From Road Glide to Roadrace

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Kevin Cameron has been writing about motorcycles for nearly 50 years, first for <em>Cycle magazine</em> and, since 1992, for <em>Cycle World</em>. (Robert Martin/)

Don’t even ask why people are racing baggers, which are cruiser motorcycles equipped with luggage and a large front fairing. It’s just a fact—people like something different, and when given the choice, tend to favor extremes. When the audience likes the show, the most important question has been answered.

Problem is, baggers as they chug from the showroom are not much use on a racetrack. Lean one over beyond about 35 degrees and parts drag on the pavement. If you persist, something grounds hard enough to jack the tires off the ground and the bike and rider become a dust cloud.

What does it take to turn a Harley-Davidson Road Glide into a factory racing machine for MotoAmerica’s King of the Baggers race series? (Brian J. Nelson/)

Baggers are heavy, and if acceleration equals thrust divided by weight, we have a job ahead of us:

1) Maximizing thrust by increasing engine power and…

2) Minimizing weight by removing all parts not essential to going fast. Well, not quite—class rules properly require a stock-ish appearance, so the large tour fairing and something that at least looks like bags must remain (Rule 2.7.11.11 h: “Each saddle bag must be able to enclose a 13.6 x 5.4 x 9-inch box and be at least 2,200 cubic inches of volume. Material is free.”). To prevent “lightweighting” from becoming ridiculous, a minimum weight of 620 pounds was set. (Builders in some 1960s auto drag racing classes used acid-dipping to eat away excess metal!)

Because the USA still has a strong hot-rod community, engine power isn’t hard to come by. In the case of Harley-Davidson, the company offers a giant V-twin crate engine of 131ci, and the Screamin’ Eagle catalog offers higher-performance parts. Beyond that, rules allow traditional porting and other hot-rod techniques. Short of sending in a bee-sized surveillance drone to bring us dyno screenshots, all we have is claims of 155 to 165 hp from the best engines of the present moment. In terms of specific power that’s a moderate 1.22 hp per cubic inch.

Related: Harley-Davidson Prepares for Daytona

Harley’s 131ci V-twin powers its factory King of the Baggers racebikes. (Brian J. Nelson/)

Racing is not about tech specs. It’s about riders wrestling 10 variables at once while staying on the track and fighting for position. It just so happens that people like the deep and syncopated roar (because of uneven firing intervals) of a giant V-twin at 7,000 rpm (that’s the rulebook redline for the Harley). Remember that these engines were designed to give peak torque at 3,000 to 3,500 rpm for strong on-ramp and highway passing performance, and to pretty much wheeze out at 5,000 or so. Yet here they are, surviving at peak revs jacked up by 40 percent. Just try boosting the peak revs of your average 14,000 rpm literbike engine and see what happens when the tach hits 20,000. Parts everywhere.

And now cornering clearance. Build a jig to rigidly hold two sheets of plywood at an included angle of 110 degrees (which implies a max lean angle to either side of 55 degrees) and try to roll your bike through it. One other thing: Compress the suspension two-thirds to simulate midcorner ride height. Anything that touches plywood must be removed, modified, or raised until that contact ceases.

As you examine the bike you see many changes. The bags are carried high, so the rider’s seat is also tall. You see this when the first rider comes in after a few laps and stops. To avoid falling over, he has to scooch to one side of the seat and point his toe to reach the ground. Tall.

Seat height and ground clearance numbers are more adventure bike than cruiser in order to create enough clearance to allow roadrace lean angles. (Brian J. Nelson/)

The large 2-into-1 pipe is routed high on the right, above the projecting timing case. Why didn’t Harley put the cam in the cylinder Vee as is done on every good old American V-8 car engine? Because there’s no room. Harley’s traditional Vee angle of 45 degrees is half of a V-8′s 90.

Because the engine, with its long four-lobe cam pushing the timing cover out on the right and the cast primary drive cover swelling on the left, width across footpegs is best minimized by machining the peg mounts as part of billet side covers. Relief is just a few keystrokes away.

The whole bike is lifted up, requiring us to refer to the rules regarding how this can be done. The frame may not be modified, which means none of that Kel Carruthers–style sawing off the steering head and welding it back on at an angle that speeds up the steering. Remember the 1200 Sportster class, in which the bikes were so jacked at the rear? Doug Chandler called that “the stink bug look.”

Longer fork legs and a greater swingarm droop angle lift the bike.

The reason for using Öhlins fully adjustable suspension is that it constitutes a highly adaptable system that has a long history of coping with racing problems. The original suspension was designed for a completely different set of goals.

Related: Why King of the Baggers Racing Is So Popular

Öhlins suspension is used front and rear on Harley’s King of the Bagger factory racebikes. (Brian J. Nelson/)

What are those two Öhlins suspension accumulators doing there, tucked between rear fender and bag on each side? The stock bike has dual shocks, that’s what. And the swingarm whose motion they control begins life as 255 pounds of aluminum billet that is chewed away by CNC to become the 18-pound truss structure we see.

Another complication is that this bike begins life with a quiet, maintenance-free toothed-belt drive to the rear wheel, but to transmit the modified engine’s power on the track it has been replaced by a roller chain. This is Rule 2.7.9.10 d: “Final drive belt systems may be converted to chain type systems.”

Per the rulebook, H-D’s race baggers run a roller chain instead of a belt. (Brian J. Nelson/)

Ideally a swingarm for a belt-drive system could maintain constant tension if pivoted on the gearbox sprocket axis, but a pivot that low, with the chain tension produced by a large engine, causes the rear suspension to squat during acceleration. I was told that over the range of rear suspension travel, amazing variations in chain slack occur. To accommodate them there is a rugged bottom run chain tensioner whose development required some trial and error.

These bikes do wheelie during acceleration, despite their long 64-inch wheelbase. That’s better than the alternative, which can result from too much wheelbase: to spin rather than accelerate (remember that unlike dragstrips, roadrace tracks are not shiny with glue). This ability to transfer weight to the rear tire during hard acceleration is another reason to build these bikes as tall as they are.

Rule 2.7.11.1 c states: “The original position (of engine, steering stem or pivots) is considered as the position in which the production motorcycle is supplied and must be retained.” That means the only way to speed up steering from the original 26-degree rake angle is to lift the rear of the chassis more than the front. Trail can be reduced from the ultra-stable stock 6.8 inches by use of billet fork crowns having offset different from stock. For each inch we raise the rear of the motorcycle, we reduce steering rake by 1.1 degrees.

Öhlins suspension is used front and rear, subject to Rule 2.7.11.2a which says, “Suspension price caps will be $6,000 for Forks and $2,000 for Shocks.” Makes me wonder what the price of that trick swingarm is, under the rule that requires custom parts to be available for sale within six weeks of their appearance on track. One thing’s for sure: There is no cheap racing.

That truss swingarm is just one of a great many clever CNC parts on these bikes. Team principal Jason Kehl had said, “You’ll see a lot of CNC parts in this class, but you’ll also see that not all of them really work.”

Plenty of machined billet on these racers, the side covers incorporate footpeg mounts. (Brian J. Nelson/)

Brembo provides 330mm twin T-Drive discs of 6.75mm thickness up front, with calipers described to me as “one step below those used in MotoGP.” Although the brakes look small in comparison with this 620-pound bike, brakes are sized not for weight but for the kinetic energy the engine can put into the bike. Harley’s KOTB bike’s all-up weight is 40 percent greater than that of a MotoGP bike, but kinetic energy is proportional to velocity, squared. If a bagger approaches the Daytona chicane at 170 mph but a “winged wonder” brakes from 220 mph, the ratio of the squares of those speeds is 1.67—more than compensating for the greater weight of the bagger.

Wheels are Core Moto forged aluminum (Titusville, Florida), in conformance with Rule 2.7.11.6 b: “Wheels can either be made from aluminum alloys or the homologated material.” Front rim width is 3.5 inches (in the ‘70s that was a big-bike rear rim width and we thought it was huge) and rear is 6 inches. A thoughtful person has caused directional arrows to be milled into the rim sides.

A low-slung exhaust won’t do in bagger racing—every degree of lean angle is needed. Harley engineers have routed the factory racers’ exhaust as high and tight as possible. (Brian J. Nelson/)

Tires are Dunlop slicks. There was a proposal under discussion to require use of DOT street tires in KOTB, but that’s more of what’s been heard in MotoGP—proposals to reduce “dangerously high” corner speeds by ordering the spec tire maker to make bad tires. Exactly how bad would you like? Is your legal team ready to defend your bad tire plan against liability lawsuits? Ah, I thought not. Better to rely upon racing slicks made for the job.

Speaking of which, when the sun went down and the testing stopped, I spent some time looking at the rear tires. The usual “beach mark” wear extended to a couple of inches short of the tire edge on the right, where the rubber looked more polished than used. Later, at dinner, with rider Travis Wyman on my right, he said to me, “You can’t get a lot accomplished when you’re down on the tire edges with this kind of power.”

I wanted to know more but time was up.

Gradual and controlled initial throttle response may seem not so race-like, but when 620 pounds is laid over on the side of the tire, it’s just what is needed. (Brian J. Nelson/)

Earlier, one of the engineers had spoken of the “control law” (program) relating motion at the rider’s right wrist to the opening of that big motor-driven butterfly. When non-racers have ridden these bikes, he said, they’ve commented on how gradual, even boring, their initial throttle is. Street guys, it seems, are excited by something faster-opening, more aggressive. But aggressive apparently doesn’t cut it when you’re down on the tire edges with such big cylinders banging away like Project Orion.

Or could it be something else? Just what happens on these bikes when chain pull acts on the stock positions of gearbox sprocket, swingarm pivot, and the swingarm droop required to keep the bike from grounding? Questions for next time.

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