Shock Absorber Rating - The Shocking Truth

Hot rodders love to improve their cars. That's the whole reason for updating suspensions, drivetrains, and bodies. Even after a street rod has been on the road for a while, there always seems to be some way to make it better. Recently we began to wonder how the ride quality of a finished car could be improved with simple bolt-on parts.

It has become very clear that racers concentrate on shock absorber rating and selection to tune for different tracks and conditions. In some forms of racing the shocks are adjustable from the cockpit during the race. Most street rods use standard-quality shock absorbers that do a pretty good job, but can performance be improved by taking advantage of the greater control offered by race shocks?

The name "shock absorber" does a poor job of explaining the function of these devices. The British call them "dampers" which is a far better description as their purpose is they damp, or control, the suspension's motion created by the action of the springs, regardless of the type. Knowing that leads to the realization that most ride-quality and bottoming-out problems are caused by improper shocks, even though we often mistakenly blame the springs. To test that theory we decided to take a proven street rod and switch to Carrera shocks to see if they made a difference. It's important to note that the other high-quality aftermarket shocks were not tested, but they can be expected to perform similarly. We used Carrera shocks due to their wide selection, our familiarity with them as a dealer, and the exceptional service provided by their street rod tech rep, Ben Abernathy.

The subject for our test was David Laney's chopped '39 Chevy. It features a Fat Man frontend and a Chassis Engineering rear leaf kit. Familiar to many rodders across the country, Dave has driven the car 42,000 miles over the past five years and never experienced a breakdown, so the car is proven. To gather objective data for the test, we borrowed STREET RODDER magazine's g-meter and drove the car over an established course, then changed shocks and repeated the tests.

As the '39 was equipped with a Mustang II frontend, selecting new front shocks for the car was obvious, but the rear was a little more complicated. Most commercial rearend kits use the rear shocks from a '63-82 Corvette with 7/16-inch upper bolts, 5/8-inch lowers, and an installed length of approximately 12 inches. However, due to variations in cars and how they sit, shock length may have to be determined for each application. Determining the shock length should always be done with the vehicle fully loaded, that means with all components in place, interior, glass, radiator, everything. You can't be accurate by having the local pie-eating champion step on the bumper.

A feature of the Chassis Engineering's lower shock brackets is they can be flipped to allow for variations in ride height, shock length, and travel. This allows the brackets to be positioned to prevent the shocks from bottoming or topping out. (A good way to check shock travel is to put a wire tie on the shock's exposed shaft and observe its position after a drive; if it's all the way up, it is bottoming out. When we checked the Chevy's rear shocks, we found they had plenty of compression travel but had little extension and may have been topping out. We flipped the brackets and went for a test ride with the original shocks to get some baseline numbers.

Our test course is a very typical two-lane state highway, complete with curves, potholes, patches, and even an area under construction. A steady 55-mph trip out and back yielded a peak g-reading of .42 averaged over three trips. After the baseline data was gathered, the car was pulled in the shop and the shocks changed. Even with 42,000 miles, all four shocks were still in great shape with resistance comparable to new units. This certainly speaks well for the quality of the standard shocks supplied in the original suspension kits.

While the car was up in the air and shocks were being changed, we took the opportunity to give it a chassis checkup. Good thing we did as the brake line on the rear axle housing had been mashed by coming in contact with the tailpipes. The line was replaced and rerouted to prevent a reoccurrence that could cause unequal braking or failure. We also found a damaged ball joint boot, which was replaced with a nifty homemade tool shown in the photos. These are the kind of simple, but important, things that are hard to see unless you get your car on a lift once in a while.

With the new Carrera shocks in place, we set up the g-meter and repeated the test drives. This time the average peak reading on the g-meter was .32, for a 24 percent reduction. That essentially means a 1/4-less feedback to the seat of your pants. That's a pretty good return on an easy morning's work and $360 worth of parts. As this is being written, we're returning from a big rod run and David reports big improvements in ride quality on the Interstates as well.

The accompanying chart is a list of the most commonly used shock on hot rods, with both Monroe and Carrera equivalents listed. As the closed length gets shorter, travel is also lost, so try to use as long a shock as possible, even if the mounts have to be reworked. Longer shocks enlarge the "window" of proper fit without bottoming or topping. To accommodate longer shocks they can be angled up to 30 degrees, which is why the factory does it, contrary to the old tale of shock angle controlling body sway. Of course, the proper lengths must always be verified, so be sure and do your homework before ordering.