Golden, Colorado
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vincent@mtbtandem.coach

Gearing: There are many good options now.

Gearing: There are many good options now.

It is an interesting time for MTB tandems now. The standard required tandem specific cranks in the past was a triple front with 8,9,10 speed on the rear. Now we have 1X or 2X options, and you can reliably use right side timing chains–meaning you can use standard cranks. The answer will be different for many of you. At the January S.O.O.R.T.A. in Tuscon, our broken frame and resulting Frankenstein fix left us with a 1X11 36 Front ring with a 11-42 rear. At the altitude of Tuscon and the terrain we were riding, with no long steep climbs, it worked out fine. In Colorado on our usual rides, it would not have worked. Last year I was using a 2X11 with 26-38 front rings and 11-45 rear using the OneUp 45T SPROCKET +18T. This worked well, but it did require some planning when choosing the front ring. Currently, we are running 26-34 chainrings with 10-42 Sram XD 11speed cassette on a Nox Composites Farlow 29 wheel. I think these cassettes are stronger. I know there are trails that I will wish I had the 45 tooth; I might install a 24 tooth small ring to get me close to that gearing, and I might be going back to the 36 big ring, but I don’t need the 38 with the 10 tooth. Just for reference, I am using 1X12 setup on my 1/2 bike with 36 front and 10-50 rear. I am not ecstatic about the setup but it is not worth it to me to add a front derailleur. I’ll make one more comment before talking about numbers. On the 36 and 38 rings, these were outer big rings and shifted really well have a lot of shift ramps for the chain. The 34 I have now does not have the same shift ramps and does not shift as well.

Let’s look at some numbers. If you have never looked at or calculated gear ratios, it really easy. There are a few ways to do it. If you are changing the gearing on your current bike, then all you need to do is compare gear ratios–that is the front divided by the rear. If you are comparing bikes with different size wheels and tires you need to use something like gear inches, so use an online gear calculator. In my case, I want to have a similar high and low gear using the Sram 10-42 11 speed cassette as I did with the 26-38, 11-45 setup I had last year. 
– Online Calculator

High gear
Last year: 38 front / 11 rear = 3.45 ratio (larger is higher)
Now: 34/10 = 3.4 (this is about 1.5% different, this is good)
Low gear
Last Year: 26/45 = 0.58
Now: 26/42 = 0.62 this is almost 3% If you look at the chart below this is about 1/4th a shift
If I change this to a 24: 24/42 = 0.57 This is a little bit lower but close.

How close can I get with a 1X 12 speed 10-50 setup:
High: 34/10 = 3.4 Same
Low 34/50 = 0.68 which is 17%, that is a lot.
What front ring would we need to achieve the 0.58 low gear?
X/50 = 0.58 , x = 50*.58 = 29. You can choose a 28 or 30. If you go with the 30 this takes 12% off your top gear.

When I think about low gears, I think about climbs and if we can pedal up them or not. When I think about the high gears, I think about top speed. with our 38X11 It seemed ~29mph was a speed we could pedal–more than that and we would spin out. With a 30 tooth front, 12% less we would top out at  25.5mph. That’s not bad for most riders, and a good reason to recommend going with a 1X10-50 setup.

Now let’s compare gear gaps, jumps, in gear between the following cassettes.

Note: to calculate ratio change it is not necessary to know the chainring, only the cog.
SRAM 12speed: 10-12-14-16-18-21-24-28-32-36-42-50
SRAM 11speed: 10-12-14-16-18-21-24-28-32-36-42
Shimano with the OneUp 18/45 kit 11-13-15-17-(18)-19-21-24-27-31-35-40-45

This chart confirms what I feel. You can see the SRAM Cassettes have larger gaps then the Shimano setup I ran last year. I’m happy with the gaps. On my 1/2 bike, I find the jump to the 50 large, I feel like basically, I have 11S with a bailout gear. The Shimano had a noticeable large jump from the 15>18

You know the gaps are too large for your team if you “hunt gears.” Meaning, you are going a steady speed and effort but keep shifting between gears. This can happen in big and small gears.

If you are planning to upgrade your gearing or buying a new tandem, here is my recommendation. 
A: 1X with a 30 or 32 front with a 1X50 rear. (unless top speed is important) and you could pair this with Archer Components shifter and need to deal with cables.
B: If you need a wider range then: 2X setup 24-34 or 26-36 front with 10-42 SRAM rear. 

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