Tubeless Endomorph

Well, yesterday I bit the bullet and put the Endo back on the rear wheel, tubeless of course.  I’m tired of getting a thorn puncture nearly every time I go for a ride, and I didn’t want to do tubeless while I was running the Floyd because I knew I’d be putting the Endo back on for the winter any day now.  We had a significant snow last week, and more on the way, so it’s time.

In contrast to the tubeless Larry on the front, I decided to try to get the tire to seat without using the compression strap.  The Endo bead does not seal as tightly as the Larry’s, so I didn’t think it would work.  However, I found that if I pushed down on the center of the tire with my thumb right over the valve stem while I was blowing in compressed air, the tire seated right away!  I suspect that the rapid flow of air formed a pressure wave that pushed the tire bead to the sides ahead of it as it raced around the tire in both directions from the valve.  All I had to do to get the process started was get the bead to seat directly over the valve and boom!  The whole thing seated almost instantly.  Needless to say, this would be futile without a pretty decent compressor.

I used the same rolling darryl rimstrip / gorilla tape combo as before.  This time, however, I forgot that the tire had been punctured by the thorn from hell just before I switched over to the Floyd — there was a 1/4″ or more cut in the tire that, although Stan’s sealed it, would bubble and sputter every time I pushed on that part of the tire.  Sadly, I had to deflate the tire and apply a tire boot.  This was a real pain: I had to bend way over and look up into the tire casing to see what I was doing, because I had to keep the area that I was booting at the very top of the wheel to prevent the Stan’s from running down the casing onto it.  I cleaned the inside of the tire with some isopropyl alcohol and applied gorilla tape, and it made a very good bond.  I’m becoming more impressed with gorilla tape the more I use it.

It took a lot more shaking to get the bead airtight at 20psi.  Much more work than the Larry.

This morning I noticed a lot of tiny little white dots on the outside of the Endo casing.  Obviously, these are pores that were sealed by the Stan’s.  Nonetheless, the tire appeared to lose only about 1-2 psi overnight, and I rode the bike to work this morning without incident.

Now I can’t wait for more snow!!!

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GDMBR Canada Tour 2012

Adventure Cycling has just announced their guided tour schedule for 2012.  They are doing the GDMBR Canada section (Banff, AB -> Whitefish, MT) from July 15 to July 24, 2012.

I actually thought for a moment about signing up for this; it would be a good start to the route, and then I could continue on by myself after Whitefish.  But then I saw the cost! $1399 for camping and carrying your own gear?  WTF?  I’d rather spend that money on an occasional well-earned hotel stay during my trip!

AC is offering one other tour that looked tempting to me: Denali.  But I’m committed to the GDMBR next year; Denali will have to wait.

Free wheeling

I discovered something really interesting about Pugsley wheels today, using the excellent FreeSpoke spoke length calculator.  FreeSpoke is a very versatile tool that not only calculates spoke lengths for any imaginable rim and hub, but also tells you what the relative spoke tension will be on each side of the wheel.  You can play around with it to design a stronger wheel.

Let’s take a look at the standard Pugsley offset wheel using the Large Marge offset rim.  The LM is in FreeSpoke’s database of rims, so you don’t need to do anything except select it.  FreeSpoke will fill in the details in the calculator window.  The LM is offset 12mm, which FreeSpoke handles as two offsets, -6mm on the left, and +6mm on the right.  (It uses two measurements instead of one to handle rims in which the spoke holes are not all drilled at the same offset — see what I mean when I say it’s versatile?)  I picked a totally vanilla hub, the Shimano M525, which has nothing particularly special about it. To handle the Pugsley offset, enter 17.5 in the “hub offset” field.  The results (for 36H 3x) are:

This is cool in several ways.  First of all, the diagram generated by the tool shows you the wheel you’ve designed, so you can spot obvious errors you might have made.  The red line is the centerline of the rim.  On a normal bike, the right (drive-side) flange would be closer to the centerline than the left, but this is a Pugsley, remember, so it’s the other way around.  Note, however, that the spoke holes are not on the centerline, they are offset too.  The result is that the rim is moved back to the left side of the bike almost as much as the hub has been shifted to the right.  But what’s really interesting (to me) is the “tension distribution”: the drive-side spokes are under only 66% as much tension as the non-drive-side spokes.  To put it another way, the non-drive-side spokes are under 50% more tension than the drive-side spokes.  The Pugsley frame offset clearly stresses the non-drive-side of the wheel.

How does this compare to a “normal” wheel?  Take a look at a symmetric LM built for a symmetric frame (this is essentially what every bike is running in the rear, although with a narrower rim, which doesn’t affect these calculations).  All I have to do is zero out the spoke offsets and the hub offsets and the result is:

This looks just like any other rear wheel; the drive-side hub flange is closer to the centerline of the rim than the non-drive-side, and as a result, the non-drive-side spoke tension is on 59% as high as the drive-side tension.

Interesting observation #1 is that, even though the offset Pugs wheel looks ridiculous, it is actually stronger than a “normal” rear wheel, in the sense that the spoke tensions are more even.  Of course we can argue about whether it’s better to put the higher tension on the drive side or the non-drive side.

But what if, I thought, what if you were to use an offset-drilled LM on a symmetric frame?  You would, of course, have to spin the LM around so that it offsets the other way.

Interesting observation #2: A symmetric fat-tire wheel is stronger if you build it with an offset LM rim.  In fact it is nearly the holy grail of wheels!

This result blew me away.  I expected the offset to help, but I didn’t expect the spoke lengths and spoke tensions to be virtually identical!  The offset of the LM almost perfectly compensates for the lopsided construction of the standard freehub.

Interesting observation #3: Let’s say you were touring on a standard Pugsley with an Extrawheel trailer (see previous post). The trailer can handle a 3.7″ tire but it can’t handle the offset construction of the standard Pugs wheel, so you build a symmetric wheel with an offset LM as shown above.  If one of the bike’s wheels suffered a catastrophic failure, it would still be possible to re-purpose the trailer wheel by unlacing the spokes, reversing the rim, and re-lacing.  (The spoke lengths are close enough to not worry about.) Sure, you lose a few hours sitting by the side of the trail, but at least you aren’t stranded.

One last thought experiment.  I want to build up a 29er wheel to try out in the back of my Pugs so that I can evaluate some 29er rubber, as I explained in the previous post. Unfortunately, a non-offset rim in a Pugsley rear triangle is going to be extremely weak. I got the following result by zeroing out the spoke bed offsets but leaving the hub offset at 17.5mm:

Ouch!  The non-drive-side spokes are under two-and-a-half times as much tension as the drive-side spokes!

Interesting observation #4: Symmetrically-drilled rims are a really bad choice for an offset Pugsley frame!

One way to ameliorate the above problem is to use a Hi-Lo flanged hub with the high flange on the non-drive-side.  Several economical SRAM hubs are available in this configuration (the 406, 506, and X-7), as well as some high-end hubs that cost 10x as much.  I will leave it as an exercise for the reader to show that using an SRAM Hi-Lo hub increases the drive-side spoke tension from 39% to 45%.  This still bites but it’s the best design I’ve found.  AFAIK there are no offset-drilled 29er rims on the market anymore (but there used to be).  Does anybody know differently?

Well, I hope you found this discussion interesting and that you get a chance to try out FreeSpoke.  FreeSpoke now joins my collection of external links on the right side of the page.  Good job, FreeSpoke!

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! 🙂