Small Wheels for Adult Cycles by Tony Hadland

SteveintheUK in Articles, Tech Info

from Hadland.me.uk

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This article was written in 1997 at the request of the US journal Cycling Science. It discusses the use of small wheels in cycles for adults. The term “small wheels” here means those with a nominal diameter less than 26″ (660mm). They can be as small as 6″ (150mm) or as large as 24″ (600mm), but today are generally in the range 16-20″ (400-500mm). All dimensions quoted are approximate.

The safety bicycle’s influence on wheel size

The key design elements of the familiar diamond frame ’safety bicycle’ evolved a century ago. Wheel diameters commonly adopted for adult bicycles have changed little since then, being generally in the order of 26 to 28″ (650-700mm). It is easy to see why the Victorians adopted the 28″ (700mm) pneumatic tyre. It worked well because it was the biggest that could conveniently be accommodated in the robust, uncomplicated and easy-to-manufacture diamond frame.

For a given tyre construction, cross-section, tyre pressure, load and road surface a bigger diameter wheel rolls more easily than a smaller one. In an unsprung frame the bigger wheel also gives a more comfortable ride. This is because it falls less deeply into small depressions in the road surface and, on hitting bumps, rises and falls more slowly. Quite simply, the 28″ (700mm) wheel gave the best balance of comfort and rolling resistance that the diamond frame could accommodate. Anything bigger would have compromised the ease of mounting and dismounting that gave the ’safety bicycle’ its name.

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Conclusion

Both the Velocio approach and that of Alex Moulton demonstrate the potential that smaller wheels offer mainstream cyclists and cycle designers. They need not merely be a fallback for special purposes, such as folding bicycles.

For a given tyre construction, cross-section, inflation pressure, load, road surface and unsprung vehicle mass, a bigger wheel will roll more easily. However, this parity of conditions is not necessarily met. Furthermore, it can often be influenced in favour of the smaller wheel.

Small wheels are stronger, lighter, stiffer, more compact, have lower wind resistance and offer more design options. They facilitate faster acceleration and more responsive handling. Used in conjunction with suspension and supple high pressure tyres, they can be particularly effective.

As Velocio put it:

“That universal agreement has fixed on 70 centimetres as the proper size for wheels does not in any way prove that this diameter is best; it simply proves that cyclists follow each other like sheep…. Make no mistake, uniformity is leading us directly towards boredom and towards routine, whilst diversity, even though it distracts us, holds our attention, our interest and the spirit of enquiry always on the watch. To change is not always to perfect, and I know that better than any others newly come to cyclo-technology. But to stand still, to sink into a rut, that is the worst of things for industries and for men.”

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