• Please note that Viking has a very detailed spring rate calculator and an extensive database of vehicle specifications in order to assist you in determining the ideal spring rate for your specific set-up and intended use. Please call for assistance.
• The intended use of the vehicle is critical. An often overlooked concept when discussing spring rate is natural frequency. For example, we may get a call where an individual states that he needs a 500 lb. spring because that is what his buddy runs and it works great. Well, if that person's car is a clone of his buddy's car, that may very well be the case. However, in reality cars are set-up / finished differently. In many cases, the example given would actually involve two totally different cars. That is why it is important to match the spring natural frequency on his buddy's car, not the rate. We have a database of targeted natural frequencies for different vehicles, uses, etc. Some of these targets result in throwing some of the discussion below out the window. For instance, certain competitive pro-touring set-ups may result in a natural frequency where the springs unload at full droop making the shock preload a different discussion. If this is the case, we recommend a 7946-101 take-up spring kit.
• General rule of thumb: The shorter the spring, the higher the rate.This is generally the case as the shorter spring will obviously have less available travel. As such, the spring rate needs to change in order to lessen the spring preload at ride height to ensure sufficient compression travel before reaching solid height. If you increase the rate on the car with all others factors being equal, the natural frequency goes up. So when considering the mounting style of a shock, the spring length required should be considered to make sure it meets the desired goals. For example, some people will convert an upper mount on a front shock for a C5/C6 corvette to an eyelet. This results in a shorter shock and a shorter spring. A shock with less stroke and a higher natural frequency may work out great for a competitive handling situation. However, for a person who just wants to cruise, this may not be optimal. It is important to understand how any potential changes will effect the spring rates / natural frequencies.
• The shock valving must match your desired spring rate. A person with a handling application may determine that an 800 lb. front rate is needed to get to the desired natural frequency. This spring must be matched with a shock that has the valving to control that 800 lb. spring.

Note: Viking designed its coil-over shocks with the longest threads in the industry providing for the most adjustability. This increase in adjustability is only useful if the coil spring has enough travel to utilize this large range of adjustment. Viking coil springs are designed to provide for the maximum level of travel at the lightest weight, giving the Viking coil-over shock / coil spring combination the largest adjustment range in the industry.

Sprung Corner Weight (SCW):

Ideally, the individual corner weights of the vehicle would be determined by utilizing a scale. If only the total front or rear weight is known, simply cut it in half to estimate the weight at each corner. Be sure to account for the driver, passengers, and cargo that will be included when the vehicle is being driven. Next, the corner weight must be reduced by the unsprung weight to derive the sprung corner weight (SCW). The unsprung weight is the vehicle weight that is not supported by the springs. These types of components include the wheel/tire assembly; the brake components, such as rotors, calipers, and pads or the brake drums, shoes, and related components; steering knuckles; wheel bearings; and the axle housing, ring & pinion, axle, differential, etc. There is also a hybrid weight category for some components where the definition is not clear and concise. These include the shock absorbers, coil springs, leaf springs, upper and lower control arms (front and/or rear), trailing arm, ladder bar, panhard bar, and driveshaft, to name a few. There is a general 50/50 rule that states 50 percent of the weight of hybrid components is considered unsprung and 50% of the weight is considered sprung. While the accuracy of this can be and is debated, it is often used for simplicity. As you can see, this calculation can prove cumbersome and difficult to determine. In general, the corner unsprung weight on a vehicle will often lie between 75 and 150 pounds. All changes made to the vehicle must be considered when estimating the unsprung corner weight based on the above given range. Before moving on from this topic, it is important to discuss the on-going debates surrounding the benefits of reducing unsprung or sprung weight. While it is argued whether or not reducing unsprung weight is more beneficial than reducing sprung weight and what exactly the benefits are for straight-line improvements versus cornering, it is agreed upon that reducing unsprung or sprung weight will improve handling and performance, period. This is why Viking designed its coil spring line to provide the greatest travel at the lightest weight. Viking springs are often more than 25% lighter than the competitions' springs. That is like getting four Viking springs on your vehicle for the weight of three of the competitions' springs. Work is often done to save ounces, which is important, as everything adds up. However, Viking springs give you an opportunity to save pounds!

Spring Preload (SPL):

When a vehicle is at ride height, there will be a certain amount of preload on the spring. Most springs have a linear rate. For example, a 200 pound spring rate means that it will take 200 pounds to compress the spring 1 inch. It will take an additional 200 pounds to compress the spring a second inch, and so forth. This would mean a 200 pound spring that is compressed two inches at the vehicle's ride height would be supporting 400 pounds, as long as it was mounted straight up and down. The amount of spring preload will also depend on the stroke of the shock absorber. Recommended ride heights generally fall within 40% to 60% of the stroke available for either compression or rebound of the shock absorber. Ideal set-ups will fall closer to having 60% available for compression and 40% available for rebound. Sometimes a taller coil spring will be used where the spring will need to be compressed in order to mount it onto the shock absorber prior to installation in the vehicle. If this is the case, this amount of preload will need to be accounted for when determining spring rate. Using the theory that 60% will be available for compression, for a shock absorber that has a 5" stroke, the shock and therefore the spring, will need to be compressed 2" in order to have 60% or 3" of the stroke available for compression when the vehicle is at ride height. For a shock with an 9.00" stroke, the spring would be compressed 3.60", and so forth. An additional 1" of compression should be added for raising the spring nut up the coil-over shock absorber, which will allow for tuning in either direction. After the amount of spring compression is determined based on the stroke of the shock, a lighter or heavier spring rate may be utilized in order to satisfy the individual's desired use. The change in the spring compression can be accounted for in where the spring seat nut adjustment ends up on the coil-over shock absorber.

Correction Factor for Spring Mounting Angle (CF):

Once the proper correction factor is determined, simply divide the calculated spring rate with no mounting angle by the correction factor. For example, if your shock is mounted at a 20° angle and the spring rate without a mounting angle was determined to be 200 pounds, the proper spring rate for this application would be 225 pounds (200/.88=227). The formulas will vary depending on whether you have a straight axle or independent suspension application.

For straight axles, the spring rate is calculated as follows:



Step 1: Determine the sprung corner weight (SCW) as discussed.
Step 2: Determine the spring preload as discussed.
Step 3: Divide the sprung corner weight by the spring preload. SCW/SPL=calculated spring rate (CSR)
Step 4: Divide the calculated spring rate by the correction factor (CF). If there is no mounting angle, the correction factor equals 1 so the calculated spring rate will equal the actual spring rate. CSR/CF=actual spring rate (ASR)
Step 5: Determine a spring rate for the application desired. The rate in step (4) provides for an excellent ride and terrific handling. In general, a range of +/- 20% from this rate can be utilized. This will allow for lighter rate applications, such as drag racing to heavier rate applications, such as road racing.

For independent suspensions, the spring rate is calculated as follows:

D1: The distance from the pivot point of the control arm to the mounting point of the shock/spring.
D2: The distance from the pivot point of the control arm to the center of the ball joint.

Step 1: Determine the sprung corner weight (SCW) as discussed.
Step 2: Determine the spring preload as discussed.
Step 3: Divide D1 by D2 to calculate the motion ratio (MR).
Step 4: Divide the sprung corner weight by the motion ratio. SCW/MR=required spring force (RSF)
Step 5: Divide the required spring force by the spring preload. RSF/SPL=calculated spring rate (CSR)
Step 6: Divide the calculated spring rate by the correction factor (CF). If there is no mounting angle, the correction factor equals 1 so the calculated spring rate will equal the actual spring rate. CSR/CF=actual spring rate (ASR)
Step 7: Determine a spring rate for the application desired. The rate in step (6) provides for an excellent ride and terrific handling. In general, a range of +/- 20% from this rate can be utilized. This will allow for lighter rate applications, such as drag racing to heavier rate applications, such as road racing.