Horse for the Course: Tarmac Disc / epic 9hr RGR

Bike and gear selection passes the all-day, dirt-road, climbing-fest test

As part of a new column, Horse for the Course, last week I wrote about a bike and gear I picked for an unsanctioned race up and over many dirt roads high in the Rocky Mountains. I took a slightly modified Specialized S-Works Tarmac Disc on the Colorado Rapha Gentlemen’s Race, which ended up climbing — and descending — about 14,000ft / 4,200 m over 107mi, much of that on dirt. Here is how my choices fared.


First, a quick recap of the course and my thinking in the gear selection. Rapha Gentlemen’s Races combine an alleycat-style of informal racing with big-mile, all-day adventure riding. Teams of six start three minutes apart, and must finish as a complete unit. It’s a cool format, encouraging teamwork and camraderie, and just enough competitive spark to keep the legs turning.

As the route is near my home, I was mostly familiar with the roads, but two sections had most riders a little concerned: a five-mile stretch of jeep road called Switzerland Trail (that we normally mountain bike), and a horrible, one-mile, 14-percent dirt climb called Lick Skillet. Aside from that, there was a generous amount of climbing and descending on somewhat tamer dirt back roads.

The brief RGR instructions specifically called out tyre recommendations: “NEW tyres of at least 25mm. Favor durability over light weight.” Last week I wrote that I would run the stock Specialized Turbo 26mm clinchers, but after obsessing a little and getting feedback from friends, I went back to my trusty Hutchinson Sector 28s. Although pumped up on the Roval CLX40 Disc wheels the Sectors were just over 1mm wider, the extra durability of a 300g tyre over a 225g tyre wouldn’t be a bad thing, I finally concluded.

Specialized’s tarmac disc was no worse for the wear after a full day of rough-road abuse: specialized’s tarmac disc was no worse for the wear after a full day of rough-road abuse
Ben Delaney / Immediate Media

The Tarmac Disc was run stock save swapping in Hutchinson Sector 28 tyres, a longer stem and a 34t little ring

The other main change to the bike was swapping the 36t little ring for a 34t ring,  thinking specifically about that bloody grunt up Lick Skillet that literally put a riding buddy on his ass during a little recon ride. Indeed, that cursed hill put a few more on their butts — and many more on both feet, walking up — on race day.

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Win Loss Draw
Frameset: Tarmac Disc X
Brakes: Shimano R785 hydro X
Wheels: Roval Rapide CLX40 Disc      X
Tyres: Hutchinson Sector 28 X
Power meter: Garmin Vector X
GPS computer: Edge 810 X
Gear selection: 52/34, 11-28 X

Of the 20 teams that started, only seven finished with complete, 6-person squads. Ours was not one of them. Crashes, fatigue and mechanicals — the race was self-supported — removed riders from various teams. We had six flat tyres, and one tyre casing ripped from the bead, which cost us a man and removed us from contention. Lesson learned: bring a spare tyre next time. Ironically, the Switzerland Trail jeep road was a non-issue; although rocky and sandy by turns, it was all an uphill grind and didn’t cause any flats or mechanicals. All our flats — and the torn casing — came on rattling dirt descents.

As for the Horse for the Course bike, it fared quite well. With the Sector 28s pumped to 90psi (I weigh 185lb / 84kg), I did not flat and was able to cruise the choppy downhills. I enjoyed the single-finger braking of Shimano’s hydraulic R785 discs; on long, jarring descents it was relatively easy to keep my hands and arms relaxed and my speed under control. Only on one long, steep section with repeated hard braking did I get them to squeal. (Read my related thoughts on disc brakes, along with James Huang’s fix for rattling levers.) The Roval Rapide CLX40 Disc wheels remained perfectly true despite some serious abuse, and nothing on the bike (seatpost, saddle, bars, etc.) slipped or squeaked. Also, notably for a disc bike with quick releases front and rear, the hubs and thus rotors stayed perfectly in alignment with the calipers. There is disagreement in the industry about whether or not road bikes with disc brakes need thru-axles. Specialized engineers contend that they do not, so long as there is ample contact surface between dropout and hub. My experience on this one, long, rough-and-tumble day seems to support that.