Rear suspension design

[6spdCR]

Can someone explain the " make the traction bar angle match the driveshaft angle" approach to me? I agree that the angle can make a difference in how well the bars work, but i dont believe that the right angle for every truck out there is the same as the drive shaft. I've built many sets of bars and many 4 and 3 link rear setups and understand instant center and roll center design and how the calculate these points BUT, im not sure how to locate either point with good accuracy on a leaf spring suspension that has traction bars installed as lower compression links under acceleration. I think instant center should be figured like a 4 link using the traction bar as the lower link, and a line drawn from the center of the main leaf directly above the centerline of the axle through the front spring eye pivot. This means shorter traction bars would raise the instant center and move it rearwards, possibly creating over 100% anti squat and causing a force that pushes down on the rear end and up on the chassis at the point of instant center. Overly long bars could cause less then 100% anti squat and allow the body to squat over the rear suspension providing very little additional downward force on the rear end housing. This all gets thrown out the window if you have a pulling sled hooked the the truck providing thousands of pounds of force on the rear tires. In this situation i think the traction bars are purely to prevent axle wrap. Where as in a drag truck the bars could be used to affect how the weight of the truck is distributed on the tires under heavy acceleration. Let me hear what you think?? Steve

[Jacob 76]

I can tell you that your not going to get too many responses that are worth a damn because you already know WAY more than most people. But the "driveshaft" rule is because on long travel suspension it will cycle the suspension in the same arc as what your driveshaft is at. The other thing is that the link needs to be the same length as your driveshaft so it keeps them parallel throughout the entire suspension cycle. On short travel suspensions it is not very important and if you understand instant center and roll center / axis you can tune a suspension way better than most people

[roachie]

Overly long bars could cause less then 100% anti squat and allow the body to squat over the rear suspension providing very little additional downward force on the rear end housing. This all gets thrown out the window if you have a pulling sled hooked the the truck providing thousands of pounds of force on the rear tires. In this situation i think the traction bars are purely to prevent axle wrap. Where as in a drag truck the bars could be used to affect how the weight of the truck is distributed on the tires under heavy acceleration. Let me hear what you think?? Steve


That right there is most of the reason you see them 8ft long. Though to some extent it is also to help reinforce the frame.

[6spdCR]

Thanks guys, I just wanted too get some input as to what various people were having good luck with. I figured that on long travel designs it would be more important to have the bars match the natural arc that the rear axle moves in as the leaf springs cycle up and down because the driveshaft has a slip yoke that is designed to allow articulation. You can never know too much, just trying to learn more. Thanks again.

[Blue250]

I think most people are using them to prevent wheel hop, but to get better traction for drag trucks I believe you are correct. L eafs are pretty much a 2 link design because the only part that locates the axle is where it bolts to the frame, if you were to design another set of bars below them and set them up correctly it should work out like you are thinking. short bars are really not a bad thing if set up right as long as you dont have alot of travel.

[klincoln]

Can someone explain the " make the traction bar angle match the driveshaft angle" approach to me? I agree that the angle can make a difference in how well the bars work, but i dont believe that the right angle for every truck out there is the same as the drive shaft. I've built many sets of bars and many 4 and 3 link rear setups and understand instant center and roll center design and how the calculate these points BUT, im not sure how to locate either point with good accuracy on a leaf spring suspension that has traction bars installed as lower compression links under acceleration. I think instant center should be figured like a 4 link using the traction bar as the lower link, and a line drawn from the center of the main leaf directly above the centerline of the axle through the front spring eye pivot. This means shorter traction bars would raise the instant center and move it rearwards, possibly creating over 100% anti squat and causing a force that pushes down on the rear end and up on the chassis at the point of instant center. Overly long bars could cause less then 100% anti squat and allow the body to squat over the rear suspension providing very little additional downward force on the rear end housing. This all gets thrown out the window if you have a pulling sled hooked the the truck providing thousands of pounds of force on the rear tires. In this situation i think the traction bars are purely to prevent axle wrap. Where as in a drag truck the bars could be used to affect how the weight of the truck is distributed on the tires under heavy acceleration. Let me hear what you think?? Stevelike post 2 your in the wrong place for that info.Get this RJ Extreme Pro Mod Intersect 4- Link Calculator (http://www.rjracecars.com/RJ-Extreme-Pro-Mod-Intersect-4-Link-Calculator-Prodview.html) good luck!