Chassis and Tuning Tips For Maximum Efficiency

Suspension Maintenance & Tuning Tips
For Maximum Efficiency
by
Tom Rix

EFFICIENCY: When changing the suspension or driveline components, what you are looking for is the LEAST amount of power to move the car the quickest!

AT HOME PREPARATION:

• Get car race ready: Tire pressure, shock settings, air bags, anti-roll bar, etc.
• Bounce car on all 4 corners. Listen and/or feel for any bind.
• Inspect all suspension components; including factory welds.
• Inspect tires, front & back. Rotate rear tires every race! Preserve the sidewalls.
• Measure the distance from the floor to the center of each fender wheel well and write it down. This is your baseline setting for future reference. “VERY IMPORTANT!” Any changes you make to the car will affect this!

THE TOW:

• Inflate rear tires to 25-30#. The tow is harder on the slicks if under inflated relative to actual racing tire pressure! Or you can tow with street tires and put the slicks on at the track.
• Inflate rear air bags to 20-25#.
• If using adjustable shock absorbers set them firmer for the tow. If a longer tow to the track consider changing at least the rear shocks to a firm street set.
• If you have a temperature gun, measure how hot the shocks get after a long tow! If the fluid gets too hot, 180 degrees +, it will lose its viscosity and effectiveness.
• Use 4 tie down straps; 2 at each end and criss-cross.
• Put the car as forward as possible on the trailer so it is supported by the trailer and tow vehicle suspensions.
• If it is too far back, consider additional measures to secure the car’s suspension.

AT THE TRACK:

• Return the car to race ready condition.
• Bounce on all 4 corners. Listen and/or feel for any bind.
(A simple trick once your car is “working” properly is to shut the car off on the return road after a pass and just coast. You will learn to identify the “normal” noises your suspension, transmission and rear end make while moving. Again, this gives you a baseline for future reference. I do this at least once every race day!)
• Measure the distance from the ground to the center of each fender wheel well and compare to your baseline settings.
• Mark white stripes on your front and rear tire sidewalls. This will be easy to see tire movement if you have someone watching or even better, video taping your run.

BURNOUT:

Pull through to the edge of the water box. Heat tires
enough to match the track temperature for maximum adhesion.
Remember the tires will “cool” a little from burnout to launch.
NO DRY HOPS!

STAGE:

Be consistent in your “spot”. I just barely turn on the
second yellow so I have consistent comparisons from run to
run.

Assuming all suspension pieces and tires are correct for your car
then proceed as follows:


STEP 1:

Make a pass. If the car violently wheel stands or bounces in
the gear change, adjust the front shocks first. If there is rear tire
shake, wheel hop, or excessive body separation, adjust the rear
shocks first.

STEP 2:

Adjusting front shocks. The goal here is to obtain a smooth
transition in the front end movement from the launch through
the first gear change. You want to eliminate all jerking and
bouncing movements.

Too loose a shock setting for extension can be diagnosed at the initial launch by a violent chassis separation and the front wheels jerking off the ground. During the gear change, loose shock settings for the extension and compression cause the car to bounce off its front travel limiter, fall down on the suspension and bounce back up again.

Too tight a shock setting for extension will keep the tires from easily lifting off the ground. During a gear change, a stiff shock in compression will cause the chassis to bounce off the tire when the chassis settles down.

To tune the shock, adjust the settings a little for each launch
until you have a smooth transition from launch through the gear
change. Watch your E.T. – if the time gets slower, back off the
shock adjustment a little bit.

STEP 3:

Rear shock adjustment. The goal is to shock the tire as hard
as track conditions will permit. Shocks control how large a force is put on the tire. Too loose a shock in extension causes excessive separation between the tire and body. Too tight a shock in extension or compression will cause high tire shock loads and cause extreme flattening of the tire. To tune the shocks, tighten the adjustment a little per pass.
Again, watch your E.T., then back off the adjustment a little bit.

KEEP RECORDS:


Write down all track and weather conditions, chassis settings,
tire pressure, engine oil and water temperature, and transmission temperature if available. Include carb jetting, timing, transmission shift points, EGT’s orO2 sensor data if available.

On your time slip not only compare 60’,330,660’,1000’ and 1320’, ET and MPH from one run to another, but more importantly compare the difference between these incrementals: i.e. – subtract 60’ time from the 330’ time so you know how long it took between those points.

If you pick up .04 in ET, you need to understand at what point(s) on the track you improved. I pay attention more to the 330’ time when making comparisons from one track to another as 60’ clocks can vary. If racing/testing at the same track, then 60’ is more meaningful. Almost all chassis changes will show up in the first 330’.

HAVE FUN!!!


OTHER TIRE TIPS:


Remember that your 2 rear tires act like an extra “set” of shock
absorbers. Tune with them also. According to Dave Morgan,
most sportsman/bracket cars run with too little air!

Learn to read the pattern on your tires. You are looking for a slight
“grainy” pattern straight across the entire tread.

If you video tape your launch pay close attention to the sidewall of
slick. As you watch the car launch from the driver’s side you
want the “wrinkles” to be from the 9 o’clock position down to
6 o’clock position or slightly past on the tire! This is what
works best for me.

The white stripe on the front tire tells you if you “dead hooked”
(pulled front tires straight up out of the beams) or drove
forward as the car hooked. See how fast the white stripe
rotates in the air to gauge this.

Tire screws, if you use them, make sure they are indexed from side to
side. Absolutely critical!

Check tire circumference with a tape. They need to be within a ¼ “of
each other

Rotate frequently!


I would like to acknowledge Dave Morgan for his Chassis Seminars, Books and Videos. Many of the concepts discussed here come directly from his literature and classes as applied to my race car operation.

I would also like to acknowledge Chris Alston Chassis Works especially regarding shock absorber concepts. http://www.cachassisworks.com/