3x9 to 1x10: Converting A Mountain Bike Drivetrain

When SRAM’s XX1 was announced I was immediately sold on the idea of a 1x11 drivetrain. Simplicity, weight savings, more ground clearance and no chain drops were some of the many advantages and all that with almost no loss of gear range. The only real problem was the cost and compatibility. I would need a new rear wheel to make the conversion possible.

Enter the Race Face Narrow/Wide chainring (or Wolftooth Components, e*thirteen, Hope, etc). These chainrings mean that with the combination of a 10 speed SRAM Type 2/Shimano Shadow Plus derailleur, you can have an XX1 type system for a lot less.

For my conversion I started with the stock drivetrain on my 2010 Specialized Stumpjumper FSR Expert: 3 (42,32,24t) x 9 (11-34t).

Because I didn't have a 10 speed drivetrain to start with I had to change over all my parts. Before I could do that I had a couple of choices to make:

1) What size chainring should I pair with an 11-36 cassette?

Chainring size totally depends on the kind of terrain you’ll be riding. In my area trails are relatively flat with no long extended climbs. Because of that I ride in my 32t middle ring 99% of the time with an 11-34 cassette. With the upgrade to an 11-36 cassette, I gain an extra climbing gear so I opted for a 34 tooth chainring because that would give me almost the same lowest gear.

To get pointlessly technical, you can measure chainring and cassette combinations in Gear Inches (Inches travelled per pedal stroke). I used the caculator on http://www.machars.net/1-bikecalc.htm

	Setup	Chainring Size	Cassette Cog Size	Gear Inches (Inches travelled per pedal stroke)
Lowest Gear	1x10	34t	36t	24.56
	3x9	32t	34t	24.47
Highest Gear	1x10	34t	11t	80.36
	3x9	42t	11t	99.27

2) What length derailleur cage do I need for a 1 x 10 setup?

With a 1x10 drivetrain you definitely won't need a long cage derailleur, but depending on the chainstay growth (which is 0 if you have a hardtail) of your bike you might need a medium cage or if you're lucky a short cage.
 

My (rough) chainstay growth measurements were: 

• suspension uncompressed: 383mm
• suspension compressed: 398mm

So my chainstay growth was only 15mm which should be well within the capabilities of a X9 Type 2 short cage derailleur for a 1x drivetrain.

Pinkbike has some good info on which derailleur cage to choose here: http://www.pinkbike.com/news/Tech-Tuesday-Chain-Length-Basics-2012.html

With those questions answered it was time to put everything together. These are the parts I chose:

Chainring: Race Face Single Narrow/Wide Chainring (Blue, 34 Tooth)

Chain: Sram PC-1091R 10 Speed Hollowpin Chain

Cassette: Shimano M771 XT 10 Speed Cassette (11-36 Tooth)

Shifter: Sram X9 10 Speed Trigger Shifter

Derailleur: Sram X9 Type 2 10 Speed Rear Derailleur (Short Cage)

Chainring Bolts: Sugino Steel Single Chainring Bolts

Assembly was pretty straight forward. I found the correct chain length by deflating the rear shock and compressing the suspension fully before installing the chain on the biggest gear of the cassette. This mimics the point where your chainstays would be the longest and thus eliminating the possibility of having a chain that's too short.

In the end I lost a front derailleur and shifter, a few chainrings and bolts and about 568g (1.25lbs). I'm looking forward to testing my new simple and silent drivetrain as the trails dry out from this abnormally long and wet winter.

Here are a couple of other links that I found helpful:

MTBR put out a great video on converting your bike to 1 x 10 if you already have an existing 2 x 10 setup: http://www.youtube.com/watch?v=IyiUoMSQfRI

Bike Radar: Trail Tech: How to convert to a 1x drivetrain:
http://www.bikeradar.com/mtb/gear/article/trail-tech-how-to-convert-to-a-1x-drivetrain-37451/

Mountain Bike FAQ: Converting 2×10 to 1×10
http://mountainbikefaq.com/2014/01/converting-2x10-1x10