Tuning Calc

The info here is a quick guide from Carroll Smith’s book ‘Tune To Win’

EFFECT ON VEHICLE – POSSIBLE CAUSES

Straight Line Instability

• Too much rear wheel toe-out.

• Not enough rear downforce.

• Too much front downforce.

• Not enough rear toe-in (under hard acceleration) –presumably for RWD.

• Too much front toe (either in or out) – car darts over bumps.

• Front ARB is way too stiff – car darts over bumps.

Instability Under Brakes

• Front end darts or wanders – too much front brake bias.

• Car wants to spin – too much rear brake bias.

Response

• Car feels heavy and unresponsive.

  • Too much downforce.

• Car feels sloppy and is slow to take a set in corners.

  • Too little shock.

  • Too much body roll (not enough spring and/or ARB).

• Car responds too quickly, is twitchy, and slides easily.

  • Too little downforce.

  • Too much shock, too much spring, and/or too much ARB.

  • Too much tire pressure.

Understeer

• Corner entry understeer – car won’t turn in at all.

  • Front tires not wide enough.

  • Too much front roll stiffness – ARBs and/or springs.

  • Not enough front bump – shocks.

  • Not enough front downforce.

  • Too much dynamic camber on front wheels (not enough static negative camber).

• Corner entry understeer – car turns in initially then starts to push.

  • Too much front toe-in.

  • Rebound too stiff – shocks (not enough droop travel).

  • Not enough front downforce.

  • Bump not stiff enough – shocks.

• Corner entry understeer – car turns in and then darts.

  • Insufficient front suspension travel in either or both directions – shocks.

Oversteer

• Corner exit oversteer – gets progressively worse from the time throttle is applied.

  • Too much rear roll stiffness.

  • Too much rear camber.

  • Too little rear downforce.

  • Too little rear toe-in.

  • Not enough rear spring, shock, or ARB – allows car to roll over on outside rear wheel.

•  Corner exit oversteer (sudden) - car takes its set then breaks loose.

  • Not enough rear suspension travel (too much shock in either bump, rebound, or both).

CAUSES – EFFECT ON VEHICLE

Springs

• Too much spring – overall

  • Harsh and choppy ride, lack of tire compliance.

  • Can’t put power down on corner exit - excessive wheelspin.

  • Car slides too much.

• Too much spring – front

  • Initial understeer.

  • Front end breaks loose in corners.

  • Front end breaks loose over bumps.

• Too much spring – rear

  • Oversteer when power is applied on corner exit.

  • Excessive wheelspin.

• Too little spring – overall

  • Car bottoms out.

  • Car feels like it’s floating.

  • Sloppy response.

  • Car is slow to take its set.

• Too little spring – front

  • Front end hits ground under brakes.

  • Too much body roll on corner entry.

  • Initial understeer – car won’t point in.

• Too little spring – rear

  • Too much squat under acceleration, and the resultant increase in negative camber.

  • Car falls over on outside rear wheel causing power-on oversteer.

Anti-Roll Bars

• Too much ARB – overall

  • Very sudden turning response and little feel.

  • Car slides or skates instead of taking its set.

  • May dart over one wheel bumps or diagonal bumps.

• Too much ARB – front

  • Corner entry understeer that gets progressively worse.

  • Steady state understeer in the middle of sweeping turns.

• Too much ARB – rear

  • Corner exit oversteer when throttle is applied.

  • Excessive sliding coming out of corners.

• Too little ARB – overall

  • Car is sloppy and lacks response.

  • Car is slow to transition, especially in chicanes and esses.

  • Car rolls too much resulting in too much dynamic, positive camber and the resultant loss of cornering power due to decrease in tire traction.

• Too little ARB – front

  • Car rolls over onto outside tire on corner entry then ‘washes out’ (understeers).

  • Car lacks steering response and is slow to change direction.

• Too little ARB – rear

  • Back end doesn’t want to rotate on corner exit under power (difficult to throttle steer).

Shock Absorbers

• Too much shock – overall

  • Very sudden car with harsh ride, sliding, and wheel patter.

  • Car crashes over road surface irregularities.

• Too much rebound adjustment

  • Wheels do not return to road surface quickly after displacement.

  • Inside wheel pulls off the road surface in a corner.

  • Lack of tire compliance over bumps and surface undulations.

  • Car may be jacked down in long corners.

• Too much bump adjustment

  • Initial reaction to bumps and curbs is harsh.

  • Initial chassis roll slow to develop.

  • Car slides rather than sticks.

  • Driven wheels hop when the power is put down.

• Too little shock – overall

  • Car floats a lot in ride and oscillates after bumps (underdamped).

  • Slow and sloppy response.

  • Chassis rolls too quickly.

• Too little rebound adjustment

  • Oscillates after bumps.

  • Doesn’t put the power down well.

• Too little bump adjustment

  • Initial bump reaction soft.

  • Car dives and squats a lot under brakes and under power.

  • Car rolls quickly and falls over outside tires – front tire on corner entry and rear tire on exit.

Wheel Alignment

• Front toe-in – too much

  • Car darts over bumps, under the brakes, and during corner entry.

  • Car won’t point into corners.

• Front toe-out – too much

  • Car wanders under the brakes.

  • Straight line instability especially over one wheel and diagonal bumps.

  • Car may point into corners then refuse to take a set

  • Understeer as a result of tire scrub in long corners.

• Rear toe-in – too much

  • Rear feels light and unstable on corner entry.

  • Car slides a bit in corners rather than rolling freely.

• Rear toe-in – too little

  • Power on oversteer during corner exit.

• Rear toe-out – any

  • Power oversteer during corner exit.

  • Straight line instability.

• Front wheel caster – too much

  • Excessive physical steering effort (probably non-applicable with the controller)

• Front wheel caster – too little

  • Too little steering feel and feedback (also probably non-applicable with the controller)

• Camber – too much negative

  • Inside of tire will be hotter than the rest and wear faster.

  • Front tires – reduced braking capacity (dive)

  • Rear tires – reduced acceleration capacity (squat)

• Camber – too much positive

  • Outside of tire will be hotter than the rest and wear faster.

  • Rear tires – corner exit oversteer and reduced tire traction.

  • Rear tires - If extreme may cause corner entrance instability.

  • Front tires – too much body roll and understeer after car turns in.

Tires

• Too much tire pressure

  • Harsh ride.

  • Excessive wheel patter, sliding and wheelspin.

  • High temperature at center of tire.

• Too little tire pressure

  • Soft and mushy response.

  • High tire temperatures at inner and outer edges.

  • Reduced contact patch