Are you measuring ride height when performing undercar service? You better. Before any alignment is performed, it is critical to measure ride height and check the condition of the springs and their mountings. If you decide to forgo this step, you could find yourself wasting critical time on the alignment rack to make a phantom adjustment.
Measuring ride height is more than stepping back and measuring visually with your thumb and one closed eye. To properly measure the ride height, the factory methods and specs must be researched. Neglecting to do this can affect all angles of alignment. A reasonable ride height is necessary to allow for suspension movement and ground clearance. Among other considerations, engineers design the chassis so that the ride height places the suspension at a particular point midway in its travel. Midway is not always center, however. Suspension design dictates how much travel is needed in both directions (jounce going up, rebound going down) from its static position.
How To Measure?
Ride height of a vehicle needs to be checked on an almost perfectly level surface while the vehicle is in a static and usually unloaded condition. But, talk to the customer to find out what types of loads they typically carry. If you feel that these loads can have an effect on the load ride height, ask them to bring the vehicle by when it is loaded to check ride height. This can help you to sell additional products like heavy-duty springs, helper springs or an air spring system. If a vehicle shows signs of bottoming, or has a trailer hitch, then heavy-duty or variable-rate springs might be suggested as a suspension upgrade.
The cost of these products is minor in comparison to irregular tire wear and additional safety and control.
Most OEMs won’t admit to the problem, but heavy-set drivers or passengers (more than 180 lbs.) can radically alter the lateral weight distribution (and side-to-side alignment) of a vehicle just by sitting in the front seat. Obviously, as weight distribution changes, so do the alignment angles of any lightweight import vehicle. When alignment angles change, a scrubbing action takes place, which accelerates tire wear.
Shimming a set of weak springs with spacers or inserts is only a temporary fix that may take care of the sagging and bottoming problems, but it won’t restore the ride quality or spring rate.
Spring into Action
Most springs are made of metal. Take, for example, a coat hanger or welding rod. If you bend it in the same area several times it will eventually break from metal fatigue. These same forces are acting on the springs. Every time the suspension is compressed, the spring is essentially bending. After a few thousand miles, this constant bending can cause the metal to change its temper and eventually fatigue.
Leaf springs date back to horse-drawn carriages. But, even with their ancient design, they have one advantage over coil spring. Leaf springs are able to dampen spring rebound though fiction in the leaves. Depending upon design, the shock absorber almost becomes a redundancy in the leaf spring’s ability to dampen spring rebound.
Coil springs have some advantages over leave springs. First, they are easier to package on today’s vehicles. Second, coil springs weigh less. Third, coil springs can be tuned to fit the vehicle better than leaf springs.
Variable-rate springs can provide many of the benefits of heavy-duty springs without increasing ride harshness. This type of spring offers a smooth ride, as well as increased load carrying capacity as the suspension is compressed. Variable-rate springs are a good choice for any vehicle that tows a trailer or hauls occasional overloads.
Heavy-duty springs are an upgrade option primarily for work vehicles such as pickup trucks. These types of springs can increase the load capacity of the vehicle, but also tend to ride somewhat rougher because of their higher spring rate.
Performance springs are typically shorter and stiffer than stock springs to lower ride height for improved aerodynamics and a center of gravity that’s closer to the ground. This improves stability and reduces body roll. But the trade-off may be a somewhat harsher ride.
If a customer wants standard replacement springs, they should have the same approximate spring rate as the original to maintain the same ride height and feel. If you haven’t noticed, some aftermarket springs have a slightly stiffer spring rate because they are somewhat shorter than the OE models. But once these springs are installed, they provide the same ride height and feel as the original springs.
If the a customer wants something other than standard springs, find out how he uses his vehicle to determine what type of spring would help him out best.
If brute handling capacity is what he needs, then heavy-duty springs should be recommended. Maybe the customer has a family vehicle application – minivan or station wagon. Variable-rate springs work in this situation because they provide a soft ride when the vehicle is lightly loaded, while extra-load carrying capacity is available when needed.
With each new set of springs you sell, try to sell new rubber insulators, too. These insulators are nothing more than a rubber seat that fits between the coil spring and the upper spring seat. If the old insulators wear out, the new springs will squeak. Most shock and strut manufacturers also supply a full line of rubber parts. Also, if you do not see an insulator when you are removing the old spring, it does not mean there was not there in the first place. Be sure to consult with your jobber or parts catalogs to see if any pieces are missing.
Sway bars are essentially springs that act against body roll. The purpose of a sway bar is to reduce body roll when cornering. It has little affect on straight line driving (unless one wheel is swallowed up by a chuckhole in which case some of the blow is transferred to the opposite wheel). Most cars today are factory equipped with front sway bars, and many have rear sway bars as well, but not all. Factory sway bars are generally tuned for everyday driving and tend to be soft unless the vehicle has a performance suspension. So there’s usually ample room for improvement here, too.
Replacing the stock front sway bar with a stiffer bar, and/or adding a rear bar if the vehicle lacks one, can make a big difference in vehicle stability and handling. Many SUVs can really benefit in this area.
Another differences worth noting between factory and aftermarket sway bars are the links that tie the bars to the lower control arms.
Most aftermarket sway bars come with heavier links and solid, or hard, plastic bushings that eliminate slop for instant response. Better still, some are adjustable.
Note: By changing the mounting position of the attachment links on either end of the sway bar, the bar’s leverage, and thus it’s relative stiffness, can also be changed. Playing around with the settings allows the bar to be fine tuned to almost any driving situation.
If you are installing an upgrade sway bar, see if the manufacturer recommends replacing both front and rear units as a set. Installing just one sway bar could create handling characteristics worse than before.
Slamming (lowering) is entering the mainstream because it looks good with 17-inch and larger wheels and it also lowers the vehicle’s center of gravity.
The desire to get closer to the ground has created a huge market for all types of lowering products. These include sport springs, coil-over kits, lowered control arms and air springs.
The right way to lower a vehicle is to install springs that are engineered to reduce ride height, or to install a coil-over kit on the shocks or struts that allow the ride height to be adjusted as desired.
Aftermarket performance spring suppliers have a wide variety of products from which to choose, so follow their recommendations as to spring rates and ride heights. A set of “sport” replacement springs, for example, might be only 15-20% stiffer than the stock OE springs and provide a significant improvement in handling without appreciably increasing ride harshness.
The next step up might be a set of stiffer street springs (25-30% stiffer) for the serious enthusiast who wants to push the envelope and is willing to suffer a little kidney damage in the process. Racing springs, which are typically 50-100% stiffer than the stock springs, are usually recommended for the track only.
Coil-over kits are a good choice for many applications because they allow the height to be adjusted as desired. Many coil-over kits allow the suspension to be lowered as much as three to five inches – or left stock. They’re affordable, too. Most kits retail in the $250-$300 range.
A coil-over kit usually includes a threaded lower spring mount that installs around the shock or strut and new springs. Some kits even use double springs (an inner and outer for a variable spring rate). Most kits can accommodate either stock or aftermarket shocks or struts. The adjuster is usually anodized aluminum and the springs are powder-coated or painted for appearance as well as corrosion protection. Some springs have variable spacing between the coils to provide a progressive spring rate for a smoother ride under normal driving conditions.
Installation of a coil-over kit is simple. Use a spring compressor to disassemble the strut, remove the OE spring, dust cap and bump stop from the strut, install the threaded adjuster sleeve on the strut and tighten the set screws to hold it in place. Then slip on the new spring, replace the bump stop and reassemble the strut.
Ride height is set with the coil-over kit by turning the adjustable spring perch to compress the spring. The adjuster is then locked in place. If ride height needs to be changed up or down later on, it’s a simple matter of unlocking the adjuster and turning it to reset the ride height. This set-up may also require wheel realignment and other suspension, wheel and tire modifications to avoid interference problems.
For those who want the ultimate in ride height adjustability, an air ride system can be installed to replace the springs entirely. Installation is a bit more complicated, and usually requires replacing the control arms to accommodate the air cylinders or air bag springs. An air ride system also needs a compressor, an air tank, and control switches and gauges to monitor and control the suspension.
Keep From Bottoming Out!
When a shorter set of springs or a coil-over kit is installed to lower a vehicle two or more inches, the stock struts or shocks may also have to be replaced with shorter ones to prevent the dampers from bottoming out. Any time ride height is reduced, suspension travel is also reduced. An added advantage with shorter struts and shocks is that they are up to several pounds lighter than the stock units.
The best approach here is to install a set of springs and shocks or struts that are engineered to work together. The dampening characteristics of the shocks are matched to the spring rate to provide the best all-round handling performance.
Adjustable shocks are a good choice for drivers who want the best of both worlds. The range of adjustment typically provides ultra-firm handling for serious racing, and reasonable ride comfort for everyday driving.