On Monday, when the winner crosses the line in the 114th running of the Boston Marathon, one thing is for certain: Ernst Van Dyk will have covered the course faster. A lot faster.

The 37-year old South African, who will be going for a record ninth win in the men's wheelchair division, set the 2004 course record of 1:18.29. That's almost 50 minutes faster than the 2:08:42 time posted by last year's fastest male runner, Deriba Merga.

But the elite runners in the men's and women's fields, who start after the wheelchair competitors are well underway, don't have to deal with any equipment more complicated than a shoelace. Van Dyk and his fellow wheelchair competitors, on the other hand, who are vying for a first prize of $60,000, rely on cutting-edge technology to cover the course at an average speed of over 20 mph.

"Ernst is a guy who's almost perfectly built to race the Boston Marathon," says Chris Peterson, founder of Top End, Van Dyk's longtime sponsor and the builder of the $6500 Eliminator OSR that Van Dyk uses in competition. "We build the chair around him."

Peterson starts by measuring Van Dyk in detail and then enters that data into a CAD program. The frame is handcrafted from 6061 T-6 aluminum tubing, used in many bicycle frames. Aluminum is the material of choice for wheelchairs because the frames must be customized to the millimeter, Peterson says. One-piece carbon-fiber construction is impractical, while titanium is lightweight, but not stiff enough.

Ernst Van Dyk has set the Boston Marathon course record in a blazing-fast 1:18.29

While weight is important—Van Dyk's OSR weighs just under 20 pounds—fit is the key for a fast racing chair. "You sit on top of a bicycle," Peterson explains. "You sit inside a racing wheelchair. You want to be almost stuck inside the chair." The OSR's narrow profile decreases aerodynamic drag, but most of all, positions Van Dyk so that he can push as efficiently as possible. Van Dyk's wheels are cambered by 12 degrees to allow for a full, smooth push, and his long arms allow him to use 15-3/4-inch hand rims—equivalent to a bicycle's gearing—which are among the biggest in the sport.

The champ's chair sports a long 76-inch wheelbase for stability and to absorb shocks on Boston's bumpy course. Because of a congenital defect, Van Dyk was born without legs, so he depends on his narrow, thinly padded carbon-fiber seat to support his torso.

Peters notes that the sport's governing body, the International Paralympic Committee, places few restrictions on the chair specifications: no gearing; one hand rim per wheel; the front wheel can't be larger than 50 cm; and each chair must have a steering device and brakes. Van Dyk's Cane Creek titanium calipers are especially important in Boston, where racers can top 50 mph on the downhill side of Heartbreak Hill. On the flip side, the hilly nature of the Boston course does string out the pack, which prevents the gruesome crashes that are sometimes seen on flatter courses.

Since Boston's undulating course places a premium on efficient coasting, fast wheels are a must. Van Dyk borrows cutting-edge wheel technology from the bicycle world. His rear wheels are 700c honeycomb core carbon-fiber disk wheels by Zipp. They're shod with 250-gram Continental tubular tires running a pressure of 160 psi. His front wheel is a deep-dish Corima with 10 aerodynamic spokes and a Panaracer tubular, although with Van Dyk's powerful push, the front wheel is often off the ground.

What's Van Dyk's biggest concern as he aims for a place in the record books? "You've definitely got to worry about flats," says Peters. "Especially in a race like Boston, where the roads are crappy." Peterson notes that some racers will use ultralight tires that will save them a few seconds, then give back minutes while changing a flat tire. While he's never had to do it at Boston, Peterson notes that Van Dyk can change a rear tire and reinflate it with a C02 cartridge in about a minute, without even removing the wheel from the chair. (Fixing a flat front tire requires that the wheel be removed from the bike, which can take more than twice as long.) "He could probably change a tire and still win," says Peterson, who notes that Van Dyk's margin of victory last year was almost four minutes. "But we'd rather not find out."

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