drnick

i have the 928 specialist bar at the front and carls bar at the rear, front is set fully stiff and rear is set in the middle. i have always assumed that both sides need to be ajusted equaly ie at the same of the three holes but i was wondering if its possible to ajust the bars in between?? in other words could i back off the front one hole on one side only?? anyone been here and done this?

martin D

So you are going racing on a NASCAR banked oval then Nick
Not sure what you are trying to achieve ( apart from better handling), have you corner weighted instead of adjusting ride height to spec.? I'm guessing this would be what you need to do instead of what you are asking about.

Martin

SharkSkin

Nick, since the bar's effective resistance to torsion is governed by both ends and their relationship to pivot points, this might just work. As long as there is no preload on the bar at rest on flat ground, what you should end up with is an overall stiffness that is between what either of the two holes would give you. e.g. if you put one side at the front hole and the other side at the rear hole, the effect should be about the same as having both in the middle. In fact, that would be a simple test right there.

drnick

dave, thats what i was thinking. i just thought that the practical reality might be different to the theory as it so often is, sometimes in only subtle but important ways! i was really hoping one of the 'racers' here on the list could shed some light from practical experience.

as far as i can tell, if its possible to ajust halfway between each pairing of holes then there are about five different combinations of setting which would give a lot more flexibility to the setup. i might email carl and DR and see what they say.

martin, i did once have the car weighed at each corner.. but at the moment its still such a porker that any smaller differences shouldnt translate to a handling problem - i hope! the car is lower than standard and has settled more on its suspension since it was set up. i think you are right though, and id like to go through the height/alinement and corner weights as well as reducing any preload in the roll bars at the next service. in the mean time though i was looking to ajust the anti roll bar between the obvious settings.

jon928se

Nick

I think Dave (Sharkskin) is correct. WRT to his comment regarding pivot points, what you probably would be adjusting is where the Roll centre of the car is. This is all due to the geometry of the changing lever arms of the drop links to a/r bar.

First get the car corner balanced with half a tank of fuel and you sat in it (with a/r bars disconnected) then attach the droplinks at your preferred a/r bar setting (same each side) and ensure the droplinks are adjusted for length so that the a/r bar is not preloaded.

drnick

ok im more confused now.. so is it ok to ajust the bar to different holes on each end or will it stiffen one side more than the other?

SharkSkin

Nick, try the test that I mentioned -- I doubt that it will handle any different with one fore & one aft vs both in the middle. The sway bar's effect on handling comes primarily from the total resistance to torsional forces. There are secondary considerations, such as the angle at which the droplinks apply that force to the bar and the difference between overcoming the pivot bushing friction with a long leg of the bar vs a short leg, but IMHO those differences will be too small to matter.

BTW, some will argue correctly that this is not the optimal way to adjust stiffness but I think that would be splitting hairs. Should still work. If there is any measurable imbalance I would think you'd need a skidpad and a very precise g-meter to detect it -- and IMHO there is still the subjective nature of quantifying minute differences in oversteer/understeer.

drnick

dave, that sounds very sensible to me and i might just try that with the front bar which is fully stiff - backing it off one hole on one side and seeing what gives

SharkSkin

You're certainly not going to hurt anything. If you wanted to prove this out for the masses, the test I mentioned in the latter half of post #3 plus access to a skidpad should be all you need to prove it does or doesn't work without negative side-effects.

Jim bailey - 928 International

they need to be even. If one side is a 3 inch arm and the other a 6 inch arm you get very different results. If the short side moves up one inch it will try to lift the long side far more than one inch to do this the spring on the long side must compress far more. Basically the swag bar borrows spring rate from the inside wheel and transferes it to the outside wheel . The stiffer the bar the more the two wheels are linked the less the spring twist of the bar the more the wheels move together the less independent suspension you have You can make an adjustable on the fly bar by introducing a flat blade link on one side BUT BIG BUT the length of the arms must be equal. You then rotate the blade from on edge (stiff ) to flat (soft) and change the stiffness of a bar ( spring)

SharkSkin

DOH! Jim, you're absolutely right -- I was only thinking of static torsion on the bar. Granted, the difference in vertical motion at the end of the bar is slight given the small distance between holes in the end of the bar, it is still different.