Suspension Discussion: Camber vs. Caster
Apr 9, 2009, 04:19 PM
#16
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II just had Perrin positive steering response bushing installed, which adds 2-2.5* of castor. The turn-in is quicker and more precise, but the steering is a bit lazy. When you let go of the steering wheel after making a turn, it doesn’t snap back to straight as quick as before. It’s not a huge difference, but noticeable. It could also be the fact that I had it aligned and went from 1 to 2.5* of camber.
Apr 9, 2009, 06:20 PM
#18
As far as I know there's no factory caster adjustment. If one has coilovers, I think the best easiest way to set caster without slotting the holes or offset bushings, is to turn the camber plates for caster adjustments and use eccentric bolts at the bottom to set camber.
Apr 10, 2009, 09:31 AM
#19
Well I picked up a set of camber+caster plates for cheap on eBay, they're from an Australian company called Noltec. I can't seem to find much info about the company they might have gone out of business but for the price I couldn't pass them up. I also bought a set of camber bolts so my plan is to maximize my camber at the bottom strut mount, keep the strut mount as far out as possible at the top to keep the steering geometry in line and get the most caster I can out of these plates. Not sure what this will equate to in degrees but they're supposed to get 10mm caster adjustment in each direction.
Thanks for the input, I can't wait to get some more caster into my car to see what it feels like.
::shakes fist in the air:: Curse you and your fender clearance!!!
Max, I'll be looking forward to seeing your new project and good luck at the DC pro, you doing any hillclimb events in PA or just auto-x, I was thinking about trying a few of those this season.
II just had Perrin positive steering response bushing installed, which adds 2-2.5* of castor. The turn-in is quicker and more precise, but the steering is a bit lazy. When you let go of the steering wheel after making a turn, it doesn’t snap back to straight as quick as before. It’s not a huge difference, but noticeable. It could also be the fact that I had it aligned and went from 1 to 2.5* of camber.
Originally Posted by goofygrin
I think I'll be ok on the track too since I'm running a fairly aggressive wheel (18x10.5+15).
Don't hate me because I have room under my fenders .
Don't hate me because I have room under my fenders .
Max, I'll be looking forward to seeing your new project and good luck at the DC pro, you doing any hillclimb events in PA or just auto-x, I was thinking about trying a few of those this season.
Apr 10, 2009, 10:08 AM
#20
Has anyone used the camber bolts? Whiteline/spc 81260/whatever in order to increase camber at the knuckle?
They are reasonably inexpensive (<$30), but since the bolt isn't as thick it won't be as strong as the OE bolt and that concerns me a bit since the car is a daily driver as well as autocross and track toy. Of course, my other option is to notch the strut until Stance gets me new lowers with offset holes (they have said they are working on it).
They are reasonably inexpensive (<$30), but since the bolt isn't as thick it won't be as strong as the OE bolt and that concerns me a bit since the car is a daily driver as well as autocross and track toy. Of course, my other option is to notch the strut until Stance gets me new lowers with offset holes (they have said they are working on it).
d
Apr 10, 2009, 12:49 PM
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Adding caster does change your pitch center on Mac Strut cars, which can chage anti-dive. On a subaru, it does lead to more dive. It can also change the cars Ackerman Steering, which is the geometry that makes the inside wheel turn mo re than the outside wheel. Still, its better to have the extra caster than to avoid its potential downsides.
donour, it does change the roll center, but depending on the angle of your lower control arm, adding camber at the strut top-hat can be better or worse. There are different ways people look at roll center, but most people believe You want your roll center to be as close to the CG as possible. if your control arms angle down towards the wheel, more strut angle would raise the roll center; closer to the CG. If the control arms level, you can do the same thing, but its going to be very hard to get close to the CG, so usually just adding camber however you can benefits the car more than trying to tune the roll center.
In the case that the control arms are past level, the roll center can be below the ground. When that happens, you should make it so the roll center never passes the plane of the ground.
As per CSU's Suspension Dynamics class.
donour, it does change the roll center, but depending on the angle of your lower control arm, adding camber at the strut top-hat can be better or worse. There are different ways people look at roll center, but most people believe You want your roll center to be as close to the CG as possible. if your control arms angle down towards the wheel, more strut angle would raise the roll center; closer to the CG. If the control arms level, you can do the same thing, but its going to be very hard to get close to the CG, so usually just adding camber however you can benefits the car more than trying to tune the roll center.
In the case that the control arms are past level, the roll center can be below the ground. When that happens, you should make it so the roll center never passes the plane of the ground.
As per CSU's Suspension Dynamics class.
Apr 10, 2009, 02:59 PM
#23
Great points guys, I'm going to have to consider this when I'm adjusting everything and I'll have to try it both ways (damn looks like I'll be spending more money on some toe plates and a camber gauge). I'll look closer at the angle of my control arms and try to figure out which would be more beneficial.
I'm planning on making a 3D model of the front suspension so this should help in figuring out the location of the roll center, does anyone have dimensions of the front suspension layout or even an approximate height of the CG? The main goal of changing the roll center is to get it as close as possible to the CG but I've never seen the actual height of the CG mentioned, I know I could approximate it but does anyone really know or are we all just guessing?
If the RC is below ground or anywhere below the car for that matter we know it's not near the CG but other than the obvious is there anything more specific?
I'm planning on making a 3D model of the front suspension so this should help in figuring out the location of the roll center, does anyone have dimensions of the front suspension layout or even an approximate height of the CG? The main goal of changing the roll center is to get it as close as possible to the CG but I've never seen the actual height of the CG mentioned, I know I could approximate it but does anyone really know or are we all just guessing?
If the RC is below ground or anywhere below the car for that matter we know it's not near the CG but other than the obvious is there anything more specific?
Apr 15, 2009, 09:35 AM
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Caster is track dependent because the effects all depend on steering angle. For something like a street course/tight course or somewhere like Road America, the casters you want will be different. At the end of the day, we're looking for some mid corner camber and mechanical balance values. I will typically run more caster on a tight course than I would at a big course. Rules of thumb are dangerous things though so please make sure you make the caster adjustments to your specific needs.
Steering feel changes because you are altering the leverage of the cornering force to the steering axis by changing the caster. More caster gives the contact patch center of force a longer moment arm to act over. This means that you need more steering effort to turn the wheel. Or there is additional pressure boost from the power steering, making the wheel feel numb. The longer moment arm also means the the center of force moves a longer distance with steering so there is more scrub. The scrub velocity also affects the steering feel and how the tire builds up cornering force. Also, since caster makes the wheels move up and down with steering angle, you are rolling the car with the steering as well.
Old theories and descriptions of the roll center show that the RC should never pass through the ground. Thats incorrect. Using force based roll centers or what I call, Newtonian physics, the RC passing through the ground doesn't have the "over center" effects of the RC going very far out sideways. It't not necessarily a bad thing, I'd focus more on the mechanical balance of the car and the cambers than exactly where the RC is relative to the ground.
One reason someone would put the RC close to the CG is to reduce the roll moment carried by the springs. The roll moment not carried by the springs is then carried by the suspension links as manifested by the "jacking force." Note that there is no significant reduction in "weight transfer" by raising the RC. You are only balancing between which part the load transfers over. The only major determining factors for load transfer are the CG height and track width. Since the suspension arms are much stiffer than the spring/damper, the response of the car is altered as well. This can manifest in a quicker roll response at the chassis, or degraded dynamic grip since the vertical load might build up faster than the cornering load can. High RCs can also mean more track change with suspension movement and more tire scrub. Again, the scrub affects the response of the tire. There is a limit to effective roll center height.
Note that changing the RC height changes the camber curve as does the caster. All of these effects are interdependent which is what makes K&C machines popular. In my opinion, its more valuable than time at a shaker rig given that you don't have the kinematic data from the car.
Hope this helps.
Steering feel changes because you are altering the leverage of the cornering force to the steering axis by changing the caster. More caster gives the contact patch center of force a longer moment arm to act over. This means that you need more steering effort to turn the wheel. Or there is additional pressure boost from the power steering, making the wheel feel numb. The longer moment arm also means the the center of force moves a longer distance with steering so there is more scrub. The scrub velocity also affects the steering feel and how the tire builds up cornering force. Also, since caster makes the wheels move up and down with steering angle, you are rolling the car with the steering as well.
Old theories and descriptions of the roll center show that the RC should never pass through the ground. Thats incorrect. Using force based roll centers or what I call, Newtonian physics, the RC passing through the ground doesn't have the "over center" effects of the RC going very far out sideways. It't not necessarily a bad thing, I'd focus more on the mechanical balance of the car and the cambers than exactly where the RC is relative to the ground.
One reason someone would put the RC close to the CG is to reduce the roll moment carried by the springs. The roll moment not carried by the springs is then carried by the suspension links as manifested by the "jacking force." Note that there is no significant reduction in "weight transfer" by raising the RC. You are only balancing between which part the load transfers over. The only major determining factors for load transfer are the CG height and track width. Since the suspension arms are much stiffer than the spring/damper, the response of the car is altered as well. This can manifest in a quicker roll response at the chassis, or degraded dynamic grip since the vertical load might build up faster than the cornering load can. High RCs can also mean more track change with suspension movement and more tire scrub. Again, the scrub affects the response of the tire. There is a limit to effective roll center height.
Note that changing the RC height changes the camber curve as does the caster. All of these effects are interdependent which is what makes K&C machines popular. In my opinion, its more valuable than time at a shaker rig given that you don't have the kinematic data from the car.
Hope this helps.
Apr 16, 2009, 07:55 AM
#25
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As far as I know there's no factory caster adjustment. If one has coilovers, I think the best easiest way to set caster without slotting the holes or offset bushings, is to turn the camber plates for caster adjustments and use eccentric bolts at the bottom to set camber.
will the studs on the camber plates line up in the stock mounting holes if they are turned 90*?
Apr 16, 2009, 08:36 AM
#26
Caster is track dependent because the effects all depend on steering angle. For something like a street course/tight course or somewhere like Road America, the casters you want will be different. At the end of the day, we're looking for some mid corner camber and mechanical balance values. I will typically run more caster on a tight course than I would at a big course. Rules of thumb are dangerous things though so please make sure you make the caster adjustments to your specific needs.
Steering feel changes because you are altering the leverage of the cornering force to the steering axis by changing the caster. More caster gives the contact patch center of force a longer moment arm to act over. This means that you need more steering effort to turn the wheel. Or there is additional pressure boost from the power steering, making the wheel feel numb. The longer moment arm also means the the center of force moves a longer distance with steering so there is more scrub. The scrub velocity also affects the steering feel and how the tire builds up cornering force. Also, since caster makes the wheels move up and down with steering angle, you are rolling the car with the steering as well.
Am I correct in thinking that initial turn-in response is increased because static camber can be less which would put a bigger tire patch on the ground when you first start to turn the wheel or does it have more to do with the change in scrub velocity that you mention?
Old theories and descriptions of the roll center show that the RC should never pass through the ground. Thats incorrect. Using force based roll centers or what I call, Newtonian physics, the RC passing through the ground doesn't have the "over center" effects of the RC going very far out sideways. It't not necessarily a bad thing, I'd focus more on the mechanical balance of the car and the cambers than exactly where the RC is relative to the ground.
One reason someone would put the RC close to the CG is to reduce the roll moment carried by the springs. The roll moment not carried by the springs is then carried by the suspension links as manifested by the "jacking force." Note that there is no significant reduction in "weight transfer" by raising the RC. You are only balancing between which part the load transfers over. The only major determining factors for load transfer are the CG height and track width. Since the suspension arms are much stiffer than the spring/damper, the response of the car is altered as well. This can manifest in a quicker roll response at the chassis, or degraded dynamic grip since the vertical load might build up faster than the cornering load can. High RCs can also mean more track change with suspension movement and more tire scrub. Again, the scrub affects the response of the tire. There is a limit to effective roll center height.
Note that changing the RC height changes the camber curve as does the caster. All of these effects are interdependent which is what makes K&C machines popular. In my opinion, its more valuable than time at a shaker rig given that you don't have the kinematic data from the car.
Hope this helps.
One reason someone would put the RC close to the CG is to reduce the roll moment carried by the springs. The roll moment not carried by the springs is then carried by the suspension links as manifested by the "jacking force." Note that there is no significant reduction in "weight transfer" by raising the RC. You are only balancing between which part the load transfers over. The only major determining factors for load transfer are the CG height and track width. Since the suspension arms are much stiffer than the spring/damper, the response of the car is altered as well. This can manifest in a quicker roll response at the chassis, or degraded dynamic grip since the vertical load might build up faster than the cornering load can. High RCs can also mean more track change with suspension movement and more tire scrub. Again, the scrub affects the response of the tire. There is a limit to effective roll center height.
Note that changing the RC height changes the camber curve as does the caster. All of these effects are interdependent which is what makes K&C machines popular. In my opinion, its more valuable than time at a shaker rig given that you don't have the kinematic data from the car.
Hope this helps.
- AlwaysinBoost I don't think he's talking about turning the top mount 90deg since its a 3-bolt pattern that certainly won't work but if you turn the mount 120deg so that the maximum camber setting is pointing in and diagonally back towards the rear of the car then the bolt pattern should line up and you can get some caster adjustment out of your camber plates. This however makes caster and camber adjust at the same time but thats why the eccentric bolts at the bottom of the strut are important at this point since they will let you then adjust your camber separately. Hope that makes some sense.
Last edited by sscottttt; Apr 16, 2009 at 08:41 AM.
Apr 16, 2009, 08:46 AM
#27
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^ that makes perfect sense and how I had invisioned it... except for the 120* part.
I have my lower camber bolts set to max camber already so I might give this a try before the next AX to see how well it works.
I have my lower camber bolts set to max camber already so I might give this a try before the next AX to see how well it works.
