Tuesday, February 05, 2013

A Carbon Fiber Fat Bike Dream

On One carbon fatty one-off
Recently I posted about a one off carbon fiber fat bike being done for On One's Brant Richards. This has been a pretty popular post here of late. It got me thinking, "So.....if we're going to do fat bikes in carbon, let's dream a little, shall we?"

Here's my list and some reasons why I think the ideas are worthy....

  • Carbon fiber is, or more correctly "can be", a great material to make a frame from if you maximize the material's unique properties. So, if On One, or any other company, wants to really make carbon worthwhile, it is good to know that some of us feel it has more than being "light weight" going for it. One of the best things about carbon fiber is that it can be shaped in ways metal can not be. Sometimes this is used as a stylistic cue by designers, but I think it could benefit fat bikes greatly. Another thing is that the material can be compliant where you want it to be, stiff where you want it to be, and strong as it needs to be without weight penalty. 
  • Let's take on the shaping. There are a lot of things that could be done here to make carbon fat bikes a good thing. I think one of those things is in the area of tire clearances. Crimping stays is really the main way metal frames gain clearances, but that technique is limited in its effectiveness.  Carbon fiber is mostly free of those limitations. I could see a thin, tall right chain stay snaking around crank rings and tire with an asymmetrical left chain stay with a beefier profile, yet allowing for a good amount of clearance. The stays could "wrap" more around the wider part of a tire, and pinch in for heel clearances which metal would be hard pressed to accomplish. A built in direct mount for a front derailleur could be shaped so that it wouldn't be a "mud shelf", as an example.
  • Frame compliance could be built in for the rider with a stiffer frame laterally which is always a nice thing. The biggest negative thing I feel on a fat bike is when it twists nose to tail on fast corners and on really rough terrain. Those big contact patches like to grip and exert forces on a frame which make steering a little weird at times. I wonder how a carbon frame might be tuned to help alleviate that situation. 
  • If I were doing a carbon fat bike, there are a few "musts" I would insist on. One would be clearances for the big Surly tires on 130mm rims. Yes- I know that you can not get 130mm rims.......yet. So, that's why it needs clearances for that big a rim/tire combo. The second thing is that I would insist on a 170mm spaced front fork. I'm not sure I would ever swap wheels, but- ya know- these wheels and tires are so expensive, having versatility makes sense. Single speed capable wheel up front, cassette in back. Plus, I think a wider front hub would make a rigid wheel that would track even better. You would ease the big tire clearance issues as well. 
  • That brings up the issue of single speed. I don't know how you get that accomplished unless you fit an EBB or someone's proprietary slider/swinger drop outs. I think a full on adventure vehicle needs to be able to do this though. (Go single speed, that is.)
Otherwise what is going on with fat bikes now is good. I'm not "all for a carbon fat bike frame", but if you're going to bother doing one, do something that pushes the boundaries and that makes sense. It's going to cost a truckload of money anyway, so why not?

Got some thoughts on this? Hit the comment section.....


KC said...

You've probably already seen this, but this is the first thing I thought of when I saw OnOne's carbon fatty:

RGB Nameless said...

First thing, that I really want - carbon fiber fatbike rims. Single wall, holed. Maybe with special inner part, that will prevent tube sliding inside the tire, at the really low pressures.

Or, maybe, true tubeless fatbike rim.

All weight on the fatbikes comes from the wheels.

Guitar Ted said...

@RGB Nameless: Well, here ya go- Rapant rumor at Frostbike was that HED will have a fat bike rim in carbon, no cut outs, because it was said that the weight/stiffness ratio was negatively affected by cutting out holes. So- ya gotta figure the weight is much redusced in their design vs aluminum cut out rims weight. My ears were hearing that the rims are being tested now. Stay tuned.......