What The Heck Are Bushings? | Maxima Plush Dynamic Suspension Lube | Development and Testing
Friction is all around us. Any two things that come in contact have some form of friction between them, and this is especially true of parts that slide—causing heat and stiction, eventually bringing things to a halt.
How does friction impact your ride? In suspension, friction is that momentary binding or stalling when moving through the travel, causing your ride to feel harsh or sluggish. It can be caused by a multitude of things, making it an ever-evolving battle to tweak, test, and iterate.
Our friction story is made up of two key parts: the bushings and lower leg lubrication.
What the heck are bushings?
Bushings are Teflon™-lined aluminum sleeves installed into fork lower legs that act as the primary contact interference between the lower legs and upper tubes. Bushings work together with lubrication to create a hydrofilm between the two, allowing the upper tubes to glide smoothly through the lower legs. There are a total of four bushings in each fork, two bushings on each side of the lower leg. The upper bushing lives just beneath the dust wiper seal, and the lower bushing lives roughly near the mid-way point of the lower leg. We consider many factors when working with bushings, but our 2023 lineup boasts a larger bushing overlap and longer lower bushings in our Ultimate-level forks.
The phrase “bushing overlap” brings to mind objects closely layered, but in this case, it’s referencing the distance between each bushing on one side of the lower leg. A greater bushing overlap means the bushings are further apart, which lessens the side load on each bushing during impacts, which reduces friction. Friction correlates directly to the side load imparted on the bushing when the fork encounters small or large obstacles. So, by increasing the bushing overlap (in this case, moving the lower bushing down) across our 2023 lineup, we reduced the amount of force loaded into the bushing and as a result, reduced friction.
Now, you might be wondering why we don't just have one bushing at the top of the lower leg and one at the bottom to have the largest bushing overlap possible. The short answer is that the fork's travel determines the lower bushing location—it's strategically placed to maintain contact with the upper tube at top-out to prevent disengagement between the two.
Design Engineer Jon Watt didn’t quit at maximizing the bushing overlap. Watt was also experimenting with different bushing lengths to see what he could find.
When you're skiing, a different length ski will have a different speed and friction. So we wondered, does a short bushing have less friction than a long one? And it turns out it's the opposite.
They found that longer bushings result in less friction, not only because they’re longer, but it also increases the bushing overlap. We effectively increased the center-to-center length by increasing the lower bushing length while keeping the top bushing in the same spot. This doubles down on friction reduction, making our 2023 Ultimate lineup our smoothest forks ever.
Maxima Plush Dynamic Suspension Lube
While an essential aspect of the friction story, bushings are only a portion of what makes up friction reduction. As we mentioned above, any two parts that come into contact have friction, so adding lubrication to the mix creates a layer of film between the bushings and the upper tubes. Like hydroplaning a car across a thin layer of water on the road, lower leg lubrication acts as a slick barrier between upper tubes and bushings.
With the launch of our 2023 collection, Maxima Racing Oils also launched their brand-new Plush Dynamic Suspension Lube, created in tandem with RockShox engineers for RockShox suspension. Our aim was to maximize the performance of our forks through its service life, and we knew that the team at Maxima would be down to experiment with us.
As an industry, we're always chasing lower friction, but many factors and variables go into making a good lube. The trick is balancing that goal of lower friction with all the other requirements in a way that isn't going to cause any unintended consequences down the line.
Development and Testing
Armed with a goal and broad ideas, Design Engineer Skyler Teachout got to work alongside Senior Test Engineer Brian Hatin. They identified which characteristics from 0W-30 they wanted to keep and what they were looking to improve. They then began testing to figure out a baseline with our existing lubrication.
In addition to providing a fluid film on which two surfaces can slide past one another, lubrication oil also helps keep those moving parts happy and reduce wear over time. However, oil is a dynamic fluid made of complex ingredients. Engineers are looking for certain qualities in the perfect lube: temperature flexibility, that 'just right' viscosity [the measurement of a fluid's resistance to flow], and how the oil affects the parts it influences. So, finding—or creating—a lubricant that has the proper viscosity for the bushings and upper tubes to slide on, that maintains that viscosity in broad temperature ranges while also playing nice with the components it's meant to lubricate, takes a lot of testing, designing, iterating, and riding.
Once Teachout and Hatin had a good idea of where to start, they started iterating through oil samples with Maxima. One sample was too thick, another too thin, the next didn’t play nice with the fork’s internal surfaces. Eventually, they identified a few solid samples and worked their way into testing different temperature ranges. The RockShox test lab has environmental chambers that help us gather data in a lab setting.
But sometimes, you need good old-fashioned mother nature to get a real-life feel for how something will perform in the field.
Fortunately, it was deep winter in Colorado, with temperatures below freezing, so Hatin stored some forks in his garage overnight. The next morning, dark and early, the engineers showed up for a blind test at Hatin’s house. The goal was to narrow in on different aspects of oil performance based on how they felt in the cold. They tested for not only static friction [friction between two resting surfaces], but also dynamic friction [the forces that resist the movement of the surfaces once they’re in motion]. Cold weather primarily affects the dynamic friction, so through the blind testing in Hatin’s garage, they narrowed down some options that maintained positive dynamic friction despite the temperature.
While Teachout was working through lubrication development, his teammates were working through other updates in our 2023 lineup: a new damper, new air spring, ButterCups, a new chassis with longer bushings. There were a lot of moving parts here. Finally assembling these components into complete forks, the team set out on a test trip to get a feel for how the system felt together. Unlike normal years, the Covid-19 pandemic forced the design team to work in silos—this test trip was a necessary step to ensure a cohesive system. Within the first hour of test riding, it became apparent things were less than cohesive. The team started working through the different levers they could pull—was it the new damper, the lube, the spring? They swapped out parts, rode, and reconvened. They made incremental improvements, but when they tried a different lube, the feeling improved by leaps and bounds. With a new understanding and a clear path forward, the team returned to Colorado, ready to fine-tune their creation.
All in all, our engineers worked through 17 or 18 different iterations with Maxima, searching for Goldilocks—that “just right” recipe that checked all the boxes. Each iteration of lubrication taught the team something new, things they hadn’t known before about the system as a whole and how it all works together to make the optimal fork. There are many aspects to suspension, but ultimately, lower leg lube ties all the components together.
Lubrication's not something that most people will notice because it doesn't have a knob or sticker. But the way it improves the performance of our products is huge. The friction, the characteristic, and the way our forks ride now is amazing, and a big part of that is Maxima Plush Dynamic Suspension Lube.
The recipe we developed with Maxima is quite literally a secret sauce, but trust us, this unique concoction will make all the difference in your ride quality. The new Maxima Plush Dynamic Suspension Lube provides riders with a longer-lasting, fresh-outta-the-box feel—maintaining that plush feeling that makes getting into your travel easy. New lube combined with larger bushing overlap—and the longer bushings in the Ultimate lineup—means riders feel a smoother glide through travel without hang-ups.
Maxima Plush Dynamic Suspension Lube is backwards-compatible where 0W-30 was used. Check out the Front Suspension Specifications Manual for your fork on RockShox.com/service. Bushings are not replaceable outside of purchasing new lower legs, which are only compatible with our 2023 Pike, Lyrik, and ZEB forks. Check out our FAQ page for more information.
Renderings by Ray Bach. Photos by James Stokoe, Mason Mashon, and Maxima Racing Oils. Words by Sarah Walter.