Few would argue that the Dodge Tomahawk defies common sense. After all, who needs a motorcycle that reaches a top speed of more than 250 mph, cranks out 525 hp, and goes from 0-60 mph in 2.5 seconds? Moreover, who needs a vehicle that – if it ever reaches full-scale production – could be priced at a staggering $250,000?
Obviously, no one needs it. But the Tomahawk isn't about need, and it certainly isn't about common sense.
"My first reaction to this idea was that it didn't seem like the most intelligent use of power," says Mark Walters, the DaimlerChrysler senior designer who masterminded the construction of the highly-publicized vehicle. "But I had to admit: it is cool."
Indeed, Walters isn't the only one who thinks it's cool. Since unveiling the Dodge Tomahawk concept vehicle at the Detroit Auto Show in January, Chrysler Group has been inundated with requests from interested parties who want to sit on, ride, or buy the vehicle.
"We get people calling all the time and saying, 'I want to buy one, and I've got cash. How much do you want for it?'" Walters says.
Like the Dodge Viper of more than a decade ago, the Tomahawk has attracted the attention of movie stars and celebrities, most of whom hope that some of its star quality will rub off on them. At one of last January's Super Bowl parties in New Orleans, the Tomahawk appeared with the likes of "Joe Millionaire," Jane Seymour, and others. It then traveled to Burbank, California for a visit with motorcycle buff Jay Leno, who wanted to see the four-wheel motorcycle do a few burnouts.
In that sense, the Tomahawk is already fulfilling its purpose. The company isn't hiding the fact that the vehicle is mostly about image, and serves mainly as a message to consumers that DaimlerChrysler is a company that isn't big on conventional boundaries. "This is a bold-faced slap against mediocrity," said Senior Vice President of Design, Trevor Creed, in a prepared statement. "Tomahawk is a scintillating example of what creative minds can do when given the opportunity to run free."
At 8.3 liters, the Viper engine was about five times the size of a big motorcycle engine, leaving Tomahawk designers with a huge packaging dilemma.
Free Spirits Lead to Creative Concepts
Indeed, the company's willingness to let creative minds run free is the very essence of the Tomahawk.
The idea originated with two DaimlerChrysler employees who also happened to be motorcycle enthusiasts. "They had this idea to build a Viper-powered bike," Walters recalls. "They wanted to take the V-10 Viper engine and put it in an existing motorcycle chassis, but never found the time to do it because they both have families."
The two employees—clay modeler, Bob Schroeder, and vehicle build specialist, Dave Chyz—ultimately brought their idea to Freeman Thomas, DaimlerChrysler's vice president in charge of advanced studios, who in turn took it to Walters. In discussing the idea with Walters, Thomas mentioned he had a vision for the bike inspired by the 1982 film, Tron, in which actor Jeff Bridges, trapped in a video game, rides a virtual, four-wheeled motorcycle.
Walters took the Tron concept, worked with it for a few weeks, and then pitched it to Chrysler Group Chief Operating Officer, Wolfgang Bernhard, and CEO, Dieter Zetsche. Using giant panels measuring 20-ft long and 6-ft high, Walters showed the executives the concept for the bike and the corporate marketing advantages. He explained that the Tomahawk would give DaimlerChrysler access to truck events, where truck buyers (many of whom are motorcycle enthusiasts) would line up in droves to see the 250-mph vehicle.
"Basically, we saw it as a way to crash a party," Walters recalls. "At the same time, we were hoping we could expose some of those consumers to the products that we make."
Zetsche and Bernhard quickly saw the merit in the concept. "They loved it," Walters recalls. "Much to our surprise, they told us to build it."
Once the corporate blessing was obtained, however, the hard work began.
By the time Walters received the go-ahead, it was already May 2002, and DaimlerChrysler executives were hoping to see a finished vehicle by January 2003. That placed him approximately eight months behind the normal concept car schedule, which calls for design work to begin in early October, approximately 15 months before a vehicle's unveiling.
"The idea came up so late that the only way I could see making it happen was to move my workstation down to the fabrication area, where I could talk to the people who would be putting it together," Walters says. "Once I did that, we were literally only a few feet apart."
Handwork: In many cases, engineers say they had to do the machining of aluminum transmission parts -- held to tolerances of 0.001 inch -- by hand because of the complex curves and valleys involved.
The real dilemma facing Walters, however, was the sheer mass of the Viper engine. With a displacement of 8.3 liters, the V-10 Viper engine is more than five times larger than a big motorcycle engine on, say, a Harley-Davidson. "The worst evil of all was the physical mass," Walters recalls. "It's a lot of weight, a lot of metal, a lot of moving parts, and an awful lot of power."
For that reason, the use of the four-wheeled motorcycle concept suddenly seemed more appropriate than ever. The four wheels, Walters reasoned, would offset the extraordinary visual mass of the motor. What's more, the four wheels provided a more natural path for transferring 525 hp to the street.
"If you've ever seen a Viper do a burnout, you know that one little contact patch is not going to be enough," Walters says.
By employing twin wheels instead of one, however, Walters doubled the size of the Tomahawk's contact patch. Doing so, he says, not only helped with acceleration, but also braking.
Still, DaimlerChrysler had to deal with the engine's mass in other ways. The sheer mass of the engine loomed as a potential balance problem, especially for shorter riders moving at slow speeds. There, engineers say, the gyroscopic effect of the wheels doesn't provide balance as effectively as it does at higher speeds. As they near stop lights, for example, riders of all motorcycles typically must place their feet down on the street to balance the bike. And while that may not be a problem with a smaller bike, it was for the Tomahawk, which was nearing an ultimate weight of almost 1,400 lbs.
Their solution was to place the heaviest part of the bike – the engine – as low as possible. To accomplish that, DaimlerChrysler designers worked with engineers at RM Motorsports (Wixom, MI), builders of custom-designed race vehicles, who suggested that they use a "dry sump" engine. With the dry sump, the Viper engine could be placed lower, they said, because the oil pan would no longer be located at the bottom of the engine.
The design team created a dry sump by employing a remote oil pan, and then using a high-pressure oil pump with a scavenging stage to transport oil back and forth to the engine through pressurized lines.
By doing so, the team moved the engine down and lowered the bike's center of gravity. The lower engine, in turn, also provided riders with greater control at low speeds.
"Keeping the saddle as low to the ground as possible helps the riders," Walters says. "If they do have to use their legs at a stop light, they're not up on their toes. They can take a wider stance and gain a little leverage."
By moving the engine lower, Walters says he also left enough room for a specialized suspension system that further helps riders to deal with the motorcycle's mass. The suspension system consists of a pair of swing arms running to each of the rear wheels, and pivoting off the output shaft of the transmission. Each of the arms is connected to a spring-loaded linkage, which compresses one of the springs whenever the rider turns.
Weight, however, wasn't the only challenge wrought by the use of an 8.3-liter engine.
"Anything that makes that much power is going to generate a lot of heat," Walters says. "And you have to dissipate that heat somehow if you expect a rider to sit on it."
Dealing with Heat
To dissipate the heat, the design team scrapped the headers from the original Viper engine, and created a custom set of unequal length headers that run from the exhaust port to a "collector" that runs straight to the rear of the vehicle. By doing so, Walters eliminated the risk of burning the rider, whose knees would be close to the excessive girth of the engine.
Tomahawk's designers also wrapped the headers with a material often used to insulate turbochargers. The material, which wraps around the headers like an Ace bandage, helps eliminate the possibility of riders being burned.
Walters says that one of the biggest heat-related challenges, however, was simply cooling the engine. "A Viper uses very powerful fans and a radiator that's really big, located in a place where it gets a lot of air," Walters says. "But packaging all that onto a motorcycle would look ridiculous."
Still, engineers from RM Motorsports believed the problem could be solved. They first recommended the use of a cast aluminum fan that incorporates an alternator, thus enabling them to solve both the airflow and packaging problems in a single stroke. At the same time, the design team incorporated a pair of small radiators, measuring about 18 inches long by 8 inches high, which they placed in the "V" of the V-10 engine. Engineers arranged them in an A-frame shape and then sealed the area in a way that forces air past the radiators, to help in cooling.
Walters says that because of the short time frame, much of the engineering was of the seat-of-the-pants variety. There simply wasn't time for complex computational fluid dynamics studies on the cooling system, he says.
"We did use finite element analysis on the suspension arms," he says. "But the cooling system was a result of engineering experience more than anything else."
Experience was also the key element in the development of a special transmission for the Tomahawk. The need for the transmission arose partially because the Tomahawk's crankshaft runs transverse to the drive axle, but also because the gear ratios that it requires aren't available in any commercially available transmissions.
With the deadline looming just a few months ahead, engineers at RM Motorsports decided to solve the problem by making a transmission from scratch. The company's engineers mocked up a prototype using available gears and wooden parts. Then they drew up graph-paper sketches of the transmission casing, which they gave to Walters. He took the drawings to his workstation, "surfaced" the case, then provided a data CD to a vendor that milled the transmission case from a 10,000-lb, solid aluminum billet.
"Even though we were working in tolerances of a thousandth of an inch, the transmission worked right out of the box," Walters says.
At the same time, engineers at RM Motorsports worked with vendors on machining of wheels, body parts, swing arms, throttle body, and handlebars from smaller aluminum billets. In many cases, RM Motorsports engineers say they had to do the machining by hand, rather than via computer numerical control.
"Parts such as the throttle body and handlebars had complex curves and valleys, and there was no easy and fast way to do it," notes Bud Bennett, president of RM Motorsports. "It was like making a clay model, only from aluminum. We could have done it with a computer program, but it would have gone too slow."
A Chrysler Group spokesman says that the resulting prototype cost approximately $500,000 to design and build. That figure, he says, is low by comparison to most concept vehicles.
Designers of the vehicle say they really don't know how fast the resulting vehicle is.
"If it were geared properly, 250 mph would be attainable," Walters says. "But right now, it's geared for acceleration, not speed." Although the company has published top-speed figures of 400 mph, Walters says he doesn't believe, and doesn't want to know, if such speeds are possible.
The company has said, however, that the vehicle accelerates from 0-60 mph in under 2.5 seconds, and reaches to 120 mph "very, very quickly." Engineers refused to place a number on the 0-120 mph speed, however.
"I've ridden it, and it makes my 1,100-cc sport bike feel like a scooter," Walters says.
Whether the automotive giant will put the Tomahawk into production is another matter. Industry insiders expect it will.