So you want to buy a set of control arms. Okay, easy enough. Do you want tubular or boxed arms? Picking a design style is fairly straightforward. Are you going to race the car? It’s a legit question. How about color? These questions are getting simpler. What bushing do you need? …um.
Chances are that’s the most difficult question you’ve had to answer yet. That’s OK, like most enthusiasts, you probably haven’t given that one much thought. Here’s the problem—it’s the most important decision you have to make! The bushings you pick will directly affect performance, ride quality, and comfort of the vehicle. If you’re just looking for a stock replacement for a worn out rubber bushing, there isn’t much need to keep reading. If you want to know why bushings are that important and want to know how to pick the bushings that will work best for you, this story is for you!
Ask five people which bushings you need in your car and chances are you’ll get five different answers. The simple fact is the choice is very subjective. There are a lot of factors that play a big roll in the decision you have to make. There are a bunch of options and each comes with its own set of pros and cons. To learn more about it we turned to the experts at BMR Suspension.
“Bushings are the direct connection between the suspension link and either the chassis or the differential (rear), or front tires and the chassis (front)” said Brett Rockey, BMR’s Product Development Manager. “Though this seems like an obvious and almost insignificant fact, the bushings do a lot more than you may think. Most importantly, torque is transferred through the drivetrain and the bushings are the first piece of rear suspension that sees the forces of that energy. In the front, the bushings directly affect steering input and performance, as well as how well your vehicle traverses imperfection in whatever road you’re driving on.”
Starting to see why they are important?
Soft, broken, or worn out bushings deflect, and deflection is wasted energy. When a bushing is compressed and deforms under load, it absorbs energy instead of transferring it to the rest of the chassis. When the bushing deflects, it also allows for unwanted movement. This movement can allow the suspension to move in weird ways, throwing off the alignment of the front or rear wheels. Bushings with harder (higher durometer) material will reduce or prevent this deflection, but there is a tradeoff.
Harder bushings do not absorb noise and vibration commonly known as NVH (Noise, Vibration, and Harshness). With harder bushings, NVH is transferred through the chassis, and things like road noise, gear noise, and driveline vibrations become much more apparent to the vehicle’s occupants. A simple way to look at it is the harder the bushing, the higher the NVH. What are considered tolerable levels of NVH is very subjective. One person may want a plush ride with no noise, and a polyurethane bushing will be too aggressive. Another person may love the race car-like feel, and solid-mounted rod ends are just right.
When cars are designed, the factory doesn’t think about performance when picking bushings. The focus is on giving the customers a product that will absorb as much NVH as possible so the ride is quiet and comfortable. They are also trying to do this as inexpensively as possibly. Thankfully, this leaves room for aftermarket suspension companies to greatly improve on the factory product.
Rubber bushings are what come from the factory. They rot, rip, wear out, deflect (a lot!), and are simply inefficient at transferring large amounts of power. But there is a plus side to rubber. It does a great job of controlling NVH. If you want a smooth, quiet, noise-free ride, then rubber is for you. For everyone else, there are much better performance options.
Polyurethane is a synthetic material that doesn’t rot or deteriorate due to normal environmental factors (oils, road salt and grime, ozone, etc.). It reduces deflection over rubber bushings, while still absorbing good amounts of NVH. It is hard enough to stand up to high compression loads (hard launches, hard acceleration), while remaining compliant enough to give you enough articulation for handling applications.
One of the biggest benefits to polyurethane is its relatively low cost. Polyurethane is a chemical that is poured into a mold, and it solidifies into a bushing. This means high volumes of bushings can me made without a huge investment in equipment or machining costs. Polyurethane is also an extremely versatile material. It is used for control arm bushings, sway bar bushings, differential bushings, engine mounts, transmission mounts, and body mounts.
Another benefit to polyurethane is the ability to make bushings in different durometer (hardness). Having different durometer bushings allows you to pick the level of performance you want. It also gives you options to how much deflection and NVH you want to live with.
Delrin is a super-hard polymer that doesn’t deflect. This is great for IRS cradle bushings or A-arm bushings where there is only motion in one direction and articulation is not important. These style bushings are not normally used for rear control arms where articulation is important. For that, rod ends or spherical bushings are the way to go.
Rod Ends and Spherical Bearings
You don’t see a lot of rod ends or heim joints used outside of hardcore race applications. This is because rod ends connect the suspension link solidly to the chassis or different, and do not eliminate any of the vehicle’s NVH. The biggest benefits to rod ends are there is no wasted energy as power is transferred through the chassis, and they offer very high levels of adjustability. These reasons are why rod ends are immensely popular in the racing community.
Like bushings, there are many options when it comes to rod ends. There are two-piece ends, three-piece ends, loaded slot ends, oversized shank ends, with PTFE self-lubricating liners, and without. It can get confusing. Luckily, companies like Viking Performance are here to help.
“When determining which rod end to use, it is very important to consider strength and misalignment angles,” said Christina King of Viking Performance. “It is highly recommended that users carefully measure the angles for each rod end application, and make sure that the manufacturer’s misalignment angle is large enough to handle the application. Rod ends will prematurely wear, bind or break if the misalignment angle is exceeded. It is also very important to consider the operating loads that your rod end will experience and ensure that the selected product has a load rating well in excess of the operating loads you expect. In addition, it is very important that the rod ends are being used correctly in the application. In general, rod ends are designed for a radial load, (pulling and pushing up and down on the rod end), not an axial load (a load pushing sideways on the rod end ball). The axial load on a rod end should never exceed 15-percent of the joint’s radial capacity for two-piece units, and 10-percent of radial capacity on three-piece units. Lastly, rod ends are wear items. They will not last forever. Rod ends need to be inspected for wear and replaced when necessary.
“It may be difficult for racers to fully understand the differences in these products. It can be quite the maze to work through with all the different manufacturers and the resellers pushing many different brands, which often includes private label brands also. The racers need to ask questions and research the brands of rod ends to truly understand where they are coming from and what the features and benefits are of each. While it can be a mistake to buy a rod end solely off of price, it is also a mistake to overpay for product that is the same or lesser quality of a more competitively priced unit.”
When it comes to picking bushings, application is key. It’s difficult to get everything you want, and there usually is always going to be a tradeoff. Soft bushings offer the least amount of performance, but the lowest NVH; rod ends offer the most performance with the most NVH. Polyurethane bushings are a great all-around bushing, but don’t give you as much articulation for hardcore handling applications. It is important to take a long hard look at exactly what you are going to do with you car, and make your decision based on what you’re willing to live with and what you can’t live without.
Street performance is probably the largest enthusiast group. Street performance can range from the guy who takes his car out once or twice a month and wants a sportier ride, to a guy who daily drives his car and hits the drag strip or road course also. This could even cover the guy who races the car regularly, but also uses the car to get to work. Whatever the case may be, most street performance enthusiasts look for a strong bushing that doesn’t deflect as much as stock, yet offers enough articulation for good handling. They also want a bushing that absorbs enough NVH for a comfortable driving experience. More often then not, polyurethane bushings are the perfect fit for the street performance crowd, as they offer the best compromise of performance and comfort.
If you are on the more hardcore end of the street performance spectrum, you can get control with a mix of bushings and rod ends or spherical bushings. This blend gives you the ability to reduce deflection with going to all solid bushings. The rod end side will transfer more noise and vibration through the chassis, but the polyurethane end will still absorb some NVH.
If you plan on using your car in a more hardcore fashion at the drag strip, road course, or autocross, rod ends might be the way you want to go. Dedicated track cars (for the most part) serve one purpose—going fast. In max-effort applications, bushing deflection is wasted power.
So now it’s time to pick your bushings. Hopefully it will be much easier to look at your wants, needs, and how you’re going to use your car or truck, and establish which bushings are right for you. Another great way to narrow the decision down is to drive or ride in as many cars with different setups as possible. Hearing and feeling the difference between stock, polyurethane, and rod ends is a great way to establish what’s right for you.
So make your decision, install your parts, and happy hot rodding!
SOURCE: BMR Suspension