Tuning Guide

Section A: Common handling problems and causes

Over steer: Corner Entry Over steer

• Too much rear brake bias
• Rear roll center too high
• Excessive rear stagger
• Insufficient cross weight
• Right rear tire pressure too high
• Right front spring rate too soft
• Right rear spring rate too stiff
• Left front spring rate is too stiff. A softer left front spring rate tightens car at turn entry.
• Right front shock compression damping is too soft
• Paved track - rear roll over steer created by suspension links
• Rear roll over steer caused by rear end housing not square
• Front track width too narrow relative to rear track width
• Axle damper shock is offset to left of weight centerline
• Bent shock absorber shaft at right rear
• Suspension linkage bind at right rear
• If car is equipped with brake floaters:
• Right link does not have enough uphill angle
• Left link has too much uphill angle
• Paved track: front anti-roll bar is too soft
• Paved track - front anti-roll bar doesn't have enough preload

Mid-Corner Over steer

• Right rear tire pressure too high
• Insufficient cross weight
• Rear roll center too high
• Excessive rear stagger
• Rear suspension linkage bind or bottoming
• Right rear spring rate too stiff
• Driver purposely loosened up car to overcome initial corner under steer
• Rear end tracking: rear end housing is shifted to the right relative to front track width

Corner Exit Over steer

• Excessive rear stagger
• Insufficient cross weight
• Excessive right rear tire pressure
• Front track width too narrow relative to rear track width
• Rear roll center too high
• Left rear spring rate too soft
• Right rear spring rate too stiff
• Insufficient torque link downhill angle Torque link is mounted to right of weight centerline
• Excessive torque link spring preload or torque link spring is too stiff
• Rear end tracking: rear end housing is shifted to the right relative to front track width

Under steer Corner Entry Under steer

• Too much front brake bias
• Excessive right front tire pressure
• Excessive right front negative camber or excessive right front positive camber (camber curve places tire patch on one edge or the other)
• Excessive toe-out
• Excessive cross weight
• Insufficient rear stagger
• Rear roll center too low
• Right front spring too stiff
• Right rear spring too soft
• Left front spring rate too soft. A stiffer left front spring loosens car at corner entry and corner exit because it subtracts cross weight from chassis
• Front weight percentage is too high
• Paved track - too much anti-roll bar preload
• Paved track - front anti-roll bar too stiff
• Rear roll under steer created by suspension links
• Rear roll under steer caused by rear end housing not square
• Front track width too wide relative to rear track width
• Use right front wheel with more backspacing or remove wheel spacer at right front
• Car pushes at turn-in: right front shock compression damping too stiff
• Bent shock absorber shaft at right front

Mid-Corner Under steer

• Insufficient rear stagger
• Excessive cross weight
• Rear roll center too low
• Rear end tracking: rear end housing is shifted to the left relative to front track width
• Corner Exit Under steer
• Excessive cross weight
• Insufficient rear stagger
• Rear roll center too low
• Driver is applying too much throttle too quickly
• Left rear spring is too soft
• Right front shock or both front shocks too soft in rebound damping
• Right rear spring too soft
• Right front spring too stiff
• Torque link is mounted to left of weight centerline
• Excessive torque link downhill angle
• Rear end tracking: rear end housing is shifted to the left relative to front track width

Corner Transition - Loose at corner entry, pushing at corner exit

• Too much rear brake bias loosens up chassis at corner entry
• Car may be loose at corner entry and corner exit, but driver uses an early apex which causes a push at mid-corner and corner exit
• Use a softer left front spring to tighten car at corner entry
• If car is still tight at corner exit:
• Increase right rear tire pressure by 1 to 2 PSI
• Take out a small amount of cross weight at left rear

Chassis does not react to adjustment

• Chassis is flexing

Instability

• Instability under braking at corner entry
• A high speed chatter at the right front is caused by torsional wrap-up of linkages holding spindle
• Lower control car, strut rod and support brackets are too light and thus flex

Car is darty on straight-aways

• Not enough toe-out

Car wanders on straight-aways

• Insufficient positive caster

Not enough steering feel or feedback during cornering

• Insufficient scrub radius at right front and left front

Braking System - Braking power diminishes during race (pedal gets soft)

• Fluid boiling due to moisture contamination
• Fluid boiling due to driver's foot dragging on pedal
• Caliper leak or Brake line leak
• Calipers and/or rotors are undersized for application
• Inadequate (or no) air ducting in severe braking application

Spongy pedal

• There is air in the system which is compressing. Bleed the system thoroughly.
• Calipers not bled with bleed screws straight up
• Fluid may be boiling because of water contamination. Drain the system, flush, and replace with new racing quality fluid (570-degree dry boiling point). Fluid will also boil because of overheated brakes caused by thin rotors, wrong pad material or brake drag.
• Master cylinder bore size too small or Pedal ratio too high
• Check for leaks at bleed screws and line connections
• Check for flex line ballooning under pressure. Apply heavy brake pressure
• on the pedal, and visually check all flex lines.
• Check for misaligned caliper. This can be spotted by tapered wear on pads, or if the caliper moves when the brake pedal is applied.
• Excessive caliper flex. Braking system-operating pressure should not exceed 1,500 PSI.

Instability under braking at corner entry

• High amount of anti-squat causes rear wheel hop under heavy braking
• To prevent this, keep anti-squat under 75%, and use an axle
• damper shock mounted above rear end center section angled uphill at 5 to 7 degrees

Pedal chatter, vibration or knocking

• Primarily caused by rotor distortion. Check lateral run-out and caliper being mounted parallel with rotor.
• Pad material build-up on rotors
• Caliper mount is loose
• Cracked rotor
• Excessive front bearing clearance
• Could also be caused by worn suspension components, such as tie rod ends, ball joints or lower A-arm bushings.

Pedal fades as brakes are applied

• Check for fluid pressure leak at internal primary seal in master cylinder.
• Check for fluid leakage at line connections or along lines.
• Check for leakage at piston caliper seals.
• Friction pad material too soft

Low pedal, but pedal pumps up

• Low brake fluid level
• Excessive free play in the pedal linkage
• Pads are worn, causing excessive fluid use
• Rotor lateral runout or parallelism problem

Brakes drag or lock

• Master cylinder pressure relief hole clogged by a small piece of dirt. This hole can also be blocked if the master cylinder piston does not fully retract.
• Pedal return spring is weak or missing Insufficient pedal free play
• Linkage bind preventing full return of pedal against its stop Caliper piston seized
• Improper caliper alignment to rotor Distorted brake pad, or wrong brake pad being used
• Tapered brake pads
• Warped rotor
• A 10-pound residual pressure valve is being used causing brake drag. Use a 2-pound valve.

Rapid brake pad wear

• Pad friction material is too soft or the wrong compound is being used for the rotor operating temperature
• Rotor surface is rough or cracked

Excessive pedal effort or excessive stopping distance

• Master cylinder bore size is too large
• Pedal ratio is too low. Use at least a 6 to I pedal ratio
• Pad material is too soft
• Pad has glazed over
• Pad material has not been bedded in correctly
• Frozen piston(s) in caliper
• The mount of the master cylinder is not rigid enough, causing deflection
• Brake pedal linkage is not rigid enough, causing deflection
• Pads worn out
• Grease leaking on rotors
• Wrong braking system for the car. Many times racers choose a light-duty system to save weight but it is not heavy duty enough for the application

Caliper leak

• Dried out or old caliper seal
• Nick on piston

Brake bias changes during brake application

• Brake balance bar improperly adjusted. Adjust the master cylinder push rods so the bias-adjusting shaft is parallel to the master cylinder-mounting surface when the brake pedal is fully depressed. When the pedal is retracted, the bias-adjusting shaft may not be parallel.

Chassis Tuning With Shock Absorbers

• Note: Shock absorbers influence how quickly weight is transferred. They have no affect on the amount of weight transferred. Shocks influence handling during transitions - braking, accelerating and cornering.

Corner entry over steer

• Stiffen right front compression and reduce left rear rebound -Momentarily reduces weight transfer from left rear to right front
• May need to use a split valve shock at left rear such as a 5/3 or 6/4 (compression/rebound)

Mid-corner over steer

• Decrease left rear rebound
• Decrease right rear compression

Corner exit over steer

• Need to get weight to transfer quicker from right front to left rear
• Use softer right front rebound and softer left rear compression

Corner entry under steer

• Reduce rate of weight transfer from left rear to right front
• Use stiffer left rear rebound
• May need to use a split valve shock at left rear such as a 416 (compression/rebound)

Mid-corner under steer

• Decrease rebound at left front Corner exit under steer
• Reduce rate of weight transfer from right front to left rear

Section B: Front Suspension Camber

• Softer right front spring rate allows more wheel travel. The more body roll a car experiences, the more negative camber gain required in bump travel at night front
• Larger and softer (more flexible) tires require more negative camber gain per inch of bump travel at right front
• Too much or too little right front negative camber means tire contact patch is not flat on track during cornering. Generally causes under steer and reduced braking capability.
• Too much negative camber at right front causes excessive inside tire heat and wear
• The more static negative camber used, the greater the temperature differential between the inside and outside edges
• An insufficient amount of negative camber at right front causes excessive outside tire heat and wear

Caster

• Increased positive caster enhances front steering stability
• A larger positive caster angle increases steering effort
• Negative caster is a destabilizing element
• Positive caster combined with steering axis inclination causes the left front corner to rise and the right front corner to drop as the car is steered left . This jacks weight into the left front and right rear and loosens up the chassis. Takes cross weight out of chassis when wheels steered left.
• The amount of left front positive caster will dictate how much the chassis loosens up at corner entry and mid-corner
• If a car is tight at corner entry, use more positive caster at the left front

Toe-out

• The adjustment range for toe-out is 1/16-inch to 3/16-inch
• Never use less than 1/16-inch toe-out
• Adding more toe-out will add under steer to the chassis at corner entry and mid-corner
• An excessive amount of toe-out will cause tire scrub both on the straight-aways and during cornering Rear Suspension

Rear Panhard bar

• Lowering bar lowers rear roll center
• A lower rear roll center tightens up chassis
• Raising bar raises rear roll center
• A higher rear roll center loosens up chassis
• When Panhard bar is raised or lowered to adjust roll center height, both ends of bar should be moved to avoid changing bar angle• More downhill angle tightens up chassis
• Paved track Panhard bar with right side chassis mount:
• Increasing bar angle (right side higher) loosens the chassis
• Decreasing bar angle tightens up the chassis

3-point suspension lower links

• An uphill mounting angle of the lower links promotes increased forward traction under acceleration
• More forward uphill angle on the lower links creates a harder, quicker bite under corner exit acceleration
• A moderate amount of uphill angle (such as 5 degrees) will produces slightly less initial traction, but will maintain the bite down the straightaway longer
• The amount of uphill angle has practical limitations due to excessive roll steer and higher amounts of anti-squat produced
• If both lower links are mounted at 5 degrees uphill, enhanced forward traction is achieved. It also creates a slight amount of roll over steer during cornering.

3-point upper link

• On pavement, with an 18 to 20-inch length, the link should be 5 degrees downhill. The adjustment range is 3 to 7 degrees.
• Adding more downhill angle tightens up the chassis under acceleration
• More downhill angle increases initial forward traction but the hook-up doesn't last as long with a greater angle

Third link lateral mounting position

• The upper third link should be mounted at the center of the lateral weight mass of the car
• If the third link is mounted to the right of weight center, under acceleration it adds more loading to the right rear tire and unloads the left rear by the same amount. This makes car looser at corner exit.
• If the third link is mounted to the left of weight center, under acceleration it adds more loading to the left rear tire and unloads the right rear by the same amount. This makes car tighter at corner exit.

Rubber bushing torque link tuning

• Adding or subtracting preload to the rubber bushings diminishes or increases link travel. The spring rate of the bushings is varied by changing the preload on the bushings. The ideal travel length is 1.5 inches.
• A type of track that provides good traction - asphalt or tacky dirt - requires more preload to reduce link travel
• A track where rear tire traction is very delicate - such as dry slick dirt - requires more link travel and less preload.

Spring loaded torque link

• The proper spring rate is determined by the amount of spring travel under acceleration
• Ideal paved track link travel is .5-inch with .5-inch preload on the spring.
• Adding preload to a torque link spring stiffens the spring rate and decreases link travel.

Paved track spring rates:

• Paved tracks require 900 or 1050' spring rate
• Tire type and final gearing affect required spring rate. If less than 1/2-inch travel is experienced, use a softer spring rate. If more than 112-inch travel, add preload. If more than 1 -inch travel, use stiffer spring rate.

Axle damper shock mounting

• If shock is mounted to left of vehicle weight centerline, car will be looser under braking at turn entry
• If shock is mounted to right of vehicle weight centerline, car will be tighter under braking at turn entry
• The rear tire with the most load under braking at corner entry will try to pull the car in that direction.
• If left rear has better traction under braking, car will be looser
• If right rear has better traction under braking, car want to turn right which creates under steer
• A distance of 6 inches to either side of weight centerline tends to have an influence on handling
• Normal uphill angle is 5 degrees - dirt and asphalt tracks
• More angle tightens the chassis under braking at corner entry
• Less angle loosens the chassis under braking at corner entry
• If rear end lightness and wheel hop continues at corner entry braking, add more axle damper uphill angle
• Do not exceed 9 degrees on pavement

Swing arm suspension link angles

• More uphill angle of both left rear and right rear lower links creates more roll over steer.
• 4-link suspension link angles
• Excessive left rear upper link uphill angle creates under steer
• Increasing downhill angle of lower links reduces roll over steer and increases indexing
• Reducing uphill angle of right rear upper link reduces roll over steer and decreases indexing
• Increasing uphill angle of right rear upper link increases roll over steer and indexing. The adjustment range is 14 to 18 degrees.
• Attaching the left rear spring to a clamp bracket adds cross weight and tightens the chassis under acceleration.
• Attaching the left rear spring to a clamp bracket reduces cross weight and loosens the chassis under deceleration
• Clamp bracket works best on a tight slick track

Rear end housing squaring

• Rear end housing must be squared perpendicular to chassis centerline to prevent roll steer during cornering.
• If static setting of housing places right rear wheel behind the left rear, roll over steer will result
• If static setting of housing places left rear wheel behind the right rear, roll
• under steer will result

Spring Rates Right front spring

• Stiffer rate makes car tend toward under steer
• Softer rate makes car tend toward over steer

Left front spring

• Softer rate tightens car at comer entry
• Stiffer rate loosens car at turn entry and turn exit

Right rear spring

• Stiffer rate makes car tend toward over steer
• Softer rate makes car tend toward under steer

Left rear spring

• Stiffer rate makes car tend toward under steer
• Softer rate makes car tend toward over steer
• Stiffer left rear spring tightens car from middle of turn and through corner exit

Chassis Tuning Elements Stagger

• More stagger loosens up a car at corner exit and corner entry
• Less stagger tightens up the chassis
• Stagger affects handling more when the car is under acceleration
• The tighter the track's turn radius, the more stagger required
• The flatter the track banking angle, the more stagger required
• Changing stagger is a more chassis-sensitive adjustment than changing cross weight
• If a car does not respond to small stagger changes, there are some other basic problems in the car, such as spring rates or weight distribution
• A one-inch difference in tire circumference makes a 5/16-inch difference in tire height
• Using more cross weight generally requires more stagger
• Don't try to correct all chassis handling problems with stagger

Cross weight

• More cross weight makes a car tend toward under steer
• Less cross weight makes a car tend toward over steer
• Changing stagger affects the amount of cross weight in a chassis
• Using a smaller circumference tire at the right rear (less stagger) will increase cross weight
• Using a larger circumference tire at the right rear (more stagger) will decrease cross weight

Tire pressure More air pressure:

• Makes the sidewall stiffer
• Reduces tire contact patch size
• Increases tire circumference and tire height

Less tire pressure:

• Makes the sidewall more flexible
• Increases the tire contact patch size - Reduces tire circumference and tire height
• A higher tire pressure at the right rear will loosen the chassis
• A lower tire pressure at the right rear will tighten the chassis
• A higher tire pressure at the right front will tighten the chassis
• A lower tire pressure at the right front will loosen the chassis
• A lower tire pressure at the left rear will tighten the chassis
• Keep a constant check on tire pressures - Racing tires bleed down constantly - Check and adjust pressures just before the car heads onto the track
• Every time the car comes off the track, check tire pressure and stagger.
• Always write it down.
• Always use an accurate calibrated tire pressure gauge
• If you drop the gauge, get it recalibrated

Alex George / Assistant Engineer /

Team West-Tec

"Rubbing is racing, get over it!"

A big thank you to Alex for giving us permission to reproduce his oval racing articles, Alex has been involed with Oval racing since 1983 when we was a mechanic with Firestone, and has working on sprint cars as well as other cars used on oval circuits across America, since 2001 Alex was worked as a assistant engineer with

Team West-Tec

the Ascar racing team based near Rockingham Motor Speedway