FWIW, I wanted
the extra teeth a road chainring could provide so that I could still realistically pedal at 33-36 mph. Great in concept, though proved to be difficult to execute:
I went through a couple of different MtB triples before realizing it wouldn’t work on a Full-Suspension MtB frame; a 48T chainring would hit the frame and the solid/integrated axle solution wouldn’t work. Going with Campy, I could use the Phil Wood axle specc’d to the
precise length, and made it possible to adjust the position by rotating the cups for the proper alignment and tension. Not terribly difficult, but I worked at it until I had the best possible clearance with as little deflection from the optimum “Q-factor”.
So far so good, however I discovered
the MtB derailleur wouldn’t fit the larger ring; the differences between 48T and 53T was enough. The best option was to purchase a matching Campy derailleur. But then the diameter of the seat tube was smaller for road than MtB, so a normal clamp wouldn’t work: The best solution was a Braze-on clamp adapter for MtB. I found one off the shelf, though it didn’t move the derailleur out far enough to align with the triple chainring range. This took a bit to cypher out, but I designed my own and had a prototype made to order. It was almost perfect: Turns out that the angle of the Seat tube is different for road bikes and MtBs; it’s like about 5 degrees difference – enough that shifting between the largest and smallest could cause the mechanism to lock up. Completely correctable if I made a second unit, but I was out of time, so I lived with the top-two range and didn’t shift to the lowest
ever.
The unanticipated third problem was that
my chain wasn’t long enough! If the front was on the largest ring as with the rear, well – the tension was beyond the shifter, plus the binding of gross misalignment. So I had to compromise and promise not to ever shift into that condition. The reverse was also true: Smallest in the front and smallest in the rear produced too much slack. With daylight burning, I chose to live with it and just get on down the road…
After 2515 miles, I have this to say: The reality of this whole experiment was that I was almost always in the largest gear forward, and the two, sometimes three smallest gears on the freewheel. I always had power to at least one wheel, so the lower gears were never utilized… and frankly the whole persuit was an expensive flight of fancy. If I had to build it again, I’d probably go with a double in the front and a custom triple freewheel on the rear: A high range of 53-11, and a low of 39-16 if it could be had. Who makes custom freewheels these days?
BTW - I wouldn’t suggest my route to anyone; it’s an edge case. Although the point I'd like to make is that the BB made it possible to adjust and set the alignment of a larger chainring within the framework. I have two beautiful brand new triples lying in a box that cost more than the single BB. For what I was trying to accomplish, it was small change, especially after fabricating the custom braze-on adapter. In the end though, you get what you pay for. It’s worth a few extra dollars to have quality equipment, although I do not make a habit of buying the most expensive – unless there's no choice. If you can work with available components, great. But in this hobby, sometimes we need to make our own.
My ½ W,
KF
