Geoff Kabush (Team Maxxis-Rocky Mountain) is best known for his exploits on the mountain bike course but the 32-year-old Canadian is also highly competitive on the North American cyclo-cross circuit, too, having captured his national championship in October and finishing a solid 11th and 4th at this past weekend's Mercer Cup in New Jersey. For mud season, bike sponsor Rocky Mountain foregoes the carbon fiber rear end of its top-end Solo CXR production 'cross bike in favor of a fully aluminum rig custom welded to better suit Kabush's lanky build.
The top tube and seat tube lengths fall roughly in between Rocky Mountain's two biggest versions but the head tube length is spot-on with the smaller size, effectively creating a fit that is taller and longer than the stock 57cm but more aggressive than the 60cm. And why no carbon rear end? According to team manager and mechanic Gary Wolff, the all-aluminum construction was simply easier to build in-house at Rocky Mountain's British Columbia headquarters.
Even without the carbon, the frame is anything but low-tech. Rocky Mountain builds the custom chassis with Columbus XLR8R tubing throughout – including the stays – but subs in an externally bulge butted Easton scandium pipe for the seat tube to save even more weight.
"I offered Geoff the choice between light and compliant or stiff pedaling and he picked light," sad Rocky Mountain product manager Alex Cogger. "That's what dictated the tubing selection."
Tube shaping on the triple butted alloy pipes and the overall frame layout are fairly straightforward. Both the flared seat tube and top tube on the moderately sloping front triangle are perfectly round while the down tube transitions from an oval cross-section ahead to a trapezoidal one below to lend more stiffness to the front end and bottom bracket. Up front there's a conventional non-tapered 1 1/8" head tube (with FSA external bearing cups no less) and both the chain stays and seat stays are medium-sized with S-bend routing.
Just as the doctor ordered, the straightforward design adds up to an impressive showing at the scale, especially for such a large size. Actual weight is just 1,320g (2.91lb) – not far off from some carbon models.
Corresponding componentry is top-notch throughout, including a Shimano Dura-Ace 7900 transmission and drivetrain, an Alpha Q CX20 carbon fork, TRP EuroX Magnesium cantilevers, Crankbrothers Eggbeater 2ti pedals, and cockpit and seating bits from Race Face and fi'zi:k. As we caught up with Kabush just prior to a muddy race in Boulder, Colorado, rolling stock consisted of Reynolds MV32C UL carbon clinchers wrapped up in aggressive 35mm-wide Maxxis Mud Wrestler tires inflated to about 40psi.
As Shimano has yet to introduce proper 'cross-specific chainrings to its Dura-Ace collection, Kabush's bike is fitted with Thorne Koksijde 38/44T rings, named after and developed by Cyclocrossworld.com proprietor Stu Thorne. In addition to being offered in a wealth of hard-to-find ratios, Wolff says the pinned-and-ramped shifting performance has been very good so far and the thicker plates' extra stiffness lends a more solid feel underfoot.
Cutting weight – but not at the expense of durability – is a recurring theme throughout. The Alpha Q fork is among the lightest available at just 470g, the brakes are similarly feathery at under 120g per wheel, and though Kabush will run Reynolds' deeper 46mm rims from time to time, Wolff says he prefers the faster acceleration of the mid-section model. As icing on the cake, nearly all of the steel bolts on the bike have been replaced with titanium bits from Wheels Manufacturing, which not only helps shave a few grams but also prevents corrosion from frequent power washing. Total weight is a race ready 7.73kg (17.04lb).
Next stop on the US Gran Prix of Cyclocross tour is the Stanley Portland Cup the weekend of December 5, where Kabush and his custom machine will hope to move up in the standings.