Gear&Tech: Tipping the Scales – Scott's XC 26ers and 29ers

Scott Scale 29

Full-carbon 29ers just keep getting lighter and are appearing more often atop the podium domestically, and, finally, internationally as well.

Just in time for the 2010 World Cup final at Windham Mountain, New York this weekend – Aug. 28-29 – and the Mountain Bike World Championships at Mont Saint Anne, Quebec the following week – Sept. 1 through Sept. 5, 29ers are winning under the world’s best cross-country riders.

Riding, literally, a brand new Scott Scale 29 RC, Scott-Swisspower’s Florian Vogel won the final round of the Swiss Racer Bikes Cup series in Muttenz, Switzerland against a stacked field.

Vogel and teammate Nino Schurter had only ridden the new superlight bike a couple times before yet decided to race it anyway, as they felt that it was ideally suited to the fast course. After a crash by reigning world champion Schurter, Vogel bested a strong field that included the likes of Julien Absalon (Orbea) and Ralph Näf (Multivan-Merida).

With two laps to go, Schurter crashed, allowing Näf and Vogel to get a gap out of the lead group of eight. With a half a lap to go, Vogel took a few seconds out of Näf and held it to the line. Behind, Schurter bounced back up, and, as he did at the 2009 world championships and this year’s World Cup opener, he once again outsprinted Absalon at the line, this time for third place. Apparently his tubular-clad wagon wheels and his 949-gram Scale 29er frame accelerate just fine.

Big Bro

The Scale 29 RC is the sibling to the 899-gram 2011 Scale 26er that Schurter and Vogel have been racing on all season. Both frames share the same technical improvements over the Scale on which Schurter won last year’s world championships. That 2010 Scale was a 26er, and its frame weighed 980 grams. It was built with “tube-to-tube” construction (like the CR1 road frame), where carbon tubes are lashed together with pre-preg carbon wrapping tape, and the joints are squeezed and heated in a mold to cure them and squeeze out excess resin.

The new Scales tip the scales at a lower weight, due to a number of technical tweaks. The 2011 Scale 26 and Scale 29 are built with Scott’s IMP3 (Integrated Molding Process), in which larger sections of the frame are molded in a single piece, eliminating sections of tubes within the joints that add nothing structurally and replacing them with large hollow areas.

For instance, molding the down tube, head tube and top tube in a single piece and increasing their outer dimensions by switching to a tapered steering tube chopped 15 grams off of the frame weight while increasing torsional stiffness by 10 percent.

Switching from a bonded-in threaded aluminum bottom bracket shell to a Press-Fit bottom bracket (either an oversized PF30 or a wider and thinner PF92 system) slashed 30 grams of weight. It also made the area 15 percent stiffer and eliminated areas of stress concentration identified through Finite Element Analysis (FEA) by making the flare out to the width of the shell more gradual and direct.

Through extensive FEA work, the vertical compliance of the seatstays and chainstays has been increased while at the same time increasing their lateral stiffness by making them tubular and oval in cross section with the long axis in the horizontal plane. To eliminate seatstay vibration on braking, the disc-caliper mounts were moved to the chainstays. All of the changes to the rear stays together shaved off 25 grams.

Going from a lightweight aluminum band-clamp seatpost binder with a titanium pinch bolt that weighed 16 grams to a 5-gram no-band binder consisting of curved carbon ears integral with the seat tube and a pinch bolt passing through two small threaded aluminum cylinders that sit inside the molded ears saves 11 grams. Internal cable routing saves five more grams. Finally, eliminating assembly pieces like the disc-brake post-mount adapter and the threaded bottom bracket cups (in addition to the afore-mentioned binder clamp) eliminates 55 more grams.

Geometrical tweaks not affecting the weight include a reduction in bottom bracket height from last year by 10mm, to 310mm (12.2 inches) — on both 26 and 29 models, an increase in effective horizontal top tube length of 10mm, and an increase in head tube height by 5mm.

Schurter and Vogel waited to race on the 29er version of the new Scale until tubular tires came available for them. They are now running special 700 X 45mm Dugast tubulars (non-production, made exclusively for the team) on Ritchey alloy tubular rims, but DT Swiss is reportedly making carbon rims for the team in the next few weeks. The bikes are otherwise all SRAM XX and Ritchey components. With identical spec, the 29er is 700 grams (about 1.5 pounds) heavier than the complete 26er bike.

Look for more 29ers in the worlds under Euro pros, even though the size has not caught on among European consumers. You can be sure that many of the Americans, like last year’s eighth-place finisher in the worlds, Todd Wells of Specialized Factory Team, will be on 29ers as the world’s mountain bikers hit North America the next couple fo weeks.