This is a handling diagnostic compiled from several articles published in Race Car Engineering, Race Tech, and others. It is by no means definitive but gives a racer a starting place in an effort to diagnose a particular handling problem. Credit should be given to the authors instrumental in establishing this list: Carroll Smith, Mark Ortiz, John Hill, and others.
Instability
Straight line instability: (general)
1. Rear toe out: either static or bump steer.
2. Vast lack of rear downforce: unbalanced with front downforce.
3. Extreme front toe out/in.
4. Broken chassis member.
Straight line instability: (acceleration)
1. Malfunctioning limited slip unit.
2. Rear toe out.
3. Deflection steer from chassis flex or mounting point flex.
Straight line instability: (darts over bumps)
1. Excessive Ackerman geometry.
2. Excessive front toe settings (either in or out)
3. Uneven front castor setting.
4. Uneven front shock forces/bump rubber settings.
5. Front sway bar too stiff.
6. Insufficient rear wheel droop.
Straight line instability: (braking: front end wanders)
1. Too much front brake bias.
2. Excessive front shock REBOUND setting.
Straight line instability: (braking: car wants to spin)
1. Excessive rear brake bias.
2. Insufficient rear droop travel.
3. Excessive rear shock REBOUND setting.
4. Insufficient rear camber (negative).
5. Unbalanced ride/roll resistance: too much at rear.
Response
Unresponsive: (car feels heavy)
1. Tire pressures too low.
2. Too much aerodynamic downforce. (N.B. if car accelerates poorly at high
speed the problem may be a rear wing Gurney lip too high.)
Unresponsive: (car feels sloppy; will not take a set; rolls too much)
1. Insufficient shock settings.
2. Sway bars too soft.
3. Tire pressures too low.
Too responsive: little feel: slides too easily.)
1. Car too stiff for driver.
2. Excessive ride or roll resistance.
3. Excessive tire pressures.
4. Excessive shock settings.
5. Excessive rear toe settings (in or out)
6. Insufficient downforce.
Understeer
Corner entry understeer: (car will not point)
1. Excessive front tire pressures.
2. Excessive front roll stiffness.
3. Insufficient front shock BUMP setting.
4. Insufficient front downforce.
5. Excessive dynamic (bump) positive camber on outside front wheel.
6. Braking too hard and late.
7. Extremely insufficient front roll resistance.
Corner entry understeer: (car points, then washes out)
1. Excessive front toe settings (in or out).
2. Insufficient front wheel droop.
3. Insufficient front shock BUMP setting.
4. Improperly set shock packers (car rolls onto packers.)
Corner entry understeer: (car points, then darts)
1. Improperly set shock packers (car rolls onto packers.)
2. Insufficient front wheel travels.
3. Too efficient downforce: nose sucked down due to ground effect.
4. Excessive Ackerman steering geometry.
Corner exit understeer: (slow corners)
1. *Can be a function of improper response to corner entry understeer:
power application exacerbates the existing understeer condition.
2. Excessive load transfer rearward: increase rear ride/roll rate, or
reduce front shock LOW speed REBOUND rate.
Oversteer
Corner entry oversteer
1. Severe rearward ride/roll rate resistance imbalance.
2. Extreme lack of rear downforce.
3. Insufficient rear wheel droop travel.
4. Broken outside rear shock or rear sway bar.
5. Excessive rear toe in.
6. Excessive rear shock REBOUND setting.
Corner entry oversteer: (progressively worse with power application.)
1. Worn out limited slip unit.
2. Insufficient rear spring rate.
3. Insufficient rear sway bar rate.
4. Insufficient rear shock LOW speed BUMP setting.
5. Excessive rear roll stiffness.
6. Excessive rear negative camber.
7. Too little rear toe in.
8. Insufficient rear downforce.
**N.B. If the car feels as if it is sliding through the corner instead of rolling into it, try reducing rear toe in.
Corner exit oversteer: (suddenly breaks loose after set is taken.)
1. Insufficient rear suspension travel: (lifting inside tire due to droop limits,
or bottoming the outside tire due to bump limits.)
2. Dead rear shock.
3. Incorrectly adjusted rear shock packers.
4. Dynamic (bump steer) change in outside tire camber.
5. Improper throttle application (due to confidence level after car takes set.)
Corner exit oversteer: (can not put power down: smooth corners)
1. Excessive rear shock LOW piston speed BUMP setting.
2. Excessive rear tire pressure.
3. Excessive rear sway bar setting.
4. Worn tires.
5. Excessive dynamic (bump) negative camber change: either from
downforce or during squat situation.
Corner exit oversteer: (can not put power down: bumpy corners)
1. Excessive rear shock LOW piston speed BUMP setting.
2. Excessive rear tire pressure.
3. Excessive rear sway bar setting.
4. Worn tires.
5. Excessive dynamic (bump) negative camber change: either from
downforce or during squat situation.
6. Excessive rear shock REBOUND setting.
7. Insufficient rear droop travel.
Understeer in, snap to oversteer on power application.
1. Insufficient front roll resistance.
· front sway bar, front spring rate, and/or front shock BUMP setting
too low. Try increase in front shock BUMP setting as quick indicator.
· If increase in front roll resistance cures understeer but car still snaps to
oversteer, add rear sway bar and/or rear spring rate. Increase in rear
spring rate will decrease traction over bumps: increase in rear sway
bar rate will not.
2. Improper inflated shape of front tires.
3. Loose sway bar linkage or sockets.
Charlie Warner
Fatto Gatto Racing
Administrator