Wheel Technology

By Chris Kostman

Originally published in the UMCA Newsletter, March 1988

Those of you who think 32 spoke wheels are hi-tech, take note!

For decades, 36 has been the arbitrary standard number of spokes in a wheel. This has seemed a "safe" number in terms of durability and longevity and is the industry standard. In recent years, most notably on so-called triathlon bikes, 32 spoke wheels have become common. As of yet, no numbers of increased wheel collapses or required truings have been reported. Could this be a hint that fewer is not necessarily weaker? I would argue yes, quite vehemently!

Why fewer spokes? Quite simply, fewer spokes, besides decreasing the weight of the wheel, also decrease the aerodynamic drag of the wheel. Aerodynamic drag is the most significant factor in bicycle racing, hence the existence and popularity of aero rims, spokes, handlebars, frame tubing, clothing, etc. Clearly, aerodynamics is of prime concern to all cyclists, and most definitely to those of us who ride competitively.

It is a proven fact that spokes put up more air resisitance than any other part of the bicycle. This is proven by totalling the combined frontal area of the spokes and comparing it to the frontal area of any other component, including the frame itself. Therefore, less spokes means less drag. The big controversy surrounds the amount of drag saved and what the relative time or speed benefit is. According to Ric Hjertberg of Wheelsmith, a pair of 24 aero-spoked wheels will save about 17 seconds per hour compared to 36 standard spokes. They will also be 192 grams, or 6.7 ounces, lighter. All of this is very significant, especially when the effects are multiplied out over the distance of RAAM. During a 3,100 mile RAAM with a nine day completion time, this would save more than one full hour. This aero advantage can be taken one step further by using disc wheels. According to Hjertberg, discs would save another full hour on RAAM. Not too bad! The merits of discs are quite controversial, though, for their advantage is can be partially or totally negated by side or cross winds. Under ideal conditions, though, Steven Hed of Hed Design claims front and rear discs will save a full minute per hour, or a staggering 3 hours and 36 minutes during a RAAM. That would have put Michael Trail well ahead of Michael Secrest in the 1987 RAAM!

OK, so you think that 24 spoke wheels are too weak or that disc wheels are too heavy and impossible to ride. Guess again! I rode all of RAAM 87 on a 20 spoke front wheel without even a single truing. In fact, this Wheelsmith wheel already had 4,000 miles on it (used in criteriums, road races, distance events, etc.) before I even started the RAAM. My rear wheel on RAAM was either a 24 spoker or a Hed disc, depending on wind conditions and terrain. Hed's standard disc, at 1100 grams, weighs favorably with most road wheels, and all for less that $500. As for riding characteristics, radially spoked wheels and discs do ride a bit harshly, but not to the point of being a problem. In side and cross wind conditions, discs are not a good idea: they're dangerous and also their effect is completely negated. One way of minimalizing this effect is to use a 24" wheel, which is what I do on my Ultra Stout bicycle. 24" wheels are even more aerodynamic, as well as being stronger and lighter. My 24" front wheels have 18 spokes with the nipples inside the rim for maximum efficiency. As for tri-spoke type composite wheels, the latest wind tunnel tests find them very inferior to both discs and hi-tech spoked wheels.

So where's the cutting edge of lightness and aeroness versus safety and durability? That's hard to say, but I think I can safely say that we have not found it yet.