Andy Hollis
Andy Hollis
6/18/18 2:37 p.m.


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Anti-roll bars are a common and inexpensive way to tune the suspension of your car. Generally speaking, adding a larger front bar means less oversteer, while adding a larger rear bar means less understeer. But that just tells us the direction of the change, not the amount.

Sure, there are plenty of formulas and calculators floating around on the Internet, and they do a great job determining the theoretical rate of bars that are shaped like a C. However, the packaging constraints of today’s cars, especially in the front, put the lever action of an anti-roll bar at all kinds of odd angles. Often, it is impossible to model such a “spaghetti” bar with simple formulas. Add in hollow bars of unknown wall thickness, and those calculations become more like ballpark guesses.

How to accurately compare one bar against another? Measure them. In fact, if you measure the bars when they’re mounted to the car, you can also determine the effect of frame mounting bushings and end links. For the sake of ride comfort, those bushings can often soften the bar for the first half-inch or so of deflection.

We recently took some measurements of a variety of bars installed on our Honda CRX. We simply jacked up the front of the car so both wheels were in full droop, removed the wheel from one side, disconnected the end link, and hung a long through-bolt down below the control arm.

We then hung a 50-pound barbell weight from that bolt. Then it was just a matter of measuring the bar’s deflection. Simple math will yield the bar rate in lbs./in., just like a traditional coil spring.

To get a sense of how much bar action is lost in bushing compliance, you can take more data points with additional weight added. That gives a curve that levels out once the bushing is fully compacted.

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Cactus
Cactus Reader
6/18/18 4:16 p.m.

So obvious, yet not something I've thought to do. I'll be sure to give this a try some day.

malibuguy
malibuguy Reader
6/19/18 11:14 p.m.

genius!!!

te72
te72 Reader
6/25/18 11:32 p.m.

Had some sway bar shenanigans pop up recently. When the weight would settle on the front left corner, a popping sound occurred. Not a good sign when you're prepping for an autocross. So, my first thought was to remove the quick disconnect end link from the front bar and retest. Sure enough... no popping. So, sway bar related, most likely.

 

Notice I didn't say definitely.

 

Greased up the bushings, removed the end link on one side and greased up the ball sockets, in case they were somehow causing the binding and subsequent popping noise. Turns out, the problem was the lower end link stud that connects to the control arm, on the PASSENGER side. The retaining nut had somehow torqued itself to the point it was preventing the little bit of movement needed.

 

Weirdest part to me, was that the sound and the symptoms both appeared in the driver side wheel well, yet the issue was actually located on the passenger side. That was a fun one to learn!

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