First off I want to be clear that I am in no way an expert in bike design (obviously), geometry, welding or really anything. This bike was a dream I’ve had for a long time, and once I was able to scrape together the skills and resources I needed to make it happen it had to be done. This isn’t a final revision, or my only full suspension frame, more of a test mule and proof of concept.
Geo/Specs
These numbers all came from personal preference and things that I didn’t like about my past bike. My opinion is that geometry is completely driven by rider preference. You go custom to get exactly what you prefer, not what the big brands are pushing.
-160/160 travel 29er
-12×148 Rear
-Threaded BB
-180mm post mount brake
-Max Tire Width: 2.5
-HTA: 63.5 deg
-STA (eff): 78 deg
-Reach: 480mm
-Stack: 645mm
-Rear Center: 435mm
-Eff. TT: 617mm
-Wheelbase: 1269mm
Design/Fab
The suspension design is a linkage driven single pivot, very similar to an evil but the shock is vertical and attached to the seattube. I’m fortunate to be tall, so I could package the shock vertically under the TT and leave room for 2 water bottles without an uncomfortable standover. Seattube and downtube bends were critical to get tire and shock clearance at full travel. The leverage curve is heavily progressive, since I wanted to run a coil. I aimed to get the anti squat set up right around 100% at sag using a 32t chainring. The anti squat curve isn’t as flat as I’d like it to be, but there aren’t many situations when we pedal in a deep compression. The main weak point of this setup is the pedal kickback, at first I really wanted to jump on the high pivot bandwagon, but I don’t think the extra complexity is worth it. In the second smallest gear in full compression there is under 8 deg of rotation which is in line with other frames, just have to remember to upshift when its time to go down.
All the tubing is .032” straight gage 4130 wall with the exception of the downtube, chainstays, and chainstay bridge tube. Huge shoutout to Andrew at bikefabsupply for bending me the meatiest of downtubes, a 1.5” .049” wall slug. That tube alone weighs probably a pound, ill just keep telling myself it keeps the center of mass low. I wanted to be sure that I don’t rip the frame in half when it bottoms out. I used a paragon stem cut in half for the main pivot, and welded some cromo laser cut washers on the backs of them as bearing seats. Paragon post mount brake tab for a 180 rotor, laser cut suspension mounting points and brake bridge. I used two sets of dropouts, one for the rear wheel and one for the rear triangle bearing housing. I saw Zoceli bikes do this and really liked the simplicity of it. I will say that using ¾” tubing on the rear triangle sections was a serious headache since the droupout hoods are around ¾” wide themselves. A healthy amount of tube forming was needed to give me a chance to weld that.
The fabrication of this bike was way more of an undertaking than I expected. I welded up the front triangle, got all excited that it was bike shaped and realized I was about 10% there. I welded in the main pivot to the seat tube before I did the front triangle and it seemed to work well. I stole the idea from Kris Henry and made a similar jig plate that located the 3 frame pivot points in relation to my main frame jig. I machined a bunch of aluminum spacers to get everything as close to centerline as I could when I was tacking the laser cut mounts to the main tubes. From what I can tell things stayed in line where I wanted, and I luckily didn’t have to ream any of the pivot mounts post welding. On the rear triangle I debated how to approach the assembly for a while and decided to make a simple jig out of square tube with the pivot locations drilled/reamed through (thanks to BTR for the inspo). Then used another handful of spacers to set up the pivots where they need to be and connect the dots with tubing. Luckily I have a good friend with access to a CNC machine for the main links and rear triangle bearing housings. I made the pull links, which is why they look like hot garbage. After 200 trips to the hardware store for stainless bits I could finally slap it all together.
First Ride
Can I get some loctite over here??? Once I got the pull link bolts fully torqued down the bike seriously surprised me. It pedals a thousand times better than I would have imagined and descends just about as well. Definitely don’t notice the extra going up but that’s probably stoke induced placebo. So far I’ve only taken the bike on a short test run up and down one of my favorite downhills in town but it was a perfect spot to do some repeat runs while changing things up (and it happens to be close to the car when I inevitably blow something up). The JadeX coil is the real deal, incredibly smooth through the travel with minimal breakaway force and the lockout feels better than most air shocks tbh. Also the fact that it’s dead silent really appeals to me, squelching air cans just sound like you’re bike is struggling to breathe. I ran a 500# coil since it came with the shock, but I will be putting on a 550 to get the sag dialed in better. Initially I thought the 500 was way too soft but I wasn’t blowing through travel. I may have made the linkage a bit too progressive, need some more time hitting drops and larger compressions to feel that out. Not much more to say about the components, nothing beats the crisp shifting of shimano for me. Most of the parts came off of my broken bike, the failure that got my ass into gear on this frame.
Geometry: seated climbing feels so comfy and upright. Even though the bike is stupid slack I feel like I have plenty of weight over the front to keep the wheel in line going up steep switchbacks. I personally prefer a bit higher stack, I’ve found it keeps my back in check on flatter trails. Using the extra stack of the headset and slightly longer headtube means I get to slam my stem and not run risers or absurd spacers. Also made fabrication much easier at that joint. Chainstay length feels good, I’m a slow convert from a shorter=better mindset. The headtube angle is slightly over the top, I’m strongly considering reducing it a degree with an angleset but I’d like to get more saddle time especially on the stronger coil. I think that will balance out the front and rear sag points better. The bars felt surprisingly close to me in the seated position probably due to the steeper seat angle and since I’ve been riding a way oversized XL full squish frame for the past month or two. Potentially could have gone further with the reach but then the front wheel would be in another time zone. Angleset and wider bars could dial that in.
If somehow you took the time to read all of this then I hope you got something out of it; if you have any questions at all or just want to talk bikes drop me a message!
UPDATE!!
After the first few test rides and the continued difficulty with the initial hardware I revised the main linkage to the sore stout and rigid design shown below. This is what I had wanted to do initially, but in fear of making the machining work overcomplicated I went with the split links to begin with and it came back to haunt me. Since putting the new link on the bike (thanks again Curtis!!) I have had much less issues with hardware coming loose and the system is much stiffer. So far I’ve put a few hundred miles on the bike and couldn’t be happier. I even managed to bend a pedal and a crank in a crash and the bike held together just fine. I did not. I also decided to go with clear powder coat to give the frame some protection while maintaining the raw look. Knowing full well that clear only offers minimal protection I have to say I’m impressed with how it has held up so far, only a few rust spots from rock strikes etc. I’ve gotten the itch to do more suspension work so stay tuned for more upcoming projects.
