Tips / Troubleshooting

How To Shock Tune Your Chassis

Study the current Bilstein set-up recommendations for your particular type of racing. These combinations are tested and proven successful, but due to the many variables that come into play under racing conditions, it is to your advantage to have a basic understanding of how shock damping rates affect your lap times. Adjustments can then be made with reason and understanding.

Simply stated, shock absorbers convert the kinetic energy of the spring movements into heat. This heat is then dissipated into the air through the shock tube or body. In practical application, shock absorbers are necessary to maintain maximum tire patch contact to the track as the car corners and negotiates irregularities on the racing surface.

Spring rates determine how far your chassis rolls, pitches or squats. Shock rates determine the length of time it takes for each of these movements to occur.

Rebound damping controls the movement of that part of the car's sprung mass that is stored in a compressed spring. The rebound damping rate determines how long it takes for the compressed spring to return to the static ride height. The larger the rebound figure, the more the shock resists the compressed spring's effort to rebound, and the longer it takes for the chassis to return to the static ride height.

Compression damping controls only the oscillation of the car's unsprung weight. Therefore, it is normal to use less compression damping than than rebound damping. The exception occurs when we choose to slow the downward movement on a particular corner of the car to mimic the effect of a stiffer spring.

Here are some guide lines to use when shock tuning your chassis at the track or making the best decision during initial set-up. We are making the assumption that you have removed as many variables as possible and are using the best combination of springs, weight, wheel spacers, tire compound, stagger, etc.

Utilizing the "Think Track" below, study the following list of suggestions. These are not rules, not even rules of thumb, but they are tendencies that are more often true than not when racing late models and modifieds on asphalt or dirt.

All you have to do is determine what you want the car to do from entry to exit. Just think it through!

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Trouble Shooting The Car On The Track

If your car is:

Loose (Over steer) from 0 degrees to 45 degrees

Increase compression rate on front. Decrease rebound rate on rear, or only on left rear.

Tight (Under steer) from 0 degrees to 45 degrees

Decrease compression rate on front. Increase rebound rate on rear, or only on left rear.

Loose (Over steer) from 45 degrees to 135 degrees

Decrease rebound rate on right front. Decrease rebound rate on left rear. Decrease compression rate on rear, or only on right rear.

Tight (Under steer) from 45 degrees to 135 degrees

Increase rebound rate on right front. Decrease rebound rate on left front. Increase compression rate on rear, or only on right rear.

Loose (Over steer) from 135 degrees to 0 degrees

Decrease rebound rate on front. Increase rebound rate on left rear. Decrease compression rate on rear, or only on left rear.

Tight (Under steer) from 135 degrees to 0 degrees

Increase rebound rate on front. Decrease compression rate on rear.

 

When analyzing corner entry, or deceleration handling, realize that the chassis is affected by:

Compression rate in front ..........&.......... Rebound rate in rear.

 

When analyzing corner exit, or acceleration handling, realize that the chassis is affected by:

Rebound rate in front ..........&.......... Compression rate in rear.

..

Bilstein shocks are famous for their superior performance on very rough asphalt or rutted dirt tracks. You may need to choose a shock with more compression damping than found on the set-up-sheets under extreme rough track conditions.

Keep in mind that there are many adjustments on your chassis other than shock absorbers. The over steer  /  under steer balance may be affected by stagger, tire compound, wheel spacing, spring rates, sway bar, pan hard and others. Shocks can be used to fine tune your chassis to gain that last few tenths of a second on the track.


Trouble Shooting Your Chassis

 
Loose Car on Entry

·   Stiffen compression on right front shock

·  Stiffen the right front spring

·  soften up the left front spring 

·  Use a larger stabilizer bar

·  decrease the caster

·  lower the pan hard bar

·  decrease the rear brake bias

·  decrease rear stagger

·  increase the diagonal weight percentage

·  decrease upper control arm angle on rear end

Loose car on exit

·  decrease the right rear spring 

·  decrease right rear shock

·  increase left rear spring

·  lower the pan hard bar on both sides

·  increase stabilizer bar pre-load

·  use a larger stabilizer bar

·  increase the angle of the upper trailing arm

·  increase the rear weight bias

 
 
Troubleshooting The brake system
 
loss of pedal during a race

·  Inadequate ducting- reposition or increase ducting

·  incorrect or bad master cylinder- change master

·  undersize brake system-change caliper or master

·  boiling fluid-replace fluid flush system

Brake Drag

·  bad master cylinder-replace master cylinder

·  warped rotors-replace rotors w/ new ones

·  calipers not square to rotors-reposition calipers

·  frozen piston-rebuild calipers, replace o-rings

Have to push too hard on pedal

·  Too large of master- put a smaller one on

·  wrong pad material-use a more

aggressive brake pad

·  frozen piston-rebuild calipers, replace o-rings

Spongy pedal or bottoms out

·  air in system- bleed brakes

·  faulty master-replace master

 Oscillation feed back in pedal

·  Excessive rotor run out-replace rotor

·  build up on rotor or pad-clean rotors

and replace pads

·  cracked rotors-replace rotors

·  excessive front bearing clearance-check

and tighten spindle Nut

pushing on entry

·  soften up the front springs

·  raise the pan hard bar

·  increase caster

·  increase the left front spring rate

·  decrease the right front spring rate

·  increase the rear tire stagger

·  increase rear brake bias

·  use a smaller stabilizer bar

·  decrease the pre load on the stabilizer bar

·  decrease the diagonal weight percentage

Pushing on exit

·  increase the right rear spring rate

·  use a smaller stabilizer bar

·  decrease the preload on stabilizer bar

·  decrease the split on the pan hard bar

·  decrease the left rear spring rate

·  increase the rear stagger

·  decrease  angle of the upper control arm

·  decrease the rear weight bias

Shock therapy

increase compression...

·  on rf when car is loose on entry

·  on lf when car is pushing on entry

·  on lr when car is loose on exit

·  on rr when car is pushing on exit

·  on rf &rr when  feels like it is rolling over

·  on lr & rr when car is pushing on exit

decrease compression...

·  on rf when pushing on entry

·  on lf when loose on entry

·  on lr when pushing on exit

·  on rr when loose on exit

·  on lf & RF when pushing on entry

·  on lr & rr when loose on exit

increase rebound...

·  on lf when loose exit

·  on rF when pushing on exit

·  on lr when pushing on entry

·  on rr when loose on entry

·  on lf & lr when  feels like it is rolling over

decrease rebound...

·  on Fr when loose on exit

·  on lf when pushing on exit

·  on lr when loose on entry

·  on rr when pushing on entry

 

 

Learn Your Tires
The key to success to largely relies on your tire education.  If you want to win on a consistent basis, you need to keep good notes and learn about you tires.  With all the different makes and model of tire, there is no "cast in stone" way to take care of your tires.  You need to keep track of your tire purchases, how you stretch them, and how they grow.  Take good notes of what happens to the sizes of the tires each time you do them, and try to find out what will make them the most consistent. Consistency is the key to success.