Stuff I like: Wheels

Wheels fascinate me.  All wheels, but most especially bicycle wheels.

The wheel goes back so far in humanity’s past that we have no idea who “invented” or discovered it.  The first wheels were these massive things made out of rough-hewn wood.  They were basically big disks of lumber.  This wasn’t extremely efficient, but it did allow draft animals to pull much bigger loads than they could carry.

We had those early disk wheels for a long time.  Then several geniuses invented two brilliant refinements; tires and spokes.

The first tires where iron bands, heated so that they expanded, and then allowed to cool and clinch around the wooden disk.  These made the wheels last longer, and roll over stuff better.

The idea of spokes was true genius.  If most of the material in that original wooden disk is removed, simply by cutting away pie-wedge sections, the wheel is both lighter and stronger.  (The idea of a rim, with individual, round, lathe-turned spokes came later.)  Those original spoked wheels bore the load in a totally different fashion than our bicycle wheels do.  In this kind of wheel, each spoke carries the load in compression.  That is it holds the weight up as it rotates through the bottom of the wheel.  To do this, spokes had to be massive columns that could withstand the crushing weight of the vehicle.

There is another way!  Some unsung genius turned the whole idea of spoked wheels around.  The revelation was simple.  “Spokes can be used in tension.”  In this arrangement the weight of the vehicle is applied to the hub of the wheel, but the hub hangs from the spokes above it.  The spoke is being pulled from below, not pushed from above.  The load is then distributed around the rim from the top down.  The other spokes, also tensioned, hold the rim in place so that it doesn’t collapse.

When spokes are “tension loaded” they can be much thinner and lighter, and the wheel is, pound for pound, terrifically stronger.  Early examples of this type of wheel were used on horse drawn racing carts.  The system has been used in automotive wheels, and is still in use on most motorcycle wheels.  It’s also, by far, the most common method of building a bicycle wheel.

Other refinements followed.  Replace the steel “tires” with rubber ones.  Then Dunlop figured that solid rubber was too rough, and started building pneumatic ones, the kind we have today.  Spoke lacing patterns help to do the job too.  Different kinds of lacing provide different strengths and weaknesses.  As a general rule, lighter is not necessarily stronger.  (There are exceptions to this, but they usually involve some pretty exotic engineering and materials.)

In short, we who ride bikes are the beneficiaries of centuries of wheel development.  Each wheel is a complex system of carefully match components, assembled with care and attention to detail.  Wheel building is a mixture of science, technology, and art.  But our wheels are a key ingredient in the “single most efficient transportation machine ever invented.”