Finding sway bar stiffness...

[fishtail8]

Anyone have an idea of figuring out how stiff of a bar to run on a front suspension? The reason I ask is, my 50 Pontiac has a MII based front suspension, with coilovers in it. Rather than scouring with a measuring tape to find a bar with dimensions to fit the chassis, and frame, the option has come up to use a torsion bar off of a sprint car suspension. A bar inside of a tube with arms off each end to the LCA's. The bars come in limited lengths, but alot of weight ranges.

The car overall is 3300lbs with me, a SBC up front and a 17G cell out back. Anyone have any ideas on how to run a bar on this thing?

[Norm Peterson]

There is a way to do what you're asking that looks at how the lateral load transfer that occurs while cornering is distributed, front vs rear. This requires knowing a number of vehicle dimensions and its weight distribution, front and rear suspension arrangements & dimensions (including all of the dimensions of the sta-bar that you're attempting to build except for the diameter), spring rates, etc. An approximate idea of tire size helps. As well as some idea as to how hard the car will be driven, your preference in ride quality vs hardcore performance, and whether you'd prefer less roll with more understeer or vice-versa.


Norm

[Rhino]

I've been reading through Herb Adams' "Chassis Engineering". He describes, in detail, exactly what you'll need to do to answer this question. You can find it used on Amazon for < $15.

It's a good reference, no matter how deep you want to get into suspension design.

[fishtail8]

Thanks for the tips guys, I've heard lots about this Herb Adams book. Definitly on the buy list...

[chicane67]

I found the "math" to do the engineering calculation and came up with >>THIS<<...

As for anything realitive... I think it would take a fixture to obtain any real associated numbers for your specific bar. Anything else would be outside of emperical... but sometimes... that is all that is necessary.

[fishtail8]

Holy crap chicane!! That link almost made my head explode! I need something a little more dumbed down than that... lol.. Thanks tho!

[David Pozzi]

I'd measure from A arm to A arm where the bar will attach, then look around for a front bar that comes close. I'd take a good look at second and third gen Camaro bars first. A 4th gen bar is wider at around 50". I put a used third gen front bar on a buddies hot rod and it worked out very well. You can always bend the arms in or out a little to make the bar fit. If the arms are pretty short, use a 1" bar, if the arms are long, use 1 1/8".

The above will get you to a point better off than you are with no bar. It's not all scienced out, but just a guess.
David

[fishtail8]

Thanks for the help David, I'm gonna try and sort it out over the winter.

[BillyShope]

There is a way to do what you're asking that looks at how the lateral load transfer that occurs while cornering is distributed, front vs rear. This requires knowing a number of vehicle dimensions and its weight distribution, front and rear suspension arrangements & dimensions (including all of the dimensions of the sta-bar that you're attempting to build except for the diameter), spring rates, etc. An approximate idea of tire size helps. As well as some idea as to how hard the car will be driven, your preference in ride quality vs hardcore performance, and whether you'd prefer less roll with more understeer or vice-versa.


Norm

I've got a spreadsheet for exactly this purpose (Page 30 of my site). Also, there was an article, the summer of last year, in "Racecar Engineering." (Unfortunately, there was a typo in the calculations, but...with the spreadsheet...you don't need the article, anyway.) The catch is that you need 3 separate points to which a transverse tether can be attached and, of course, a set of wheel scales. It's just a matter of the spreadsheet solving 3 equations for 3 unknowns (roll center heights and roll stiffness distribution).

http://home.earthlink.net/~whshope

[Bow Tie 67]

Well I have been looking into sway bars and know that I can not accomplish either one of these procedures mentioned.

I drive my car very hard at the track. Currently I have no rear sway-bar and am considering the sway-bar setup that the mule and Camaro X have on there Quadra-links. As far as the front Chassisworks clip I'm toying around with making my own setup instead of just plopping down the mola for their " G-machine " bigger bar.