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.

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.

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.

Quick releases on a disc hub? Specialized engineers contend that it's not problem, and I didn't have any alignment issues despite the rough roads

A few items weren't perfect, like the 34t ring I swapped for the 36t. The bike came with the semi-compact 52/36, and with Shimano Di2, shifts flawlessly, even when under load. I discovered that my desperation move for more gear compromised this perfection slightly; on two or three occasions the front shifting hiccuped, probably because of a bigger-than-recommended jump between rings and the absence of Shimano's paired ramping on both rings (the 34t is FSA). My fault. Those hiccups were rare, though, and really only amounted to a little noise on the downshift. Grinding slowly up Lick Skillet, I was so glad to have the 34, and would have gladly used something smaller. Matter of fact, I was in the 34/28 for a fair few other sections, too. A friend on a 52/36 pointed out that he had installed a SRAM 11-32 cassette on his Shimano bike to achieve the same result, and it was shifting fine.

Another small annoyance was my Garmin Edge 810. On the plus side, it handled the important stuff — keeping us on track — just fine. Being an unofficial race, there wasn't much in the way of course marking; riders were responsible for self-navigation. So, having turn-by-turn directions on the Garmin was key. I alternated between following lines on the map and the turn-by-turn directions, both of which update in real time. Having been stranded technologically by the Garmin Edge 1000 a few weeks ago at hour five of a six-hour ride, I brought a small charger, just in case. It wasn't needed. (For the record, the Edge 1000 has far superior turn-by-turn mapping and directions to the 810, but at a substantial battery cost.) My one asterisk on the Edge 810 on race day was that it froze up on ANT+ heart-rate and power data at about mile 70. Relatedly, the Garmin Vector power-meter pedals performed fine until then.

A nine-hour day on dirt proved a good test for riders, bikes and tyres

My teammates had various luck with their tyres, running everything from 23mm Continental Gatorskin (one flat) to 28mm Clement LGG (three flats). Our ill-fated rider who had to abandon first flatted and then severely tore a Forte Pro+ 25mm. (Forte is the house brand of retail chain Performance Bike, which, for UK and AU readers, is similar to Chain Reaction.) But another, lighter rider had the same tyres with no issue. Tyre pressure and rider weight can certainly play a role — those Clement Strada LGG were set to less than 80psi under a 175lb rider, who pinch-flatted twice, then tore a valve stem. And dumb luck certainly factors in — a much more skilled rider than I flatted his Sector 28s on a rough descent, whereas I had no problems all day. Another teammate had Continental Gatorskin 28mm's, with cyclocross tubes (28-35mm) installed with plenty of baby powder, set to 105psi for a 188lb guy. Also no flats.

All in all, the Tarmac Disc was a great bike for the day. I may have pushed it a little beyond its intended use, but it came up roses.

Stay tuned for more Horse for the Course trials and tribulations, across road, mountain, cyclocross and even - dare I say it - triathlon bikes.

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