Here's Your Single-Sided, Carbon Fiber DIY Linkage Fork

On a scale of one to ten, how much of a do-it-yourselfer are you? Burnt-out lightbulbs and hanging picture frames are the limits for some of us, whereas others are happy to DIY their way through just about anything short of a shuttle launch. Back in 2018, we saw Jean-François Boivin's homemade carbon downhill bike that used a gearbox and a stanchion tube from a Fox 40 for its rear shock, as well as Vladimir Yordanov's dual-link carbon downhill bike.


There's surely lower hanging fruit than such an important, consequential component like a fork. ''I think that most other parts of a bike are pretty solid in terms of their function,'' he replied before admitting that there's little to no way for him to improve on a stem, handlebar, or other relatively straightforward parts. On top of that, the major brands focus their time and efforts on telescoping suspension, leaving plenty of room for the smaller outfits to experiment.

Kalym's focus was on the chassis, not the spring and damper, which greatly simplified the process. ''This meant that all I had to worry about were wheel path, leverage curve, and a few other bits and pieces,'' a process that took about two years of on and off work and ten different iterations before he decided on what you see here. Some of those were dual-sided, but the simpler single-leg layout won: ''Of course, this caused some packaging headaches, but I got there in the end. Also, going single-sided meant that I could increase the diameter of the fork leg to 50mm, and therefore increase the stiffness while keeping the overall weight the same as if it were two-sided."




If you've spent any time on Cannondale's single-sided Lefty, you already know that a fork doesn't require two legs to be torsionally rigid. The Lefty is a very different chassis, though, and its abilities come from a square (newer models are three-sided) stanchion that rolls in and out of the massive upper tube on strips of roller bearings. But Kalym wanted his fork to offer anti-dive abilities, and to increase trail as it goes into its travel to stabilize handling, neither of which are possible when using stanchion tubes. And he didn't want it to look horrendously complicated or require a one-off, non-standard hub, all of which led him towards the leading-link layout you see here.




The benefits of increasing trail and anti-dive have been proven, with those traits creating handling that can't be matched by a telescoping fork, and Kalym admits to still learning what this means on the trail. ''It makes sense on paper to keep the head angle consistent and slacker when braking and cornering, but is that more beneficial than having the suspension completely free and active? I’m not sure yet, and there’s a lot more testing to be done,'' which is a rather refreshing attitude.

"The link itself moves through 47.16 degrees of rotation from full extension to bottom-out, which means that the brake caliper rotates around the disc a large amount, which equates to a lot of anti-dive.'' The trail grows from 130mm to 165mm at bottom-out, he says, which, ''equates to an offset of 45mm at rest, and 17mm at full compression.''

Kalym is working on a second version of the fork that will have a four-way adjustable floating brake arm to suss this out.




While the kinematics are still in the works, Kalym knew from the outset that he'd be using an off-the-shelf shock to handle the spring and damper duties. ''If you think about it, the rear of your bike is incredibly adjustable in terms of the shock choices you have. You can simply buy a new shock, bolt it on, and ride. You also have a choice of cheap or expensive, feature-poor or feature-rich, air or coil, and so on. However, if you want to change the spring and damper in your telescopic fork it’s a lot harder, and sometimes it’s not possible, especially if you want to go from air to coil and back again.''

So instead of thinking classic front suspension, Kalym wanted to design a chassis that could accept most shocks on the market. Prefer a simple air-sprung shock with a lockout lever? Not a problem. Want to bolt on an exotic coil-sprung shock from EXT, Push, or someone else? Go right ahead.

The rear suspension approach to front suspension also requires a progressive leverage curve to resist bottom-out, whereas a telescoping suspension fork is a straight 1:1 ratio. ''I was limited in what I could do because I went with a directly driven shock design, but I ended up with a curve that starts at 3:1 and ends at 2.54:1, which feels good even with a coil shock,'' he explained. An air-sprung shock would provide more ramp-up if that's what you're after.




The massive aluminum link pivots on 20mm x 32mm x 7mm bearings, there's a 20mm diameter axle through it all, and an M10 bolt holds it all together. ''It's pretty bombproof,'' Kalym told me, and it uses a normal Hope Pro 4 hub.

The massive upper leg was made by Carbonwasp, an outfit in Yorkshire that specializes in one-off, prototype carbon components. ''I’ve known Adrian for a little while, as I’ve done a few other 3D printed prototype things before doing the fork. He probably got sick of my emails, to be honest! But he was great in advising me the best way to go about certain things, and the way they do carbon made the whole project economically feasible." The single-sided leg was new to them, but Kalym says that the finished product is overbuilt and, "insanely stiff." Even so, he's planning to go with an aluminum leg for the next version as it'll make anti-dive adjustments and other modifications easier.

After a few year's worth of time and a hell of a lot of work, Kalym is ecstatic with how his fork performs: ''The sensitivity and activeness are like nothing else, much plusher than anything I’ve ridden. The amount of grip that the fork gives is really confidence-inspiring, and the increase in trail is noticeable (I think). Stiffness is also noticeable, with steering feeling much more precise and less delayed. I think the only thing that needs more exploration is the anti-dive."




There are no proper plans for a production version, though, with Kalym having been down that road before with the archery release aid. ''It just took the fun out of it for me,'' he said. ''If it grows organically then that would be awesome, but if it never happens I’ll be happy just to ride around on a fork that I designed and built. Obviously, something like this would be a niche product, and I think would be for people who are simply interested in performance above all else. There will be other forks that look better, weigh less, and cost less, but I’m certain there’d be a small group of people that would love to reap the benefits of a fork like this.''

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Reviews and Tech First Looks Linkage Forks Rocksled Suspension Diy