Coil Spring Information

Common spring rates for Suzuki modification

Tracker Sidekick 2dr Convertable

452.8 PPI Front 156.5 PPI Rear

Tracker Sidekick 4-dr

508.7PPI Front 177.9 PPI Rear

Ford Ranger 4wd front coils (Rangerstation.com) 500 PPI

Jeep Cherokee front coils (Rangerstation.com)
Rancho's #6423 3" lift spring for the Jeep XJ is rated at 240 PPI

This article is on going and not yet complete

I frequently get the question, Can I just swap springs.... Welll Yes, And No !!!

Read the "Facts about coil springs" listed below to get a better understanding of what you can and can't do.

Here are some facts about coil springs.

What is Spring Rate?

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Spring rate refers to the amount of weight needed to compress a spring an inch (Example:500# per inch) To understand and properly check a spring for rate you need to know the factors that determine the rate of the spring. Fortunately, there are only three things that affect spring rate, so there's not that much to remember!

1. Wire diameter. This affects rate since greater diameter wire is stronger than lesser diameter wire. So, when wire diameter is increased, spring rate increases.
2. Mean diameter of spring. Mean diameter is the overall outside diameter of the spring less one wire diameter. When mean diameter increases, the spring rate decreases.
3. Active coils. Determination of the number of active coils varies according to spring design. Count the total coils minus two for springs with both ends closed (includes all AFCOILS). Count the total coils minus one for springs with one end closed and one end open. As the number of active coils increases, the spring rate decreases.

If a spring's rate is linear (most racing springs have linear rates) its rate is not affected by the load put onto the spring. For example, a linear rate spring rated at 500#/inch will compress 1" when a 500# weight is placed onto the spring. If another 500 pound weight is put onto the spring the spring will compress another inch. At this point the load on the spring has increased to 1000 pounds. The rate of the spring, however, remains constant at 500#/inch.

If the load put onto a spring increases the rate of the spring, the spring is said to have a progressive rate. Progressive rate springs are sometimes used on torque arms to absorb engine torque. Keep in mind that the load (or preload) put onto a progressive rate spring can greatly increase the rate of the spring.

Typically, progressive rate springs are made by varying the spacing between the springs' active coils. During compression the close coils bottom out and deaden. This reduces the amount of active coils and spring rate increases as a result.

Springs that are designed to include coils of different diameter or are wound using a tapered wire will also produce a progressive rate.

Most coil springs are actually progressive to some degree

The front springs on a IFS Suzki (used in a A-arm aplication) are under twice the load of those used in a solid axle configuration. In Short most solid axle type coils will collapse under the leverage weighted load on the front of a Suzuki IFS vehicle.

Pictured below are Cherokee fronts on a 4-dr Kick...

These springs are fully colapsed / bottomed out. They will not support the weight of my Kick due to the IFS A-arm leverage.

Here is a formula to find the PPI measurment of Coil springs....

http://therangerstation.com/tech_library/coilspringrate.htm

Coil Spring Rate Formula:

11,250,000 - Torsional Modules For Steel (Constant)

CSPWD - Coil Spring Wire Diameter (How thick is the wire?)

8 - Constant

NOAC - Number Of Active Coils (Coils that are free to move. Not coils seated. It may be that 1/2 of the top and bottom coil is seated causing a spring with 8 coils to have the distance of 7 free.)

CMD - Coil Mean Diameter (The diameter from center to center of the coil. Measure the diameter of the coil from wire center to wire center. If you know the coil is .5 inches thick and the outside diameter of the coil spring is 3 inches, then the Coil Mean Diameter would be 2.5 inches)

(11,250,000 x (CSWD x 4)) {Divided by} (8 x NOAC x (CMD x 3))

All Measurements in inches - Enter as decimal
For Inch Fractions To Decimal Chart, Click HERE

http://therangerstation.com/tech_library/fractionstodecimals.htm

Those Ford Ranger Guys at therangerstation.com have certinly done their home work and have a very nice site.