Before the complaints and warnings start, please be advised that the following road crankset is not being used as intended. The tester weighs a whopping 140lb and it was used on a single speed race bike because, well, because we wondered if it could be done. You'd be just as foolish as we are to do the same. So there.
Once upon a time, mountain bike cranksets had a an outer bolt circle diameter of 110mm and an inner BCD of 74mm. As climbs got steeper and riders tougher, though, smaller granny gears than the 74mm would allow prompted the move to compact (94/68mm) and 4-arm bolt patterns, and 110mm BCD cranks and rings began to gather dust on bike shop shelves around the world. Eventually, though, road climbs got steeper too, and riders too macho for a third chainring began looking for smaller inner rings. The standard road 130mm BCD was too big, though, so the 110mm standard was resurrected.
When we saw that, we wondered, "how cool would that be for a single speed?" Heck, 110mmx34t chainrings are readily available and there are some cool, light road cranks out there. Road cranks also tend to be narrower, allowing for a narrower Q-factor (think stance, or lateral distance between your feet), which is generally accepted to be a good thing. "It would be cool..." we thought, and then forgot about that thought.
Fast forward a year or so... At the local bikeatorium, we spotted a sexy carbon fiber external BB crankset on sale for not much more than a new Shimano LX crankset (~$190). End of year, they were a long-for-road 175mm take-offs, and we needed cranks for our Scandal anyways. The shiny new TruVativ rings were bartered for a matte black (accidentally-ordered) 110mm, 34t Spot chainring and we were on our way with 830g of carbon fiber sexiness.
As the Scandal has a 68mm BB shell (road cranks don't work with the wider 73mm shells), that didn't prove a problem. Mounting was much the same as most external BB cranks- the cups go in, and the drive side arm (with attached BB spindle) slides in. Unlike Shimano units, though, there are no pinch bolts on the non-drive side. Instead, the BB spindle is slightly tapered (like a massive ISIS BB), and there is a captive 8mm bolt/crank puller holding it all together, spun the cranks, and they stopped with a grinding sound. Damn. It turns out that there is very little room between the back of the spider and the 29er's chainstay. Little as in virtually none (see picture, right). We had to pull out our prized vintage Tioga purple chainring bolts and replace them with the ever-so-slightly lower included Torx bolts. Now, there was enough space for a playing card in there, but that was about it. We recon that other frames, especially those with 26in wheels, may well have more clearance, but haven't tried any.
We were worried, but pretty much committed at this point, so decided to go for a ride. We hoped that there wouldn't be enough flex in the frame to allow the chainring bolts to rub the frame under hard pedaling. Well, as it turns out, the Scandal is a pretty stiff frame laterally, and there were no grinding noises from down below and we rode it. We rode harder and harder and eventually forgot about the minimal clearance altogether.
Almost a year later, we've had no problems. TruVativ had the good sense to put an aluminum spine inside the carbon fiber from the pedal thread down to the BB axle. The clear coat is pretty scuffed at this point thanks to our duck-footedness, and we worry a bit when we hit the pedals on rocks, but nothing has made it through the clear coat. No noises, no catastrophic failure. Seeing as TruVativ have to make their product stand up to meathead Iron Men and roadies twice our weight, we're not concerned at this point. The bearings as well have held up fine to off road use, dirt and stream crossings, and feel pretty much like they did when new- not Campy smooth, but without a trace of gritty-ness. We're not sure what the included pedal spindle washer does, but seeing as they went to the trouble to tie it to the pedal hole, we figured it was important and should be used. The big spider fills the chainring nicely and seems to help keep any flex away, too, as we can't feel anything moving down there.
All in all, we're happy with the purchase. Light, sexy, and a heck of a deal- there's not much more that one could ask for... So yes, it can be done. The cranks don't have to be carbon, and any decent road shop should have more and more take-off compact road cranks lying around. If the price were right, we'd do it again in a minute. Now if we could only win one of those purple Kooka rings that comes up on eBay from time to time...