Hi all. I am familiar with the process to find front roll center for IFS, but can't find any info as to how to determine front roll center for solid axle with transverse spring. Is it set by panhard bar height the same as a 4 bar/coilover rear end? Can anyone help me out here??? Diagrams would be good if available. Also info for front solid axle with coilovers would be helpful. Don't panic, not going OT here. It may just help with understanding the dynamics of a solid axle. Thanks. @Kerrynzl, @gimpyshotrods, @ELpolacko, @Ned Ludd . Have read a lot of the excellent info you guys have posted. I am sure this is something that should be obvious but would appreciate your guidance.
Have a look thru this thread and possibly PM the person you think best could offer you some information if you don't find what you are looking for. https://www.jalopyjournal.com/forum/threads/tranverse-springs-tech-info.1112840/
Just doing chassis and suspension design for '28 closed cab pickup build. Trying to keep front roll center as low as I can to try and get good handling characteristics. Would like front roll center to be adjustable, but don't know if this is possible. Steve.
Thanks Russ. Have already read that thread. Ned Ludd talks about two roll centers. Having trouble getting my head around that. Surely there can only be one, but I am more than likely wrong about that. Steve.
As soon as you've got a lateral locating device like a Panhard bar, the two-roll-centre conundrum goes away. Then, indeed, the lateral locating device will determine your roll centre. If you're looking for a low roll centre, take a look at a Mumford link. I don't think I've ever seen one applied to a hot rod front end, though. Be careful not to put the roll centre too close to the shackle instant centre, or the spring will do very little to resist roll; hence my recommendation of shackles as close to vertical as you can practically get them to work. What steering are you using? If cross-steer, a Panhard bar is the preferred lateral locating device. Then the roll centre can only be as low as the physical position of the Panhard bar (assuming the bar is straight.)
Thanks Dawie. Will be cross steer. Good to know that roll centre is determined by panhard bar height. Looking at another option of wishbone 3 link with the triangulated link at the bottom and attaching at the centre rear of dropped axle. This will fix the roll centre position and negate the need for a panhard bar (I hope ???). Toying with the idea of multiple height mount on rear of axle to make roll centre adjustable. Rear roll centre will be adjustable as well. Is this all worth the effort ? Steve.
Dawie, So what you are saying is the roll center falls on the straight line between the pivot points of the panhard bar? Bob
Precisely. It's where that straight line crosses the centreline (or central vertical plane) of the car. With that lower A-bracket and upper links arrangement you'll want fore-and-aft steering with the drag link mimicking the motion of the driver's side link. Cross steering needs the part-circular motion a Panhard bar gives. The steering cross-link has to mimic the motion of the Panhard bar. That is why it is often pointed out that the cross-link and the Panhard bar should be as close as possible to the same length, and parallel as seen in front elevation. A few years ago I did a theoretical analysis of a Panhard bar which runs diagonally under the engine, with a steering diagonal link running alongside it. The steering gear would be near the firewall on the driver's side. It seemed workable enough. The advantage was that it was possible to "project" the front roll centre a short distance below the physical bar, by angling the other links a bit. The disadvantage was a slightly more pronounced "Panhard waggle".
If you watch NASCAR - This is precisely why the teams/drivers change the rear Panhard bar height, to raise and-or lower the rear roll center. to give the back of the car different roll characteristics while going into, into, and out of the corners. Mike
So, what sort of front and rear roll centre heights should we be aiming for? I know this is a question that is based on other variables, not least of which would be centre of gravity height. Maybe what I should ask is what roll couple length (difference between roll centre and centre of gravity) would be optimum front and rear? Then maybe it could be worked out downwards from centre of gravity to determine roll centre heights. Street application - NOT wanting full race set-up. Steve.
Was wondering that myself. From all I can find on the subject, it doesn't seem to be something that is a concern. A sensible approach to suspension setup seems to be all that is required for street use. Dropping roll centres too low looks like it would open a whole different box of frogs to deal with (too much body roll, so the need to fit and tune anti-roll bars, etc). Front roll centre level with dropped axle / rear panhard level with rear axle centre (and adjustable) seems easy to set up as a starting point. Tune rear to taste. Steve.
Examples of a Mumford link for those who maybe interested. Probably works great but not all that tempting for a hot rod IMHO.
Something I wrote a while back: https://www.jalopyjournal.com/forum/threads/this-brouhaha-about-roll-centres.629334/
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