Raceday Shock Tuning Advice From The Experts

Race car suspensions are a pretty complicated system of links, springs and shocks. A good combination of these components that are fine tuned to the track can be impressive, while a suspension that is not quite dialed in can put you in mid-pack or make you a back marker. We talked to the oval track shock experts at QA1 and AFCO Racing to find out what you need to know about fine tuning your suspension at the track with shocks for quicker lap times.

Understanding the Role of Shocks

Shocks affect the speed at which weight is transferred under braking and acceleration. Transferring weight too fast can make the car loose and make the front end light. (Photo by Ken Wagner of Wagtimes.com)

In a single word; handling. Shock absorbers play a significant role in the way a race car handles on the track. No matter if you are road racing, drag racing or oval track racing, shock absorbers control the rate of weight transfer. QA1 Sales Manager Corey Flynn tells us that “On the oval track, the role of shock absorbers is critical during cornering when weight is transferred from back to front under braking and then from front to back under heavy acceleration. Controlling that movement is crucial in getting your suspension to handle properly.”

It’s important to understand that shock do not have any effect on the amount of weight that is transferred but they do have a dramatic effect on how quickly the weight is transferred. The timing of this event may be instantaneous but it is a very important part of the handling response during that weight shift event.

Flynn cautions, “Drivers have different styles and preferences, so the set-up needs to be comfortable to the driver. Fine tuning with shocks should take place after you have narrowed your baseline set up with springs and linkage adjustments”.

According to AFCO Racing’s Oval Track Specialist, Ben Baker, “Chassis tuning is a compromise. There are many components that affect handling. Shocks, while a very important part of the set-up, are still only a part of chassis tuning.” Baker encourages racers to follow the chassis manufacturer’s guidelines for shock recommendations and fine tune the handling characteristics for each track’s individual characteristics.

Dirt track suspensions can be a complicated system of shocks, springs and links.

On the oval track, the role of shock absorbers is critical during cornering when weight is transferred from back to front under braking and then from front to back under heavy acceleration.

Let’s say you don’t know who the chassis manufacturer is or you have a chassis built by the local garage chassis builder, how do you tune your chassis with shocks? Most experts agree that using a 50/50 shock on all four corners will help you select the right springs before you fine tune the chassis with shocks. A 50/50 shock means that the compression and rebound rate are the same. Shocks that have different rates of compression and rebound are referred to as “split valve” shocks. Trying to tune your chassis with split valve shocks before making sure your spring rates are correct will most likely cause you to spend countless hours and laps chasing your setup.

AFCO’s Baker recommends using a regional shock dealer that knows the local tracks for help in getting dialed in. Knowledge of the track’s characteristics are important when setting up suspension. “Dirt on the East coast is different than dirt in the Midwest. Dirt in the Midwest is different than dirt in the Southwest. Our regional dealers have a much better feel for what the local track conditions are like and can help racers get their suspension set up more precisely,” says Baker.

Fine tuning not Major Changes

Baker and Flynn both agree that tuning suspension handling with shocks is more “fine tuning” to the existing track conditions rather than taking a big swing at correcting an ill-handling car.

An evil handling car is best sorted out with correct springs and weight distribution which means starting back at zero and putting the car on the scales. That’s another topic for another time. But if your car is anywhere from mediocre to “pretty close” to being hooked up, a shock change with different valving might get your car on rails around the track.

Looking at the cornering as three separate sections will help decipher handling issues. Viewing each end of the track as having an entry, mid-corner and exit is one of the easiest and common ways to breakdown the cornering.

 

First Phase: First Things First!

Flynn explained that the easy way to decipher handling problems at the track is to have someone designated to watch the car as it completes laps. “Looking at a set of corners as one complete end of the race track with an entry, mid corner and exit is the most common way of detecting a problem,” says Flynn, adding “A car that is loose or tight on exit or entry will be easier to spot when you view the turn as three equal sections.”

Baker added; “Always start tuning by concentrating on the problem that happens first in the turn.” Watching the car’s entry into the corner can tell you a lot. For example, if the car looks loose exiting the turn, it could be caused from a tight entry into the set of turns. A car tight on entry forces the driver to use extra steering input to drive through the push. That extra steering input makes the car loose from mid corner through the exit.” According to Baker, fixing the push condition on entry could make the loose exit condition go away.

Have your spotter check your car's attitude compared to the other cars around you on corner entry. If your car looks like the white #99 above, this is probably a sign of a loose on entry condition.

Second Phase of Cornering: Taking a Set

The second phase of the corner is roughly the mid corner or between 60 degrees to 120 degrees at the end of the track. Flynn explained, “This is where most dirt track race cars “take a set.” Somewhere in this area is where the driver is completely done with braking and should be getting ready to pick up the throttle again. The second phase of the cornering is where the race car is more influenced by chassis geometry and roll center than by shock valving.” As a spotter you should still be concerned with how the race car appears to handle in this phase of the cornering and decide whether it is a linkage adjustment/spring rate problem or if the car is loose or tight in this phase because of a condition in the first phase of cornering.

Third Phase of Cornering: Exit With Control and Speed

Fine Tuning in Phase 3

If your racecar is loose at the exit:

  • Decrease rebound in right front
  • Decrease compression in left rear
  • Increase rebound on right front
  • Increase compression on rear or right rear only

If your race car is tight at the exit:

  • Increase rebound in right front
  • Increase compression on rear or right rear only

Many problems will show up as the driver is coming out of a set of turns, and drivers will often complain about having to “wait on the car’s suspension” or being too tight or loose exiting the turn. Flynn and Baker reminded us that problems on exit may be a symptom of a problem that is happening earlier in the corner.

Once you are sure that the tight or loose condition on exit is not generated by a problem earlier in the corner, you can concentrate on trying to fine tune the problem at hand. As Flynn pointed out, “there are many adjustments on the race car chassis other than shock absorbers. An tight or loose condition can be caused by a combination of tire stagger, wheel spacing, spring rates, panhard bar adjustments or other things, so shocks adjustments should only be used to fine tune your suspension.”

To put it in layman’s terms, if your race car is wildly out of shape on exit or pushing straight up to the wall, a shock change is probably not going to eliminate the problem, but if you are looking for an extra couple of tenths on the track for a winning setup, a shock change can make the difference.

 

Getting Help

AFCO Racing’s Baker explained that it may “help to think in terms of softening or stiffening the shocks motion.” For example; increasing compression on a corner of the race car would be stiffening the compression, while decreasing the compression would soften the suspension at that corner.

QA1’s Flynn explained how a shock’s internal parts work to allow for different rates of motion:

“A shock resists motion when its shaft, and the piston assembly attached to the shaft, are moved causing fluid inside the shock to be forced through small orifices. Some of these orifices are always open and others are covered and allow fluid to pass through only when the fluid reaches a certain pressure. Since there is fluid on both sides of the piston, the shock is able to resist the movement caused by suspension travel. The size of the orifices and the pressure  at which the closed orifices become open dictate the stiffness of the shock at various piston speeds.”

This is referred to as “staged valving” and is helpful in suspension control by determining the rate of resistance required by the suspension when a tire goes over a large bump or a much smaller one.

Baker explained that shocks have different resistance levels at different piston speeds. “We check a shock’s resistance at a minimum of three different piston speeds. Checking resistance at low, medium and high piston speeds helps making a more precise determination on how the shock will affect the overall handling.”

The shock's valving, the size of the orifices and the pressure at which the closed orifices become open dictate the stiffness of the shock at various piston speeds.

About Shock Piston Speeds

For the best handling to occur, the resistance of the shocks at low, medium and high piston speeds must be matched to the needs of the race car and the track.

Baker broke things down into simple form for us. “Shock control at low piston speeds affect how the race car handles through the corners. Middle and high piston speeds affect how the race car handles whenever it encounters bumps and ruts.”

 

It’s All About Balancing The Traction

How the valve stack and piston are located on the shock shaft.

The traction capability of a tire will determine each individual tire’s influence on the race car. Traction capability is greatly affected by the load put onto the tire. Finding the right balance between left side and right side tires can be helped with shock absorber changes making the race car handle better through the corner.

Ben Baker offered these clues to managing traction:

1. Softening the rebound of the left side shocks will cause the left side tires to unload sooner during cornering. The balance of traction between the left and right side tires moves toward the right tires more quickly which results in the chassis becoming tighter on corner entry.

2. During acceleration, the balance of traction between the rear tires can be adjusted with shocks also. A softer left rear shock will quicken the weight transfer effect to the left rear tire during acceleration. The result is a left rear tire that has added influence initially in accelerating the race car off the corner. A race car will tend to be tight off the corner whenever the balance of traction between the rear tires favors the left.

3. Forward traction can be enhanced by softening the rebound control of the front shocks. This enhances the front to rear weight transfer process and helps to load the rear tires for improved forward traction. Keep in mind that a softer left front shock may tighten corner entry handling also.

4. Remember, shocks are a compromise like any other suspension component. Be careful when using split valve shocks with soft rebound controls so that handling over bumps and ruts does not suffer. Generally, side bite (cornering ability) can be improved by softening the shocks (and/or springs). This adjustment can stop the race car from skating up the corners on slick, smooth tracks.

8 Shock Tips from QA1’s Corey Flynn

1. When changing to a shorter track, softer valving all the way around usually will improve handling.

2. When changing to a track with a higher degree of banking, stiffer valving should improve handling.

3. When changing to a more flat track, slightly stiffer rebound on the left side and softening the rebound on the right side will generally enhance the handling of the car.

4. When measuring compressed or extended mounting lengths, measure from the center of the loops or from the shock shaft shoulder.

5. Keep dirt and debris out of shocks as much as possible by wiping the piston rod regularly. Use of a shock cover or shock shield may help.

6. Using the shocks as a travel limiter is extremely hard on the internal components of the shock. Consider installing a limit strap to reduce the wear and tear on your shock absorbers.

7. When mounting the shock away from the mounting bracket to gain extra clearance, use a smaller diameter spacer. Using large diameter washers or nuts could hit the shock bearing loop as it goes through suspension travel.

8. Before every race, check the clearance on all suspension arms, shocks and springs through the entire range of travel. The extra clearance could mean the difference in being competitive after contact with another car or a DNF due to a bent suspension component.

Balancing the traction is a compromise. If you don't have the traction balance, like the car in the photo above, you are probably going to be heading in the wrong direction.

Don’t Forget: It’s a Compromise

By changing the stiffness of the shocks on your race car, you can adjust the speed in which weight is shifted. This changes the loading of the tires at different points on the track. When done correctly, your race car will seem to be glued to the track and great handling will result.

Both our experts point out that chassis tuning is a compromise between many suspension components. Shocks are an important part of your chassis set-up, but they are only one part. Make sure that you aren’t wearing blinders when adjusting your suspension and take a look at the full picture.

Article Sources

About the author

Bobby Kimbrough

Bobby grew up in the heart of Illinois, becoming an avid dirt track race fan which has developed into a life long passion. Taking a break from the Midwest dirt tracks to fight evil doers in the world, he completed a full 21 year career in the Marine Corps.
Read My Articles

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