Q: Looking at the F355 Challenge Suspension & Swaybar setup vs. all other later challenge cars it seems the sway bars are now thicker at the rear vs the front? F355CH use 24mm front and 19mm rear whereas all later challenge cars use thicker bars at rear? I am sure a lot has to do with springs, weight and downforce but I would like to hear what you all think as to why the change?
A: Good question, one that many have…. This question highlights the difficulty in comparing one car to another, especially across different chassis….
When determining a chassis component specifications such as springs and anti-roll bars the engineer must take into consideration numerous factors, some of which are opinions/ generalized performance and marketing goals, some of which are hard facts like cost.
He begins with the chassis itself, as stiffness in bending and torsion are the ultimate determinants of performance. Then must choose springs based first upon obtaining “flat ride” (so that the chassis rises uniformly in heave when reacting to bumps) then the bias toward sporting or comfort.
Anti-roll bars (ARBs) specifications are determined first by choosing the amount of roll in corners; for many sporting road cars 2 degrees/ lateral G is the target.
Plugging the spring specifications, chassis specifications (like sprung weight) and the chassis roll specification into a series of equations for roll moment, roll gradient (2deg/G), etc. the engineer discovers the anti-roll torque specifically needed from the ARBs (springs impart an anti-roll torque too).
With anti-roll torque known (on paper), he takes the physical dimensions of the chassis to determine ARB packaging, what will fit and what won’t. Ultimately it’s what fits physically in the chassis (and the geometry of the ARB linkages) that determines the exact diameter of the ARB that’s in torsion plus the length and stiffness in bending of the ARB arms that attach to the control arm.
Thus is the challenge at hand when “comparing” one car to the next. I am sympathetic to the complexities of the task… it’s easy to comprehend “spring rate” and ARB diameter, hence so tempting to use said specifications to then “compare” one car to the next.
Reality is that the specifications to compare are wheel rates (vs. spring rates) that take geometry into consideration, both of the helical springs and the ARB springs.
So, what’s the simple answer to “Should I install bigger ARBs?” Go with a proven supplier, call or email your questions, make sure your supplier knows how you will drive your car, what you like and don’t like about the ride and handling. ARB design must integrate into your existing or intended suspension system… notice the word “system”, each component affects the other… countless guys have paid good money to destroy the handling quality of their car (including your humble author)!