight transfer.

Overall, each corner will be as low as possible, with one or more corners adjusted for maximum tire grip and overall neutral handling balance.

Not to be interpreted as too little, but a corner lower than the others will induce weight transfer to that corner increasing the load. This may be what is wanted.

Not to be interpreted as too much, but a corner higher than the others will induce weight transfer to the opposite corner decreaseing the load on the adjusted corner.

Testing Scenarios

Before getting into the test scenarios, one thing to be clear about is the general test methods to use. Analyse the handling performance of the whole track, look at tire temperature data, determine whether a slight, moderate, or major adjustment is needed. Remember -- change one thing, test, and re-analyse the data. If the change was not an improvement, set it back to where it was, and try something different. Always change one thing at a time. If the change was positive, but not perfect, then continue by adding smaller degrees of changes. For example, you might make a major change like switching to a stiffer rear sway bar, then add a moderate change by adjusting just the front shock settings up one notch stiffer, and finally make a slight teak with a right rear tire pressure drop of 1 psig.

To make major changes, adjust the alignment (usually toe & camber), change springs, change sway bars (different stiffness bars), or change shocks.

To make moderate changes, adjust shock settings of two or four wheels, make significant sway bar mounting adjustments by lengthening or shortening the mounting point by several positions, or make large tire pressure changes (>2psig). Small alignment changes could be considered moderate, but without the equipment and know how, this is really a major change for a hobbyist driver with a street car.

Slight changes are usually accomplished by adjusting tire pressure by 1 psig, adjusting the settings of one or two shocks, or making single position change on sway bar mounting length.

Laptimes and segment times are the final judge of performance improvements (along with tire wear). If you're tuning to get faster through section X, then be sure to time just section X to see if the changes are in fact improvements. Next, you'll want to know total lap times to make sure the improvements for section X didn't sacrifice time on the rest of the track for a net loss and slower lap time. Finally, you'll want to be sure the changes aren't causing accelerated tire wear.

Understeer entering sharp corners only

Driving
Technique

Brake earlier, ease off the brakes more gradually, possibly trail brake into the corner a little longer, and start the turn-in a little earlier with a smoother arc towards the apex.

This problem is common with inexperienced drivers. The tendency is to go for that awesome late brake, but the subsequent panicy turn-in causes the front tires to break traction and slide through the initial turn-in. Relax, and make the turn-in smoother.

If the problem is only with one or two corners, and the car handles well everywhere else, then driving technique is definately the recommended cure. Don't ruin a good handling setup to improve one or two minor corners using hardware changes.

Tire PSI

If the driving technique doesn't help, try a tire pressure tweak first. Two possible options: decrease the front, or increase the rear pressures. To decide which one to do, look at tire temperature profiles. In particular, look at the center temperatures. If the front center temps look a little high, then decrease the front tire psi by 1 psig. If the rear center temps look a little low then increase the rear tire pressure by 1 psig. Try one, then the other, if necessary. If neither works, put the pressures back to what they were.

Shocks

Two options: soften both front shocks, or increase the stiffness on both rear shocks.

If the trouble is only with left turns then try softening the left front shock, or stiffening the right rear shock.

If the trouble is only with right turns then try softening the right front shock, or stiffening the left rear shock.

If none of these changes works, restore the original setting before moving onto the next solution.

Springs

For this problem, a spring change is probably not suitable.

Anti-Roll Bar

Same as shocks: either soften the front, or stiffen the rear.

Alignment

Add another 1/16" more total front toe out.

Add another 1/4 or 1/2 degree negative camber. This is a big adjustement typically only suitable if all corners have big understeer.

Once we get more scenarios like this defined, we'll convert them to separate pages with a list to choose from. The solutions from Driving Technique to the various suspension components will be ordered in the preferred order of solutions.

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