hutch325
Mechanical
- Apr 30, 2004
- 32
A tangential offshoot from another recently-started thread.
I'm doing some kinematics analysis on a front suspension with that's McP strut with the L-shaped control arm (i.e., not a two-link with a virtual steering axis). Scrub radius is near zero from the factory.
I'm investigating the differences in the regular and "motorsport" versions of the car, and what was changed through the life cycle of the models. I'm looking at it from a race car prep perspective, trying to figure out the effects of common modifications such as offset bushings, strut mount modifications for more negative camber, etc.
Any thoughts on increasing KPI on a strut front suspension? Some initial sensitivity studies indicate that increasing it makes the camber curve a little steeper but I have some concerns:
- What about negative effects for steering feel?
- Practical implicaitons of less negative camber on the outside wheel as a function of steering ? It seems like for smaller steering angles like on a road course, the improved camber compensation may win out?
Thoughts on increasing or decreasing castor? First, some observations:
- Increasing castor to the "motorsport" spec by moving the strut mount rearwards without making any other changes other than re-setting toe (i.e. not correcting bump steer) seems to reduce the steering feedback somewhat. I attributed this to greater mechanical trail.
- The "motorsport" version of the car has about 7-8 degrees of castor as opposed to 4-5 for the regular version. The manufacturer changed the upright to change the longitudinal relationship between the CA outer balljoint and wheel center. Presumably this is to achive the desired amount of mechanical trail, but I haven't completed the kinematics model so I don't have real numbers.
Next, some questions. Realistically,:
- How much of a benefit is the additional outside wheel negative camber with steering resulting from larger castor angles?
- Any recommendations on how much mechanical trail is reasonable?
- Thoughts on asymmetric jacking forces?
As a side item, a brief conversation with one of the engineering directors from the manufacturer seemed to indicate they have been reducing camber change as a function of travel in recent models in an effort to improve the behavior of run-flat equipped cars when going over bumps. I'm guessing tire wear, stability over bumps, and keeping it in the understeer regime are more important to the manufacturer than maximizing the cornering power of the front end.
Any thoughts, and particularly real-world experience, are welcome.
I'm doing some kinematics analysis on a front suspension with that's McP strut with the L-shaped control arm (i.e., not a two-link with a virtual steering axis). Scrub radius is near zero from the factory.
I'm investigating the differences in the regular and "motorsport" versions of the car, and what was changed through the life cycle of the models. I'm looking at it from a race car prep perspective, trying to figure out the effects of common modifications such as offset bushings, strut mount modifications for more negative camber, etc.
Any thoughts on increasing KPI on a strut front suspension? Some initial sensitivity studies indicate that increasing it makes the camber curve a little steeper but I have some concerns:
- What about negative effects for steering feel?
- Practical implicaitons of less negative camber on the outside wheel as a function of steering ? It seems like for smaller steering angles like on a road course, the improved camber compensation may win out?
Thoughts on increasing or decreasing castor? First, some observations:
- Increasing castor to the "motorsport" spec by moving the strut mount rearwards without making any other changes other than re-setting toe (i.e. not correcting bump steer) seems to reduce the steering feedback somewhat. I attributed this to greater mechanical trail.
- The "motorsport" version of the car has about 7-8 degrees of castor as opposed to 4-5 for the regular version. The manufacturer changed the upright to change the longitudinal relationship between the CA outer balljoint and wheel center. Presumably this is to achive the desired amount of mechanical trail, but I haven't completed the kinematics model so I don't have real numbers.
Next, some questions. Realistically,:
- How much of a benefit is the additional outside wheel negative camber with steering resulting from larger castor angles?
- Any recommendations on how much mechanical trail is reasonable?
- Thoughts on asymmetric jacking forces?
As a side item, a brief conversation with one of the engineering directors from the manufacturer seemed to indicate they have been reducing camber change as a function of travel in recent models in an effort to improve the behavior of run-flat equipped cars when going over bumps. I'm guessing tire wear, stability over bumps, and keeping it in the understeer regime are more important to the manufacturer than maximizing the cornering power of the front end.
Any thoughts, and particularly real-world experience, are welcome.