Understanding Vehicle Dynamics

[Unity112]

I took this off honda.tech, but the information is spot on and I think it would be a beneficial piece of info for everyone. I edited part of it for incorrect terms used.

Understanding Vehicle Dynamics

Before we start we have to have an explanation of common vehicle dynamics terms. We had better understand the common ways to describe the different aspects of vehicle dynamics before we even turn a wrench, so here we go:

Friction circle: This is basically a vehicles performance envelope. It's expressed in lateral G

[Unity112]

Suspension adjustment-->Affect on vehicle balance--> Symptom of TOO MUCH adjustment

Front spring rate increase. More understeer .Terminal understeer, front of car hops in corners, excess wheelspin in FWD car

Front spring rate decrease. Less understeer. Too much oversteer, oversteer then understeer if spring is so soft that the car bottoms under lean, car bottom excessively with a jolting ride

Rear spring rate increase. More oversteer .Too much oversteer, hop in corners, twitchy

Rear spring rate decrease. Less oversteer. Car understeers, if way too soft car understeers then oversteers as car bottoms out under lean, car bottoms out excessively with a jolting ride

Front anti-roll bar stiffer. More understeer. Terminal understeer, Lifts inside front tire off the ground which can cause massive wheelspin, also not good for most effective tire usage as inside wheel is now doing nothing

Front anti-roll bar softer. Less understeer. Oversteer

Rear anti-roll bar stiffer. More oversteer. Big time oversteer, Can cause the inside rear tie to lift off the ground which is not two bad on a FWD car.

Rear anti-roll bar softer. Less oversteer. Understeer

Front tire pressure higher. Less understeer. No traction as tire is crowned so more understeer, bad wheel spin, jarring ride, center of tires wears out

Front tire pressure lower. More understeer. Edges of tires wear quickly because tire is folding over, feels mushy, tires chunk because low pressure means more heat build up

Rear tire pressures higher. Less oversteer. No traction as tire is crowned so more oversteer, bad wheel spin on RWD cars, jarring ride, center of tire wears out

Rear tire pressures lower. More oversteer. Edges of tires wear quickly because tire is folding over and cupping upward, feels loose in back, tires chunk because low pressure means more heat build up

More negative camber (Front) Less understeer .Poor braking, car is road crown sensitive, twitchy, tires wear out on the inside edge

Positive camber (F) More understeer .Poor braking, car is road crown sensitive, twitchy, tires wear out on the outside edge You almost never want to have positive camber unless you are a dweeb

More negative camber (R).Less oversteer, more rear grip, less breakaway warning when limit is exceeded/-3 degrees. More oversteer, car feels twitchy in back, tires wear out on inside edge

More positive camber (R) More oversteer Car feels twichy in the back, tires wear out on outside edge

Ride height too low Car twitchy with unpredictable dynamics

Toe-in front. Car is stable while going straight. Turn in is average. Car has slow twichyness under braking, feels odd, kills the outside edge of tires.

Toe-in rear car is less likely to suddenly oversteer when throttle is lifted. Weird slow rocking movement in back, feels slow but still unstable, wears the outside edge of tires.

Toe-out front. Car turns in well, works pretty good in FWD cars as they tend to toe-in under load. Car is real twitchy under braking, car is very road crown sensitive, car wanders on straight road, kills inside edge of tires.

Toe-out rear. Helps the car rotate, useful on tight low speed courses and slalom events. Not to good for street driving, causes lift throttle oversteer, car makes violent side to side rocking motions in rear, tires wear more on insides .

[GTS LAID]

very nice... i'll edit it for PDF format and have larry stick it on the main site for reference

[vvtlikick]

That second post strongly reminds me of a old SCC article, and it's still as useful info as ever :).

[Maelfyn]

This is the best thread... EVAR ;)