Tuesday, April 16, 2013

A game of compromises

Finally making some progress on the Travelers Check build and in the process coming to several realizations.
At 43 cm, this frame is cartoonishly small.
A short wheelbase, (989.9 mm/39 in.) will make for a nimble steed, but with the caveat of massive toe overlap.  Only 300 mm between 700x40c tires at their closest point. 
Even with it's diminutive dimensions,  during initial fitting, the frame's top tube reach and stand over are already looking to be borderline large for the bike's intended pilot (5' 3" with 29" inseam).
With the routes of the upcoming tour focused on back-country travel and technical single track, comes the necessity of shoehorning the fattest possible rubber into the frame-set  which will only exacerbate the above described issues.
Smaller tires will help to lower stand over height, slightly decrease toe overlap, and increase efficiency on the smoother tracks, all while sacrificing off-road capability, versatility,  traction, and ride comfort that large volume tires offer. 
We had originally conceived the Travelers Check to take the form of a monster-cross dirt-pounding all-terrain touring machine, but I was being forced to envision a new approach to the build. The needs are to maximize off-road capabilities of the bike by lowering stand over, decreasing toe overlap, while maximizing tire volume for comfort, control, and traction.
  The answer to this quandary lies in the niche of the 650b wheel size.
Long heralded by retro-grouches, randonneur aficionados, custom frame builders, and forward thinking designers like Kirk Pacenti, the 650b (or 27.5 as some are calling it) wheel size is positioned snugly between the 26" and 700c/29er wheel.

Pick up any mountain bike magazine right now and you can read all about how 650b/27.5 wheels and tires are the greatest thing since sliced bread, which in many accounts I tend to agree.
Back to the question at hand regarding the Travelers Check;  Successfully converting the frame-set will require hacking off and rewelding the brake bosses to achieve proper brake allignment with the decrease in wheel circumference from 700c to 650b, no small undertaking from a financial and logistical perspective.
26 vs 650b vs 29


  1. What about building 650b wheels with a 3spd coaster brake in the rear and disc brake up front? (with a different fork obviously.)

    Problem solved, right?
    Glad I could help.

  2. Are you facing legitimate toe overlap for Monica's small feet, or just toe-clip overlap as you build?
    Looking at the last picture of the bike I can't imagine her feet filling those toe clips if the ball of her foot is anywhere near the pedal spindle.

  3. I like your suggestions on the 3 spd coaster brake, but this build will need to accommodate a larger range of gearing to conquer the rugged Icelandic back-country single track. Fortunately the bike Gods are smiling upon me and an 8 spd Shimano Alfine IGH is finding it's way to my door step, and the frame/fork were just sent out to a frame builder (A-Train Cycles) to get the brake bosses re-positioned.

    I was facing two problems: toe overlap and lack of stand-over clearance (this was with the 700x40 tires mounted up). Admittedly the toe overlap with the 40c tires was minimal, and would be acceptable if the bike would see mostly road, gravel, or dirt path use, but the ultimate goal of the build is to make the Traveler's Check an off-road machine capable of navigating technical single-track, which means tight handling and fat rubber. My ideal tire size of 700x47-700x50 would only exacerbate the toe overlap and the stand-over issues, and also compromise the ability to fit fenders.

    Going to 650b solves all these problems: lowers the stand-over, increases clearance to fit fatter rubber, while decreasing overall rolling diameter to hopefully eliminating toe overlap and providing fender clearance. An extra bonus is that the immediate "spin-up" acceleration of the smaller 650b wheels will require less energy from Monica's short legs, also favorable for mountain biking.

    Lastly, I just like the idea and panache of a 650b cross-bike with couplers and FAT rubber.