Krampus Wheelbuild

WP 7 37

Building wheels for Cass’ Surly Krampus has called several considerations to mind.  The Rabbit Hole rims supplied by Surly for this build are designed with 64 spoke holes, to be built with 32 spoke wheels  The spoke holes are patterned in pairs so that the the wheel can be built symmetrically as a “normal” wheel, using holes on alternating sides of the rim.  The wheel can also be built asymmetrically, to a single row of holes on one side of the rim.  This is the required method if building a 29″ wheelset for a Pugsley, whose frame is also offset.  But the Krampus has a normal rear spacing and doesn’t require any wheelbuilding tricks.  Why consider building to the rim asymmetrically?

On typical rear wheels for road and mountain bikes, the drive-side flange is spaced toward the centerline of the wheel to accommodate the growing number of cogs in modern drivetrains.  Technically, the width of the freehub has not grown since the leap from 7-8 speed systems, as modern 9 and 10 speed cassettes simply use narrower cogs and chains.  The disparity between the location of the left and right flange from “center” creates mismatched bracing angles (the drive side spokes are more vertical), and unbalanced tension (drive spokes require almost twice the tension).  Worth noting is these perceived imperfections are not a problem for most people in the real world– these are mostly theoretical considerations.  As long as the wheel is designed for the task at hand with appropriate materials and is properly built, few wheels cause problems for their users.  The Surly Rabbit Hole rims used in this build present an interesting question.  If the wheel is built to one side of the rim, asymmetrically, the spoke angles are then well balanced and the tension is even.  But then, is there anything wrong with a wheel whose spokes are biased to one side of the rim?

Building the wheel in the obvious mode by alternating spoke holes provides a positive bracing at the rim, as spokes connect to either side and support the structure of the rim.  The second option is to build to one side of the rim only, favoring the row of spokes on the non-drive side to balance the tension in the wheel and reduce the chance of spoke failure.  For reference, a “normal” wheel is also shown below.

Normal rear wheel

This is how a normal wheel would look, built to a rim such as a Velocity P35 with spoke holes down the centerline.  This rim is notable as one of the wider 29″ rim on the market and would be a suitable platform for both the 3.0″ Knard tire, and standard width 29″ tires.  Note, the drive-side spokes are more vertical than the non-drive side and thus, under higher tension.  This is how most multi-speed wheels look; the red line is the centerline of the frame:

Wheel dish 3 php

Normal wheel build: Phil Wood disc hub to Velocity P35 rim

Bracing angle: L-6.5°, R-4°

Tension distribution: L-62%, R-100%

 

Assymmetric wheel build with Rabbit Hole rim

The wheelbuilder would suggest that balanced angles and spoke tension are ideal.  Traditonally, only drive-side spokes were prone to failure as drivetrain forces put greater strain on this side of the wheel.  WIth the proliferation of disc brakes, the opposing forces on the opposite side of the wheel are known to cause spoke breakage in relative frequency, especially as these spokes are relatively undertensioned.  From the perspective of the wheelbuilder, with the option to build to an asymmetrical rim, building to the row of holes on the non-drive side would be best.  This is how an asymmetric build would look, offset 5mm to the non-drive side:

Wheel dish php

Assymmetrical build, Phil Wood disc hub to Rabbit Hole

Bracing angles: L-5.4°, R-4.8°

Tension distribution: L-91%, R-100%

Symmetric wheel build with Rabbit Hole rim

The rider, the mountain biker, would look at a rim with spokes to one side and would wonder if the rim could withstand the forces of riding, as if it would fold over itself sideways.  It may even seem an unfounded concern as the rim is still comprised of 700g of aluminum, but it would be prudent to ask such a question.  This wheel is built to alternating sides of the rim, and spoke holes are offset 5mm from center.  Note, drive-side tension is proportionally greater than in the “normal” wheel, but within an acceptable range.

Wheel dish 1 php

Symmetrical build, Phil Wood disc hub to Rabbit Hole rim

Bracing angles: L-5.3°, R-2.9°

Tension distribution: L-55%, R-100%

The crux of this discussion is whether the rim, a singlewall (sorta doublewall) hoop with cutouts can effectively act as a rigid structure.  If the rim were made of solid steel, we would readily opt for the ideal spoke angles of the asymmetrical build.  But, can the Rabbit Hole support the load of a full-sized man with a bikepacking load, who sometimes rides like an Ogre or a Troll?  Prudence says only “maybe”, but I have been riding offset wheels for a year, including the lightweight singlewall Marge Lite rim. The construction of these rims is similar, yet the offset of the Marge Lite is more than twice as great as the Rabbit Hole.  On my Pugsley, my front wheel is built symmetrical to a dynamo hub, while the rear is laced to one side of the rim only.  I haven’t had any problems over many months of touring on Marge Lite rims.  Rabbit Holes should be fine.

Both approaches to building a wheel with Rabbit Hole rims would be fine, and there is no clear winner.  Which would you choose?

Feel free to justify your vote in the comment form below.

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24 thoughts on “Krampus Wheelbuild

    • Lighter and lighter and lighter. Cool video. A heavy bike like mine doesn’t require too much engineering though. I’m sure most of the product development is selecting paint colors and designing decals.

  1. I’ve built up a bunch of symmetrical (single speed) rear wheels, and one or two “symmetrical” and “asymmetrical” rears. If I can balance spoke tension, that’s what I’m going to do (to the extent of having my dish ever-so-slightly off on my most recent rear build to encourage more balanced tension).

    • Noah, To clarify, the ‘assymmetric’ build shown here is properly dished as it makes use of 5mm of offset in the rim. Some people do not like the idea of such a significant offset, although 10-12mm of spoke hole offset is commonly used on the Pugsley. The “wheelbuilder” choses improved spoke tension.

    • This would also be my choice, and as much as I talk about the dearth of offset rims for 29″ wheels, it didn’t really occur to me until after the wheel was built that the offset was not only for Pug wheels. Still, I have full confidence in the way it is built, and the thick flanges on the Phil hub should reduce the chance of failure at the elbow.

  2. Nick

    Seven speed cassette freehubs are narrower then 8-11 speed freehubs.

    Thanks for the wheel building info. So, are you going asym or symmetrical?

    • Yes, the switch from 7 to 8 speed systems widens the freehub, as the chain and cogs are about the same dimension. The wheel is built symmetrically, as one would normally expect. I didn’t really consider the assym option until after the wheel was built.

    • Cass already has a Rohloff, currently built into a 26″ wheel. It spent some time on several different bikes recently, including a Santos, a Thorn and a Surly Troll. (http://whileoutriding.com/my-bike/) It will be built into a 29″ wheel sometime soon. Something like the Velocity P35 will work nicely as it balances the width of the Rabbit Hole and standard width rims, thus providing a good platform for tires ranging from narrower touring models (1.75-2.0 Schwalbe) to 2.4″ knobbies, and even the 3.0″ Surly Knard tire for the Krampus.

      Technically, the Rabbit Hole will accept a 2.0″ Dureme or Mondial, as I fit a 2.35″ Big Apple on 65mm rims. If Cass decides the extra width and tire profile is valuable, we may consider building the Rohloff to the RH.

      I’ll get a Rohloff when the used/cheap bike parts tree stops fruiting. I take it you are happy with yours?

      • I’d planned on building the Rohloff with P35s – for the versatility, as Nick mentions. But if the Rabbit Holes are up to the task – and play ok with the Duremes – then I could see the benefit of taking full advantage of the Knard/Rabbit Hole combo. I’ll see how both stand up to long distance touring.

      • The Rohloff has really provided piece of mind in SE Asia, where there are very few bike shops that can service a modern bicycle. I also enjoy the perplexed look on peoples faces when the determine that my fully loaded monstrosity is a single speed.

        For my 26″ build I went for the only rim that Rohloff recommends, the Rigida Andra 30 for wide flange hubs. This is the heaviest double walled monstrosity I have ever encountered, but the non-eyeletted spoke holes are drilled at an angle to prevent a bending of the spoke at the nipple. They seem to be working nicely and I have a Schwalbe Marathon XR (no longer in production) 2.25″ mounted to it. This has worked well when the paved road suddenly turns rocks and potholes.

      • David, With any SS or IGH, a normal symmetrical build would be best. I’ve been curious about the Nuvinci for a while, but for most of my riding a standard derailleur drivetrain has served me well. Let us know how the wheel works out for you. New Krampus frame?

        nicholas

  3. hi regarding building a 29er rear wheel for a pugsley. have you thought of just building up a wheel undished (equal spoke tension). using freespoke i found that a wheel built this way would be about 8mm off centre towards the driveside. surely there would still be enough clearance for 2.4(maybe 3inch) 29er tyres and a standard drivetrain.
    any thoughts.
    tony

    • I have built a 29″ wheel for the rear of a Pugsley. When properly dished the tension is not ideal, but it works if the wheel is well built. Hubs with taller non-drive side flanges alleviate the problem a little, including the inexpensive SRAM 506, but an offset rim such as the Rabbit Hole helps a lot.

      I would consider dishing the wheel a little to improve the wheel, although I wasn’t too concerned with the way my wheel turned out. More here: https://gypsybytrade.wordpress.com/2012/05/08/bigger-and-bigger/

  4. Good Lord. I just got back from five days of constant motion involving jets and cabs and hiltons and rental cars and subways (in LA!) and the ghost of Jim Morrison and buses and no end of familial drama and I came here to my favorite wilderness location only to find some kind of aerospace discussion and charts of farts. Me, first thing I did after 24 hours of planes trains and automobiles was get on my bike. I would like to report a joyous reunion but what really happened is after the first ten miles the gastro-intestinal bindage of way too many falafels and far too much time in the sky resulted in a sad moment in the bushes at roadside that I am sorry to have to mention. Be that as it may, Nicholas, this Gypsy page has matured and increased and I suspect you are going to be a Voice, soon. If not already.

    Don’t stop.

    tj

    • Can i ask a question? What would be the angle and tension of the spokes, if the spokes on the transmission side of the hub were laced to the nipple holes furthest to the left and the spokes on the disc brake mounting side were laced to the nipple holes furthest to the right? In effect, making an additional cross in the pattern of the spokes.

      • I’ve considered this as well. It addresses both tension and rim bracing, although it is even more of a fringe option, if only because it seems strange to people. Motorcycles use lacing patterns like this frequently.

        Bracing angle: L-7.2deg, R-4.8
        Tension distribution: L-67%, R-100%

        Spoke lengths would be 298mm on both sides.

    • TJ, Welcome back from reality and chasing the ghosts of Morrison. Moments by the roadside are quite normal in my life, and are to be savored. I have been quite busy in your absence. I sorta like the idea, but being a Voice sounds like a lot of pressure. I’d rather just be a gypsy or a trailer park cyclist or something where expectations are low. Really, none of this bike riding stuff is that complicated, but we make it that way for some reason.

      I hope your schwinns and mongeese are rolling well.

      nicholas

      • Apologies, a second stupid thought has crossed my mind… if you could find a tandem hub that would fit the rear drop out (with double the number of spoking holes) you could employ both spoking options ~ creating a super strong rear wheel, with some additional weight plenties.

      • cycle tramp,

        Assuming the flange dimensions are the same as on the hub used above, you would be stuck with the same scenario: offset build to the rim (asym), or imperfect tension if laced to both sides. Yes, more spokes are always better. For this build, I really do think that either method of building, and even your crossed spoke method would be fine. The Surly Clownshoe rim (100mm rim for Moonlander, etc.) uses a 20mm spoke hole offset. The 5mm offset on the Rabbit Hole should not be a problem.

        As well, 64 hole hubs are simply nonexistent, save for this prototype model from Phil Wood: http://philwoodco.wordpress.com/2012/04/10/64-hole-snow-hub/

        This hub is most likely a part of their concept DH Fatbike shown at Interbike, which was a full-suspension fat bike, featuring long travel suspension, 100mm rims, and 4.8″ Surly tires. It is an example of the current ultimate in the go-anywhere fatbike concept– and elegant monster. Curiously, Phil Wood accidentally received some prototype Surly rims with 72 spoke holes (to be laced to 36h hubs normally), so Phil built the bike with 72 spokes in each wheel and with a symmetrical 185mm rear end.

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