Determining and choosing the right length of Coilover spring is crucial to getting a smooth and safe ride. However, without knowing the right method of calculating tricks, many make mistakes while choosing the right Coilover spring. An accurate Coilover spring length is needed when lowering your car or increasing ride height. Therefore, knowing the basic information about how to determine Coilover spring length is needed.
Before replacing or changing the springs for your car, ensure the Coilover spring length is perfect. Incorrect size or shape springs are dangerous in many cases. It not only causes improper performance but also damages the shock absorbers immediately. Often, if the springs are not settled perfectly, the car will move up and down at inconsistent velocity.
So it is not an avoidable factor to measure and choose the correct height, weight, and size. Skipping it means you nailed your feet willingly. It’s advisable to determine the exact Coilover spring length to meet the best ride always.
Steps to Determine Coilover Spring Length Without Doing Mistakes
Usually, the spring length should be determined by determining the shock travel. Let’s give an example to get more clear and concise thoughts. Suppose, you have 14 inches of Coilover with a leveled spring plate. In this case, the lowering spring should be 16 inches and the upper spring 14 inches. To know more details about this, read this section carefully.
Step 1: Calculate the Lower Spring’s Height Under Load
Calculating lower or leaf spring height is straightforward when it’s under load. The first thing you should do is to air up all the tires. To do it safely and risk-free, ensure you have the tire pressure set for your vehicle. Next, you need to figure out the center cap on the wheel.
Take the measurement of the wheel’s diameter. At this stage, calculate the accurate spring rates according to the existing springs. As the vehicle is seated under its own weight, adjust the preload so that at least a quarter of an inch of the shaft is exposed.
Then, measure the bottom spring for one time. It supports the entire vehicle’s corner weight. On the other hand, the upper spring has limited operation as it has a stop nut.
Keynote: Remember one thing before measuring the new spring. New Coilover can stick in one place, especially in lighter vehicles. So when you go to measure, it is wise to shake or cycle the suspension in every possible direction.
Step 2: Measure The Compressed Length
Knowing the accurate dimensions of the Coilover spring is essential to measuring the compressed length of any spring. Also, the expected force at a certain height should be calculated before calculating the length.
Therefore, you need to identify the inner diameter, outer diameter, free length, total coil, and wire diameter. The formula to get exact and accurate data is ID= OD – 2D. Here, 2D double-wire diameters.
Again, move forward the suspension to the complete compression position so that measuring can be effortless. But if you have a heavy and solid vehicle like a heavy-duty truck, the measuring process is different. In this situation, you must get the job done to keep it horizontal, left and right tuck position.
There might be complications in placing the upper or lower mounts often. If so, you need to concentrate on putting the top mounts on the top in a high position. Another thing that should be considered is to look for the largest shock fitting so that you can limit the down travel with limited straps at any time.
Step 3: Measure The Extended Length
Getting the accurate and perfect Coilover spring length needs to ensure you calculate the spring extended length. Here the limiting factor could be the drive shaft and CV shaft angle, suspension binding, and shock’s expandable length.
However, it is recommended to limit the shock travel to 14” or less than 14” at about 1” and 2” for 16” or more than 16” larger shocks. When you accurately measure the extended length, you’ll go a step ahead to determine the perfect length of Coilover springs. Otherwise, the spring can’t be attached and the money will be wasted.
Step 4: Check The Lower Spring Specifications
Another important factor in determining the right spring length is to check the lower spring specs. It is essential for calculating the sprung corner weight and free height for the small coil, including its spring rate.
Remember the spring rate should be calculated in lbs. In most latest coilovers, there is printed data that shows you the specs of the springs like inner diameter, height, and spring rate.
Here is another term included and that is to measure the effective sprung corner weight. Here you should go through the following things.
- First, find how much the lowest spring compresses under load.
- Then minus the already-gotten height from the free height.
- After subtracting, write the result and calculate the effective corner height.
- Finally, multiply the subtracted result with the spring rate to get the effective cornering weight
Suppose, you have a 10” lower spring under load and the specification is 2.5 x 12″ x 350 lb.
Effective sprung corner weight = [ 12″ (Free Height) – 10″ (Measured Height) ] x [ 350 lbs. (Spring Rate) ]
= [2”] x[ 350 lbs.]
Step 5: Calculate the Needed Spring Rate
This process combines 3 different measurements. That means, to complete the measuring of the required spring rate to get accurate lengths, go through the following steps.
- First, you need to determine the desired ride height.
- Second, compute the required spring squat, and
- Finally, calculate the entire sporting rate.
Let’s discuss them in detail. First, determine the ride height that is needed. As you already have the effective corner weight, figure out the exact amount of correct spring squats. It should be done to keep the vehicle’s exact ride height or below the desired height. Remember to measure the data in inches for effortless calculation.
Now, time to calculate the exact spring squat. It is straightforward and the calculation is time-saving. Just put the value of the desired height and subtract the desired height from the entire Coilover spring’s travel.
Formula: Required Spring Squat = [Coilover Travel] – [Desired Ride Height]
A 16” Coilover with a 7” desired ride height can be considered.
Required Squat = 16”- 7” = 9”
Finally, you need to calculate the entire spring rate by applying the following formula. Just divide the required spring squat by the effective corner height.
Formula: Required Spring Rate= [Effective Corner Height] / [Required Squat]
Example: 750 lb Load with 9” required Squat
Therefore, Required Spring Rate = [ 750 lb ] / [ 9” ] = 83.33 Lbs. inch-1
Step 6: Pick New Spring Rates
Usually, there are 3 main types of spring rate Coilover available– single, double, and triple. The single Coilover spring rate is between 8” to 10” in height. The measurement of this particular spring is described already. You can choose the spring rate nearer to 84 lbs, which is closer to 100 lbs.
The double-rate Coilover spring height is between 8” to 16”. In this case, the Coilover has two springs. This is why you need to multiply the needed spring rate by 2 and split the sub-triplicate. So if you double the above date (84 lbs.) you will get 168 lbs. Here you need to choose both springs that match this rate. In this particular case, it is wise to choose a 150 lb. top spring and a 200 lb. lower spring rate.
Third, the height of the triple Coilover spring ranges from 16” to 18”. This Coilover spring is specially used in applications with a lower ride height. There is an extra spring that soaks up the additional space. The calculation process of the triple spring rate is similar to the dual spring rate. But here you must subtract the compression of the tender spring from the shock travel.
Step 7: Shock Size Determination
Before determining or measuring the right spring length, measure the accurate shock size. What type of coil spring rate you choose mostly depends on the shock’s size. Here is a table (well-known shocks King) to understand the size of the shocks and correct length according to the diameter.
|Size of the Shock (Inches)
|Compressed Length [2.0”]
|13.0″ – 19.0″
|14.0″ – 20.0″
|15.0″ – 23.0″
|16.0″ – 24.0″
|17.1″ – 27.1″
|18.4″ – 28.4″
|19.6″ – 31.6″
|20.7″ – 32.7″
|21.6″ – 35.6″
|23.3″ – 37.3″
|23.6″ – 39.5″
|26.0″ – 42.0″
Step 8: Choose the Right Spring Size
Spring size is another considerable factor in determining the correct length. There are two types of Coilover spring plates– raised and flat. If you have raised spring, then choose two springs that are a perfect match for the travel
Suppose, you have a 14” raised plate Coilover. In this circumstance, you need to run dual 14” tail springs. But when you have a flat spring plate, you need to choose the lower spring 2” taller than the shock’s travel. So the math is easy here, isn’t it?
Step 9: Shock Cylinder Size
Measuring the Shock cylinder size is also going to be a considerable factor in getting the right Coilover spring length. Shock travel is related to the shock and spring length.
Again, cylinder size is directly related to the energy. It is advisable to go for the shock that is slightly big. So measure the cylinder size, tire size, and any other related terms to achieve the accurate length coil spring.
How to fix the damaged Coilover spring: Troubleshooting Guide
Coilover springs are crucial to reducing excessive road bumps, sagging, premature tire wear, and many more. But sometimes, they can be broken or damaged and need to be fixed immediately. Though it’s recommended to replace the damaged springs instead of repairing them, it is costly. Therefore, knowing how to fix the Coilover springs is handy.
- Identify the Problem: The first thing you should do before repairing the coil spring is to determine the exact problem. The problem might be a broken coil spring, rusty and decayed rod, loosened Coilover spring, etc. Remember before checking, you must lift your car at a minimum height (top of your head). If you find the spring is broken, then come to the next point.
- Open the Wheels: Lower the car slightly down and pop the rear wheels off. Here you can use the earthquake XT impact gun from Harbor Freight. Pull the nuts out and take off the wheel. Take off the other tires this way. If the coil spring is loose, change it immediately.
- Take off the Spring: Now, take apart the springs and check how much it damages. If the damage is tiny, fix it by yourself or take it to the garage. But if the damage is noticeable, replace them immediately.
- Take them into the Workshop: Take the deviated spring to the workshop and leave it for them. Fixing the Coilover spring is pretty expensive because the required parts are very complicated too. However, if you are determined to fix them, replace the seals and fill the Coilover with a certain amount of hydraulic fluid.
- Purchase New Coilover springs: It is the best solution to replace the whole parts instead of repairing them. Repairing can be a short-term solution. But if you replace the old one with a new one, the performance, smoother ride, and all the great things will happen. Needless to say, the repair costs you little and will provide a better ride for a certain period.
Coilover springs play a crucial role in providing discomfort-free, shaking-free, consistent, and smoother driving with accurate ride height. But before that, the length of the springs needs to be accurate. In most cases, vehicle owners are not concerned about this.
As a result, they can’t get the performance they want. The article above shows you how to determine the Coilover spring length and the fixing procedure when it’s broken. Hopefully, this step-by-step guide will be helpful for you to buy your next Coilover springs.