For reference, my current setup is an XTR 960 front crank with a 22t chainring, and a Dura-Ace 7700 12-25 cassette. The thought process is that it yields two options north of 1:1 in the event that things get ugly. It also represents a pretty light package.
The cranks have a Q-factor of 170mm which has never necessarily bothered me, but I do notice it, as it is a departure from my narrower road stance. I had casually sought a more conventional crank option, but it always seemed to burrow down a rabbit hole from which I never emerged. You may start to sense that in this post.
Adam had a great point a few weeks ago on the topic of gearing. We were discussing the viability of a 34t compact crankset, mated to a SRAM 11-36t (10spd) cassette. More to the point, that anything easier is not going to yield a 1:20 finish. Having had some time to process this, it had to be worth trying. I can tell you from experience that on a climb like this, if you have easier options, you are eventually going to break down and use them. You might end up with a pleasant spin in the end, but you’ll be light years away from a PR.
I actually have a 34t compact crank sitting around doing nothing, and an XTR short cage derailleur in a similar state of retirement. But then it starts to get messy. If you haven’t guessed by now, my climbing bike has a 9-speed shifter. I do have a 9 speed MTB cassette on hand, but it’s a PG-990, which tops out at 34t. My only 9-speed 36t cassette option looks to be a Deore-level 12-36, and it is a #@!@#^ porker, topping 400g. I’m not even sure I want to turn that for evaluation purposes. You can see that replicating the 34/36 on a 9 speed level is going to be a hassle. And I’m sort of married to 9 speed right now on this bike and really don’t want to go through the expense of changing it all out.
In the past I made up custom cassettes from individual cogs; they were heavy, but they were exactly what I wanted. IRD used to produce them and I bought a slew of them. They topped out at 29t though. Sure I could buy that Deore, drill it out, take the 32 and 36, make a great little 30-32-34-36 run, but the weight penalty is certain to be unappealing.
Unappealing because I could easily just put a bigger ring on my XTR 960 to balance things out and yield similar, but more gradual ratios to the 34/36 setup. The only hangup is the XTR Q – is it really that big of a deal. I mean, it’s not a big deal, but I sure wouldn’t mind if it was brought back in, and more like cranks I’ve put thousands of miles on. But look at the amount of work it would take. Some kind of tubby 9-speed hatchet job, or a complete drivetrain redux that I don’t want to subsidize.
Or we can have this conversation all over again and talk about the implications of a triple crankarm. See where this ends up going? It’s out of control.
I may just buy a ring. The Rotor folks have informed me of a 23t for this crank that looks perfect. 21 on the low end, 24.5 on the other.
chasing 1:20 
Too many numbers for my pea brain to follow, but I go lower than 1:1 and I do use the granny, but there's also a fatigue penalty for mashing gears that can also detract from one's 1:20 chances. The mountain has so many ways to beat ya.
LikeLike
you only go as fast as your easiest gear.
indisputable rule of thumb.
LikeLike
Funny, I never notice the Q-factor difference; but then again roadie bikes and mountain bikes are so different, it's just one more thing.
Personally I'd stick with the little-ring-and-12/25, since it has very small gaps between gears. MTB cassettes have *massive* jumps between gears – so you get in a situation where one gear is too easy, but the next is too hard.
If the Q-factor does bother you – swap out the XTR for a triple. You can mount that 22t on a road triple, lower the Q-factor, and have small jumps between gears. Plus, you can bolt up the other two rings, and actually ride the bike somewhere else other than Mount Washington… think about places like Okemo, where you need a big ring *and* gears for the super-steep.
LikeLike