Camber Gain Vs. Roll Center Height

[ckiesz]

Since I am asking suspension questions, here are a couple more. The first one is more of a theory question:
On a wide car with a rather low center of gravity, very little body roll or suspension movement in general (think Super GT car), how much camber gain is really needed? (through suspension travel)

The second question is related to what I am learning while playing with my current project:
I am finding that there are two ways to bring the roll center height down to where I want it. The first being to increase the swing arm length, which is giving me the best roll center stability, but little camber gain. The second way is to keep the swing arm length shorter but lower the instant centers. While I can set a more aggressive camber gain, the roll center is much harder to nail down and wants to move all about.

It is nice having the long swing arm length and being able to roll and bump the suspension on the computer, with the roll center staying fixed in relation to the center of gravity, but the camber gain is becoming very minimal. I suppose this brings me back to my first question.
Can you tell I am anxious to get started with the fabrication?
Christian

[ubrben]

Originally Posted by ckiesz

Since I am asking suspension questions, here are a couple more. The first one is more of a theory question:
On a wide car with a rather low center of gravity, very little body roll or suspension movement in general (think Super GT car), how much camber gain is really needed? (through suspension travel)

The second question is related to what I am learning while playing with my current project:
I am finding that there are two ways to bring the roll center height down to where I want it. The first being to increase the swing arm length, which is giving me the best roll center stability, but little camber gain. The second way is to keep the swing arm length shorter but lower the instant centers. While I can set a more aggressive camber gain, the roll center is much harder to nail down and wants to move all about.

It is nice having the long swing arm length and being able to roll and bump the suspension on the computer, with the roll center staying fixed in relation to the center of gravity, but the camber gain is becoming very minimal. I suppose this brings me back to my first question.
Can you tell I am anxious to get started with the fabrication?
Christian

You can of course use a long SAL to control camber in bump and use caster to add negative camber with steer to correspond with roll. Only number off the top of my head is an LMP2 that has 7 degrees caster and around 39mm trail, but that has power steering.

Why do you care about kinematic roll centre migration BTW?

Ben

[ckiesz]

My car will also have power steering. I am interested in how camber is gained though caster in high speed corners. I suppose it would also relate to how much SAI is also present. Most of the more stock cars I drive have 6-9 degrees of caster and I really like the feel.

I was tought that roll center migration can be felt by the driver(me), so it is a goal to keep it as stable as possible. The car I drive daily and track day once-in-a-while has a very stable roll center as well as many of the well handling cars I have studied.
Thanks for the reply,
Christian

[ckiesz]

Also, could someone define "trail" to me and if it is nessesary? I would guess it is how much the wheel center is behind the line through the pivot points? Is this at ground level?
Christian

[tristancliffe]

Yes, with the car at static ride height. A vertical line through the wheel centre, and a line through the top and bottom ball joints. The distance at ground level is trail.

However, this may change with ride height, depending on suspension design, and also with vehicle pitch as the vertical line remains vertical even though the car's overall rake angle is different.

[ckiesz]

thanks for that, very helpful.
Christian