Gravel bike evolution shows little sign of slowing – treading on the toes of mountain bikes with ever-wider tyres – and, running alongside that, riders continue to conduct their own experiments in the name of off-road speed.
For Keegan Swenson at Leadville, that resulted in this wild ‘Frankenbuild’ – not a gravel bike, but a drop-bar MTB that mashes together the best, as Swenson sees it, of both worlds: a Santa Cruz Blur with RockShox suspension, SRAM Transmission components, Maxxis Aspen 2.25in tyres, road pedals and SRAM Red shifters mounted to a drop handlebar. Oh, and aero fairings on the fork.
The Leadville 100 has become the unofficial home of the drop-bar mountain bike. The 100-mile race in the high mountains of Colorado’s Rocky Mountains was first run in 1994 and has become one of the most important MTB marathon races on the calendar.
The race starts in the town of Leadville at an altitude of more than 10,000ft and includes more than 12,000ft of elevation gain over the 100-mile route, reaching a peak of 12,600ft in Colorado’s high mountains.
As far as mountain bike courses go, Leadville’s terrain is at the tamer end of the spectrum, and in recent years, riders have used that as an opportunity to experiment with go-fast setups specifically designed to tackle a 100-mile mountain bike race.
In Swenson's case for last weekend's race, that meant combining comfort and control through the Blur, with the aero advantage and handling characteristics of a drop handlebar.
Having ridden a drop-bar-equipped Santa Cruz Highball hardtail to victory last year, this year Swenson opted for the full-suspension Blur, the US brand’s lightweight XC platform.
The size-medium frame was paired with a RockShox SID Ultimate SL fork with 100mm of suspension travel, dialled for the “relatively smooth course”, and a SID shock.
Both were equipped with RockShox Flight Attendant, a system which automatically adjusts the suspension settings as you ride, launched back in 2021.
Most interesting, though, are the fairings attached to the rear of the fork – is this the latest development in off-road aero marginal gains?
The fairings feature RockShox’s Black Box branding – Black Box is the company’s research and development unit, responsible for prototyping components that often make it into production.
In terms of drivetrain components, Swenson’s Frankenbuild featured a 40t SRAM XX chainring, with a OneUP chain guide, paired with a direct-mount SRAM XX Eagle Transmission rear derailleur and 10-52t cassette for the high-altitude race.
The drivetrain used a chain treated with two Silca SpeedChips, Silca’s race-day wax additive. It’s designed, Silca says, to be used with a hot wax to improve drivetrain efficiency.
The cockpit combined an aero-profile drop handlebar with a stubby 60mm, negative rise stem, to position the bar in a lower, aero position. SRAM Red AXS road shifters kept the gears moving for 100 miles.
Before the race, Swenson described the rolling stock as “special Leadville-edition wheels”, combining Reserve GR25 rims with DT Swiss 180 mountain bike hubs. “A little lighter, a little faster,” he said.
Those wheels were wrapped in 170tpi Maxxis Aspen ST 2.25in tyres with Tannus foam inserts to “provide a little extra protection to run a lower pressure, for good traction,” according to Swenson.
The Aspen ST is an ultra-low-profile XC tyre from Maxxis. The brand says it’s primarily designed for short-track XC racing, but clearly it’s more than capable over 100 miles of racing at Leadville, too.
Finishing touches included a set of Look Keo Blade Carbon road pedals – “a little lighter, a little more aerodynamic,” Swenson said – and a carbon rigid seatpost, “because it’s Leadville and you don’t need a dropper.”
There was also a Hammerhead Karoo 3 bike computer to capture Swenson's ride data. “I rely pretty heavily on that at Leadville, because the pacing is important,” he said.
As for Swenson’s closing comments on the bike, pre-race he described it as “ready to go fast” and, with one of the biggest names in the US off-road scene aboard, that proved to be the case, with Swenson winning the Leadville 100 for the fifth year in a row.
