Un article malheureusement en Anglais sur le sujet :
This article was written in 1997 at the request of the US journal
CyclingScience. 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 onwheel sizeThe 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.
Specialised uses for small wheels
Despite the enduring dominance of the larger wheel formats,
Sutherland's tyre and rim
listings include substantially more small formats than large.
1Many are rare or used
mostly for non-cycling purposes, such as wheelchairs, barrows and
handcarts. However, established
cycling uses include:
- children's
bicycles, for obvious reasons of scale,
- the
front wheels of carrier cycles, leaving extra space above for cargo,
- portable
cycles, to reduce the space needed to stow the machine when folded or
separated,
- unisex
'one size fits all' family shopper cycles, to allow good luggage
carrying capacity over the wheels, and to allow extra height adjustment
of saddle and handlebars,
- BMX,
for fast acceleration and quick steering,
- front
wheels of pursuit and motor-paced track cycles, to enable closer
drafting of the vehicle ahead,
- front
wheels of time-trial cycles, to facilitate a lower, more aerodynamic
riding position,
- the
front wheels of recumbents, to facilitate convenient location of the
cranks and drive train without impeding steering, and for aerodynamic
reasons, including easier incorporation of fairings.
Most of these uses are for special purpose machines and
capitalise on one or more
advantages of the smaller wheel (most often simply its smaller size) in
a trade-off for certain
disadvantages. [The various advantages and disadvantages of small
wheels are listed in
Table
1.]
However, over the years some powerful advocates have argued
for smaller wheels for
regular bicycles. Surprisingly, it is nearly a century since balloon
tyres of 12 to 16" diameter
(300-400mm) were tried for club cycling in England.
2A Mr. Edmunds who rode a machine
with wheels about 12" (300mm) diameter and 5" (125 mm) wide around
Birmingham was "a racer of some
ability" whose youthful challengers "sometimes received quite a
surprise."
3Subsequently the two principal advocates of smaller wheels
have been the eminent
French cycle tourist Paul de Vivie (in the 1920s) and the distinguished
English engineer Alex
Moulton (since the early 1960s).
The Vélocio approach - medium diameter
balloon tyres
Paul de Vivie, alias 'Vélocio', was the 'father' of French
cycle touring. In the
1920s he advocated balloon tyres of up to 2.25" (57mm) cross-section on
20" (500mm) rims, giving an
overall diameter of about 24" (600mm).
4 He
reached his conclusions during a lifetime in
which he cycled the equivalent of 15 times round the world 'all of it
as careful experimental
touring work with a view to improving machine design and method of
riding'.
5As early as 1911 he wrote:
"My own experience has gone no further than to 50 centimetre
wheels furnished with 50
millimetre tyres, but I can guarantee that in an experiment extending
as far as 15,000 kilometres
covered, they will not have the smallest disadvantage from the point of
view of their running. It
simply seems to me they are more prone to skidding, but this is perhaps
due to the fact that their
tyres have no tread and that the bicycle is very short."
6Vélocio died in 1930 and his obituary in the CTC Gazette
7included a
photograph of him with an open-framed small-wheeler. Over the next ten
years several British cycle
tourists emulated his use of smaller wheels. They included A.C.
Davison, Cycling magazine's
technical expert, and Medwin Clutterbuck, the CTC Consul for Sussex.
Both riders used tyres of
about 24" x 1 5/8" (600mm x 40mm). [Clutterbuck used 22" x 1 3/8" rims
(560mm x 35mm).] Davison
covered some 5,000 miles (8,100 km) on his 'Little Wheels' and declared
it "a quite satisfactory bicycle".
8Medwin Clutterbuck had two small-wheeled cycles built by
F.W. Evans of London. On the
first of these he toured the Alps, Dolomites and Norway, often on
poorly paved roads. In England he
covered up to 200 miles (320 km) in a day. Half a century later he
still considered his second
Evans-built small-wheeler "the epitome of what a touring machine should
be".
9The idea of a reduction of tyre diameter being matched by a
corresponding increase in
cross-sectional area certainly has merit. The volume of air and
pressure remains the same as in the
conventional tyre, while the wider cross-section compensates for (and
can even improve on) the
otherwise harsher ride of the small wheel.
As for rolling resistance, a reasonable
prima facie indicator
is the length of
the tyre print (under a known weight) divided by the inflated tyre
radius.
10 For a given
tyre pressure and load, the contact patch
area is
approximately constant, regardless of tyre
diameter. (For example, a tyre inflated to 50 psi and carrying a load
of 100 lbs has a contact
patch with an area of approximately 100/50 square inches, ie. 2 square
inches, whatever format the
tyre may be.
11) However, with the Vélocio
approach to small wheels the patch is wider
but
shorter. Thus compensation is obtained for the
otherwise higher rolling resistance.
However, this compensation
depends on superior
lightweight tyre carcass
construction. This is difficult to achieve because, the
larger the cross-section, the stronger
the carcass must be to hold a given pressure. For economy of
manufacture, the strength of wide
section tyres often comes from thicker, heavier and less flexible
materials, and results in a
higher rolling resistance
13.
Vélocio therefore advocated canvas-backed, thin, flexible
carcasses produced by
Edwardian English tyre manufacturers. In 1911 he bemoaned the fact
that, for fear of warranty
claims, such tyres were not made in France.
Apart from the warranty issues, stronger materials that enable thinner,
lighter and
more flexible construction cost more and there may be little demand. It
is significant that Medwin
Clutterbuck abandoned his small-wheelers after World War 2 because it
was no longer possible to
have his tyres custom made by the Constrictor company.
Above: Vélocio with his 'Carrosse de Gala' small-wheeler in 1907 Above: Vélocio with his 'Carrosse de Gala' at the foot of Les Alpilles, Provence, in 1905Above: Vélocio and companions at Les BauxThe
above three pictures are reproduced courtesy of Raymond Henry from
whose collection they come. They appear in Raymond's excellent book in
the French language entitled Vélocio
and edited by The Museum of Art and Industry of Saint-Étienne.
The Moulton approach - small
diameter high pressure tyres and suspensionAlex Moulton (b.1920) is an engineer with a background in
steam power, aeronautical
engineering, automotive suspension and rubber technology. His
great-grandfather introduced
Goodyear's rubber vulcanising process to the UK and the Moulton family
has been involved with the
material ever since. Alex Moulton's rubber and fluid-interlinked
suspension systems have been used
on millions of cars, from the Mini to the MGF. Yet he is probably best
known for his small-wheeled
bicycle concept, to which he has devoted much of the last 40 years. The
story is recounted in two
books by the author.
14Moulton noted the lack of development of the diamond-frame
bicycle since the 1890s.
He decided "to take the evolution of that most remarkable device beyond
its classical form ... to
produce a bicycle which was more pleasing to have and to use."
He argued that, apart from those for use on soft ground:
- wheel
sizes for virtually all vehicles have decreased as design has evolved,
- this
reduction of the encumbrance of large wheels is always sensible.
Moulton's background in rubber technology enabled him to demonstrate
that 16" x 1
3/8" (400mm x 35mm) tyres inflated to 50 psi (3.4 atm) could match the
rolling resistance of the
then standard lower pressure roadster tyres.
15It is important to note that Moulton did
not use standard juvenile tyres but small diameter versions of the
Dunlop Sprite, a good touring
tyre of the time. Most series-produced Moulton bicycles of the 1960s
and 1970s used tyres of this type.
To eliminate the rough ride given by a high pressure small
diameter tyre, Moulton
added suspension. This not only gave a generally smoother ride than a
conventional bicycle, but
also reduced momentum losses. Recent tests of the Primo high pressure
16" x 1 3/8" tyre indicated
that on a real road a fully sprung 1960s Moulton rolled significantly
better than a semi-sprung
Brompton using the same tyres.
16A notable feature of the Moulton bicycle has been its sporting success.
Moultons have
performed well in time trials, solo and four man pursuit, criterium,
ultra-marathon, triathlon,
Audax and HPV races. The flying 200 metres normal riding position solo
record has been held by a
Moulton-based HPV for more than a decade.
Early racing Moultons, such as that used to break the
Cardiff-London record in 1962,
used sew-ups (tubulars) of 18" (450mm) nominal size, with an actual diameter
nearer 16" (400mm). In 1964
Moulton, again working with Dunlop, produced a clincher (wired-on) replacement.
This matched the performance
of the sew-up but was considerably more robust. To enable riders to
switch between sew-ups and
clinchers, rims for the latter had the same brake radius, hence the
birth of the unique Moulton 17"
x 1 1/4" format (430 x 31mm, ISO 32-369).
This tyre, made available from 1983 until circa 2000 in a version by Wolber, is noted for its high performance. Tests have
shown it to have a rolling resistance on smooth surfaces that matches a
high quality 27" (700mm)
clincher touring tyre or a cotton road sew-up.
17An
even faster slick version is also
available. This was evolved as part of the General Motors Sunraycer
solar-powered car project. The
slicks were used in 1990 on Miles Kingsbury's fully-faired recumbent
Bean. This broke the world HPV
record for the greatest distance covered in an hour by a solo rider.
In
2009, 17" tyres for Moultons are made by Bridgestone and Schwalbe. They
have also been made in the recent past by Continental.
With the
availability of high quality, high pressure, narrow section tyres in
the widely available 406 format (nominally 20" but often nearer 18.3"
in reality), some Moultons now use this tyre format. The four machines
below are all current models in 2009: the first two use the 369 (17")
tyre, whereas the last two use the 406 (20" nominal) format.
Bridgestone Moulton Sports (369 tyres)Moulton AM Esprit (369 tyres)Moulton AM Double Pylon (406 tyres)Pashley Moulton TSR30 (406 tyres)
ConclusionBoth the Vélocio 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 Vélocio 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."
References and notes
1. Sutherland, H. et al,
Sutherland's Handbook for
Bicycle Mechanics,
Sixth Edition, Sutherland Publications, Berkeley, CA, 1995.
2. Barrett, R., Photograph of Sharrow CC,
The Boneshaker, Vol.11,
No.99, p.15, Southern Veteran-Cycle Club, UK, Spring 1982. This shows a
club rider using
approximately 16" diameter balloon tyres.
3. Davison, A.C., 'Actual Experiences with Some Freak Bicycles',
Cycling, UK, June 31, 1939. This briefly describes
Edmunds' machine.
4. Clutterbuck, M.,
Unpublished letter to the author, December
30, 1988.
5. Bowerman, L., 'Paul de Vivie ("Vélocio"),
News &
Views,
Veteran-Cycle Club, UK, April/May 1988, p.24.
6. De Vivie, P. (writing as 'Vélocio'),
Le Cycliste,
France, 1911.
(French original provided by Raymond Henry. English translation
commissioned by Tony Hadland.)
7. The CTC is the UK's Cyclists' Touring Club.
8. Davison, A.C., 'Actual Experiences with Some Freak Bicycles',
Cycling,
UK, June 21, 1939.
9. Clutterbuck, M.,
Unpublished letter to the author,
December 30,
1988. Medwin Clutterbuck was then 84 years old.
10. Whitt, R.R., 'Tyre and Road Contact',
Cycletouring,CTC, UK,
February/March 1977.
11. The word
approximately is used here because,
in addition to the
air pressure in the tyre, a very small measure of support is provided
by the stiffness of the tyre
sidewalls. The fact that the contact patch area for a given load and
given tyre pressure is
approximately constant regardless of tyre format comes as a surprise to
many experienced cyclists.
It is, however, a matter of simple physics and is confirmed by leading
cycle design engineers Mike
Burrows and Alex Moulton whom the author consulted when preparing this
text.
12. On some rough surfaces the wider tyre will roll slightly better.
This
is because it absorbs more of the road roughness, saving a greater
proportion of forward momentum
from being dissipated in repeatedly lifting the whole bike and rider
over the bumps.
13. Van der Plas, 'Rolling Resistance',
Bicycle, UK,
February 1984.
14. Hadland, T.,
The Moulton Bicycle, Pinkerton/Hadland,
UK, 1982
and Hadland, T.,
The Spaceframe Moultons, Pinkerton/Hadland,
UK, 1994.
15. The recommended pressure for 26" x 1 3/8" tyres (650 x 35mm) was
about
30 psi (2 atm). See Camm, F.J.,
Every Cyclist's Pocket Book, Newnes,
UK, 1950.
16. Henshaw, D. (writing as 'Professor Pivot'), 'Pivot Points'
,
The
Folder, The Folding Society, UK, August/September 1996. This
test was not conducted under
strict scientific conditions but was on real roads, rather than
linoleum or steel.The rider was
David Henshaw, who wore the same clothing on both machines. Saddle and
handlebar height were
approximately the same on both. However, the more stretched riding
position of the Moulton will
have given it a slight aerodynamic advantage. So too will the combined
weight of Moulton and rider,
which was about 3% higher. However, with both machines on Primo tyres
running at 70 psi (4.76 atm)
the Moulton, at 15.6 mph (25 kph) was almost 2 mph (3.3 kph)
faster. The testers considered
this to be significantly more than could be attributed to the slight
differences in weight and aerodynamics.
17. Kyle, Chester,
Unpublished letter to Alex Moulton,December 7,
1984. See also Moulton, Alex,
The Moulton Bicycle,Friday Evening Discourse transcript, The
Royal Institution, London, February 23, 1973.
18. De Vivie, P. (writing as 'Vélocio'),
Le Cycliste,
France, 1911.
(French original provided by Raymond Henry. English translation
commissioned by Tony Hadland.)
19. This is why Moulton pioneered 9 tooth sprockets, which he made
available on his machines in 1983. In 21st century, Shimano make the
Capreo groupset for performance small-wheelers, which includes
sprockets as small as 9 tooth.
The author
Tony Hadland has been riding adult small-wheeled bicycles of
various types since
1964. He was the first editor of
The Moultoneer and
has written books on the Moulton,
Sturmey-Archer and (with John Pinkerton) portable cycles. His articles
have appeared in a number of
British cycling magazines.
Acknowledgements
The author thanks Alex Moulton and Mike Burrows for reviewing
and commenting on the
draft of this paper. The views expressed are the author's and do not
necessarily represent those of
the reviewers.
© Copyright Tony
Hadland, May 1997, additional illustrations added and minor amendments made July 2009.
Table 1 - Advantages &
Disadvantages of Small Wheels