The Need For A Low-Cost Tubeless Spoked Wheel

It’s said that necessity is the mother of invention.

Innovative spoke mounts invented by the author create an affordable tubeless spoked wheel.

It’s said that necessity is the mother of invention, but all the inventions I’ve been involved in have typically been driven by more than one necessity. And when an invention is first proposed, it may happen that all the necessities—all the problems to be solved, in other words—are not readily apparent. In some cases, during the process of developing an invention, new and more pressing problems surface and need to be resolved.

Consider spoked wheels. Problem: Conventional wire-spoke wheels aren’t compatible with modern tubeless tires. Solution: Design a wire-spoke wheel to be compatible with modern tubeless tires.

There are, of course, many tubeless-compatible spoked wheels out there. The simplest solutions use conventional rims with the spoke nipple holes sealed, though this still presents a risk of leakage. The best solution may be BMW's rim with its spoke attachments along the outer edge, outside the area that must retain air. Still another approach is to use a rim that has a center flange (or flanges) on the surface of the rim that faces the hub for the spokes to attach to. This is the method used on the Yamaha Super Ténéré, the Triumph Explorer, and the new MV Augusta Brutale 800 Dragster.

I used this last method when designing the wheels for the Eller Indian project in 1998 and for Bernard Li’s Vincent prototypes in 2002. For both those projects I used rims made by BBS in Germany that had a substantial center flange that was “blank” and could be shaped and drilled for spokes. BBS has since discontinued these rims.

A friend and machine shop operator recently approached me about building spoked wheels for supermoto racing. Those bikes use tubeless roadracing slicks, but a lot of racers still install tubes for reliability—which also adds weight and increases tire heat. Could we come up with a relatively inexpensive, proprietary tubeless spoke wheel? Tooling for a forged rim is very expensive. First we tried making a spun rim (spinning involves forming the rim from sheet stock spinning on a lathe) from two halves that were welded together at the center flange. The rims looked like the BBS rims, but we couldn’t get reliable strength and hardness. They didn’t hold up to supermoto punishment.

This is where the new “necessity” entered the project. The tooling, development, and testing of unique rims was beyond our cost limits. Was there a way we could repurpose already available standard dirt bike rims? To do this, we would have to abandon the center flange spoke attachment location. And since conventional rims are drilled for spokes, we would have to get undrilled rims direct from a manufacturer. That turned out to be possible.

In our new design, the spokes attach to the rims through small aluminum plates, two spokes per plate. The plates are actually doubled, with an inner plate resting against a shallow machined flat on the tire side of the rim. The outer plate holds the spoke nipples. Two short, 6mm screws attach the outer plates to the inner plate, through holes in the rim that are sealed with O-rings sitting against the machined flat surface. Once the two plates are screwed together, they don’t need to be disturbed again even to replace spokes, and the O-ring seals have proven absolutely reliable.

How does the wheel work? Husqvarna-supported racer Sean Butterman, son of the project’s machinist partner Johnathan Butterman, won the 2014 AMA Pro Supermoto 250 Championship and placed third in the 450 Championship using these wheels. The wheels have proven reliable through two full seasons of racing, including dramatic jump landings that trashed other wheels.

This project started out to design a tubeless applicable spoke wheel, but the job description changed to designing a tubeless spoke wheel using an absolutely standard manufactured rim. This invention had more than one mother.

James Parker designed his first original motorcycle in 1971; his most recent design is the Mission R electric superbike. In between, he worked on multiple other motorcycle projects, including 30 years spent evolving the RADD front suspension system used on the Yamaha GTS1000 and various other prototypes.