What side view roll axis inclination do you guys usually target and why?
Here are some observations:
The inclination of the roll axis effects the roll-yaw coupling. Having the axis inclined so that it goes up as it goes rearward causes the body to yaw out of the turn as the body rolls.
The Maurice Olley notes suggest that due to the roll yaw coupling, a roll axis that goes up as it goes rearward adds roll damping. The roll causes a yaw out of the turn. A roll velocity causes a yaw velocity. The yaw causes a lateral accel that tries to unroll the vehicle. This is all proportional to vehicle speed so it could be thought of as a form of roll damping. The increased roll/yaw damping can reduce occupant head toss.
An inclined roll axis will also effect turn in behavior. The more it is inclined up as it goes rearward, the slower the turn in response should be since the body is yawing out of the turn.
If the axis is inclined so that it goes down as it goes rearward, the yaw roll coupling will cause some self feeding. The roll will cause a yaw that turns into the turn which creates a lateral accel that also turns into the turn which adds to the roll angle…
Inclining the roll axis also has effects on TLLTD. If it is inclined so that it goes up as it moves rearward, there will be a larger TLLTD to the rear suspension from the RCH contributions. This could probably be easily mitigated by tuning the Anti Roll Bars, but it is something to think about. With a high enough rear roll center a rear Anti Roll bar may not be necessary.
Does any of this matter if your front suspension is a strut? Struts typically have RCH vertical migrations of ~2:1 in ride motion. This also causes a RCH lateral motion in roll. If the front RCH is moving all over the place (OK up and to the outside wheel) as you roll does the initial Roll axis inclination mean much?
What do you guys do?
Here are some observations:
The inclination of the roll axis effects the roll-yaw coupling. Having the axis inclined so that it goes up as it goes rearward causes the body to yaw out of the turn as the body rolls.
The Maurice Olley notes suggest that due to the roll yaw coupling, a roll axis that goes up as it goes rearward adds roll damping. The roll causes a yaw out of the turn. A roll velocity causes a yaw velocity. The yaw causes a lateral accel that tries to unroll the vehicle. This is all proportional to vehicle speed so it could be thought of as a form of roll damping. The increased roll/yaw damping can reduce occupant head toss.
An inclined roll axis will also effect turn in behavior. The more it is inclined up as it goes rearward, the slower the turn in response should be since the body is yawing out of the turn.
If the axis is inclined so that it goes down as it goes rearward, the yaw roll coupling will cause some self feeding. The roll will cause a yaw that turns into the turn which creates a lateral accel that also turns into the turn which adds to the roll angle…
Inclining the roll axis also has effects on TLLTD. If it is inclined so that it goes up as it moves rearward, there will be a larger TLLTD to the rear suspension from the RCH contributions. This could probably be easily mitigated by tuning the Anti Roll Bars, but it is something to think about. With a high enough rear roll center a rear Anti Roll bar may not be necessary.
Does any of this matter if your front suspension is a strut? Struts typically have RCH vertical migrations of ~2:1 in ride motion. This also causes a RCH lateral motion in roll. If the front RCH is moving all over the place (OK up and to the outside wheel) as you roll does the initial Roll axis inclination mean much?
What do you guys do?
