Effective spring rate of the bar is also going to depend on the coilover springs being used. Isn't that how the front sway bar works? Under roll, the loaded outside corner is compressed, and the unloaded inside corner is acting against this compression with its springs?

 

If I were trying to figure out the spring rate of a bar, I'd attach the two bushing mounts to some kind of a rigid table. Then one of the endlinks to that same rigid table. Then pull up/down on the one free end to get a force/deflection table. I'd bet that's what he did.

Motion ratios are definitely needed to relate to spring rates, however the above is a useful way to compare two swaybars.

 

Bryan, just to make sure (Mike knows this stuff, I'm sure), you measured the "arm length" perpendicular to the center part of the bar, not along the (slightly diagonal) arms, right?

 

Correct John, exactly what you said...



hope everything is well down south.

 

chetly, this still doesn't make sense to me. You posted numbers in lbs. That is of course a force, not a rate. What are the real units you guys measured?

 

There is a thread about swaybar motion ratios that might be useful.

Also, using a program vs measuring it physically can make a difference. Computers might work find if the bends don't change between bars, material type etc.

 

the units i have for wheel rate is lb/in for some calculations im doing.

 

Sounds to me like he calculated the rate as opposed to measuring the rate. The calculations are simple, however, the measured rate can be considerably softer depending on the deflection in the bushings. In the past, I modeled a 2001 front bar and FEA gives me a calculated rate of 394 lbs/in. This is per inch of deflection at the end links. Based on his numbers, I'd assume he's using the same force/inch of deflection unit.
Front spring motion ratio is about 0.7. Front bar motion ratio is about 0.53.
The roll stiffness contributed by the bar is dependent on the springs as was mentioned.

 

That's what you'd think and it was my estimate. I took the saner bar (at the middle setting) off, added 100lbf/in to the springs in the front, and just about died the car was so loose. Ok, maybe that's an exaggeration, but it was 3-4 seconds slower on a ~1:20 track. Hence the motivation do some calculations this time around before I throw more money at the wrong springs.

[QUOTE=GEARHEAD,Oct 15 2010, 10:10 AM]This is per inch of deflection at the end links.

 

[QUOTE=FormulaRedline,Oct 15 2010, 07:35 AM] That's what you'd think and it was my estimate.