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, Tue, 11 Dec 2001 10:20:37
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Peter,
I am must disagree with your syopsis of the causes of pulling.
Alignment plays a very important role in a vehicle's ability to go straight. To help illustrate my point I will mention try to explain. Caster angle is not quite as important as caster trail for pulls. Caster trail is distance from the tire center to the intersection of the king pin and the ground. (Measured in side view. In front view the same dimension is scrub radius) The caster trail causes a steering moment about the kingpin axis. If the caster trail is equal left to right the moments balance and the car goes straight. (assuming all else is equal)
Camber will also generate a lateral force (although much less than a steer) The lateral force due to one degree of camber is approximately one tenth of that due to one degree of slip angle, but it still generates a force. Unequal camber left to right will cause the car to pull left to right. (again all other things being equal)
Conicity is when the tire shape is slightly "cone like" such that an apparent camber angle is found even when the tire is held vertically. pulling forces due to conicty are similar to those due to camber, but the amount of conicity is usually small. Nonetheless most domestic automanufacturers sort tires for conicity for car applications.
Other things that will effect pull are load distribution and road slope Some vehicles are actually designed with cross car caster differences to take into account the above effects. By dialing in a certain pull with caster, you can negate the pull caused by the road/weight bias of the vehicle. Unfortunately when this is done, it is usaully done assuming that the road slopes down to the right (for most single lane roads) and the road slopes down to the left in the left lane of an interstate. So a car with cross car caster will go perfectly straight in the right lane and pull heavily to the left in the left lane.
Tire pressure can affect pull, but not a 1-2psi difference left to right. A front/rear tire pressure differential will have a very weak to nil effect on pull, but some effect on understeer coeficient.
-joe
posted by 198.208.6....
, Tue, 11 Dec 2001 10:21:00, Tue, 11 Dec 2001 10:20:37, Sat, 15 Dec 2001 20:51:08
, Tue, 11 Dec 2001 09:21:00, Tue, 11 Dec 2001 11:59:40
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