We install Ranchos new coilovers in our Project TJ. click here to see the process!
Besides the cool factor, they do the job of controlling the body and tires much better than standard dampeners. Most coil-overs can be custom valved and adjusted to your needs. Allowing allot of suspension travel, they have the benefit of spring force through the entire range of moment. The spring rates are easy and fairly inexpensive to change. Allowing for custom applications and changes in vehicle weight. The remote reservoir aids in cooling, and in general these units can take a beating.
The longer springs allow for a softer spring rate improving on and off-road ride. This is why they are so cool.
So why go with the Ranchos?
The main reason is the adjustability. You can change the valve response with a turn of a knob, or even from in cab on the fly. Also the Ranchos are fairly compact for how much travel you get from them. They come in two sizes; 32 inch extended length (19 inches compressed) giving you 13 inches of travel, and the 36 inch extended length (21 inches compressed) giving you 15 inches of travel. Other manufactures with 14 inches of travel are up to five inches longer in the body of the unit, taking up lots of room under the vehicle.
The threaded sleeve gives you the ability to dial in the ride height. This allows you to compensate for added weight like a new bumper or winch.
Based on the RS9000 series, the coilovers have an adjustable valve. It is a nine position knob, setting of '1' is the softest, and '9' is the firmest. Set on the firmest setting the shocks are near rock hard on lighter vehicles. The 15 stage valve on the piston is set to hold the vehicle to the road, and give on harsh bumps. Giving a firm but smooth ride.
The spherical ends are a standard half inch. They are welded to the body and rod. They are not replaceable, but should last under regular off-road conditions. We cant even get the Jeep past 90mph on the highway, much less 120mph in the desert, so they should last a long time.
Rancho makes selecting springs easy. They have a chart of spring rates you can order with the unit. They also have a worksheet in Adobe format on how to select the proper rates for your application. We have a page dedicated to this to help show how its done, here.
Springs are measured in pounds per inch. This means that the spring will support X lbs for ever inch of compression. This is measured in a press with a scale. Some are measured from the start of the compression, others are measured in the ride height range. Basically a 250 lb spring will compress one inch for every 250 pounds placed on it. So at 500 pounds the spring will be compressed two inches, and at 1000 pounds four inches.
Spring rate is determined by the size of the material used, the diameter of the coils, and how many coils there are. A spring made from a constant size wire, and symmetrical coils will have a linear rate. The coils that are in contact with the mounts do not move and are considered dead coils and do not contribute to the spring rate. Also when a coil contacts another coil it is considered in a bind, and dead.
A progressive spring is one that increases the amount it can support per inch as it compresses. At the start it may only be 100 pounds per inch, halfway through the compression it may be 300 pounds per inch.
This can be achieved several ways. Reducing the diameter of the coil at the end will increase the rate. This can be seen in the rear springs of a TJ. The coils taper near the ends, however they do this fairly quickly, and the change in rate is not significant until near full compression. Changing the size of the wire stock while making the coil is an obvious way. Changing the spacing of the coils can cause coils to contact each other sooner than others creating more and more dead coils while compressing, increasing the rate overall of the rest of the compression.
Progressive rates using two or more springs.
Most off road coil-over designs use two springs or more springs. This gives a progressive rate effect similar to changing the diameter of the wire used in one spring. The smaller springs are called tender springs. The heaviest one is called the main spring. The springs work together. The result of the combination is a softer spring rate than any of the springs separate. Pictured to the left is an 80 lb spring on top and a 250 lb spring on the bottom. If you place 300 pounds on the springs the tender spring will compress 3.75 inches and the main spring will compress 1.2 inchs. This of course totals 4.95 inches. This is 60 pounds per inch, less than either spring alone. This combined spring rate is in effect until the tender is compressed all the way, at which point the spring rate becomes that of the main spring.
Little known facts.
A little information about springs, as few persons know (for sure) about the coil springs under their vehicle. A spring does not bend as it compresses, it twists, like a torsion bar. Also it will not change its rate over time. A spring may take a new 'set' if it is over stressed, meaning it may loose height, but the rate will not change. For instance, set up a torsion bar test jig in your shop. A torsion bar can only rotate so far before deforming. Lets say 90 degrees for this instance, when you rotate it past 90 degrees it deform and will not return to its original position. However it will still have the same spring rate (or very close to it). A tall spring with few coils may not be able to compress all the way down without loosing its original set. However a spring can be designed to compress and contact itself (bind) before it reaches this point of no return and hold its set. The latter is how most tender springs are made for coil-overs. The disadvantage to this design is that the coils bind fairly quickly. In some cases a 12 inch spring will only have 6 inches of motion before it binds, while a lighter spring the same height will travel 8 inches.