|Suspension / Brakes / Chassis All suspension, brakes and chassis discussions.|
|12-04-2009, 05:30 PM||#1|
Drives: 1st through 5th gen Camaros
Join Date: Sep 2009
Location: Sante Fe Springs, CA
Choosing a Sway Bar
Recently there have been quite a few technical posts about choosing swaybars, hollow vs solid, made in the USA vs foreign parts, etc. We thought we'd clear up a few points that seemed confusing. At Hotchkis, we believe grudge matches belong on the racetrack, not in the forums, and we are thrilled that there are so many options for Camaro enthusiasts to choose from. Having choices is good for the public and it's good for the aftermarket, so we're just here to help you make informed choices.
Hollow vs Solid
We get asked this question quite often. Right off the bat, let's clear something up: just about every major new high performance sports car on the market uses tubular sway bars. That includes the ZR-1, Porsche GT3, Viper ACR, Mustang GT500 and Ferraris and more. The OEMs could certainly afford to use whatever process they wanted, and they choose tubular bars because they offer the best balance of strength, performance and light weight. That's why we use the same process. We could make solid bars if we chose to, it's a much less expensive process, but we use a CNC bender and high-strength domestic steel because it works. We can all agree that weight is the enemy in all things concerning automotive efficiency. Why drag around a extra heavy bar when a lightweight, efficient tube will work even better? It's true that the process of designing optimally balanced hollow sway bars is more expensive then bending up a solid iron bar, but our 2000 hours of testing over the last 15 years has shown the benefits.
Sway bars work off of torsional force (twisting motion). Therefore, the material in the center of a solid bar plays little role in the resistance of torsional force. With this in mind, we have eliminated some of the center material and also moved some to the outside of the tube, where it is most effective. In turn, this produces a sway bar that is lighter in weight and just as stiff, if not stiffer than solid. For example, a 1'3/8" hollow bar is equivalent to a 1'1/4" solid. But the 1'3/8" hollow bar is 6% stiffer and 43% lighter than the 1'1/4" solid. “
Solid bar aficionados point to stress levels. Yes, hollow bars tend to have more stress then solid ones, but to what degree? As an analogy, what if hydroformed chassis frames were solid hunks of metal instead of hollow? Sure, they would be able to endure a lot more stress, but why would they need to? We design our bars to have enough twist resistance and still be more than durable without all the weight of a comparable solid unit.
There are many ways of designing products. Basic stabilizer bar equations are the first step for us at Hotchkis, but it does not end there. We model all of our stabilizer bars in CAD and use FEA (Finite Element Analysis) to determine deflections values. FEA allows us to obtain more accurate bar rates since it takes into account the entire shape of the bar.
Speaking of bar shapes, our bars are CNC bent with tight tolerances. With dealing with larger bend radii, the tube bend does distort slightly. The overall diameter DOES NOT reduce or shrink as it bends. Our tests have shown negligible differences in rate and durability due to this phenomenon. Instead, the tube elongates vertically very slightly giving more strength to the lever arm.
Real Durability Testing
All the formulas in the world won't replace real world testing. We have a lot of experience with stabilizer bar fatigue/cycle testing. Before we release a new product, we contact an independent testing laboratory to conduct extensive fatigue/cycle testing. This involves applying a load on a stabilizer bar in the same manner as if it were in the vehicle for a certain amount of cycles. Deflections up to a punishing 2-3 inches in each direction with 100,000 cycles are not uncommon.. These tests allow us to determine the durability of a variety of diameters and wall thicknesses. This helps us decide on the best tube material for a given application. Actual bench testing also allows us to verify our results from FEA.
Lab testing is still not enough for us, we are regular visitors to local tracks and races where we put our cars through real life track testing. After all, a lab test won't tell you if you will be comfortable in your car, and we know that most of our customers plan on both street and track use.
Camaro Canyon Run
The Bottom Line
Hotchkis has been designing, developing, and manufacturing suspension parts in the U.S. using high quality domestic steel for 15 years. We are constantly reviewing our products and processes. If we find something new that yields better results, you can be sure we'll start work on it immediately. Our goal is to design high quality affordable products that you can bolt on the day you receive them and start enjoying your car.
Hope this helps, and please call us with any questions you might have.
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