cibachrome
Automotive
- Jan 16, 2007
- 512
This old topic caught my eye. thread800-68031
Ratios of trails for high performance & race cars ought not be set in stone. The total trail should be set by tie-rod load requirements for feeling at the steering wheel given the overall ratio and steering gain. The tire is but 1 of three components to total trail. "Race" tires that I have seen usually have low trails. This includes "radial" race tires that aren't radials. Thus, caster is added to make up for low pneumatic trail. The last component of trail is caster offset (hub lead). The spindle is not on the kingpin axes. Sometimes this is forbidden in some racing circles, but whose actually measuring it, anyways? You should then wind up with a positive tire-rod load gradient up to the max mu. Any driver using aligning torque based trail to gauge max lateral performance ought to be replaced unless running in the back third of the pack is ok with the sponsor. These drivers will believe the car is "loose" because of the steering wheel tendency but it is actually "tight". Caster & caster offset have dynamic effects, too, because they interact with tire transient properties, especially aligning moment (an element of inital body motion, not necessarily steering wheel feel). This effect is third order, so getting it right for the load change effect of caster at the slip and camber angles you are at in the turn is the challenge. This includes wheel fight modes. Certain German sleds add +caster angle and -hub-lead to achieve good transient feel with good steady state feel.
Ratios of trails for high performance & race cars ought not be set in stone. The total trail should be set by tie-rod load requirements for feeling at the steering wheel given the overall ratio and steering gain. The tire is but 1 of three components to total trail. "Race" tires that I have seen usually have low trails. This includes "radial" race tires that aren't radials. Thus, caster is added to make up for low pneumatic trail. The last component of trail is caster offset (hub lead). The spindle is not on the kingpin axes. Sometimes this is forbidden in some racing circles, but whose actually measuring it, anyways? You should then wind up with a positive tire-rod load gradient up to the max mu. Any driver using aligning torque based trail to gauge max lateral performance ought to be replaced unless running in the back third of the pack is ok with the sponsor. These drivers will believe the car is "loose" because of the steering wheel tendency but it is actually "tight". Caster & caster offset have dynamic effects, too, because they interact with tire transient properties, especially aligning moment (an element of inital body motion, not necessarily steering wheel feel). This effect is third order, so getting it right for the load change effect of caster at the slip and camber angles you are at in the turn is the challenge. This includes wheel fight modes. Certain German sleds add +caster angle and -hub-lead to achieve good transient feel with good steady state feel.