Fm3 Tuning Guide.docx

TROUBLESHOOTING - TABLE OF HANDLING CAUSE AND EFFECTS 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. o Too much downforce. Car feels sloppy and is slow to take a set in corners. o Too little shock. o Too much body roll (not enough spring and/or ARB). Car responds too quickly, is twitchy, and slides easily. o Too little downforce. o Too much shock, too much spring, and/or too much ARB. o Too much tire pressure.

Understeer 

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Corner entry understeer – car won’t turn in at all. o Front tires not wide enough. o Too much front roll stiffness – ARBs and/or springs. o Not enough front bump – shocks. o Not enough front downforce. o Too much dynamic camber on front wheels (not enough static negative camber). Corner entry understeer – car turns in initially then starts to push. o Too much front toe-in. o Rebound too stiff – shocks (not enough droop travel). o Not enough front downforce. o Bump not stiff enough – shocks. Corner entry understeer – car turns in and then darts. o Insufficient front suspension travel in either or both directions – shocks.

Oversteer 

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Corner exit oversteer – gets progressively worse from the time throttle is applied. o Too much rear roll stiffness. o Too much rear camber. o Too little rear downforce. o Too little rear toe-in. o 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. o Not enough rear suspension travel (too much shock in either bump, rebound, or both).

CAUSES – EFFECT ON VEHICLE Springs 

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Too much spring – overall o Harsh and choppy ride, lack of tire compliance. o Can’t put power down on corner exit - excessive wheelspin. o Car slides too much. Too much spring – front o Initial understeer. o Front end breaks loose in corners. o Front end breaks loose over bumps. Too much spring – rear o Oversteer when power is applied on corner exit. o Excessive wheelspin. Too little spring – overall o Car bottoms out. o Car feels like it’s floating. o Sloppy response. o Car is slow to take its set. Too little spring – front o Front end hits ground under brakes. o Too much body roll on corner entry. o Initial understeer – car won’t point in. Too little spring – rear o Too much squat under acceleration, and the resultant increase in negative camber. o Car falls over on outside rear wheel causing power-on oversteer.

Anti-Roll Bars 

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Too much ARB – overall o Very sudden turning response and little feel. o Car slides or skates instead of taking its set. o May dart over one wheel bumps or diagonal bumps. Too much ARB – front o Corner entry understeer that gets progressively worse. o Steady state understeer in the middle of sweeping turns. Too much ARB – rear o Corner exit oversteer when throttle is applied. o Excessive sliding coming out of corners. Too little ARB – overall o Car is sloppy and lacks response. o Car is slow to transition, especially in chicanes and esses. o 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 o Car rolls over onto outside tire on corner entry then ‘washes out’ (understeers). o Car lacks steering response and is slow to change direction. Too little ARB – rear o Back end doesn’t want to rotate on corner exit under power (difficult to throttle steer).

Shock Absorbers  

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Too much shock – overall o Very sudden car with harsh ride, sliding, and wheel patter. o Car crashes over road surface irregularities. Too much rebound adjustment o Wheels do not return to road surface quickly after displacement. o Inside wheel pulls off the road surface in a corner. o Lack of tire compliance over bumps and surface undulations. o Car may be jacked down in long corners. Too much bump adjustment o Initial reaction to bumps and curbs is harsh. o Initial chassis roll slow to develop. o Car slides rather than sticks. o Driven wheels hop when the power is put down. Too little shock – overall o Car floats a lot in ride and oscillates after bumps (underdamped). o Slow and sloppy response. o Chassis rolls too quickly. Too little rebound adjustment o Oscillates after bumps. o Doesn’t put the power down well. Too little bump adjustment o Initial bump reaction soft. o Car dives and squats a lot under brakes and under power. o Car rolls quickly and falls over outside tires – front tire on corner entry and rear tire on exit.

Wheel Alignment  

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Front toe-in – too much o Car darts over bumps, under the brakes, and during corner entry. o Car won’t point into corners. Front toe-out – too much o Car wanders under the brakes. o Straight line instability especially over one wheel and diagonal bumps. o Car may point into corners then refuse to take a set o Understeer as a result of tire scrub in long corners. Rear toe-in – too much o Rear feels light and unstable on corner entry. o Car slides a bit in corners rather than rolling freely. Rear toe-in – too little o Power on oversteer during corner exit. Rear toe-out – any o Power oversteer during corner exit. o Straight line instability. Front wheel caster – too much o Excessive physical steering effort (probably non-applicable with the XBOX controller) Front wheel caster – too little o Too little steering feel and feedback (also probably non-applicable with the XBOX controller) Camber – too much negative o Inside of tire will be hotter than the rest and wear faster. o Front tires – reduced braking capacity (dive) o Rear tires – reduced acceleration capacity (squat) Camber – too much positive o Outside of tire will be hotter than the rest and wear faster. o Rear tires – corner exit oversteer and reduced tire traction. o Rear tires - If extreme may cause corner entrance instability. o Front tires – too much body roll and understeer after car turns in.

Tires 

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Too much tire pressure o Harsh ride. o Excessive wheel patter, sliding and wheelspin. o High temperature at center of tire. Too little tire pressure o Soft and mushy response. o High tire temperatures at inner and outer edges. o Reduced contact patch