Chainring size for 1x with 26” wheels.

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Chainring size for 1x with 26” wheels.
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Posted: Jul 29, 2021 at 5:45 Quote
So I am upgrading from a 3x10 to a 1x11 on my 26” trek fuel Ex 7. The cassette is a 10-51. I am trying to work out how big of a chainring to go for. I am thinking either 34t or 36t. I live in quite a flat area but still want to be able to climb when necessary. How big of a chainring would you guys recommend?

Posted: Jul 29, 2021 at 5:58 Quote
I'd go 34 or smaller. I had a 32 and went down to a 30, but the climbing here can be brutal and I don't have horse DNA nor do I have a 26" wheel - it's 27.5 - so a little more torque required.

You can sort the teeth yourself too with a calculator. Look at what chainring and what sprocket your normally need when you climb. Count the teeth on each one and work the ratio out.
Now look at the available teeth on your cassette and consider the number of teeth on your two 1x chainrings. Which chainring will get you the ratio you need for climbing: the 34T or the 36T?
The math is yours.

Or just look at the number of the teeth on the chainring you use when you climb and try to get as close to that as you can. If you're always on the smallest (24T maybe?) then I'd go with the smaller ring on your 1x setup. If you're always on the biggest ring (42T perhaps?) then get the biggest. If you're in the middle then try to match or go a tooth smaller.

I hope this helps. Good luck.

Posted: Jul 29, 2021 at 6:10 Quote
If you divide the number of teeth on the front chain ring by the number of teeth on the largest rear sprocket, you'll get the amount of rear wheel rotation, per 1 rotation of the pedals.

So for example, if you were to use a 30T front:

30 divided by 51 = .588

32 divided by 51 = .627

To give a real world example: 26" and the bike is a 44lb brick that I use for cross-training. I have 30T up front and 50T in the back, so I'm at .6 of a rotation of the rear wheel. I started out after my drive conversion, with a 30T round, and then after a few trips up the very steep mountain I ride on, I installed an Absolute Black Oval 30T. I used to be pinned on the 50T as soon as I stated climbing. Now I can shift down 1, and sometimes 2, sprockets at the back.

If I were in your shoes, I'd go with a 32T Absolute Black Oval.

Posted: Jul 29, 2021 at 9:19 Quote
I compared the ratios between the old and new first. Use this, you can go up or down on chainring depending on what you feel may work better compared to old ratio.

Posted: Jul 29, 2021 at 19:53 Quote
The two biggest variables that will determine your ideal size are:

1. Your average riding conditions. This basically means the local terrain (is it flattish, hilly, or alpine?), but average ride length (daily lunch ride, or weekend epics?) will make a difference, too.

2. Your preferred pedaling cadence. I myself tend to favor lower gears and faster spinning, but a lot of this is due to riding with older roadies in my formative years, and being encouraged to "spin to win". This was mostly on fire roads or rock-free singletrack, and as I got older and rode in more varied conditions, I got to appreciate the advantages of a larger gear when it comes to avoiding pedal strikes and muscling over obstacles in quick stabs.

So, my advice is to go to your local bike shop or favorite online shop and compare prices for 32t, 34t and 36t chainrings that work with your drivetrain. If you find something on sale or closeout, buy it. Give it a few miles to get used to it, and you should be able to determine yourself whether your spending too much time at the top or bottom of your cassette, wishing for more.

Posted: Jul 29, 2021 at 23:32 Quote
I was thinking about this for a 29er with a 10-45 cassette (an Ibis Ripmo AF, but order got cancelled so I'm back to ground zero). I experimented with other bikes to determine the lowest gear I wanted and I settled on a 28t to go with this cassette though I thought seriously about a 26t (not many options for that, but they do exist). Obviously your choices are even teeth from 28 to 34 usually and you need 29/26 = 11% bigger chainring to make up for smaller wheels. 11% bigger than 28 is 31.2 so you pick 30 or 32 if you don't really need a fast pedaling gear and want to crank up the steepest hills in high cadence (my preference). On the low end, you have the 51 though and not the 45 like I was gong to, so if you want to go up another 13% (31.2 to 35.4), it seems the 36 isn't that unreasonable even for a hill climing gear. Just check there are no issues with your frame (I think some bikes say 34t is the max - I guess the issue is how big a ring will hit the chainstay).

You should know your own riding and what top gear you like and what bottom gear you like. You should be able to get those with a 510% range rear cassette. If it were me, I'd be looking at a 34 and maybe even a 32, but probably not the 36.

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