just did a little noodling
it looks like a 1" move at the end of the sway bar is .992deg on A arm swing w/ the new style front underbody bars

so anyone know how much further out on the A-arm the ball joint is?

I looked at this before on my '82. It's about 275mm from the center of rotation to the ball joint. Wait... did you mean 9.92 degrees? That would put motion ratio at about 1.9:1 wheel to sway.

no .992deg/in which is very close to the motion ratio

so 275mm from the A-arm axis to the balljoint center?

Re: the two sides acting in the swaybar … while true, the force applied to the swaybar by the unloaded side of the car is small because it’s basically limited to the unsprung weight of the suspension/wheel assembly acting in the downward direction. The loaded side has the force of the weight transfer acting in the upward direction. I don’t have data to quote, but this force is substantial, or we’d have no need for swaybars in the first place.

As for the force delivered by the swaybar in resisting upward suspension movement on the loaded side, it will be the full force of the bar. I’m not seeing why it would be half. Or maybe I misunderstood the assertion.

I don't know either, just thinking out loud, if there is 400# up on one end there has to be 400# down on the other end, obviously the down end is doing nothing as it is unloaded and the shock limits droop. I guess I agree that the full force is applied at the loaded end

as to the geometry, I've resigned myself to get under there tomorrow and do some measuring, it looks as if the sway effective point is ~3/4 of the way out from the pivot

if that were so, then 400#/in is an effective 300 lb/in

we''ll see when I get the #s

Yep, 275 from the axis to the ball-joint center, measured perpendicular to the A-Arm axis. A little tricky to measure as the ball-joint is rear of the torsion bar cap so it's a bit of a projection from the cap.

I'm not tracking the math on the angle, maybe I'm misunderstanding which angle you're talking about; 0.992 degrees at the A-Arm center of rotation is only 4.8mm at the ball-joint.

Even at full load the sway bar is trying to lift the unloaded tire, so the force is acting against the spring. There's always going to be some balance in deflection between the springs and sways. There's some fun equations in there.

The correct calculation is the motion ratio squared, so it's not gonna see 300 lbs of wheel rate.

If the length of the lower control arm from the ball joint to the center of the torsion bar tube is 11.5" and the centerline of the hoop for the sway bar is 4.5 inches from the ball joint the calculation should look like:

(11.5 - 4.5) / (11.5) = 0.6087. square that and you get 0.3705.

Measured rate of bar = 400 lbs/in x 0.3705 = 148 lbs/in wheel rate.

W?O a lift available it's been impossible to get good measurements

anyone have some A-arms laying around that can tell me what X is(it should be ~5-6"
I believe that the 275mm(10.826771in) is correct

http://forums.pelicanparts.com/uploa...1727363815.jpg

as best I can measure w/ the car on the ground
the sway is .46 of the pivot to ball joint distance- -4.9"

where did the 11.5 come from?
dis you measure that?

the other # I have for that is ~10.83"
why squared?

anyhoo I think that we are getting close

here's what I have so far in beta

4 different t-bar setups for the same car otherwise, all w/ 20/18 underbody sways
http://forums.pelicanparts.com/uploa...1727381425.jpg
http://forums.pelicanparts.com/uploa...1727381425.jpg

Yes, I crawled on my belly like a reptile and measured them, but I was assuming the hoop attachment for the underbody bar and not the through the body bar. (Actually, the car was up in the air a little bit)

The motion ratio is squared in the calculation to get the correct wheel rate. Once for the force and once more for the distance. Also, the calculations change for the metallurgy, so keep that in mind. I have notes somewhere for the two most common materials and tempers used. Or bolt the bar to a bench or table and put a bathroom scale under one end and a dial indicator under the other side, then apply force with a big pipe wrench.

Good to know, next time i put mine on a lift I'll double check that

dug out my Puhn and that confirms the square aspect

my confusion was that the motion ratio for the torsion bar isn't the same as the motion ratio for the sway bar at either end.

I'll use your #s for now and check down the road

i do have the bench measures for some 993 sways, but not 911

not concerned w/ metallurgy as I'm mostly concerned w/ the factory bars

thanks for your help!!

now for the rear

as best as I can measure he OC distance from the t-bar pivot to the axle is ~19"
and the OC distance from the t-bar pivot to the sway bar mount is ~11"

can anyone confirm or provide a better measure?