Everything You Need To Know About Coilovers

How To Select & Install Coilovers For Your Hot Rod

By Ron Ceridono – Photography By Tate Radford

Coilover shocks have been around for a long time. It was so long that several unnamed Modern Rodding editors had a full head of hair when they first began to find favor with chassis builders. Initially, coilovers were only found on race cars, but it was our good friend, the late LeRoi “Tex” Smith, who has been credited with first installing them on a street rod. He hung a pair on the rear of his America’s Most Beautiful Roadster trophy–winning XR-6 in 1962 and coilovers have been with us ever since.

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02 To determine the proper length shock absorber the front suspension was positioned at ride height — To determine the proper-length shock absorber, the front suspension was positioned at ride height then secured with a simple angle iron strut. It was then simply a matter of measuring for the correct coilover shock.

While coilovers have been popular on sports cars and smaller, pre war hot rods, they have also become popular for use on larger, heavier post war cars, like Colin and Sue Radford’s 1957 Ford station wagon shown here. And why shouldn’t they be? It’s simply a matter of selecting the correct combination of shock absorber and spring to make them work as they should, and with help from Strange Engineering that’s what we did.

03 Strange Engineering coilover shock bodies eyelets spring seats and adjuster nuts are machined from aircraft quality aluminum — Strange Engineering coilover shock bodies, eyelets, spring seats, and adjuster nuts are machined from aircraft-quality aluminum. After assembly they are dyno tested at every extension/rebound speed to ensure proper valve seating and durability.

For decades Strange Engineering has been a source for quality driveline and suspension components, including a comprehensive line of coilover shocks. To make selecting the correct coilovers easy Strange Engineering offers a chart with all relevant dimensions. For our application the front shocks used are single-adjustable (extension damping only) PN S5205 with the following specifications: extended length 15.40 inches, collapsed length (without the bump stop) 10.76 inches, recommended ride height of 12.625 to 13.250 inches, and a stroke of 4.64 inches. In the rear, the double-adjustable shocks (extension and compression damping), PN S5007: extended length 19.15 inches, collapsed length (without the bump stop) 12.64 inches, recommended ride height of 15.25 to 16.00 inches, and a stroke 6.52 inches.

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04 Strange Engineering shocks are rebuildable and may be returned to the company to be re valved to a different “range” of adjustments — Strange Engineering shocks are rebuildable and may be returned to the company to be re-valved to a different “range” of adjustments.

With the shock dimensions determined the next consideration was what springs to use. Strange offers quality Hyperco springs because they are cold wound from heat-treated chrome silicon (SAE 9254) wire. The ends are ground smooth, the springs are thermally stress relieved, and shot peened.

05 This is a pair of double adjustable Strange Engineering coilover shock absorbers — This is a pair of double-adjustable Strange Engineering coilover shock absorbers. On the top shock the compression adjustment can be seen, on the opposite side of the bottom example is the rebound adjustment.

Coil Spring Identification

Coilover springs are identified by length, diameter, and spring rate. Length and diameter are determined by the shock absorber body, while spring rate is dependent on several factors, including vehicle weight and the intended use. Spring rate is simple enough; it’s the force required to compress the spring 1 inch measured in pounds. Hyperco springs are tested for spring rate, which is then stamped directly on the spring.

06 At the bottom of the shocks are the adjustable spring seat and the jam nut — At the bottom of the shocks are the adjustable spring seat and the jam nut. Before installation the threads on the shock body should be coated with an anti seize lubricant.

How To Determine Spring Rate

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There are a variety of methods to determine spring rate, the problem is the requirements vary so greatly depending on the vehicle and its use that it’s virtually impossible to make useful spring recommendations. The basic goal is to have the shocks compressed roughly 40 percent with the car stationary, but the best way to determine the spring rate required is to use the program found on hypercoils.com.

07 The springs are retained at the top of the shock bodies by a spring seat that slips over the shaft and registers in the upper eyelet — The springs are retained at the top of the shock bodies by a spring seat that slips over the shaft and registers in the upper eyelet. Note the rubber bump stop that prevents damage if the shock bottoms out.

How To Calculate Unsprung Weight

To use the spring rate program some basic information will be required. First and foremost is vehicle weight, specifically corner or wheel weight. The most accurate way to determine that is to axle weigh the vehicle. If that’s not possible, published overall curb weights are the next best thing, figure 55 percent of the total weight will be on the front, 45 percent on the rear. Divide the axle weight in half and you have the corner weight of the car. The next factor to consider is unsprung weight, which is the weight of the components not supported by the springs, such as the wheels and tires, brake components, half the weight of the control arms, rear axle assembly, and half of the coilovers. A good guesstimate of unsprung weight would be 70 to 150 pounds.

08 Strange Engineering supplies a special wrench to be used on the adjustment nuts — Optional spring seat bearings are recommended to ease spring adjustment after the coilovers are installed. Strange Engineering supplies a special wrench to be used on the adjustment nuts.

How Does Shock Angle Affect Spring Rate?

With all the information required, including length of the shocks at ride height, we plugged the numbers into the Hyperco calculator and it indicated 200-pound springs for the rear of the wagon. Keep in mind another consideration when selecting coilover springs is the mounting angle, so changing that angle will have an effect. The greater the installed angle, the stiffer the spring rate must be to support the same weight. A general guideline for reduction in effectiveness is:

10°………………………………….. 0.98
15°………………………………….. 0.93
20°………………………………….   0.88
25°………………………………….   0.82
30°………………………………….   0.75

09 The spring seat bearings are made up of a top and bottom thrust washer with a bearing assembly in between — The spring seat bearings are made up of a top and bottom thrust washer with a bearing assembly in-between. When making spring adjustments the vehicle should be jacked up to reduce the load on the springs and adjusters.

As an example, our 200-pound springs would effectively be reduced to 186 pound when mounted at a 15-degree angle. In some cases, changing the angle of the rear shocks can be used to “tune” ride quality.

10 Here is the assembled coilover ready for installation — Here is the assembled coilover ready for installation. Note both the compression and rebound knobs can be seen and the spring preload is in the middle of the adjuster’s travel.

Motion Ratio In Suspension

To determine what front springs to use on the ’57 the same basic information was required plus what is called the motion ratio. Think of the lower control arms as levers applied to the springs, which means stiffer springs would be required when compared to a solid axle (front or rear)—that’s motion ratio. For an independent front suspension, the distance from the control arm pivot point on the subframe (centerline of the bushing) to the point on the control arm directly under the center of the spring or coilover assembly will be required. In addition, distance from the control arm pivot point on the subframe to the centerline of the ball joint will also be necessary. With all the shock angle numbers entered into the Hyperco program we determined 550-pound front springs would be required.

11 The Ford’s rear suspension is typical of many ’50s and ’60s cars a pair of semi elliptical leaf springs and tube shocks — The Ford’s rear suspension is typical of many ’50s and ’60s cars, a pair of semi-elliptical leaf springs and tube shocks. The springs not only support the body, they locate the rear end front to back and side to side.

Leaf Spring To Coilover Conversion

When changing the rear suspension from leaf springs to coilovers, some sort of axle locating system is required. Four-bars and four-links position the axle housing in the chassis front to rear. Four-bars are normally parallel and have fixed mounting points (threaded ends allow minor adjustments for wheelbase and pinion angle adjustments) while four-links allow the attachment points of the links to be altered to tune the chassis. Four-links are most commonly used in drag racing to alter how the vehicle launches from the starting line.

12 Art Morrison Enterprises four bars and a new Strange Engineering 9 inch Ford axle housing — In this case the rear suspension was updated with Art Morrison Enterprises four-bars and a new Strange Engineering 9 inch Ford axle housing. The fronts of the four-bars attach to a new crossmember that was fabricated and installed.

Four Bar Suspension & Lateral Locator

To control sideways movements four-bars and four-links require a lateral locator, such as a Panhard bar or a Watts link. Diagonal locators may also used, however they are more suited to drag race applications than the street. A variation on the four-bar theme is a triangulated four-bar. Two-bars run parallel with the framerails with two additional bars running at an angle from the axle housing to the frame that locate the housing side to side, eliminating the need for an additional link. Colin elected to use Art Morrison four-bars with a Panhard bar.

13 Four bar and four link rear suspensions require a lateral locator of some sort — Four-bar and four-link (shown) rear suspensions require a lateral locator of some sort. Arrow A is a lateral link, arrow B is a Panhard bar. These examples are from Art Morrison Enterprises.

Benefits of Coilovers

There are a variety of advantages to using coilovers, not the least of which is they are compact by virtue of combining the shock absorbers and springs. But arguably their biggest benefit is the ability to tune the suspension by simply changing springs, mounting angles, or in the case of adjustable shocks the compression and rebound rates. Simple and effective, coilovers are the best kind of shock therapy.