Any body roll that includes lifting of the chassis while cornering is detrimental to handling. This is true for all suspensions. This has been proven on vehicles with "active" suspension. Body roll exists to help make the ride bearable, however a small amount is also beneficial, on most applications, to aid tire traction.
On the Twin I-Beam system, the track width may actually widen a bit with a lot of roll, but not enough to offset the disadvantages. Body roll, without chassis lift, is nearly as forgiving with this system as a solid axle (as far as camber changes, etc). However, with chassis lift, it is less stable while cornering due to major changes (in camber, etc.) than a double wishbone system. Sometimes it may also aid the inside wheel geometry slightly, but this is more than cancelled out by negativly affecting the outside tire which is doing more of the work. These, and weight concerns, are why it has been mostly abandoned as state of the art for unlimited racing.
Tony, Here is something to think about... What if you used your body roll to your advantage???? Every truck has its differnt quirks. As a driver I know that. The Dodge trophy truck I drove loved to dive in the nose just enough that you could pre load the suspension in a whoop and it would fly the next 3 whoops. Turners 7 open truck Dives too much so if you try to jump the next 3 whoops you end up monkey fliping the thing becuse the rear end wants to come over the top.... So getting back to body roll... I remember having a conversation with Robby Gordon About the Hay Hauler 66 Ford class 8 he drove for Venable. That truck had a crazy body roll to it, more one side then the other. But Robby figured it out to his advatage and could pre load the body to actually fly to the right or left... Hence he could pass a Buggy in the air with one side of the truck high and one side still on the ground... I guess what I'm getting at in dont worry so much about the book work on this stuff... Dont get me wrong.. GET CLOSE... But there are way to meny things that come into the eqation in the desert then you can caculate on paper.. and sometimes what you might think is a screw up is really a blessing...So it really goes back to doing it over and over untill you get a FEEL for it. Just something to ponder...
You may be picturing body roll as consisting only of the side of the body going down that is on the outside of the turn. You must also consider that the side of the body that is on the inside of the turn raises significantly. This is especially true for trucks. If you raise the inner end of the beam, you will be tilting the corresponding wheel toward positive camber. Positive camber is bad for traction and stability. Racers know this and that is why they put in tons of negative camber when the beams are modified or fabricated. This way, they only achieve positive camber when the truck is nearly airborne. This also leaves them with excessive negative camber most of the time. Negative camber is generally good up to a point, but it wears tires out rapidly. Even a stock I-Beam equipped truck has accelerated tire wear compared to a double wishbone system. The twin I-Beam is tough and if you set the camber right, it would be OK for a street/pre-run truck. Just expect to spend more on tires and be careful at higher speeds on and off the road.
After talking about this with Arizona this weekend, I have come to the conclusion that it is not actually the body roll persay that is helping you corner but a quality valved shock. I was doing 70 around an overpass this weekend and was thinking that if my sway-away's were not valved properly or I was running a low quality shock then my truck would be bouncy and uncontrollable at speeds with long travel, Just a thought, not as technical of an answer as sheaves and fabricators but thats alright
Fabricator, you make some good points. I am not sure if you just didn't go into detail or didn't consider roll center? This is a very important part of the equation.. If the roll center is closer to the outside tire than the piviot point for the beam then you are right that it will cause the tire to go positive ( camber ). But if the roll center is closer to the piviot for the beam this will cause the outside tire to go negative . So I guess the ? now is how to figure out the roll center. Bob I think you might be the best to answer this.
Your probably right in Bob getting into this...It sounds like your still thinking of only the outside of side of the body going down and not the inside going up. It doesn't matter where the roll center is as far as lifting the end of the beam and causing the corresponding tire to go toward positive camber. The dynamic roll center of a vehicle equipped with twin I-beam suspension is an elusive creature. This is true for any suspension with a single control arm for each wheel. When the beams are horizontal, the roll center is substantially the same as a solid axle. A unique characteristic of this is that under certain conditions the inner side of the body can raise up and change the dynamic roll center. Where is the roll center on a swing axle VW, the old Corvairs, or the Wompuskitty...? To put it more bluntly, Twin I-beam should not be confused or compared to more sophisticated suspensions. It is OK for a stock pick up and for stock use, and speed up to a point. Like all vehicles equipped with a single control arm per wheel, if you pass that point watch out! If it were not for the substantial width that is always applied for performance use, it would be a disaster.
I have read the posts here and all contain pieces of what happens in the dynamic body. Unfortunately, I am tied up at work on development issues and I am unable to take the necessary time to completely answer this until this coming weekend. Please bear with me-when the "General" and the "Rising Sun" get into an argument, I gotta jump in (Dear Lord, please help me not to kill anyone smaller than I am....) 'cause that's what they pay me for.