I may have to reconsider the gearing on the MLCM
When I built the MLCM, I set it up with a 1×8 gearset (giving me a little under 300% range; 40" to 115", which means that my typical cruising gear of 90" sits right in the middle of the cassette and, conveniently, right on the best chainline) so I wouldn’t have to deal with a front derailer and to encourage me to not push the bicycle up ramps at less than walking speed (the latter is important, because my reaction to steep ramps is to drop down as many gears as possible then stomp my way up the hill.) This works fairly well, because a 40" low gear is enough for me to shove my way up really steep ramps at juuuust faster than walking speed.
But when I’m in my dump gear (48×32, or ~40") the chainline is ridiculously non-optimal. Which means that unless the rear derailer is positioned juuust right, the chain hops when the grade pitches up and I have to stomp to keep the bicycle moving. And if the chain starts hopping and I don’t correct the derailer position immediately it tends to hop right off the chainring and then derail off the back and into the spokes.
This is not a good long-term plan, because eventually I’ll lose the chain off the cassette in such a way that it does damage to the wheel before I am able to stop and pry it out.
If I had a lot of money, I could get one of the new Shimano 11-speed internal hubs (409% gear range, so I could go between ~110" and ~27") but the “lot of money” part would include having to hire someone to fabricate a downtube (or barend) shifter for it (I don’t have nearly the metalworking tools to build one myself.)
Or I could go to a 2×8 drivechain, and use a very large gap between the front chainrings; If I did something like a 48/28 front (and could shift it!) and a 11-25 cassette, I could get 115" to ~30" with only a 3-gear overlap between the two front rings, at the expense of having to add an additional shifter and front ring.
Given my druthers, I’d jump for the Shimano (which isn’t even released in the United States yet) because that would give me only one chainline & no external gears/derailers at the cost of perhaps a pound (and, um, about US$800 once I threw in a custom downtube shifter.) It would run the risk of the “here I am 400km out on a R600 and the hub just locked into top gear at the base of a 2500' climb. Ooops!” but I could paranoiacally deal with that by carrying a small front chainring and doing field surgery to temporarily convert the mlcm into an awkwardly geared singlespeed. Which I what I would do if the mlcm’s derailer disintegrated in midflight, modulo changing the chainring (the good chainline is ~80", which I can shove up moderately steep hills without too many tears, and I can always push the bicycle up anything steeper.) But the cheaper solution would be to go to a 2×8 gearset, which would “only” cost me about $160 ($50 for a pair of silver shifters, $30 for a cassette, $30 for a 28 tooth biopace chainring, $50 for a front derailer, and I’d just pull the shifter cable out of the partsbox) and the shame of having more external mechanical parts to break on me.
Or I could just leave it as is, and continue to have all of my brevets interrupted by at least one complete derailment and the corresponding stop by the side of the road to remount the chain. Perhaps it’s time to buy a lottery ticket, and then I’ll make a decision.
Comments
Comments are closed
Where on the wide earth are you getting biopace chain rings?
I’ve been looking at the SRAM Apex in 50/34 front, 11-34 rear; about 400 CAD for crankset, chain, cassette and both derailleurs. Still leaves one with the front derailleur, but it’s more or less meant for what you’re doing.