Whether you're trying to raise or lower your vehicle's suspension, the basic idea is simple, but how you accomplish it is not. Changing the ride height covers everything from springs to shocks to spindles -- and more. Several different products are available for almost any imaginable application, but every vehicle is different, so it's difficult to compile a list of lifting and lowering parts that covers them all. Instead, we'll provide a broad overview of these different applications, and the how they can impact your vehicle's ride and handling.
Coils and Ride Quality
To get an idea of what's involved in the lift/lower process, let's start with just the springs, covering some basics on form and function. How much a spring compresses or extends is determined by its "spring rate," measured in pounds-per-inch of deflection. For instance, if the rate is 100 pounds per inch, under a load of 200 pounds the spring will deflect two inches. Several factors determine spring rate: the number of active coils, the diameter of the coils, and the diameter of the spring wire.
To lower a vehicle, you could simply cut a coil out of the spring with a welding torch, but that's not recommended because it will likely sacrifice ride quality and may affect the suspension geometry. To preserve ride quality, it's better to replace it with a drop coil that compensates for the change in ride height with variations in the factors mentioned above.
For example, some companies offer progressive-rate coil springs, which start out relatively soft but get stiffer as they're compressed. The springs are wound progressively looser from top to bottom, creating the variable rate.
Alternatively, to raise the vehicle, you would need to use a spring with more coils, and/or a larger diameter of coil and tubing. For coil and leaf springs, the general rule is that the taller the spring is, the stiffer it is. On most coil and leaf-spring-equipped suspensions, ride firmness will remain close to stock on lifts up to four inches. From there on up, ride becomes increasingly firm.
Along with this increase in height come performance tradeoffs. A tall spring will cause the vehicle to feel unstable during cornering. This instability is because the more distance a spring compresses or extends, the more the vehicle "rolls" around on its suspension. This rolling is called weight transfer, and it is caused by centrifugal force acting on the weight of the vehicle as it goes around a corner. Weight transfer can overload a tire's grip, which ultimately hurts traction and handling.
Adding Other Components
The complexity of the raising/lowering equation increases when modified springs are used in concert with other suspension components. Combining drop coils with a dropped-spindle kit can really turn your car, truck or SUV into a pavement scraper. (We're talking about 2WD vehicles here, since there are few parts for dropping a 4WD suspension.) The location of the axle in the drop spindle is higher than stock, thus lowering the vehicle. Drop spindles are available in two- to three-inch drops, depending upon which vehicle you own. (Some trucks, such as pre-'97 Fords, have I-beam fronts, and can be lowered using a dropped I-beam kit instead.)
Another method is to use lower control arms that replace the stock ones and essentially move the coil spring down. However, problems may arise if the control arm lies below the scrub line (the distance measured from the ground to the bottom edge of the wheel rim.)
For lifting, you may be able change the mounting point of the control arms, but that doesn't necessarily work for every type of suspension (as with spindles, think in reverse: a lower mounting point raises the body, a higher one lowers it). In some cases, it may be necessary to change the mounting points of just the lower control arms, and then modify the spindle to make up the difference in spacing.
To the Rear
If your truck or SUV has leaf springs in the rear, the same basic principles used on coils apply to lifting/lowering: alter its shape and stiffness by adding or removing a leaf or two. Or you can use dropped leaf springs that replace the stock leaf springs with a flatter (less arched) mono-leaf design. Using dropped leaf springs usually means sacrificing some of your payload capacity. They're available in one to five-inch drop applications.
Shackles provide one to two inches of lowering. They move the rear leaf springs higher to make your truck lower. Hangers, which attach at the front of the leaf springs, essentially move the leaf spring mounting location up two inches. They are usually combined with two-inch shackles for a total of four inches of lowering. Just keep in mind that any changes in stiffness and height will have an impact on handling and ride quality.
Another way to change ride height in the rear is to insert blocks, for either lifting or lowering. If you've already installed a flip kit (which relocates the axle from below the leaf springs to above), blocks placed between the axle and leaf springs will lower a vehicle farther. The blocks are mounted in the rear by using extended U-bolts in place of the stock U-bolts.
It's really important to note that front lift blocks are illegal in nearly every state because they are unsafe and turn a vehicle into a severe road hazard. And by rear lift blocks we don't mean bricks, hockey pucks, or wood 2x4s. Store-bought lift blocks aren't expensive and won't stiffen your ride.
So, what are the cons? Lift blocks increase spring wrap and long U-bolts can often work loose. Adding another leaf to the rear for lift is a much better alternative to adding lift blocks, but you don't get as much lift. Adding only one more leaf is best because the more you add, the stiffer the ride, and you may not continue increasing the height with every leaf added. Thin, full-length add-a-leaves generally give a better ride than short, thicker ones.
Airbags offer an ideal combination of features. They provide an adjustable ride, load-leveling capabilities, and even ride-height adjustment. Airbag systems are available in many different configurations. By adding airbags to a truck, heavy loads can be handled easily without bottoming out. Some airbag systems replace leaf springs and provide up to eight inches of height adjustability.
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