An Australian motorcycle specialist came to Bill King more than three years ago with an idea for what seemed like an impossible stunt. He wanted to modify a motorcycle so it could ride under a massive wave in Tahiti.
Robbie Maddison — who gained fame as an X Games medalist by setting the world record for motorcycle jumping in 2008 and jumping the Tower Bridge in London with a backflip in 2009 — had seen motorbikes fitted with a conversion kit for skiing on snow. King had helped engineer the kit, called a RadiX, for 2Moto Snowbikes in Boise. Maddison approached King in December 2011 to see whether a similar application could be developed for riding on water.
“It probably took me 20 minutes of thinking how to do it. It took years to figure out how to do it,” King said. “The concept is pretty much the same. It just took a long time to dial it in.”
In April, more than three years after Maddison and King met, Maddison rode his modified motorbike across a massive wave in Tahiti. The resulting video, posted on YouTube on Aug. 2, has received more than 17 million views.
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“If you watch the video, it shows him in the beginning going through a jungle,” King said. “I saw the bike and said, ‘That’s my stuff.’ He did it. He finally did it.”
King, 53, felt satisfaction: “I’m an engineer. I solve people’s problems. That’s what I do for a living, and that was very exciting to see,” he said.
King earned a bachelor’s degree in mechanical engineering from Northern Arizona University. He spent six years designing rocket motors for the now-defunct Morton-Thiokol Inc. in Utah and later worked for Hewlett-Packard in the disc drive and inkjet divisions in Boise and Corvallis, Ore.
King joined fellow engineers and tinkerers Vernal Forbes and Vard Williams in 1996 in developing the RadiX. Two years later, they had a prototype that they rode in the snowy forests around Idaho City. The first kits went on sale in 2006.
King also serves as president of in-Finite Solutions, an Eagle company that specializes in product design, development and improvement.
The RadiX kit replaces the front wheel of a motorbike with a ski and the back wheel with a track similar to that of a snowmobile. Maddison wanted to keep the wheels so his machine retained the look of a motorbike.
Maddison’s bike was fitted with skis and sand tires. The back tire has small paddles to maintain traction and the bike’s grip on the water. It sounds easy in theory, but a lot of tinkering went into developing the optimal ride.
King said he studied how V-shaped planing hull boats glide through the water and the distribution of pressure against their hulls. He also reviewed fluid mechanics and water skiing.
“From there it was like, ‘How do I make something move and do what it’s supposed to do?’ Not only does it have to ski, but when it hits a bump, the suspension has to work also,” to keep the skis and wheels in contact with the water, King said.
He also looked at how water spraying on the engine would affect performance and how drag created by turning would affect speed.
King tried three tires with varying numbers of paddles. Maddison experimented with at least two additional designs. The skis had to be modified many times, as did the angle at which they met the water.
“We tried so many different skis,” Maddison told XGames.com. “Some went faster, some turned better. We didn’t have a water tank and a laboratory; it was just the two of us riding and testing and tinkering.”
One of the biggest challenges when trying to modify a dirt bike to ride on water is the water itself. If the rider fails to keep the bike on the surface, it sinks and water floods the engine. During test runs over an 18-month period, Maddison sank his bike at least 100 times.
“You have to pull the bike apart. You have to clean it out and dry it out. You’re talking about two hours or so after you sink a bike before you can get to ride it again,” King said. “That’s a lot of hours.”
It took two days of testing on a pond near Middleton three years ago before Maddison was able to hit fourth gear and ride on the water for a half-mile. “It was the best feeling I’d ever had,” Maddison, 34, told XGames.com.
But success on the still, glassy surface of the Idaho pond didn’t lead to immediate success when Maddison tested the bike on the Pacific Ocean in Southern California.
Altitude, the salinity of the water and the water temperature all affect how the bike runs. The water temperature in the South Pacific Ocean at Tahiti averages 78 degrees, more than 10 degrees warmer than in Southern California.
“If the altitude changes a lot, your engine won’t run the same,” King said. “The water density and temperature changes how slippery, if you will, the water is and how heavy it is, and that changes how it acts.”
He switched bikes from a Honda with a four-stroke engine to a KTM 300 with a less-complicated two-stroke.
In Tahiti, Maddison ran into further problems.
“Most people thought the bike would perform better in warm, salty water because it’s buoyant,” he told XGames.com. “But warm saltwater is less dense than cold freshwater, and the density is what’s important. The tires didn’t have as much grip in salt water, and the paddles (on the back tire) didn’t have as much drive. Instead of topping out at 58 mph, I could only go 35.”
After days spent making modifications, Maddison got his bike to work on the final day before he was going to give up, King said. He used a 70-foot ramp placed on a barge in the ocean to get up to speed before hitting the water.
“A lot of this stuff, there’s no computer to do it, so you have to use your mind and your understanding of the basics,” King said. “You just have to feel your way into a solution.”