Last Saturday, an impeccably-restored sandcast Honda CB750 won Best of Show at the Quail Motorcycle Gathering. It’s a beautiful machine, but if you’ve been following this site for any length of time then you know I’m a sucker for well-used bikes and oddballs. I’m weird, which is why I should never be asked to judge these kinds of events. Despite that Nathan asked me what my personal Best of Show would have been. Here’s my answer.
This is the RoHorn Racer, built by Robert (Bob) Horn of Yuma, Colorado, and it was in the Custom/Modified class of this year’s Quail. Mr. Horn, an industrial mechanic, started the three-year process of creating this motorcycle in 2009, but the origin story goes all the way back to 1987. In that year, Kevin Cameron wrote an article in Cycle magazine entitled “Beyond Telescopic Forks”. The tagline was simple:
“Telescopic forks, utilizing coil springs and hydraulic dampers, have been a technological fixture for 40 years. Why? Where’s something better?”
As we’ve come to expect from Mr. Cameron, it’s an excellent piece that’s worth delving into if you appreciate technical details, and you can check out the full ten page article here. I want to focus on the last page, in which Kevin says that funny front ends may offer “advantages in braking” but that they don’t help a motorcycle turn in any quicker. He theorizes that the only solution may be “steering the front and rear wheels simultaneously” but quickly diminishes the average reader’s interest:
“Here is how the turning process would look with two-wheel steering; the rider countersteers to initiate the turn, and both wheels simultaneously steer, whipping out from under the machine to roll it over into the turn. In this process, the wheelbase doesn’t matter, because there is no delay as the front wheel tries to steer the rear wheel with the wheelbase as lever-arm. Once the machine is rolled in, front and rear tires steer towards the turn center, and in a fraction of a revolution develop cornering forces simultaneously at both ends of the machine. At this point, the rear wheel assumes a straight-ahead direction, and steering corrections are made by front wheel alone. There is no delay in developing the force at the rear because we don’t have to wait for the steered front tire to drag the front of the chassis around to establish a steer angle and cornering force at the rear.
Making such an idea work would be a nightmare, but conceptually it offers big gains in speed of steering response, and separates handling variables from wheelbase so that off-turn wheelies can be eliminated and turned into acceleration (emphasis added).”
One of the many examples detailed in the Cycle article.
Kevin’s theory was just that, a theory. But Bob Horn decided he’d bring it to life. First, he experimented with a Harley-Davidson Sportster and designed a front end steered by a ball-and-socket joint with 2 virtual pivot arms (here’s an example in the automotive world if that means nothing to you). The “Horn Harley” was featured in the October 1991 issue of Motorcyclist, January 1992 issue of Hot Bike, and Summer 1997 issue of Battle2Win.
Bob’s Sportster in Motorcyclist magazine.
The Sportster was sold off, and Horn looked into a Harley Big Twin powered-project for some more oomph. That didn’t pan out, but in 2006 he created a lightweight electric recumbent as a proof of concept of Kevin Cameron’s theory. After hundreds of test miles, Bob knew it was time to create a full-fledged motorcycle.
He started with the drivetrain from a Kawasaki Ninja 500. It’s cheap, reliable, and it puts out almost exactly 50 horsepower to the rear wheel. Other than that, the only other stock parts are the suspension (Honda CBR954RR units) and the wheels, sort of. They’re Ninja 500 wheels, though the hubs were machined by Kosman. That work is one of just two components that Bob outsourced – the other was heat treating the virtual pivot arms. Impressively, everything else was done by him.
The front end is an evolution of what Bob implemented with his Sportster – here’s what the front steering looked like years ago with the bodywork off:
This was how I saw it at the Quail:
The front end steering is interesting by itself, but what really makes this unique is what’s happening in the back. That’s Rob in the glasses on the left.
Through a series of linkages, the rear wheel automatically turns at 34% of the angle achieved by the front. Both wheels turn in the same direction.
What’s that, you say? You want to see it in motion?
Nathan filmed Bob and I for a short video that we’ll try to get out soon, but until then I’ve got some tidbits to share. The theoretical lean angle is 55 degrees, though Bob knows from experience that it will run out of traction first as the Ninja 500 wheels don’t allow for great rubber. It’s set up with GP shift, which Bob likes to joke is “1 back, 5 forward”. And the “757” racing number has no special meaning, it was just an available option with the Motorcycle Roadracing Association.
When I asked Rob why he went with a recumbent design, he told me that he originally planned on going with a modified Kneeler design as that is still fairly similar to the traditional motorcycle riding position, but it wasn’t as aerodynamic or as comfortable as the recumbent position. In addition, the Kneeler layout was too front-heavy from a weight distribution standpoint. The current design weighs 414 pounds with an empty fuel tank. With fuel and a rider that weighs 150 pounds, the RoHorn Racer has a 50/50 weight distribution. And it’s not just a racer on paper, Rob regularly tracks this machine:
JT Nesbitt (the man behind Bienville Studios, designer of the Confederate G2 Hellcat and Confederate Wraith, and designer of the upcoming Curtiss Hades – more on that when I share my recap of the Quail) came up to me while I was chatting with Rob and had nothing but positive things to say. He called it “fascinating” as well as “the coolest bike here [at the Quail]”. It was a nice moment as Bob was clearly a fan of JT’s work and it’s always nice to be complimented by someone you admire!
Rob’s motorcycle is the result of years of hard work, the kind of thing that’s only possible when someone is dedicated and tries not to think about how much an hour of their own labor costs! With that said, he was able to build this bike for less than $1,500 of material costs. I was in awe the entire time I listened to Bob describing his pride and joy, but that dollar figure took my surprise to an even higher level. This wasn’t the prettiest motorcycle at the Quail, and it didn’t win any awards. But it’s an awesome engineering achievement, and it’s one of many examples why I love what the Quail has to offer. I’m just excited that I get to share this with you.
But wait, there’s more! Development on the RoHorn Racer is just about done, and Rob is dreaming big. Specifically, he’s planning on using what he’s learned with two-wheel steering designs to create an improved racer powered by a supercharged Kawasaki KX500 motor. On paper, he’s expecting an outrageous 125 horsepower. Expect it to be much narrower and to have a single sided swingarm that connects both wheels…but you should also expect it to take years because motorcycle building is a part time endeavor for Mr. Horn. I can’t wait to see what the future holds. Until then, check out Rob’s site to learn more about his history and to keep tabs on what comes next!