Projects & Tools
This page is for learning more about your suspension – upgrades, tools, parts, & more…
What are bushings? Bushings are a guide for the top half of the fork. They are what your fork stanchions slide on/in inside the lowers. Without them, the fork stanchions would not be centered in the lowers and would wobble around, causing all kinds of damage.
Why do they need to be sized? The upper legs of a fork need the guidance that bushings give them, but they also need to be allowed to move up and down as freely as possible. Bushings that are too tight will cause a lot of stiction in the fork’s movement. If they are too loose, the fork stanchions will have too much play. You want the perfect balance between tight and loose.
How do you size bushings correctly? There are tools for this. They are designed to be slightly larger than the stanchion itself. Generally by .03-.10mm larger. So if you have a Fox 34 with 34mm stanchions, your bushing sizing tools will be 34.03 -34.10mm. You want to make the bushing just that little bit larger than the stanchion allowing oil to live in between and create a nice slippery connection.
There are manual tool sets and auto sets that are attached to a drill. Both are doing the same thing but the auto bushing sizing tools take the grunt work out of it. You want the sizing heads to do the work of spreading the bushing to the right width. This is only half the battle of getting a fork to feel truly buttery…
Hub spacing: this is how your fork comes alive…
Getting your bushings square and opened up properly is a good step in allowing your fork to feel buttery and active. But once you tighten down your fork to the hub, things can get a little squirrely. A modern Boost 15mm hub typically measures 110mm wide, give or take a hundredth of a millimeter. If you have a matching Boost fork, the bottom of the lowers are spaced to 110mm also. Given that you have two sets of bushings that are dictating where the stanchions can and cannot go smoothly and also a hub that will only allow the lower legs of the fork to sit at one given width, there can be some issues here. If the bushings and hub don’t agree with each other, you will end up with stiction in the forks stroke. In other words, the fork will feel sticky and bound up. This can be barely perceptible on the minimal end and very noticeable on the extreme end. While there are other factors that can introduce stiction in a fork also, if your hub and bushings don’t agree, the fork will never feel good.
In order to get the bushings to play well, there are a few things you need to do first before measuring and either shimming or shaving. The damper, spring, and wiper seals need to be removed. You only want the uppers and the lowers in play here. The bushings should be sized to .03-.10mm depending on your taste, making sure each bushing is not tighter than the other. You want as much consistency in all four bushings as possible. Then inserting the uppers into the lowers is where you begin the testing phase to find out where the fork legs really want to sit.
This is a tool that helps you dial in very minute amounts of width into the legs. Sometimes the difference of only a fraction of a millimeter is pretty dramatic in how well a fork cycles without stiction. It acts as a hub, allowing the axle to be installed and tightened, replicating the fork being installed in the wheel. The tool width is able to be changed by turning the end, introducing either less or more width into the fork legs.
Below is a good example of the difference in stiction comparing stock hub width to where the fork really wants to sit.
Once you find the sweet spot, you can remove the spacing tool and measure the width of it to get the spacing your hub needs to be at. The hub then needs to either be shaved at the hub caps ends or shims added inside. Splitting the difference to each side…