To be totally honest, i almost didn’t attempt this build. But since i have a thing for softails I wanted to give it a try. Mike has somehow coerced me into making or modifying a few weird frames over the years that I would likely never have tried on my own (see here & here) and the Miser is no different. Just to be clear, this is not a model in name or frame that I’ll be producing in the future, it’s just the name of this frame that is stingy on travel. The design was created decades ago by Daryl Funk and even though it’s not patented to preclude anyone from copying and using the design, it just doesn’t feel right to do so. But since this is a “one and done” I agreed to do it.
Ready, steady, go!
The frame design is the same system as the Funk La Ruta, a titanium flex-stay air/oil shock softail that gets around 60mm of “pivotless” suspension. It’s actually got a pivot where the shock bolts to the frame so when compared to the Castellano SilkTi or Moots YBB it’s not a true pivotless suspension frame but…close enough. The wheel hits a bump, the chainstay plate yoke flexes, the seatstay’s machined flats flex (we’re calling these “flexures”), and the shock does it’s job of responding in whatever way the user has set. The seatstay flexures provide up to a few degrees of vertical flex to allow for a smoother shock stroke – placing less sideload and stiction on the shock. Pivots, along with all the other stuff they do for suspension kinematics, ensure the shock can work to its full potential by not introducing load from any direction other than straight, but this is a Softail so no pivots allowed, just the natural flexibility of Titanium.
As already noted, unlike a YBB or SilkTi, the Funk design uses an air/oil Rock Shock Monarch RT3 that allows you to tune the suspension, lock out, sag, and change damping on the fly. (Old guy trivia: it used to be an option to have a QR lever on the YBB to reach back and lock out but I’m not sure that’s a thing anymore.) Almost all softail’s are super clean designs that have been around for decades and in my opinion make great cross-country mountain and gravel bikes, but they also make for excellent bikepacking bikes and wonder if we could see a rebirth of softails because of that. They’re lightweight, have few parts to creak, wear out, and break than pivoted dual-suspension designs, and they provide a little suspension to take the edge off and improve rear wheel grip. Hardtails haven’t disappeared – and have seen a resurgence – even with the numerous, well-designed and performing short-travel dual suspension bikes. But for some reason softails still get the eye-roll. Like a hardtail, if you don’t need or want a lot of rear wheel travel for how and what you ride…why would you want that added complexity and weight? It’s the singlespeed of suspension frames, it’s always ready to go (and because softails are a type of URT you can convert them to a singlespeed without tensioner!)
So why did I copy a Funk? Mike loved everything about his La Ruta but just wanted more tire clearance. When he reached out to Funk about building a new version he didn’t get a reply so asked me and I have trouble saying no apparently. The stock La Ruta fits 29 & 27.5 x 3″ tires but he wanted space for 27.5 x 4” tires like the 45N Vanhelga, Terrene Cake Eater, or Bontrager Hodag with as low a Q-factor as possible. This meant designing a new rear end from scratch. Daniel Yang once again helped me with the CAD design to make sure all the parts fit within the tight tolerances required. He designed and ordered the US-made 3D printed parts from Silca, and designed the brake mount and chainstay flex plate to be cut while I worked on everything else including the seatstay flexures.
Having recently built myself the SilkTi, we changed a few small things on the Miser to distinguish it from the La Ruta. First, we used a slightly thicker 4.7mm flex plate. The thicker the plate, the more lateral stiffness in the system. The SilkTi uses a 6.4mm thick plate but spans the entire length of the chainstays so it can flex enough. The La Ruta was measured to be 4mm thick but the plate ends right around the widest point of the tire tread. At that point it is welded to 7/8″ diameter tubes that go back to the dropouts. Because the flex plate is so much shorter than the SilkTi it needs to be thinner to flex more over a shorter distance. Daniel ran some simple FEA to see what happens with this type of flex plate, enabling us to see it’s shortcomings but also be aware of it’s potential (within a certain load range it can perhaps live forever).
In addition, we changed the design of the seatstay flexures. These are machined from solid Ti bar from the top of the “halfpipe-shaped” part to where they are welded onto the dropouts. The orientation is also parallel to the rear axle as seen in the photo below. Daniel designed the ISO brake tab to meet just below the flexure and ensure a solid connection that wouldn’t need a support bridge down to the chainstay.
We chose to make a 3D printed shock collar to ease with fabrication, fixturing, and to narrow the calf clearance as much as possible with the wider rear end. The seatstays come up at such a steep angle to the shock that it makes welding them and the binder bolt difficult without a lot of distortion and post-weld reaming to smoothly fit with the machined aluminum shock mount. With the short 30mm long printed component I just had to slot the binder, clean up some of the ‘texture’ to fit the bolts and nuts, and make straight cuts on the s-bend seatstays and voila! Something like this would be great for the SilkTi design in fact – removing the need to bore the I.D of the shock collar after welding the seatstays and binder. (In the photo below you can see the integrated ridge on the plug which Daniel added to provide “filler” material when fusing the tube and collar.)
Mike will be using an old but rebuilt Fox Float 27.5+ fork that is sadly no longer made. It’s the “Unicorn” of plus bike forks because it will fit almost whatever you want and has 140mm of travel using their the 3-position Fit 4 damper with lockout. If you know you know. Here’s a link to his blog about the new bike. Enjoy!
Some process shots below showing the “creative” fixturing needed when making a one-off frame design. Funk has dedicated tooling developed over years to facilitate each step so it comes together in a planned and efficient manner. Backward engineering such a design was fun and rewarding but very time consuming. I’ll be doing fewer of these types of builds and focusing more on a couple stock frame designs. If you have any thoughts on what you’d like to see leave a comment!
Amazing work as always Whit! If ya working on a couple “stock” models then I reckon a mid-fat (4″) midtail is worth considering. I reckon like there’s a (tiny!) gap in the market there now since the Salsa Blackborow and Surly Big Fat Dummy have both been discontinued. And you’ve built enough similar bikes to be able to nail the design and fabrication on something like that.
Such a rad bike!