Wheels

[andygates]

The spoked wheel is one of the critical technologies that makes bikes work: it is incredibly strong, incredibly light, and pretty much changed the world.  The social revolution that came with the bike depends on the cheap reliable ubiquity of tensioned, tangentially-spoked wheels.

Building wheels makes me smile.  The whole blacksmith thing comes in: taking bits and making a whole using skill and a little finesse; ending up with a whole greater than the sum of the parts.  It is to fettling what compiling is to code: you get something useable at the end of it, but you may need to frotz around a little first.  But it's not a black art, unlike, say, regex or the perfect flapjack.

These are my new race wheels: stock Bontrager hubs, DT Swiss RR 1.2 deep-section aero rims, laced up with black Sapim double-butted stainless spokes.  Should be tough and fast and durable.  The front is radial, mostly for looks; it's my first full-size radial wheel, and they're fussier to build than tangentially-spoked wheels.  And not finished a moment too soon, either: these are what I'm racing on on Sunday morning.  So if I screwed up, that's when I get to spit out my dental work :)

Comments

[andygates.livejournal.com]

A tangentially-spoked wheel has spokes exiting the hub flange at a tangent and crossing over before entering the rim. Half the spokes on each side face forward and half backward. This gives the wheel really good resilience because the forces aren't all direct ground-rim-spoke-wheel; instead there's a degree of shock absorption and a great degree of lateral stability from the crossings - radial pennyfarthing wheels are notorious for collapse, but tangential ones much less so. The tangential pattern is effectively pre-wound in both directions, so it also delivers torque from hub to rim and back superbly.

Radially-spoked wheels transmit everything directly, so they are harsher to ride. They are not as strong due to the uncrossed spokes, and they also put greater forces on the hub flange which can cause hub failure. The advantages are slight: shorter spokes are lighter so a radial wheel saves a couple of ounces of spinning weight; radial wheels have a cleaner aerodynamic profile.

Radial lacing is unsuitable to deliver torque - it would just "wind up" the spokes. Radial front wheels are relatively common on road bikes; on a rear you'd only see radial lacing on the non-drive side. You can't use a radial with a disk brake for the same torque reasons.

As for tension and truing, a tangential wheel is a big bucket of averages, so it's very easy to get very nearly right. As long as the spokes are the right length, it's hard to make a really bad wheel. One generally adjusts tension in pairs. With radials, each spoke directly affects two points on the rim: its immediate entry, and its opposite. It's basically less subtle, and I suspect the reason it's harder to do is because mostly, people build tangential wheels - they're almost always better for the job!

Really bored bike mechanics do other, more elaborate spoke patterns. They're almost entirely decorative.