Horse for the Course: 13,400ft of climbing, mostly on dirt

Will a modified Specialized Tarmac Disc with a 34/28 cut the mustard for a 10-hour day?

The invitation email was abrupt and vague. An unsanctioned race in a few weeks, about 100+ miles, much of it on dirt backroads high in the Rocky Mountains, and 10,000ft of climbing, “plus or minus 5,000ft”. No support of any sort, no specific course listed, and the only rule being that your team of six all had to finish together. Team BikeRadar was in.

What sort of bike do you ride on something like this?

After some deliberation — and after reading a subsequent email that outlined the course with 13,400ft of climbing — I decided to go with a Specialized Tarmac Disc that showed up for test, with a few modifications.

Gearing modifications

With a good chunk of this 107mi boondoggle being uphill — and with a healthy portion of that being on dirt roads if not babyhead-strewn jeep roads — low gearing will be key. The Specialized Tarmac Disc comes with 52/36, the ‘semi-compact’ crank that really is ideal for most serious riders, most of the time. Ten years ago, my ego if not my fitness would have said fine, bring it, a 36t ring with an 11-28t cassette is plenty low. But one look at the vertical ascent total had me out in the garage, looking for that 34t ring.

Yesterday, a buddy and I did a little recon on part of the course, including the Lickskillet Road climb, a one-mile grunt up a loose-dirt road that averages 14 percent. At one point, he stood up to get more power, lost rear traction and tipped over. Well before that, I had stopped, defeated, and put a foot down, gasping and sweating and wondering if I could fit something smaller than a 34t ring on the 110 BCD cranks. This Lickskillet climb, which according to Wikipedia is the steepest county road in the United States, comes at mile 88 of this weekend’s unsanctioned race course, after 12,000 vertical feet of climbing are already in the rear-view mirror. Perhaps I should bring some hiking boots…

Tire selection

Next up, tires. I’ve had great luck with the super-fat Hutchinson Sector 28s, run tubeless on Easton EA90 SLX wheels. On a similar dirt-heavy, 100+mi venture, Panache’s Mustang Ride, I smugly enjoyed going flat-free all day while guys and gals all around were popping tubes on goatheads or rough roads. But, considering that Mustang day was relatively flat, the Sector 28s are not super-light, I’m lazy about changing tubeless tires, and the 26mm S-Works Turbos that come stock on the bike have largely proven dependable on dirt roads… I’m going to stick with the Turbos.

Will 26mm be enough?

The dirt roads for this unsanctioned race are a bit choppy. Cyclingnews publisher Richard Schofield rode a few of them recently, and swore that he’d “never, ever complain about the roads around Bath again.”

Some of my teammates will be running 25mm tyres, and one little climber will just stick with the 23mm Continental Gatorskins that he uses on dirt all the time. Others in the event have mounted fatties north of 28mm. We are all bringing plenty of tubes, and perhaps even a spare tyre.

Other modifications

I switched out the stem to a PRO Vibe, but that was just to get my position dialed. It unfortunately meant ditching Specialized’s neat little Di2 junction box holder that mounts on Specialized stems at the bolts.

I added a K-Edge Garmin mount to secure a Garmin Edge 810 that will hopefully keep us on course and record the stats (you better believe this ride is going on Strava).

K-Edge mounts are rock solid

And although Stages is my personal power meter of choice for price and convenience, I’m using Garmin Vector pedals here with the new, wider pods for compatibility with the S-Works cranks.

Since the nutrition support is DIY (read: stop at little stores if and where you can find them on these back roads), I’m considering running additional bottle cages behind the saddle. But that’s probably just too much triathlon training recently ruining my brain…

The rest of the stock

The Tarmac Disc itself is the best disc road bike I’ve ridden, in part because it feels just like a race bike – not a long-chassis disc bike with stretched-out chainstays. But here is the crux: to keep the tight geometry and add in a 135mm hub for a disc, Specialized tweaked the offset of the hub to reduce the chainline yaw. This means you can’t swap in another disc wheel without switching the derailleur hanger, adjusting the derailleur and, perhaps, sacrificing some drivetrain performance in cross-chain situations. It is this fact that has had us reserve judgment on posting a review until we have more time on the bike. However, if this carbon-rim wheelset can hold up over such a brutal course — and it is certainly fast on the paved flats — then do you really need to change wheels on a clincher wheelset?

I’ve had two Tarmacs over the years as a personal bike, so I feel right at home with the geometry.

The Shimano electric/hydraulic drivetrain is currently the cream of the crop. Switching from a 36 to a 34t smaller ring didn’t affect shifting at all, and the integrated chain catcher adds a little peace of mind. Without cable tension to keep the levers snug, I have noticed some rattling over rougher roads, especially when you are holding the bars loosely. It isn’t as pronounced as the rattle on first generation SRAM Hydro R levers, but certainly perceptible.

Shimano's R785 levers can rattle a bit, with no cables to keep them taut, but it's the squealing rotors that I'm concerned about

The disc brakes… will be interesting. The two times I’ve done fairly long, steep and windy descents where I had to brake a lot, they ended up squealing like stuck pigs. After a few minutes of cooling down, they reverted to quiet operation. I am curious to see what extended braking over the course of a long day does to them — and to the eardrums of my riding mates.

Judgement day is coming

The event is Saturday. I’ll report back on Monday about whether my gear choices were correct.

Horse for the Course is a new BikeRadar column where we will pick a bike for an event, modify it as we see fit, then report back on our luck — or lack thereof. Whether good, bad or ugly, we will bring you along for the ride. Got any events or bike set-ups that you recommend? Let us know in the comments section.

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