Porqupine82
New member
I figured I would share a little bit of good knowledge regarding spring rate, and how it applies to you. This will help you decide what suspension is best for your application, and what your needs really are.
Let's get started.
What is spring rate?
Spring rate refers to the amount of weight that is needed to compress the spring one inch. If the rate of the spring is linear, its rate is not affected by the load that is put on the spring. For example, say you have a 400 lb. per inch spring - it will compress 1” when a 400 lb. load is placed onto the spring. If another 400 lbs. is put onto the spring, the spring will compress another inch. At this point the load on the spring is 800 lbs. But... rate of the spring remains constant at 400 lbs. per inch. This is contingent upon the spring being mounted completely vertical.
If your spring is mounted at an angle (most are) you will need to factor that into your spring calculations. Measure the angle of your spring from vertical (A) in degrees.
ACF=COS(A)
Shock Angle Angle Correction Factor (ACF)
10° .98
15° .96
20° .94
25° .91
30° .87
35° .82
40° .77
45° .71
The greater the angle at which the spring sits, the stiffer the spring rate needs be to support the same weight. Therefore, you should determine the spring needed for the application if the spring is installed completely vertical. Factor in everything the springs will support, such as front bumper, engine, dual batteries, winch... EVERYTHING. Then, to compensate for springs at different angles, find your ACF using the information above, and divide your straight mounted spring rate by your ACF.
Straight Mounted Spring = 400 lbs.
Spring Mounted at 30° = 400/.87 = 459 lbs.
Spring Mounted at 15° = 400/.96 = 416 lbs.
Etc.
For reference here are various spring rates of some manufacturers. This was obtained from ExPo and some personal knowledge
Factory 4th gen 4runner: 500 lb/in approximate
OME: 590 lb/in
All Pro, Fox, Walker Evans: 600 lb/in
Icon, King, Swayaway: 650 lb/in
Radflo: 600 or 650 lb/in
Overland Warehouse (Radflo 2.5 dia): 700 lb/in
Dobinsons MRR: 586 or 730lb/in
Let's get started.
What is spring rate?
Spring rate refers to the amount of weight that is needed to compress the spring one inch. If the rate of the spring is linear, its rate is not affected by the load that is put on the spring. For example, say you have a 400 lb. per inch spring - it will compress 1” when a 400 lb. load is placed onto the spring. If another 400 lbs. is put onto the spring, the spring will compress another inch. At this point the load on the spring is 800 lbs. But... rate of the spring remains constant at 400 lbs. per inch. This is contingent upon the spring being mounted completely vertical.
If your spring is mounted at an angle (most are) you will need to factor that into your spring calculations. Measure the angle of your spring from vertical (A) in degrees.
ACF=COS(A)
Shock Angle Angle Correction Factor (ACF)
10° .98
15° .96
20° .94
25° .91
30° .87
35° .82
40° .77
45° .71
The greater the angle at which the spring sits, the stiffer the spring rate needs be to support the same weight. Therefore, you should determine the spring needed for the application if the spring is installed completely vertical. Factor in everything the springs will support, such as front bumper, engine, dual batteries, winch... EVERYTHING. Then, to compensate for springs at different angles, find your ACF using the information above, and divide your straight mounted spring rate by your ACF.
Straight Mounted Spring = 400 lbs.
Spring Mounted at 30° = 400/.87 = 459 lbs.
Spring Mounted at 15° = 400/.96 = 416 lbs.
Etc.
For reference here are various spring rates of some manufacturers. This was obtained from ExPo and some personal knowledge
Factory 4th gen 4runner: 500 lb/in approximate
OME: 590 lb/in
All Pro, Fox, Walker Evans: 600 lb/in
Icon, King, Swayaway: 650 lb/in
Radflo: 600 or 650 lb/in
Overland Warehouse (Radflo 2.5 dia): 700 lb/in
Dobinsons MRR: 586 or 730lb/in
