Fatbike Innovation: Shaft Drive, IGH.

Brief post to ponder for today…

The fat bike world obviously needs more tire choices. I’ve whined talked about that already. What else does the fatbike world need? Well, we’ve also talked about full suspension and related nifty ideas. Here’s today’s idea…

As I related in my Mukluk 2 review, fat bikes are wonderful in sloppy conditions, deep snow, off-road, muck and mud, and related crud. I’ve had wonderful rides that ended with hours of bike and drivetrain cleaning.

And there are those who have addressed this issue with the use of internal geared hubs…which makes a lot of sense in some conditions, but still leaves the chain.

Those photos courtesy of Pursuiter, on MTBR. (He happens to buy his fat bikes at North Central Cyclery as well).

(Heck, there are even people talking about Hammerschmidt + IGH).

I was screwing around on the internet doing important research when I came across this picture:

A shaftdrive bicycle. Let’s talk about advantages:

1. Can have a completely enclosed and sealed drivetrain, impervious to outside conditions.

2. Look at the clearance under the BB (no chainrings) and at the rear wheel (no rear derailleur hanging low to be snapped off).

3. Could use with an IGH for a completely sealed drivetrain that is more than a foot off the ground (i.e. can go through reasonably deep water without even submerging the sealed drivetrain).

4. Can run bevel gears in front and rear gearboxes, to permit a narrower q-factor at the bottom bracket, with a driveshaft that runs parallel to the chain stays (shaftstays?) and still clears the tire.

5. Can design chain stays and tire clearance without having to worry about a chain that moves laterally across cassette and chainrings.

For that matter, let’s look at the picture again…

You could put that front gearbox (and crank) anywhere that it would clear the front tire–higher or lower, and set up as much (or as little) ground clearance as you wanted, without any chain line issues.

The downsides? The obvious ones are weight, complexity and cost. Weight could be addressed somewhat by integrating the gearbox and driveshaft into the bike frame (which would provide even greater clearance). Complexity and cost are what they are. But think about it…no exposed drivetrain. An extra 3-4″ of BB clearance. No rear derailleur to snap off. Ride through mud/water/snow/whatever, and hose down the whole bike afterwards. (No need for dry cleaning). No drivetrain adjustments. Throw a brake in the hub, while we’re at it, too…sealed drum that would be waterproof and relatively maintenance free. There are conflicting reports on driveline efficiency, but based on what I’ve read, I’d surmise that ultimately, a well-designed and maintained chain drive would be more efficient than a well-designed and maintained shaft drive…but the durability and weather/debris-proof nature of the shaft drive bears thought.

That–that would be an expedition worthy fat bike. (In the interests of full disclosure, I did google shaft drive fatbike, and came up with kapow!’s post on MTBR). But it’s a pretty crazy idea to put together.

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3 thoughts on “Fatbike Innovation: Shaft Drive, IGH.

  1. My experience with a friend’s expensive european shaft drive bike left me unimpressed. So much energy loss I wouldn’t want to pedal it to the store.

    I find that with an IGH a chain needs next to no maintenance. The odd squirt of lube. I rarely if ever clean my IGH chains beyond hosing them down and lubing them. I buy $14 SRAM 8 speed chains and I just replace them as needed.

    Chains are simple, cheap and easy to work on in the field. I have never seen the appeal of a belt or shaft.

    Fat bikes do present the tire width problem that normal bikes don’t, but the Moonlander has room for 5″ tires with a derailleur. I’m not sure how much bigger fat bike tires will practically go, but a jackshaft and two chains might still be the better option.

    safe riding,

    Vik

    • For rides like the one I did yesterday, chain drive will never be as good of an option as a sealed shaftdrive…unless it was sealed chain drive, which is an option. Most of the shaft drive designs I’ve seen for bikes have been pretty inefficient designs…in a design realm, the potential drivetrain efficiency difference between chain and shaft can be pretty minimal. I do think shaft drive offers some unique options that make it potentially well suited for this application. For example, a chain has to be both above and below the point being driven (looped around a gear). Shaft drive could be located entirely above the point being drive, for greater ground clearance.

      I think shaft drive fat bikes are probably not that likely to happen, but it is an interesting idea with some potential benefits.

  2. Pingback: Single Sided Swingarm: Why Not? | ridingagainstthegrain

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