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Coilover Spring Rate Chart - Selection and Installation

Tags: Tech, Hot Rod, Street

Coilover shocks have been around since the late 1950’s and are still going strong on Street Rods and Race cars today. Coilovers offer benefits other springs and shocks may not, including tight packaging for custom suspensions, easy ride height adjustment, and the ability to swap springs at a low cost. There are many factors that go into selecting the correct coilover assembly in order to get a good performing suspension. We will go over some of the basic pieces of information that will help you get the right parts the first time.

Vehicle Weight

The most overlooked factor that we run into is incorrectly estimating the weight of your vehicle. Two of the same make and model cars can vary a great deal depending on how they are configured. You also don’t want to weigh it before the car is completely assembled. Fenders, engine accessories, radiators, etc. it’s all weight and can add up to several hundred pounds in some cases. Do yourself a huge favor and weigh your car. It can save lots of time and frustration down the road!

During the build process, we understand how difficult it can be to get your car on a scale when it isn’t mobile yet. Best case scenario is to have access to a set of scales (such as our part number 475-72593). A much more economical option is to purchase a set of our mock-up coil overs (Speedway part number 916-36037). These are an adjustable, ridged mounted strut that will allow you to build an entire car and transport it to a scale before you buy your shocks! Another great builder’s tip is to buy a piece of roll bar padding (part number 60-415) and put it over the mock up strut. This will simulate the diameter of the spring so that while you are building your suspension you can account for the actual room the finished shock will consume!

Shock angle

The angle that the coilover assembly is installed at has a large effect on what the spring rate will need to be. The greater the angle of the spring, the stiffer it will need to be to support the weight of the car. A coilover with a 10” 225 lb. spring that is installed at 0° straight up and down (90° from the axle centerline) will support 1450 lbs. That same assembly, when installed at a 45° degree angle would need to be a 450 lb. spring to support that weight! A great tool for figuring angles quickly is our part number 910-89409 from Deco.

Installed length

When deciding what installed length you use is another important decision you will need to make. In order for the shock to work to its full potential you should allow at least 2 ½” inches of compression before you hit the bump stops. You want to make sure that you have your ride height established, and then locate mounting points that will allow for sufficient travel in either direction. If you need a 12” mounted length at ride height you should get a shock that is approximately 9” compressed and 14” extended. When selecting the mounting points and ride height of the shock, select the longest shock that you can within reason. The more stroke the shock has, the less risk you will be at for bottoming out or overextending your shocks.

When you give us a call at Speedway Motors to help select your coilovers, have all three of these pieces of information ready to go and we will be sure to help get you the best coilover for your car!

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