Aftermarket Suspension Components - How It Works

Fatman Fabrications reveals the science, technology, and engineering behind aftermarket suspension components.

Stephen Kim Jan 29, 2013 0 Comment(s)

Chevy II Upgrades

Early Chevy II Novas had a very primitive front suspension. Fatman Fabrications has developed a MacPherson strut IFS for these cars which has proven very effective. This arrangement preserves the stress path for the car’s weight as designed, carrying the suspension load through the shock tower and back into the firewall via the strut tower bracing. Since the upper control arm is eliminated, the shock towers can be cut back as much as 4 inches per side, but is not required for proper installation. Our current Chevy II IFS is a second-generation design that uses a front-steer configuration steering rack. This allows a normal GM rear sump oil pan to fit, making LS engine swaps more practical. Likewise, the Chevy II IFS also uses a full 5/16-inch plate crossmember with tubular lower control arms that eliminate the strut rods. Customers like the idea of losing the strut rods, and we supply a replacement front corner gusset plate to serve as the structural function of the stock strut rod bracket. By bolting the main plate into the original lower control arm holes, the frame is greatly strengthened. In stock form, it has virtually no crossmembers taking structural loads. That has always been a problem with the stock suspension holding alignment. The plate also adds rigidity to the total feel of the car, and also serves as a skidplate under the car and allows for two more inches of ground clearance. Since this kit uses ’82-87 Camaro spindles, it’s very easy to upgrade to 13-inch disc brakes. We supply a lefthand engine mount to make the steering connection quite easy, along with the U-joints and shafts needed to finish the job. Excellent header clearance is the result with big- and small-blocks. The strut conversion also offers adjustable height when coilovers are mounted in the strut cartridge.

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Aftermarket tubular control arms are very popular upgrades, but the truth is that changing the shape of the arms doesn’t change the geometry unless you alter the position of the bushings and the ball joints. Fatman Fabrications was actually the very first company to build tubular control arms for GM cars. We backed into that because our original purpose was to make narrowed arms to solve the track width problems for street rodders who had unwisely chosen to install a GM subframe in a car too narrow for proper tire clearance. After our first sets of control arms hit the market, the Camaro and Chevelle guys wanted them as well. By making them so long, we found constant improvement by using an offset upper control arm shaft, urethane bushings in some cases, and relocating the upper ball joint. We also came up with a modular spring mount on the lower control arms that accommodate coilovers and air springs. The 3/16-inch offset shaft was first developed by MOOG, as even old lady cars were prone to sagging over time, making it difficult to maintain proper alignment specs. Add to that lower raked cars with altered settings, and the ability to change the length of the upper arm 3/8 inch by flipping the shaft in its bushings can eliminate the crazy stacks of shims that might have been necessary.

Additionally, we make the upper control arms just slightly longer to allow reaching optimal camber, settings on a car with a sagging frame. The offset upper shaft then helps if the arm ends up being too long. In essence, we have found that old cars can be a moving target, so we allow more latitude in fitting them to the car. We also move the ball joint back 3/4 inch in all applications. This allows four more degrees of positive caster to counter the loss of caster that results from having a low front ride height, and to allow more stability at high speed with power steering.

Lowering

Installing lowering springs and drop spindles, or cutting the stock springs, are all effective methods of lowering ride height. Cutting coil springs works well as long as you don’t go too far. It is true that removing a coil raises the spring rate, but the effect is negligible up to one full coil. A good rule of thumb is that every full coil is worth about a 2 inches of ride height. Cutting more raises the spring rate excessively, but more importantly, can cause loss of travel by bottoming out the shock or bumpstops. It is also true that a lowered car requires a higher spring rate. If you decelerate the same mass within half the travel, you will produce twice the g-forces. That translates to twice the force in the seat. That is another reason why excessively short springs are a bad idea.

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Dropped spindles are generally my first choice for lowering a car since all they change is the position of the wheel on the suspension. They preserve full suspension travel and shock stroke, and also make it easier to add disc brakes. The dropped spindles with a raised ball joint height also provide handling advantages. Generally, a 2-inch drop is the limit before outer tie-rod clearance issues come up. You can also combine shorter springs and dropped spindle to get 4 inches of total drop with minimal affect on ride quality. I would always recommend the drop spindles first, except on cars that have too short of a spindle to begin with, which results in the upper control arms sloping the wrong way. In ’88-93 GM pickups, S-10s, and ’78-87 G-body cars that lack a tall spindle option, a short spring may actually result in a geometry improvement. The shorter spring will move the upper control arm closer to level, and reduce the improper camber change normally seen.

Bushing Materials

Rubber, urethane, and Delrin are materials that are commonly used in suspension bushings. Rubber has the most compliance, urethane has less, and Delrin has the least compliance. Drag racers like Delrin for minimum compliance and friction for maximum suspension rise, while autocross guys like the precision it offers. When it comes to bushings, the real question is what are they trying to do with the car? Compliance is not always a bad thing. The earliest independent front suspension designs in the ’39-53 era often used steel or bronze bushings for virtually zero compliance. This was precise, but wore quickly while providing very little isolation from road shock, jarring people in the car. Since the bushings wore so quickly, they were often allowed to wear loose, thus negating the precision they might have provided when new. Urethane is a good compromise. On all upper control arms, you can use urethane to maintain precise location of the ball joint with little effect on ride quality. On the lower control arms, I personally only like to use urethane when the material wall thickness exceeds 3/16 inch. Otherwise, rubber bushings in good condition will not flex excessively while still maintaining some separation from road shock. Urethane works well on the lower control arms as well if precision is really favored over comfort.

Camaro Subrames

The aftermarket front subframe assemblies we produce for first- and second-gen Camaros offer more ground clearance, and a narrower track for tire clearance. Our first-gen Camaro subframes also yield superior handling due to improved geometry compared to the OEM design. The front-mounted rack-and-pinion setup offers much better clearance for the lefthand exhaust, making a big-block swap much easier. It’s also nice to build a car with a cleaner framerail design that has much better looking welds than the OEM subframe. Likewise, our first- and second-gen Camaro subframes offer substantial handling advantages over stock. It is based on the ’74-78 Mustang II IFS, but only the spindle remains stock. We upgrade the brakes, sway bar, control arms, and crossmember in our subframe design. Some seem to think that this suspension is too weak, but I would counter that the Mustang II was a 3,500-pound car. It has an excellent symmetrical geometry, making fabrication easy and parts less costly. A very strong forged steel spindle is used with wheel bearings larger than on an OEM Camaro, and both the OEM Mustang and common screw-in Chrysler ball joints are larger than those on a stock Camaro. Strength is not an issue, and our Camaros and ’57 Chevys have put down numbers on autocross and slalom courses right in line with the fastest Camaros featuring Corvette-derived IFS designs. We have amply shown to any open-minded person that the Mustang II design can deliver world-class performance.

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Sources

Fatman Fabrications
Charlotte, NC 28227
704-545-0369
http://www.fatmanfab.com

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