29+ Bikepacking Granny Gear: Surly OD Crank vs Wolftooth vs Rohloff
The Surly OD Crank is a pretty piece of metal, not to mention one of the only options for setting up a 2x system on a 29+ bike… and one of the few options for yielding a granny gear for bikepacking. Also, a comparison by the numbers…
I have already touted the many benefits of the 29+ platform, so it shouldn’t be a surprise that I recently added a Krampus to the stable. The Krampus comes set up with a 1×10 drivetrain, out of the box. This could make climbing a little rough if you have it loaded for a bikepacking trip through steep and rugged terrain, like that of Pisgah. For now, here are my thoughts. Lots to nerd about when you’re talking Monkey Nuts with granny on a Krampus:
There are a couple options for putting a true granny gear in the drivetrain of the Krampus, or the ECR. Ultimately I would like to have my Rohloff set up for both so I could switch the back wheel, but that’s not in the cards for this iteration. Plus, I’ll be using the Krampus as a trail bike as well. The simplest alternative would be to add a 42t Wolftooth cog to the cassette. This would provide a granny(ish) gear and keep the sleek 1x setup. The other option is to add a front derailleur and a capable crankset with a wider chain line to get around the beefy 3” tires for a 2×10 setup. Note: the OD has a chain line that’s about 6.5mm wider than a traditional Shimano 2x crankset.
I opted for the latter option, obviously. I bought a cheap SLX front derailleur and spent some time in the garage mating it with the OD. Getting it all bolted together was easy, but tuning it was a different story (although I can’t claim to be an excellent wrench when it comes to derailleurs). When I first started toying with the OD I had a few issues including the Shadow derailleur hitting the chain when the wheel was mounted in the rear dropouts using Monkey Nuts (Monkey Nuts clamp into Surly horizontal rear fork ends (aka dropouts) to make spacing the wheel back easy). Also, the front derailleur required some finesse. In the end I ditched the Monkey Nuts, but eventually I will probably get a different derailleur in order to reinstall them and add a little space between the tire and seat tube. But nevertheless, it works beautifully and I have a true granny gear. For shits and giggles I thought I would take a look at some numbers in comparison to the other options and put the 29+ granny gear in perspective… or complicate it depending on how your mind works.
Chain Inches: Wolftooth vs Surly OD vs Rohloff
To do this I will illustrate each of these drivetrains on a 29+ (3” Knards) using gear inches. From Wikipedia: Gear inches is one of several relative measures of bicycle gearing, giving an indication of the mechanical advantage of different gears. Values for ‘gear inches’ typically range from 20 (very low gearing) via 70 (medium gearing) to 125 (very high gearing); as in a car, low gearing is for going up hills and high gearing is for going fast. Essentially to calculate gear inches, use this simple formula: Gear Inches = Wheel Diameter x (Chainring Teeth/Rear Sprocket Teeth).
Surly OD Crank
Here are numbers calculated from my Krampus setup. For each of these I use the lowest three gears to show range:
- Crankset: OD Crank (39/26t)
- Cassette: 11-12-14-16-18-21-24-28-32-36t
- Granny gears: 22.2 (26/36t) / 24.8 (26/32t) / 28.3 (26/28t)
- High gear: 108.1 (39/11t)
- Edit: Switched to 36/22 18.6 low / 99.8 high
Wolftooth Components 42t Cassette Cog
This is a pretty cool cog replacement for enabling a granny gear on a 10 or 11 speed cassette. The installation procedure involves removing the 16, 17, or 18t ring and adding the 42t Wolftooth to the back. For this example I referenced a 32t front chainring on a traditional 1x crank. A friend of mine uses a 30t, but there is chain rub with the Knard when engaged with the 42t Wolftooth ring, so he is planning on switching to a 32t up front which should do the trick.
- Crankset: Traditional with 32t ring
- Cassette: 11-12-14-18-21-24-28-32-36-42t
- Granny gears: 23.2 (32/42t) / 27.1 (32/36t) / 30.5 (32/32t)
- High gear: 88.7 (32/11t)
I was actually pretty surprised at these numbers considering a 38t/16t ring combination on my ECR almost killed my knees. Of course that was with racks, and a load for international travel that included all of this stuff. About 2 weeks into our Africa tour I ended up switching to a 34t and here is what I was getting:
- Crankset: Traditional with 34t ring
- Rohloff: SpeedHub 14sp with a 16t ring
- Granny gears: 18.1 (1) / 20.4 (2) / 23.3 (3)
- High gear: 106.8 (14)
So, in conclusion, the Rohloff gets the lowest granny gear (18.1 gear inches). However, the 2×10 gets a slightly better range with a low of 18.6 and a high gear of 108.1 (vs 106.8 on the Rohloff).
Now, if you made it down here, go drink a beer or two and burn off that nerd knowledge.
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