Boonen’s Roubaix-winning bike comes to shops in 2009
By Ben Delaney
Specialized is on a roll with its sponsored athletes and not-yet-released bikes. Christoph Sauser just won the world mountain bike championships on a new Epic, which will be formally introduced next week and available later this year. But the bike that’s here now is the Roubaix SL2, the bike Tom Boonen won Paris-Roubaix on this spring, well before it was available for sale.
The Roubaix SL2, available at retail later this year, is a thorough overhaul of the Roubaix bike first introduced in 2005 (the first year Boonen won Paris-Roubaix, incidentally). The basic concept of the bike is a high-performance road racing machine that keeps the rider comfortable over the roughest roads pro racing can dish out.
Compared to a more aggressive and traditional race machine, the Roubaix has a slightly longer wheelbase, slighter slacker head tube angle, taller head tube and vibration-damping technology. It’s no “comfort bike,” however (reference Paris-Roubaix, Boonen, Tom).
For Boonen’s 2008 Paris-Roubaix charge — and for riders worldwide next year — Specialized’s road engineer Luc Callahan made two major changes: raising and widening the lower bearing of the fork to 1 3/8 inches (from the current standard of 1 1/8-inch) and widening the modified wishbone design of the chainstays.
The first change stiffens and strengthens the front end. In addition to wider diameter tubing being a stronger design in and of itself, the 1 3/8-inch bearing, which is set higher on the crown than standard, allows for straighter alignment of the carbon fiber. (Carbon, being basically thread, is strongest in tension. Thus, the straighter the fibers, the stronger the design.) The Tarmac SL2, and a few other road bikes on the market, have 1.5-inch lower bearings.
The second change allows for greater lateral stiffness. The bike’s rear end already has great vibration damping, courtesy of vertically flexing, chicane-style seatstays with Zertz dampers. But Callahan found that by increasing the width of the seatstays at the brake bridge, he could significantly stiffen the rear end laterally. Under riding load, seatstays can move somewhat independently of one another, much like two parallel parts in a parallelogram. Since the seatstays are joined at the brake bridge (and the rear hub), expanding the width of the bridge increases the triangulation and therefore stabilizes the structure within that plane.