Race car suspension systems endure stresses not even anticipated by the OEM engineers. That means the components that came from the factory, like stock rubber bushings, are not up to the rigors of racing conditions. As heavy loads are placed on stock rubber bushings they will begin to deform which results in unpredictable changes to the suspension geometry. Needless to say, this is a bad thing. But it can be resolved by swapping out the flexible stock rubber bushings with spherical bearings. These types of bearings articulate smoothly and are virtually free from deformation. If you are racing on OEM rubber bushings, it’s time to seriously consider putting them out to pasture.
A the race track, stock rubber bushings are too compliant for track use, causing alignment problems which turn into handling issues and abnormal tire wear. Here is an example of how this kind of defection in a rubber bushing can cause problems. If you set front negative camber at 3.5 degrees and go hard into a corner under braking, your car will roll, which sets the front tire at 0 degrees of camber, keeping your front tire perfectly flat on the asphalt surface.
However, as you load the suspension, a stock rubber bushing will begin to deform and may end up with 2 to 3 degrees of positive camber. This is not good as it lessens the tire’s contact patch. The car will begin to push which will slow your speed considerably in a corner. To rectify this issue some teams will add more static negative camber to their setup, 4.5 to 5 degrees, hoping to get closer to a full tire contact patch mid corner. The increase in negative camber causes other issues as well, but more importantly, your car will still feel loose or sloppy because of the deflection is the rubber bushings.
A far better solution is to replace the pliable, inconsistent OEM rubber bushings with spherical bearings that are capable of holding the correct alignment even during heavy loading. A range of spherical bearings are available from companies like QA1 Precision Products.
Besides a lack of deflection, the smooth articulation of a spherical bearing is a side benefit of the application. You don’t want suspension to bind in its range of travel. Binding causes less fluid movement and sudden unloading and loading of a car. There may be binding issues with some urethane bushings, which have side friction and can stick at their articulation points. Spherical bearings don’t have this issue and allow the suspension system to move up and down fluidly.
There is an argument for using urethane bushings as they are a considerable upgrade from stock rubber and the kits are extremely affordable. You can purchase an entire chassis bushing replacement kit from Energy Suspension for an Acura Integra for $178 and press them in yourself. It is an easy weekend project that will significantly improve the handling and response of your car. Be certain to use plenty of lube on the bushings so as to lessen the amount of bind in the suspension system. Energy Suspension provides lube with its kits and also offers it separately. High performance urethane bushings are a good solution for cars that see double-duty on the racetrack and on the street. But if you have a dedicated track car, spherical bearings are the best, albeit more expensive, route.
To maximize handling on our Honda Challenge race car we deleted every single rubber bushing throughout the chassis and replaced each component with spherical bushings. This was not an easy or inexpensive endeavor. We spend more than $178 (the price of the entire urethane chassis kit from Energy Suspension) for just one single spherical bearing. There were a total of 26 bushings to replace in our car. This upgrade is certainly not easy on the wallet, however the results were worth it.
Trever Degioanni, who works for Motion Control Suspension (MCS) and helps road racing teams across the country with their setup, said he has seen as much as a five mile per hour improvement in going through the esses at Road Atlanta by switching to sphericals. “Spherical bearings really keep the suspension points exactly where they should be,” said Trever. “And that really makes a noticeable difference when you have weight transfer from side to side.”
There are some less expensive options when transitioning your race car from rubber to spherical bushings. PCI makes replacement components, like their rear upper control arm which comes with spherical bearings already in place. Purchasing their component and just replacing the entire upper control arm was less expensive than trying to install spherical bearings in a stock arm. Hardrace also sells rear toe adjusters with spherical bearings inside.
Craig Watkins, engineer for Flying Lizard Motorsports and owner of Smart Racing Products provides a different take on spherical bearings. Since he is an engineer he will tell you that all materials deform, flex, and change shape during heavy loading. “We set up cameras looking at the rear wheel of our Porsche RSRs during testing and we saw that not only did the suspension flex, the wheels flexed as well,” said Craig. “All materials will deflect some amount. Spherical bearings will certainly deflect less than a rubber bushing, but there is still some movement. The key is to use materials that don’t deflect as much and won’t break under loading.”
Because of the lessor change in deflection from urethane to spherical bearings it meant we could dial in less static camber in our initial setup. This helped us with straight line acceleration on our front wheel drive car. According to Chris Brinson, owner of Kingpin Machine, who builds custom American made control arms with spherical bearings for road racers, it is very common for racers to use less camber once they make the switch to spherical bearings. “Lack of deflection allows reduced static camber requirements, thus minimizing uneven tire wear and increasing traction,” said Chris. “These bearings also improve steering feel and precision as steering input is directly translated into wheel movement. Additionally, reduction and elimination of dynamic toe change, which along with handling benefits can also provide stability under braking.” Testing our car we found the same results, much more stability under hard braking.
Besides the higher cost, there is one other major disadvantage to spherical bearings: they wear out. Street cars can go 300,000 miles on rubber bushings. Racers have installed urethane bushings and never looked at them again season after season. With spherical bushings there is maintenance and inspection involved. I have seen spherical bearings wear during one 25 Hours of Thunderhill endurance race (they lasted the race but needed to be replaced immediately after). Admittedly, 25 hours is a heck of a lot of racing, however, it showed us that these bearings do wear and need to be checked. And on the street, expect dirt and grit to enter the bearing and wear away on the surface. It isn’t a difficult process to check for wear: simply grab the suspension piece and see if there is any movement at the bearing. If you hear any clicking sounds, the bearing most likely needs to be replaced.
Another issue that arose once we switched to spherical bearings was that we found other parts on the car began to fail, specifically our rear wheel bearings. The amount of loading we were putting on the rear bearings during a race was significant. However, when we had urethane bushings we never had a rear wheel bearing fail. Once we installed a solid set of spherical bearings throughout the suspension suddenly we were killing rear wheel bearings every other weekend. We attributed this to the amount of flex and deformation the urethane bushings were accepting. The bushings were taking the hit and deforming providing a softer blow to the rear wheel bearing. Once we stiffened things up with the sphericals, the wheel bearing began to take more abuse and thus began to fail.
Spherical bearings bring a significant increased level of performance to a race car, but they do so at a higher price and more maintenance. These types of bearings aren’t legal in every class and in the NASA Super Touring rules they do add points to your build. Do your research and see it if is right for your car and then be prepared to get your wallet out.