Mountain Bike Setup: 2×9 Drivetrains

With the introduction of 2×10 components from SRAM and Shimano, there has been increasing talk amongst mountain bikers about the benefits of converting their 3×9 drivetrain to a 2×9 drivetrain. This is something I have been doing for a long time now on all of my mountain bikes, so let’s get into the nuts and bolts of what you gain and lose by converting to a 2×9 setup on your sled.

2×9 Mountain Bike Setup

What does it take to run a 2×9 setup on your mountain bike? Well…if you want to be really simple about it, you can just drop your big ring and replace it with a bash guard. While this is the simplest way to get to your goal, there are other things that you can swap out to improve the performance of your shifting at the same time. Let’s take a look at my ideal 2×9 setup and why I think it is the best way to do it.

• 11/34 Cassette – Most bikes come equipped with an 11/32 cassette (where 11 is the amount of teeth on the smallest dog and 32 is the number of teeth on the largest). By switching to an 11/34, you can a wider gear range that will help with climbing. Since you are not running a big ring, it is easier to get away with a larger rear setup (even if it is small) because the largest you will ever be running up front is your middle ring. I run an XT 11/34 on my personal rigs.
• 36T and 24T Chain Rings – The typical stock setup is a 32T and 22T for your middle and granny rings. In a 2×9 setup, it is good to get a little bit of extra rang out of the front so your buddies don’t leave you in the dust with their big rings on forest service roads. In typical trail riding, you can get away with a 32T in most situations just fine. I like to run the 24T as a personal preference but a 22T works out just as well. Remember, you gained some low end by going to the 11/34 cassette in the rear. I run 36T and 24T Blackspire rings.
• Medium Cage Rear Derailleur – Almost every bike on the market (unless it came to you as a 2×9 setup like the Specialized Enduro) somes with a long cage rear derailleur. You need the long cage on 3×9 setups because of how long the chain has to be and how far you have to stretch to get over the big ring. In a 2×9 setup, you no longer have that big ring so you can dial it down to a medium cage RD. You will get crisper shifting and less chain slap as a result. I run a medium cage X.9.
• Chain Tensioner – This is not required, but it does become an option when you are running a 2×9 setup when you couldn’t use one with a 3×9. A chain tensioner (like the Blackspire Stinger) helps prevent the chain from dropping off the rings. It also heavily reduces chain slap and general sloppiness in the drivetrain. Remember all of those technical downhills where all you could hear is that chain slapping the chainstay?! Most of that noise is gone with the aid of a chain tensioner.

So Why 2×9 On Your Mountain Bike?

Now that everything is cleared up on how to setup 2×9 on your mountain bike, let’s run through why I run it and the situations where I believe 3×9 is still the right setup.

I like technical riding. Things like log crossings, rock gardens and technical trail is what I day dream about during the day. With a bash guard setup, I can through the bottom of the bike into trees and rocks without the worry that I will break a chain ring. Also, in most technical riding situations, about the only way to keep everything quiet on a 3×9 setup is to run in the big ring which can cause excess shifting and gearing issues in varying technical terrain.

In all honesty…big rings scare me. That’s right…I am scared of that 40+ tooth ring that is just begging to rip something up. I have good reason too…35+ stitches in my right knee because of a wreck where the big ring decided to let me take a look at those cool, yellow, finger looking fat bodies that they show you in high school biology. With a 2×9 setup, I feel a lot safer during unscheduled dismounts.

A 2×9 setup is also just cleaner, quieter and still give me the range I need for 99.9% of my riding. For me, it just makes since to simplify things down a little bit when I am gaining more than I am losing.

When Do I Use A 3×9 Setup?

There is really only two situations where I still like to have a 3×9 setup on my mountain bikes and both involve hardtails or short travel full suspension bikes.

1. Fast XC Racing
2. Endurance Racing

I do not do either one of these very much because when I race things my competitive edge doesn’t let me have very much fun, but…when I do…I’m on 3×9. You are not going to win either of these events without the aid of a 40T+ ring in most cases.

In fast XC races, I setup in the big ring and never leave it. You do not have time to be waiting on the front rings to shift and…in most cases…if you need to shift down to the other rings you are already going too slow to win.

In endurance racing, you spend a lot of time on non-technical, flat terrain. The only way to keep speed is to have a big ring like on a road bike. You are just going to be a hampster in a wheel otherwise.

What do you think?

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