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Spring Rate Calculator

Coilover Overview: Page 1 | Page 2 | Page 3


 
The steps below will help you to find an approximate spring rate for your coil-over application. Enter your suspension measurements in the white boxes below.

This calculator will only give approximations depending on the accuracy of your information. Use at your own discretion.

*Yellow fields denote calculated cells, you do not have to enter values in them


Find your Spring Rate for:
Choose which end
Vehicle Front End:
Vehicle Rear end:
Step 1 – Determine Sprung Weight
Corner Weight:
(1/2 the front or rear weight)
Use an accurate racecar scale that will weigh each corner of your car. A trucking company scale meant to weight 80,000lbs may not be accurate enough for a 3000 car. Make sure the vehicle is loaded with driver, passenger and cargo just like you will drive it or race it.

Approximation of Curb Weights
Body
Type
Avg Weight Avg Front Corner(55%) Avg Rear Corner(45%)
Street Rod 2500-4000 687-1100 562-900
Coupe/Convertible 3000-4000 825-1100 675-900
Sedan 3000-5000 825-1375 675-1125
SUV 5000-8000 1375-2200 1125-1800
Street Trucks 5000-8000 1375-2200 1125-1800
See Specific Vehicle Weights for Cars and Trucks

The weight balance between the front and rear of a vehicle can range widely from 50%/50% (Front/Rear) to 60%/40% (Front/Rear). If you guessing blindly use a 55%/45% weight balance, however its much more appropriate to measure your car.

Example corner weight using weight balance:
To get the corner weight of your car, take an example total weight of 3800 lbs, multiple it by the front end weight bias.
ex: 3,800 x 55% (front end weight balance) = 2,090.

Then divide that number by 2 to get the corner weight of the front end of the car,
ex: 2,090 / 2 = 1,045.

Unsprung Weight:
(1/2 the front or rear weight)
“Unsprung weight” is vehicle weight not supported by the springs. Examples include: Tire/wheel assembly; brake rotors and calipers (or brake drums and components); wheel bearings; steering knuckle; hanging weight of the control arm (or trailing arms on rear axles); differential and axle weight; 1/2 of the spring and shock absorber weights. Unsprung corner weight is usually around 70-120 lbs.
Sprung Weight: Sprung weight = Corner weight – Unsprung weight. It is the weight supported by the spring and is the only weight used in calculating spring rates.
Step 2 – Calculating Motion Ratio
The “motion ratio” is the mechanical advantage (lever ratio) that the wheel has over the spring in compressing it.
Dimension A: Dimension A – Measure 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 the “coil-over assembly.”
Dimension B: Dimension B – Measure the distance from the control arm pivot point on the subframe to the centerline of the ball joint.
Motion Ratio: Motion Ratio = Dimension A / Dimension B
Step 3 – Coil Spring Angle
Spring Angle: Using a protractor or similar measuring device; measure the angle of the centerline of the spring or “coil-over assembly” from the horizontal of the control arm (or axle if calculating the rear). In most cases this will be somewhere between 75 degrees and 90 degrees. Most conventional springs and many strut suspensions are very close to 90 degrees, and 90 degrees can be used for the angle. This measurement helps determine the “force angle” and resultant spring force applied to the control arm.
Step 4 – Select your shock stroke and spring length
Select your shock stroke and spring length
The left drop down box includes all popular front end coilover dimensions that RideTech offers. You will want to select the shock stroke that will fit your suspension design
Step 5 – Spring Rate
Below are approximate spring rates for your coil-over application. This calculator will only give approximations depending on the accuracy of your information. Use at your own discretion.
Cruiser / Daily Driver Performance Driving Racing
Spring Rate: Spring Rate: Spring Rate:
Preload: Preload: Preload:
Part Number:
 
Part Number:
 
Part Number:
 
Recommended spring rate to optimize ride quality. Its best used for crusing, day to day use, and long distance driving. Recommended spring rate for performance driving in events like an autocross or simple roadcourse. Recommended spring rate for full on racing with sticky tires.
Note: Preload
Preload is the distance you will want to tighten the lower coilmount on the coilover to compress the spring, this will put shock compression near 50% of its stroke when the car is resting at ride height. This should be done before the coilover is installed. To do this you will need a spanner wrench. Adding more preload will raise the car.

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