On a few of my bikes I am already running 1 x 8/11 drivetrains with an IGH. Typically the smallest chainring you can get for 104mm BCD cranks is 32T which limits the lower end of your gear range on this common crank type. So I was interested to try out the two 30T rings I found for 104mm BCD cranks. Extralite.com makes the one on the left and Andersen’s Machine makes the one on the right.
I decided to install the Andersen’s ring on my Nomad turning it into a 1×9 with a 30T x 11-34T cassette. The only reason I selected the Andersen’s ring is it looked more robust than the Extralite ring. I don’t care about weight on my Nomad, but it gets abused a lot so beefy is good. I should be able to flip the 30T ring around once it’s worn and wear it out going the other way to double its service life.
The reason 30T rings are not common is that you get physical interference between the chain and crank on such a small ring. The solution is to file away a bit of the ring’s arms to create the needed clearance. This only takes a few seconds with a flat file. Don’t get carried away!
The 30T ring bolts up in seconds and you are ready to rock.
Shimano sells a 28T inner ring which can also be used to move your single ring drivetrain’s gear range around as required. Having a 28T/30T double is probably pointless as there isn’t enough difference between the rings to bother. The 30T ring is also spaced inwards a bit more than normal to help with chain clearance. This buggers up your indexed shifting setup with a granny.
Once installed on my Nomad the 30T ring provides a very useful low gear with a 34T cog on the cassette. Low enough to climb just about anything while still providing a reasonable high gear. With the uber wide range 11-36T cassettes available a 30T front ring makes a single ring drivetrain feasible for a lot of MTBers.
For my needs there is no reason not to go with a 1 x 8/9/10. Ultra low gearing results in too much torque which spins the rear wheel on techy climbs and the gear inches are too low to get me over the gnar in the one to three power strokes my puny legs have. By using a higher low end gear I can maintain speed as I approach some tech, I can’t break the back wheel free as easily and I can usually power over the tech before I lose steam.
I never need a big ring on my MTB. I’m riding fairly steep terrain so when I point the bike downhill I’m not looking to go any faster than gravity is powering me!
Funny thing is that 5yrs ago I would have told you that not having a triple on a mountain bike was crazy! 3yrs ago I would have said the same thing about a double ring setup. ;)