That Willow Koerber (Subaru-Trek) is the best American mountain bike cross-country racer right now is no surprise – she led the UCI rankings earlier this year after back-to-back second-place finishes on the World Cup circuit, landed third in Champéry, and currently still sits in third place overall with one round remaining.
What is surprising is that she's done all of this on a hardtail 29er – despite standing just 1.57m (5' 2") tall.
Koerber's not the only one, either, as teammate Heather Irmiger is also a 29" aficionado with both riders citing the larger format's faster roll on rough terrain, improved cornering prowess, and enhanced stability relative to industry-standard 26" hoops.
"My bike feels like a natural fit to me and I am always amazed at the flow I feel when I am riding the 29er," Koerber told us. "I had zero problems getting my fit dialed."
Sizing may have been problem-free but still not exactly standard, especially with the updated version of Koerber's Trek Superfly Elite. Though Trek says the new chassis is 150g lighter and fifteen percent more rigid thanks to its direct-fit bottom bracket bearings, larger tube profiles, and tapered front end, the intended fork travel has also gone up to 100mm, adding 20mm to the stack from last year's Superfly.
Compounding things further is the carbon fiber steerer tube on RockShox's early-production Reba XX 29", which uses a gradual taper that is great for distributing impact load but doesn't play well with Koerber's extra-short 103mm head tube.
Luckily for Koerber, team mechanic Matt Opperman and the rest of the Trek technical support crew have managed to get around the issues, adding a small spacer beneath the crown race to move the taper further down in the head tube, dropping the fork travel (and thus, crown-to-axle height) by 10mm, swapping to a -12° stem, and also trading in last year's riser bar for a flat one instead.
Opperman says that RockShox is revising the fork's steerer shape, too, so eventually he'll be able to add the travel back in or drop the bar height even lower depending on Koerber's preferences.
The build kit is relatively off-the-shelf, including a nearly complete SRAM XX group (Opperman has to use standard all-steel G3 rotors on the US domestic race bikes since he doesn't have enough XX rotors to go around and a custom-fit SRAM Force front derailleur stands in while the direct-mount XX unit is finalized), Bontrager Race X Lite wheels, tires and cockpit components, crankbrothers Eggbeater 11 pedals, a fi'zi:k Vitesse k:ium saddle, Nokon cables and housing and ESI Racer's Edge silicone foam rubber grips.
Total weight is a 9.62kg (21.21lb) – undoubtedly race worthy but still relatively heavy as compared to other 26" race bikes on the circuit, which still undercut it by more than a kilogram. And in terms of rotating mass, Koerber's 1,692g wheel weight doesn't help, either.
Opperman says that Koerber's new World Cup bike now closes that gap at just 8.9kg (19.7lb) thanks to a new 1,390g wheelset built with Stan's NoTubes 29" rims, a made-by-DT Swiss rear hub and thinner Revolution spokes, and Trek's new FCC front hub.
In addition, Opperman has also included a more comprehensive complement of go-fast goodies such as more titanium hardware, ceramic bearings and, "a few other bits to lighten it."
Koerber will debut the new lighter-weight rig later this month at the final World Cup round in upstate New York – where she'll undoubtedly be seeking that still-elusive win.