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Car Setup and Troubleshooting Guide
Taken from the book "Performance Handling" by Don Alexander (Motorbooks Intl. Publishers)
[
Suspension Changes ] [Tire
Temperatures ] [Solving Handling Problems ]
Effect of Suspension Changes
Before making
changes to suspension components and settings, it is good to know how the
changes will effect performance and ride. The following chart will help give
you a general idea of the effect a specific change will make to handling and
ride.
Spring Rate Changes |
|---|
| Modification | Effect on
Suspension |
|---|
| Increase front and rear
rate |
Ride harshness
increases; tires may not follow bumps causing reduced traction. Roll
resistance increases. |
| Increase front rate
only |
Front ride rate
increases. Front roll resistance increases, increasing understeer or
reducing oversteer. |
| Increase rear rate
only |
Rear ride rate
increases. Rear roll resistance increases, increasing oversteer or
reducing understeer. |
| Decrease front and rear
rate |
Ride harshness
decreases; tires follow bumps more effectively, possibly improving
traction. Roll resistance decreases. |
| Decrease front rate
only |
Front ride rate
decreases. Front roll resistance decreases, decreasing understeer or
increasing oversteer. |
| Decrease rear rate
only |
Rear ride rate
decreases. Rear roll resistance decreases, decreasing oversteer or
increasing understeer. |
Antiroll Bar Changes |
|---|
| Modification | Effect on
Suspension |
|---|
| Increase front
rate |
Front roll resistance
increases, increasing understeer or decreasing oversteer. May also reduce
camber change, allowing better tire contact patch compliance with the road
surface, reducing understeer. |
| Increase rear
rate |
Rear roll resistance
increases, increasing oversteer or decreasing understeer. On independent
rear suspensions, may also reduce camber change, allowing better contact
patch compliance with road surface, reducing oversteer. |
| Decrease front
rate |
Front roll resistance
decreases, decreasing understeer or increasing oversteer. More body roll
could reduce tire contact patch area, causing understeer. |
| Decrease rear
rate |
Rear roll resistance
decreases, decreasing oversteer or increasing understeer. On independent
rear suspensions, more body roll could reduce tire contact patch area,
causing oversteer. |
Shock Absorber Changes |
|---|
| Modification | Effect on
Suspension |
|---|
| Increase rebound and
bump rates |
Ride harshness
increases. |
| Increase rebound rates
only |
On bumps, tires may
leave track surface. |
| Increase bump rates
only |
Body roll resisted;
outside tire loaded too quickly; car won't stabilize into a
turn. |
| Decrease rebound and
bump rates |
Ride harshness
decreases; car may float over bumps. |
| Decrease rebound rates
only |
On bumps, tires follow
track surface more effectively; car may continue to oscillate after
bumps. |
| Decrease bump rates
only |
Body rolls quickly; car
is slower to respond to turn-in. |
[
Suspension
Changes ] [Tire Temperatures ] [Solving Handling
Problems ]
[
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The Importance of Tire Temperatures
In the course
of testing the handling of a car, use tire temperatures and driver feel to
make adjustments. It is critical to monitor tire temperatures often. They
offer valuable clues to the setup of the car. The areas of adjustment that
tire temperatures are used for include: tire pressure, camber, body roll,
shock settings, wheel width and transient handling
response.
Troubleshooting Tire Temperatures |
|---|
| Reading | Handling
problem | Reason |
|---|
| All tires too
hot |
|
Compound too soft for
track and ambient temperature conditions. |
| Front tires too
hot |
Understeer |
Front tire pressures
too low. |
| Rear tires too
hot |
Oversteer |
Rear tire pressures too
low. |
| Inside edges too
hot |
Too much body
roll |
Too much negative
camber or too much toe-out. |
| Outside edges too
hot |
Too much body
roll |
Too little negative
camber, too little toe-out or too much toe-in or wheel width too narrow
for tire width. |
| Center of tread too
hot |
|
Tire pressure too
high. |
| Edges on too
hot |
|
Tire pressure too
low. |
| All tires too
cold |
|
Compound too hard for
track and ambient temperature conditions or car not being driven to
limit. |
| Front tires too
cold |
|
Inadequate load on
front tires. |
| Rear tires too
cold |
|
Inadequate load on rear
tires. |
[
Suspension Changes ] [Tire
Temperatures ] [Solving Handling Problems ]
[
Back to Top ]
Solving Handling Problems
The key to
setting up your suspension is in diagnosing what the handling problems are and
resolving how to fix them. While car enthusiasts often baulk at the "black
art" of suspension tuning, there's no reason to. As with working on the
mechanical aspects of an engine, the trick to suspension tuning is in the
troubleshooting; there is always a cause and an effect.
Solving Handling Problems |
|---|
| Problem | Manifestation | Solutions |
|---|
| Steady state
understeer |
All turns or low-speed
turns only |
If front tire temps are optimum and rears are low, stiffen rear antiroll bar; if front temps are too hot, soften front (most likely).
If front tire pressures are optimum, decrease rear tire pressure. Increase if chunking occurs.
Improper front camber.
Too much body roll at front, causing excessive camber
change.
|
| Steady state
understeer |
High-speed turns
only |
If front tire temps are OK, increase front downforce.
If front tire temps
are too hot, reduce rear downforce.
|
| Steady state
oversteer |
All turns or low-speed
turns only |
If rear tire temps are optimum, with fronts too low, stiffen front antiroll bar; if rear temps are too hot, soften rear antiroll bar (most likely).
If rear tire pressures are optimum, decrease front tire pressure. Increase if chunking occurs.
Improper rear camber.
|
| Steady state
oversteer |
High-speed turns
only |
If rear tire temps are OK, increase rear downforce.
If rear tire temps
are too hot, reduce front downforce.
|
| Corner entry
understeer |
|
Front shocks are too soft in bump resistance.
Too much front toe-in;
use a small amount of front toe-out.
|
| Corner exit
understeer |
|
Rear shocks are too soft in bump.
Front shocks are too stiff in
rebound.
|
| Corner entry
oversteer |
|
Rear shocks are too soft in rebound.
Rear ride height is too high (too
much rake) compared to front.
|
| Corner exit
oversteer |
|
Rear shocks are too soft in rebound.
Too much rear toe-in or any rear
toe-out.
|
| Straightline
instability |
|
Tire pressure is too low in one or more tires.
Too little positive front caster.
Too much front toe-in or any toe-out
in rear.
|
| Straightline speed too
slow |
|
Too much overall downforce.
Too much toe-in or toe-out.
Ride height is too hight.
|
| Excessive steering
effort |
All turns |
Too much positive caster.
Front tire pressures are too
low.
|
| Chassis or suspension
bottoms |
|
Spring rates are too soft.
Shock absorber bump rates are too soft.
Inadequate suspension travel.
Inadequate ride
height.
|
[
Suspension Changes ] [Tire
Temperatures ] [Solving Handling Problems ]
[
Back to Top ]
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