Not wanting to cough up $600 for a Comptech bar but reading that the Saner bar isn't quite as stiff as some would like, I decided to explore the option of designing my own sway bar and having it fabricated. I don

 

Neat analysis. It appears as though folks are determining the stiffness increase based solely on the torsional section. So what you're saying is the arms of the stock, hollow bar are flexing quite a bit more than the arms of the solid, Saner bar. Enough that it's affecting the spring rate by a significant amount.

 

Right. Basically not including the arms yields innacurate results.

The real results that matter are obviously the performance of the car, and the stiffness of the comptech bar appears to be what the nationals-level drivers want. It just makes it a bit harder for me to calculate the proper diameter bar that will yield me Comptech stiffness in a simple solid bent-up bar.

 

I think the 2nd generation Comptech bar is stiffer than V1. My installation instruction say that at the stiffest setting the bar is 278% stiffer than OEM bar.

 

Right. That's equivalent to 2.78 - 1.00 = 1.78 times the stiffness. Or, 178% of the stiffness of the stock bar.

 

Call me dumb but rather than try to work this out in relational terms can you not just measure the torsional stiffness of the stock sway bar and then work from absolute terms? Trying to design a bar that is twice as stiff in relation to an unknown seems overly complex but also prone to a significant amount of error. Errors in your calculation on the reference will be magnified 2 fold in the final product.

 

Why would I call you dumb?

I read on this forum that the stiffness of the stock bar was 295 lb/in. However, I don't get similar numbers in my simulations. This could be because I don't know the material properties of the stock bar. I don't have the facilities to measure the stock bar either (although rigging something up should be too hard. Since I don't have all the info regarding the stock bar, working on relational terms is all I've got.

I'm open to suggestions...

 

www.emachineshop.com might build one for you.

Warren

 

To me, "278% stiffer than stock," means that it's 375% the stiffness of the stock bar, not 178%. After all, "50% stiffer," means 150%, not 50%, right?

Having said that, I also suspect that Comptech meant to say "278% of the stiffness of the stock bar", not "278% stiffer".

Slow night...

 

For the stock MY00 front bar, I calculated a "raw" stiffness of about 630 lb/in -- is that any closer to what you're simulating?

Note that the effective roll rate at the wheel is much less due to the "installatio ratio" of the bar within the overall suspension geometry. That is, the A-arm acts as an additional lever arm on the bar, causing more deflection for a given force than the raw stiffness might lead you to expect.