[millerxc]

got a question on body roll, does the instant center have an effect on body roll even while not under power? if it doesen't what besides roll center effects body roll?

 

[whiteDI]

Suspension can play a large role in body roll such as spring rates as well as center of gravity and angle of, if you are running them, coilovers or air shocks. Not positive though.

 

[desertCJ]

Roll axis vs center of gravity and also spring rates/shock valving in practical application. Mount your coil-overs or air shocks as far out on the axle as you can....

 

[Bigger Valves]

I don't exactly know where you're going with this, but lemme see if I can help.. First of all, which ic are you talking about? Either way, your instant center/s are going to define the location of your roll center for something like a triangulated 4 link. Vehicle roll is created by the lateral forces and how they interact with the roll center and cg. This of course is irrelevant of whether the drive wheels are under power or not. So by the fact that ic's define roll center they do partly determine the magnitude of your roll moment independent of any power being applied to the drive wheels since it dictates the roll center height. Does this make sense? Then further from this, the amount of roll you see is a function of how this roll moment is reacted by your shocks/springs/rollbars/front rear roll distribution/etc.

 

[millerxc]

what I'm trying to determine is whether suspension design or spring rate is effecting my body roll, my instant center forward from the rear end is out in front of the truck, and about the same height as the center of gravity, the roll center on the rear is 4" over the rear diff, I like the soft ride but don't like the body roll, my choices now are stiffer springs, sway bar, or change some susp angles, I don't want to change susp unless I'm sure it will effect body roll, moving the RC is almost impossible in this app , the IC is possible but will it help.

 

[Bigger Valves]

IC will only really help by moving the roll center. However, the difference will be very small given a small change in link location. Look towards springs, spring mounting configuration, arb's, etc. to best address your issue.

 

[millerxc]

the springs are as far out as they can go, I really don't want stiffer springs so I'm leaning toward a sway bar , only finding room for it is gonna be difficult. I know moving the frame end upper link to a lower point brings the IC back but doesn't change the RC. but moving the axle end upper link to a higher point brings the IC back and RC higher, but the latter is most difficult. I guess my question is would a couple inches higher RC change body roll drasticly.?

 

[Azrckcrawler]

I guess my question is would a couple inches higher RC change body roll drasticly.?

My last build up I raised the roll center about 3 inches and it didn't seem to change the amount of body roll I had before the change. At best it lessened it a tiny bit, only way I could tell was I broke my swaybar while wheeling (didn't realize it) and in a few really off camber spots it was leaning more than I was used to.

 

[catzuk]

How are your links designed? are you getting any rear steer when your suspension flexes? (The oversteer/understeer numbers in the calculator I believe) if so that can amplify the body roll issue. flattening the lower links or lowering the lower link mounts at the frame and angleing them in at the frame can help relieve that.

Any pics of your set-up?

 

[Toddy]

I have been wanting to ask this sme question for a long time. When I gas my buggy it wants to roll. I notice it really bad when I am turning, as long as I am on the gas it will stay tilted up. I will try to post a couple pics of my link set up later and get the numbers on it.

Toddy

 

[Bigger Valves]

Changing your roll center by a couple inches is not going to make a huge difference. Only major geometry changes will be really noticeable..

Toddy, sounds like you may be having other issues dealing with roll that are possibly geometry issues since it sounds like a torque lift thing.

What's your setup?

 

[bnine]

the springs are as far out as they can go,

Where are your shocks? Depending on their location, and orientation, they can have a huge effect on body roll. There is also the shock valving to consider.

If there is nothing to be done with the shocks, you could look at a sway bar.

 

[Azrckcrawler]

Bigger Valves;7324326]Changing your roll center by a couple inches is not going to make a huge difference. Only major geometry changes will be really noticeable..

I am still trying to figure out what determines the body roll potential, so far I have come to the conclusion that the suspension "numbers" aren't going to tell you what you need to know. Both of these setups are very close but one needs a swaybar and one doesn't. The other differences are valving, spring rates and the way the coilovers are mounted.

 

[vetteboy79]

You're right, in that you can't tell just from looking at a chart like that what the roll characteristics will be like.

Roll motion comes from the center of gravity acting over the roll center, and the bigger that distance is, the more of a 'roll moment' you'll have. Your springs, shocks, swaybar, etc. are what resist the roll motion, and the rate and placement of each of those things is what will make the difference between two given rigs.

 

[Toddy]

Changing your roll center by a couple inches is not going to make a huge difference. Only major geometry changes will be really noticeable..

Toddy, sounds like you may be having other issues dealing with roll that are possibly geometry issues since it sounds like a torque lift thing.

What's your setup?

4 link in the rear. SAW air shocks and sway bar. Loweres have a little bit of triangulation from the chassis to the axle. Tops are from chassis to middle of the housing. Probably about 4 to 5 inches of seperation at the chassis and about 8 at the axle. Shocks are mounted as far out as possible. Could move the sway bar in a couple holes but want to figure it out before I start bandaiding it. Will try to get pictures tonight.

Toddy

 

[Azrckcrawler]

You're right, in that you can't tell just from looking at a chart like that what the roll characteristics will be like.

Roll motion comes from the center of gravity acting over the roll center, and the bigger that distance is, the more of a 'roll moment' you'll have. Your springs, shocks, swaybar, etc. are what resist the roll motion, and the rate and placement of each of those things is what will make the difference between two given rigs.

Cool, that is the direction I am heading. The rig was sitting a little tall after the rebuild with the shocks being more vertical so I am in the process of experimenting with some shorter/lighter springs along with some valving changes.

 

[Bigger Valves]

4 link in the rear. SAW air shocks and sway bar. Loweres have a little bit of triangulation from the chassis to the axle. Tops are from chassis to middle of the housing. Probably about 4 to 5 inches of seperation at the chassis and about 8 at the axle. Shocks are mounted as far out as possible. Could move the sway bar in a couple holes but want to figure it out before I start bandaiding it. Will try to get pictures tonight.

Toddy

This problem is in 2wd, right?

 

[Bigger Valves]

I am still trying to figure out what determines the body roll potential, so far I have come to the conclusion that the suspension "numbers" aren't going to tell you what you need to know. Both of these setups are very close but one needs a swaybar and one doesn't. The other differences are valving, spring rates and the way the coilovers are mounted.

Vetteboy nailed it for ya. The cg and roll center pretty much define how much roll moment is created by a lateral force. Now, what you feel is how that roll moment is reacted by the suspension setup. If the springs and shocks are soft or mounted inefficiently you'll see more body roll for the same roll moment. The geometry dictates your roll moment and how you can change it, but it does nothing to address how your springs, shocks, and roll bar resist it.

 

[Toddy]

This problem is in 2wd, right?

Yes it is.

 

[millerxc]

I was hoping some geometry change might resist body roll, looks like a sway bar is in my future. I'll try to get a good pic of susp , now all I have is cell phone pic, can't see enough detail, is real crowded with a steer rear.