The Q Factor – or – another half-fat idea

I have to admit I’m having some misgivings about touring on the Pugs.  The problem is the Q factor of that 100mm bottom bracket shell.  It tweaks my knees just a bit.  It doesn’t really bother me at present, commuting 8 miles at a time, but I worry about riding 30-40 miles, day after day while on tour.  A small annoyance can become crippling in circumstances like that.

Another problem with touring on the Pugs is that the offset wheels are not something you are going to find at every small-town bike shop.

So I started thinking about how one could fix these problem on a fat bike.  Some fat bikes use a 170mm rear hub, which allows for a symmetric wheel while still providing proper chainline.  But 170mm hubs are a rarity.  You could build a symmetric frame with 135mm rear spacing, and simply not use the 2 or 3 lowest cogs on the rear (or space the cassette over and lose the 2 or 3 highest cogs instead). But if you think about it, the rear tire size mandates a minimum bottom bracket width: even if you built a custom frame, the BB would still have to be wide to prevent the crankarms from striking the chainstays.

This led me to thinking about going half-fat: fat on the front, fat-lite on the rear. Surly frames in general have a reputation for taking fatter-than-average rubber.  Many people report having run 3″ wide tires on a Karate Monkey for example.  It got me thinking that the perfect off-pavement touring bike might be a KM or the new Ogre 29er. With a straight (non-offset) Pugsley fork on the front, you could have symmetric wheels both front and rear, with room to run a Larry up front.  I’ve found that Larry on the front eliminates the need for a suspension on anything but really gnarly stuff.

Now the question is, is this enough cushion in the rear?  According to my calculations, the volume of a Larry is about 13 liters of air; the volume of a 29×3 is about 10 liters.  (Compare with other tire volumes on this chart.)  This is not too bad.  I guess the only way to answer this question with certainty is to try out a few different tires on the rear of the Pugs. Worse comes to worst, a Cane Creek Thudbuster could be used to smooth out the bumps.

This all begs the question, is this even a good idea? The biggest problem with using a setup like this for expedition touring is that the tires are not interchangeable between the wheels.  Worse yet, you can’t even carry a single spare that would work on both wheels – Larry fits on a 26″ rim, and the rear wheel is a 29er!  This would seem to spell doom for this approach.

But hold on a second.  When I tour, I plan to use an Extrawheel Voyager trailer to tote my gear.  The Extrawheel is rather unique among bike trailers in that it uses a full-sized wheel.  This allows you to use it as a spare wheel in an emergency. The trailer (w/o wheel) is extremely light – about 5 pounds.  The 3rd wheel is not all wasted weight, however, since it obviates the need to carry a spare tire, at least.  In the extreme, if you were to completely destroy one of the bike’s wheels, you could ditch the trailer (literally) and cannibalize the trailer’s wheel to get you to the nearest town where you could have a replacement wheel shipped.

So the strategy would be to use the same 29 x 3 semi-fat on the trailer as is on the rear of the bike.  Now the trailer wheel can swapped with either of the bike’s wheels (the Extrawheel is able to accomodate a 3.7″ tire). Note that the big disadvantage of using the Extrawheel with a Pugs is that Pugs wheels are damn heavy, and having to accelerate a third one is not something I’m looking forward to!  But with the half-fat setup, two of the three wheels are lighter than a Pugs wheel.

To summarize, the propsed setup is:

  • Karate Monkey or Ogre or similar 29er frame
  • Replace fork with a Pugsley non-offset fork
  • Larry on the front
  • 29 x 2.5-3.0 on the rear, whatever fits
  • Extrawheel trailer with the same 29er wheel
Is this a good idea? Opinions are appreciated!  In any case it’s a great excuse to buy and build another bike! 🙂

3 thoughts on “The Q Factor – or – another half-fat idea

  1. I’ve been enjoying the blog, and love to see that fatbikes are finding varied uses these days. I rode much of the Great Divide Route this summer and am moving to Alaska for the winter, so I just bought a used Pugsley this week. It seems that the full Pugsley set-up is what you want to be riding, and thus, should ride. It is not a heavy bike, considering the value of having huge tires, and it rides quite well. The bike will not hold you back. My concern is that the trailer may sap some of the joy out of riding; climbing will be a bit more of a chore and descending less thrilling. To be able to ride, uninhibited, is one of the personal joys of touring, as you have also found from your supported tours where minimal gear was carried.

    Washboard comes in and out of play, but is not a huge concern. The USFS does an excellent job maintaining roads, and most GD roads are of surpisingly high quality. Snow and mud may arise, but should not be primary considerations, as the remaining 2000+ miles of the route will be graded, and occasionally dusty dirt roads. Unless of course you are planning a winter passing of the Divide…

    In many cases, you will require less food and water than you may expect from reading ACA literature, etc. Most often, only 1-3 days of food is necessary, and as much as a few liters of water, which can easily be carried on the frame. A few instances may require more food or water, but adding a 2L bottle for a short stretch is simpler, and less costly than adding a trailer for increased capacity. Full suspension bikes are not the standard GD bike as the ACA likes to say. There is so much variety, there is no standard. I rode a rigid bike with 1.75in (47mm tires), while others ride much larger MTB tires; one rider this summer was on an early nineties Specialized Crossroads, with 700×40(?). Plenty of LHT’s do the route, and Europeans often come through on Thorns and Koga-Miyatas, rigid. It all works just fine.

    With fat tires and panniers, or your luggage of choice, you will easily be able to carry all of your gear and still enjoy a fast, comfortable ride.

    Note: The Troll, Ogre, and Karate Monkey are all awesome bikes for the job, each with gigantic tire clearances.

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