|Our coilovers will typically
use a Dual Rate spring setup. We use a Main Spring and a Tender
The Main Spring is
the bottom spring that covers the shaft of the shock. The Main Spring should
have the same or higher spring rate and a longer length than the Tender
Spring. The rate of the Main Spring will be the Secondary Rate.
The Tender Spring
is the top spring that covers the body of the shock. The Tender Spring
should have the same or lower spring rate and will most likely be shorter
than the Main Spring.
A Dual Rate spring
configuration will have a Primary Rate that is a combination of the Main
Spring and Tender Spring. When the Tender Spring coil binds or hits the
stopper, the Secondary rate will take effect.
To figure spring rate, we
must know the vehicles WHEEL TRAVEL, SPRUNG WEIGHT, and DROOP PERCENTAGE.
We need to know the suspension configuration as well. (A-Arm, I-Beam, Four
Link rear, etc.) See Figures 1-3
You will need to measure
the distance from the suspension pivot, to the lower shock mount, and the
distance from the suspension pivot to the end of the arm, or tire centerline.
If your shock will be mounted at an angle, you will need to measure that
angle as well. For our calculator, 0 degrees is straight up and down. The
further away from vertical, the higher the angle number..10 degrees, 15
The SPRUNG WEIGHT
is the weight that each shock is supporting (i.e., the corner weight less
unsprung weight). Unsprung weight is the tire and wheel, hub, upright,
brakes, and about half the weight of the shock and A-Arm or I-Beam. For
the rear suspension of a truck, the unsprung weight is the tires and wheels,
the entire rearend and half the weight of the shock and trailing arm.
The DROOP PERCENTAGE
is the desired ride height as a percentage of total wheel travel. (i.e
if you have 10" of wheel travel, and you want the vehicle to sit right
in the middle of the wheel travel at ride height, that would be 50% droop.
If you wanted it to sit lower..say 7" into the wheel travel, that would
be 70% droop.) Most desert cars get around 40% droop, with rockcrawlers
getting up to 70% droop.
Below is the information
needed to properly calculate Spring Rates.
1. Wheel travel
2. Sprung weight of each applicable vehicle corner
3. Pivot to lower shock mount distance (D1, D3, or D5)
4. Pivot to end of suspension arm or tire centerline (D2, D4, or D6)
5. Desired droop travel
6. Shock angle from vertical (in degrees)
Enter the above info into
our calculator to get your recommended spring rates.