MTB gearing, how low should I go?

Reposting a question here that didn't get any attention in the Pedalsports thread:

So the lowest gear on my bike is 22t-34t (on a 26" wheel) and I've been wondering if I should go for anything lower...back when a 28t sprocket was my biggest on the rear, the bike was clearly gear-limited when climbing, but now it's hard to tell if I'm more gear-limited or balance/wheelie-limited. Climbing steep inclines near this gearing/wheelie/stamina coffin corner is really physically taxing and could perhaps be easier, on one hand. On the other, that would mean less speed which means more difficult balance, and being clipped in while ninja-pedaling your way up a hill, knowing that if you turn away from a direct uphill line or slow down or break torque for longer than it takes for a quick gear shift you're going to do an instant stop-and-drop and then likely tumble down the incline you're climbing is a terrible feeling, and lower gears might just be raising the stakes in that regard.

I'm also really pushing the limits of my rear derailleur and normal chain length with the 11-34t rear cassette, which is made of high-enriched unobtanium (although higher and lower range cassettes aren't too hard to get), and was thinking maybe I should get a smaller bottom chainring in the front instead of giving the bike a more potentially explodey setup in the rear with an even bigger cassette and derailleur hanger extension.

What do you think? I can get a 20t or 21t chainring for the front of the 3x drivetrain.

I think this comes down to where you ride. My race bike has much higher gearing than my full suspension because it gets used for different sort of things. The latter is 22-32 on 26" wheels, and it works pretty well for me even on slickrock climbs. I've got a lot of personal torque available, though.

That said, a front chainring is cheap and easy to swap out so you could always just try :)

Definitely depends on where you ride.  I ride the Front Range of Colorado, which means a lot of climbing, right out of the parking lot.  I *love* my 50T!

At some point you get to a low gear where it makes more sense to walk.  I live in Missouri, where it's pretty flat, with some short, punchy climbs.  I don't think I'll ever go back to multiple chainrings.  If I were in your shoes, I'd pick a low-ish front gear (28t or so) and a wide-ish range cassette.  It makes for easier tuning, less stuff to go wrong, less weight, etc.

This bike gets used for a mix of everything, including climbing stupid steep stuff which is almost the only place the 34t sprocket gets used, other than if I want to take a break on a long climb without coming to a complete stop. Getting off and walking would absolutely be the safe and practical thing to do, but if you're walking you're not cycling

If I were to get a totally different bike with a boost/superboost rear axle I might consider a 1x12 setup, but on the other other hand I also enjoy my 42t-11t combo for hill bombing

docwyte said:

Definitely depends on where you ride.  I ride the Front Range of Colorado, which means a lot of climbing, right out of the parking lot.  I *love* my 50T!

What chainring are you running?

In reply to GameboyRMH :

It's a SRAM Eagle X01 1x11.  Can't remember what the front ring is.

In reply to GameboyRMH :

Gotta ask wheel size these days too, we 26ers are getting to be a rare breed.

In reply to Keith Tanner :

So are 27.5's!  Which is what I have, I didn't like how the 29er's rode

I thought 27.5 was newer than 29? At least in the mountain bike world :) 

We've got actively ridden 26, 27.5 and 29 in the shed spanning at least 15 years of production. Makes spare parts a pain.

I have a 32/48 as my lowest gear on a 29er (1x11).  so about 19.26 gear inches.

Using this calculator here, I calculated my lowest at 17.1 gear inches:

https://www.sheldonbrown.com/gear-calc.html

I also looked into the sprocket change some more and it turns out there's a good reason that front chainrings smaller than 22t are hard to find - the chain can ride up on the chainring bolts with such a small sprocket. You can probably get away with it with 21t, but with 20t the bolts need to be filed down after installation and become non-reusable.

Another fun calculator to play with that makes cool graphs, makes me think a 21t-30t-42t chainring set may be a decent idea:

https://mike-sherman.github.io/shift/

Edit: Not such a simple change though...the difference in teeth between chainrings needs to be both within a certain range and may also need to be an even number of teeth.

Even number of teeth only matters for a narrow/wide single chainring. Derailleur capacity will determine if you can go to a smaller chainring though, might not have enough swing at the back to handle 21/11 and 42/34 or a cage on the front to not rub in those same gears.

Edit - Front chainrings tend to be designed to work together to get optimal shifting but that probably matters the most for the middle and big rings as they'll have some ramps and pins to pull the chain up onto them. The chainrings will be marked if that is the case.

Yeah I found that I don't have to worry about even/odd tooth differences...but the more I research it, the more I find that I'm running into the mechanical limitations of a 3x bolted crankset. For the same reason running a smallest chainring of less than 22t is troublesome, a middle chainring of less than 32t is troublesome - the middle sprocket has to mount to the inside of the 104bcd holes, and if the chainring is less than 32t, the chain will ride on the chainring bolts for sure. The fit is already so close that nobody's tried to make a suitable chainring of less than 32t apparently.

Theoretically if it were possible to make a 3x drivetrain with chainrings that attached to the crank axle using splines (like some 1x chainrings attach with) it would overcome these limitations, but no such thing exists.

I know that selecting 42/34 already threatens to rip the derailleur off so I've just been careful to avoid that combination...did it once with the bike resting upside-down as a test and barely got out of it without disassembling anything.

So it looks like the only practical change that can be made at the chainring is swapping the 22t to a 21t or maybe 20t.

I used to have a race-bred bike (Fisher AL-1, circa 1990) that had a short-cage rear derailleur. There were certain gear combinations you couldn't use (basically, big at both ends or small at both ends) , but it was easy enough to avoid those in practical use. So you could go bigger in the back if you really wanted to. Just have a dedicated crawler gear. It's no different than having to remember you can't shift into 4WD without a center diff unless you're on a loose surface :)

The 34t rear sprocket is basically the dedicated crawler gear already - the upper jockey wheel rides on the outside of the chain slightly in this gear, even with maximum clearance, and it can't be used in combination with the 42t front chainring, or it will run out of chain length.

So I ordered the 21t chainring, also a spare 11-34t cassette (whether I get it is another matter, took me 3 attempts to get the one I'm running) and some 10t jockey wheels to gain a hair of clearance in the crawler gear.

I looked into longer cage options, but it appears the only remotely replaceable option would be to run a 9-speed derailleur with the 8-speed shifter - may be worth trying if I want even more range in the future and can get a good deal on a clutched model.

Edit: Other option - custom-fab a SunTour LePree-style triple-jockey cage Apparently these reduced chain slap quite nicely and generally worked well.

Found a good fallback derailleur option that should give a hint more range, the Shimano Acera RD-M360 long cage. No clutch on this model unfortunately...but I'm actually going to try to put a LePree, or at least something with the 3-pulley cage from one, on this bike first.

The 22t front ring is essentially your "crawler" gear and with a 34t rear cog is generally equivalent to a 1x setups with a 50t rear cog.   A gear any lower than that and you're basically walking. The chain length should be set so that you can go big-big without destroying the derailleur, but it lets you know it's not happy about it.  Like Keith, I also ran a short cage RD with a triple and couldn't go big-big, but like him, that was on a XC race bike. 

Yeah once I get a different rear derailleur on there with more wrap capability, I'll definitely increase the chain length a few links so it will at least survive a big-big selection. Stock was 108 links, I normally have to shorten 116-link chains so that's an easy fix. If I add links with the current RD I could get a loose chain with some combinations.