Ed note 3/29/17: browsing the archive is often more like looking back at old bad haircut photos, but occasionally there are gems like this one from Mark V. Dropbar MTBs are a current topic again (8 years later), driven by the interest in gravel, or mixed-surface category.
So Travis Brown ran the Leadville 100 on a dropbar-equipped Trek Top Fuel, a full-suspension mtb. It’s unusual to see a dropbar on a top athlete’s machine rather some crackpot bike blogger’s bike, so I was really interested in Brown’s parts pick. Some choices were obvious, some were initially mystifying, and some were really esoteric.
Brown ran a standard road dropbar, some sort of Bontrager VR (Variable Radius curve) model. Though I didn’t find the size quoted, Bontrager lists 46cm (c-c) sizes on their website, 2cm wider than the norm. As Brown is a fairly tall rider, I assume that he would have chosen the widest available. Personally, I think the true road-style dropbar looks rather slick on his bike, yet I don’t think I can choose that over a widely-flared dropbar like the Soma Junebug or On-One Midge. The flare allows me to keep a more comfortable wrist angle during out-of-the-saddle technical riding, as well as allowing better brake lever placement.
As a teammate of Lance, a SRAM-sponsored athlete, Brown would have access to the uber-new and high-end XX mtb component group. But the SRAM Red road shifters could only work with an XX rear derailleur, 10sp cassette, and crankset since the Red levers are not hydraulic nor does the left lever pull enough cable for a front mtb derailleur. The brakes would naturally be the SRAM BB7 disc calipers for road levers, as the only other quality cable-actuated brake would be a Shimano product. But what was confusing was the choice of a Dura-Ace 7803 triple crankset and a 7800 double front derailleur. Why wouldn’t Brown just use the XX crank with its optimized chainrings of 42/28, and instead he uses a triple crank with the big ring stripped off, leaving him with 39/30?
Well, dear Watson, that would be because Mister Brown prefers to use a 180mm crankarm length. SRAM XX is not available currently with a 180mm option. Using a mtb triple crank would not have given him the benefit of a narrow chainline and q-factor, which are two of the XX most compelling features. Yet a SRAM road crank would not be an option for two reasons. First, the smallest chainring available possible on even a compact double crank is still 34t, too big for Leadville’s infamous climbs. Secondly, the q-factor is likely too narrow for the Top Fuel frame. The crankarms would almost certainly hit the chainstays. However, a DA 7803 triple crankarm has the same q as an XX crank, so all is well.
What still mystifies me is the choice of a DA 7800 double front derailleur. I cannot think of a reason why Brown isn’t using a Red front derailleur, except for one possible argument, as follows: A; the inner chainring of a road triple is more inboard than that of a road double. B; clamp-type front derailleurs may be able to swing inboard further than a braze-on-type front derailleur mounted on a clamp adapter. C; Red front derailleurs only come as braze-on. It’s a stretch, but I can’t think of another logical explanation.
Well, there is the odd top-pull adapter that Brown has attached to the DA front derailleur. All road front derailleurs are bottom-pull, but the adapter is essentially a small machined piece that attaches to the derailleur’s cable fixing bolt and changes the cable fixing position. This transforms the bottom pull road derailleur into a top-pull lever suited for use on the multitude of mtb’s that couldn’t otherwise use a road derailleur. This is apparently a hot setup for those World Cup racers who were brewing up their own mtb double ring racers. Not only is road derailleur better designed to shuttle the chain across just two rings, but it’s lighter to boot. Maybe Brown had access to an adapter that fits a DA derailleur but not a SRAM unit. You may ask why he didn’t just use an XX front derailleur, and the answer may be that a Red shifter might not pull enough cable to work with the mtb derailleur. Don’t ask me how competent the shifting is with a SRAM Red shifter, DA derailleur, and a top-pull converter on the inner two rings only of a DA triple crank…your guess is as good as mine.
By the way, the Velonews article which featured Brown’s bike described the adapter as a Bontrager item, but every search I launched on Bontrager and adapters failed to yield a lead. I did however find a company selling similar if not identical items: Speen of Germany. Oddly, they do offer models to fit SRAM Red.
I’ll let you know how well such adapters work when I get my own in a week or so. SRAM XX cranks will be available to everybody late next month, and when I get one I’ll need to find a new derailleur for my Bianchi. The XTR E-type front derailleur cannot be adjusted to accept the smaller (42 vs 44) big ring, so DA derailleur is an obvious choice since I have DA road shifters.…