| TROUBLESHOOTING - TABLE OF HANDLING CAUSE AND EFFECTS |
| |
| Herein lies the ‘Holy Grail’ of tuning. I’d love to take credit for it, but at the expense of being a plagiarist, I can’t. The information in this section I’ve pretty much paraphrased from Carroll Smith’s ‘Tune To Win’ – Chapter 11. The guy really knew his stuff… |
| |
| 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.
- 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 XBOX controller)
- Front wheel caster – too little
- Too little steering feel and feedback (also probably non-applicable with the XBOX 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
|
| |
