Racecar drivers know to keep their eyes up and look far beyond the hood of their racecars while driving. This is a good practice. However, we are so busy looking to the horizon, it is difficult to see what is happening below our butts. We really have no idea what is happening to the suspension bushings of our racecars, because we can’t see those bushings while driving. We can “feel” them or guess what they are doing, but we generally have no visible evidence of their activities under loading. Well, let me tell you, they are moving around quite a bit more than you think.
When manufacturers design road-going cars, they engineer them to get little Johnny to preschool and make beer runs to 7 Eleven. For this reason, rubber suspension bushings are used to lower noise, vibration and harshness. This is referred to as NVH by engineers, who design passenger cars to have easy rides for grandma. This is great for Cadillacs going over potholes, but not what we racers are looking for at the track.
When suspension bushings deflect, it changes the entire geometry of a suspension system. All the time you spent getting your camber, caster and toe just perfect was a waste of effort. One rubber bushing under load can take you from 3 degrees negative camber to 2 degrees positive camber. Your car will not handle like you want it to. This occurs more frequently at race tracks than driving to the supermarket, because at the track we are pushing our cars to the limit. Additionally, Toyo Proxes RR racing tires stick a lot more to the pavement than the whitewall tires on grandma’s Caddy. That “stick” causes a great amount of force to the vehicle’s suspension. With all of that force acting on the suspension, the weak link will give, and that weak link is the rubber suspension bushings.
Because of the amount of slop rubber bushings produce, one of the first upgrades for many racers do to their racecars is to replace all of the rubber bushings with urethane. This is a really inexpensive modification that yields solid improvement. The July 2016 issue of Speed News had an article on how to replace rubber bushings with urethane even if you don’t have a press. You can replace every bushing in a vehicle in less than a day’s work. Urethane is much stiffer than rubber and will help suspension geometry maintain the positions they were designed to be in from the factory. One trip to the racetrack and you will agree with the improvement from rubber. What you don’t see — because you can’t see under your butt — is that urethane flexes too. Not as much as rubber but it still flexes. Your suspension geometry is still affected under load. You can do better.
All materials, even metal, have some displacement or flex under loading. The question isn’t whether it will flex, but how much? Spherical bearings, made of metal, flex much less than rubber, urethane or Delrin. If spherical bearings are so great, then why don’t all vehicles have them? Because spherical bearings are expensive, harsh, and they wear. This makes them great for racers, but bad for grandma’s Cadillac. To learn more about spherical bearings, we decided to talk to a guy who makes them for NASA racers, Chris Brinson, of Kingpin Machine Inc. in Buford, Ga.
We have been using Kingpin Machine spherical bearings at Double Nickel Nine Motorsports in our Honda Challenge cars for three seasons. We have found more speed and consistency with the spherical bearings versus rubber or urethane. Kingpin’s Brinson says we gained that speed because lack of deflection in the suspension allows reduced static camber requirements, thus minimizing uneven tire wear and increasing traction. Traction is a good thing for racers. Brinson also stated that we probably noticed improved steering feel and precision since steering input is directly translated into wheel movement. Under braking, we reduced dynamic toe change which provided stability while we were hard on the “whoa” pedal. Maybe I wasn’t able to detect all of that while driving like a madman around the track, but Brinson was correct. We did feel improvements on all of those fronts when we switched to spherical bearings.
Installing spherical bearings is easier than installing new rubber or urethane bushings. Instead of pressing or burning out rubber bushings, we simply replaced the entire component with parts from Kingpin Machine. As we went through the process of replacing all of our bushings with spherical bearings, we upgraded other parts of our suspension system (hardware, adjustable camber, etc.) at the same time.
Brinson at Kingpin Machine is a bit of perfectionist, which is what racers are looking for when purchasing parts from an aftermarket manufacturer.
“Stock control arms and suspension housings simply are not produced with the same level of precision as our products,” said Brinson. “There is no reason for automakers to hold to exacting tolerances when using stock compliant rubber bushings. We produce our bearing sleeves in a range of outside diameters and the proper sleeve is chosen to produce just the right amount of interference when pressed into the control arm.”
Before we tried spherical bearings from Kingpin Machine, we experimented with a number of different products. Admittedly, some of these products were much less expensive, but did come with spherical bearings installed. What we found was that they quickly wore out. After just one weekend of racing, we were hearing a banging near the rear of the car. After a session we checked to see where the noise was coming from and found a Chinese-made adjustable rear upper control arm had two spherical bearings that were already loose. The banging sound was movement in the bearing and any movement meant our suspension geometry was screwed up under loading. After trying a few different product manufacturers, we moved on to only using Kingpin Machine products, which only uses U.S. steel.
Brinson stated why he uses only U.S. steel in his products. “Manufacturing quality products from properly graded, U.S.-sourced metal and utilizing the best available U.S.-produced bearings ensures that you are running the safest and best performing parts available on the market.”
Quality does come at a cost. Kingpin Machine products are much more expensive than a set of urethane bushings or Chinese knock-off parts, but we have seen them last three entire seasons and counting, which is an impressive amount of time on a hard-driven racecar. We inspect our bearings after every session on track, but haven’t seen any issue with them since we upgraded to Kingpin Machine parts.
Like any racecar modification, plan ahead before you make the jump to spherical bearings. More importantly carefully read your series rule book. For example, page 14 of the NASA Super Touring 5 and 6 (ST5/ST6) rules for 2019 details:
“Non-OEM metallic and/or spherical design replacement suspension bushing modifications on control/camber/toe arms/links, panhard rods, watts links, and torque arms (includes replaced, modified, adjustable, or altered control arm ball joints) = – 0.2”
What that means is for ST6 if you are trying to hit a weight over horsepower ratio of 18.00 pounds over 1 horsepower, and your car weighs 2,550 pounds and has 141 horsepower you are already at 18.08. If you add spherical bearings you will need to subtract 0.2 which puts you at 17.88, which is outside of ST6 specifications. You will either need to add weight or lose horsepower to be in compliance. It certainly may be the correct modification to make. You will gain performance with the spherical bearings, but you need to investigate to totality of the modification.
One of the things we found after switching to spherical bearings was that limited movement in our suspension geometry due to less defection in the suspension bushings meant the static camber settings we used with urethane bushings were too great. We now run less negative camber with our spherical bearings than we did with our urethane bearings. This is an advantage under straight-line braking and straight-line acceleration because it puts more of the tire’s contact patch on the race track. We use Smart Racing Products’ Smart Camber and Smart Strings to align our cars in the shop and at the track. We check our settings after each session to ensure nothing has moved from our specifications. We have found with the spherical bearings, our settings remain more consistent, providing more assurance making the switch to spherical bearings was the correct one.
The move to spherical bearings won’t be cheap. Our Honda Challenge car had 28 individual suspension bushing points to replace with spherical bearings. But hey, nobody ever said racing was cheap.
Rob Krider is a NASA National Champion and author of the novel “Cadet Blues.” To read more, or to contact him, go to www.robkrider.com.
