The packbike

This past weekend Jason, Casey and I talked about talking about a packbike, but never got around to actually talking about it. So now I’m writing (and drawing, badly) instead.

IMG_7768

A packbike is a bike purpose-built for trips which will involve carrying the bike for significant distances on a pack. Bikes like this one; trips like this one. There are two design criteria which must be addressed; making the bike light and compact to carry, and making it ride well on the sort of terrain which might be rideable on such a ride.  My ideas and rationale are as follows (numbers assuming a medium frame, and adjusted accordingly up and down).

  • Stack of 630mm.
  • Reach of 420mm.
  • ETT of 610mm.
  • 50mm BB drop (with a 26″ 2.5 tire).
  • 70 degree HTA (with a 440mm fork).
  • 73 degree STA.
  • 170mm head tube.
  • 440mm seat tube
  • 430mm chainstays.

The conceptual basis is my 2011 Mukluk, I’ve spec’d comparable geometry with a longer reach/ETT, and less BB drop and shorter chainstays to make it a bit more nimble and suit smaller tires better.  The long head tube keep the bars high and allows for plenty of frame bag space, even on a smaller frame with tons of standover.  Handling is slow enough for a rigid bike off trail, but tolerable on pavement.  Long ETT is built for a short stem, which saves weight and space when the bike is carried, and is my preference in more technical terrain.  All this is both the guts of the bike, and the easy stuff.

  • Rear dropouts should be Ogre/Troll style.
  • Rear racks mounts which do not interfere with disk brakes.
  • Available in both ti (lightest, pricey) and a tougher gauge steel.
  • Canti bosses for 26″ wheels.
  • 135mm rear spacing.
  • Clearance for 26″ by 3.8″ tires on 65mm rims, or 29″ by 2.1″.
  • Stock fork would be 135 spaced, canti bosses for 26″ wheels, rear disk brakes (for wheel swaps).
  • Direct mount front derailleur, provision for full length housing runs only.
  • One set of bottle bosses under the downtube, none in the main triangle.

The idea here is flexibility.  Gears or singlespeed, 26 inch wheels of any persuasion (smaller diameter makes them lighter and easier to pack) or cross wheels.  Disks, cantis, v-brakes, or any combination thereof, even fixed with no brakes.  You couldn’t have both 3.8″ tires and lots of gears, but that’s ok.  I don’t know enough to estimate what kind of bottom bracket shell would work best here.  The stock fork would be a specialized item, but the common axle-to-crown would allow for a variety of other options.  No bosses in the triangle to wear on a framebag.

As for the pack, I’d get HMG to modify their 2400 Ice Pack with a burlier lumbar pad, removable hipbelt (perhaps a 1.5″ webbing belt for riding with a light load, and padded wings to fit on when carrying the bike), stays and harness from the 4400 series (skinny shoulder straps mandatory), dual full length daisy chains on the back, and a modded center-back panel to hold the bike.  Casey has had success using the Osprey Variant to tote his bike, with the ice tool straps around the top and down tubes near the head tube, and the middle of the seat tube strapped down over the lid of the pack.  A comparable system, with specially reinforced (possibly double) straps in a similar spot would work well.  Daisies would facilitate strapping on the wheels.

Thoughts?  If you build it Jason, we’ll test it.

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6 thoughts on “The packbike

  1. I wonder if a purpose-built framebag could serve as the mounting point to the backpack, since a framebag already has a tight grip on all of the main frame tubes? Added advantage would be not having to dismount/empty the frame bag for portaging.

    Just spitballin’ here.

    • Not a bad idea. A hipbelt/lumbar setup could attach to the headtube and framebag, and a shoulder harness could attach to the framebag. Might have issue with head clearance and the rear triangle. A light backpack for riding could attach to the other side of the framebag as a compression panel.

  2. I’m intrigued to try a homebrew system like the euro packs that have a hook for bike carry:

    http://www.dynafit.com/product/equipment/x4-dy-n-a-backpack

    The under arm carry seems less then ideal for longer carries but it would be great to not have to take the pack off for quick carries. I wonder if you could rig a diagonal back carry system similar to a rando race pack where you hook a strap from the waste belt to the bottom bracket, sling the bike across your back and hook the head tube with a strap over your oposite shoulder.

    • The Dynafit system seems designed for short (<1/2 mile) carrys, the sort of tech sections I assume are common in the high Alps. The sideways sag of the whole pack in the third photo is less than inspiring. The old saddle nose on the shoulder trick seems just as good, especially if you put some foam under your saddle nose.

  3. This is an interesting concept. I love the versatility of it, the potential ability to cater the bike to the particulars of the trip in mind. I think the canti-bosses might pose a design issue. To make cantis/v-brakes workable on both fat and regular width rims would, I think, require some funny offsets. With 135mm rear spacing they might cause clearance issues too, especially if you want to be able to fit 3.8’s. I guess versatility and weight are the reasons for wanting a 135mm rear rather than 170mm?

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