the weight of a racing bike is crucial. The
1 craft of building a racing machine is to make it as lean and precise as possible. The better the bike, the less there is of it. In the early days of cycling, building quality frames was a craft tradition which required skilled hand-brazing of lightweight alloy steel tubes. In the 1970s, manufacturers developed versatile alloy steels designed for machine-welding, and mass-produced, inexpensive lightweight frames became widely available. In the 1980s, the development of aluminium tubing for frames further reduced the weight and cost. In the 1990s and beyond, the choice material is now carbon-fibre, which is far stronger, stiffer, and lighter than either aluminium or steel.
DECORATIVE LUGS
The hand-finished metal lugs reinforcing
brazed joints were quite often an ornamental
design feature. In this classic lugged and brazed frame, the lugs are tapered to help distribute the stress evenly. Bike builders such as Alf Hetchins raised lugwork to a real art
form, hand-sculpting designs such as the Magnum Bonum, an elaborate combination
of fleur-de-lys, whorls and swallow-tails. STRENGTH: Lugs increase the joint strength by providing an extra surface area for the brazing metal.
•Thicker walled at ends
Thin walled at centre
DOUBLE-BUTTED TUBING
The evolution of double-butted tubing served to accelerate the craft tradition in frame building. It was tricky to
work with, but saved a pound in
weight over plain-gauge tubing.
Thick wall gives strength at joints
STEEL FRAME
The Reynolds 531 double-butted tubes in this traditional lugged and brazed
frame below are heat-treated steel alloyed
with manganese and other exotic elements.
Alloy steels are light yet extremely strong. With normal use, a steel frame will last a lifetime. Many cyclists prefer the feel of steel frames despite the additional weight. FINE TUNING: Steel frame tubes are
sold in sets, but builders mix different strengths to fine-tune a frame for one rider. SEAT STAYS: Every
detail is honed and % refined from many years of racing experience. The seat stays have bi-concave fluting.
RANGE: Steel frames
come in many different grades and strengths to suit specific
road racing, time-applications such as 1.01;
trialling or touring. 0
FORK CROWN: The fork crown is a cast, semi-sloping design.. LUGWORK:
Decorative details in the lugwork identify the bike maker.
SECTION: Oval-section fork blades have greater resistance to braking stress than do round blades.. HAND BRAZING
Brazed alloy steel frames are joined using
brass or silver; metals which melt at lower temperatures than steel and serve as a metallic solder, holding the tubes together.
TIG welded frames in steel, aluminium,
or titanium, are joined by heating the tubes until they melt and fuse together.
LS. OVERBUILT: Aluminium
frames fatigue but are designed with extra strength for safety reasons.
LARGE TUBES: Aluminium is light but soft. Large-diameter tubes are used to increase rigidity and strength.
• HANGER:
The derailleur gear hanger i replaceable.
TIG-WELDING
The Cannondale 3.0 aluminium TIC-
welded frame is one of the lightest and stiffest frames in any material (above).
Cannondale use the frame for their top-
MOST STRESS: The
down tube is biggest as it bears much the greatest forces.
line racing bike, as well as several budget ready-to-race models. Despite a wide gap in price, the bicycles differ in component quality only: the frames are the same.
GLUED FRAMES
With many aluminium frames the tubes are glued together, rather than welded together. Glues are simple to work with and are usually stronger than the materials they join.
MATERIAL PERFORMANCE Steel and aluminium are both well-developed materials which are now near to their performance limits. The future for lightweight frames belongs to carbon-fibre. A carbon-fibre frame can weigh at least 30 per cent less than an aluminium frame, giving an overwhelming advantage in a race.
2 lbs (0.9 kg) of steel produce less than half a complete frame.
2 lbs (0.9 kg)of aluminium give a frame a third as big again.
A carbon- fibre frame can weigh 2 lbs (0.9 kg) or less.
WISHBONE: The wishbone lug neatly separates the seat stays and provides a mounting point for the rear brake.
RESISTANCE:
Carbon-fibre tubes are often covered with a layer of amarid or fibre- glass to resist any abrasion.
MATERIAL: Many testers feel that carbon-fibre is the best material for bike frames. SHAPE: While used for conventional tubing, carbon-fibre can also be formed into any shape required.
FRAME CONSTRUCTION
LANDMARK FRAME The Giant Cadex
980, (below), is an
historic landmark: a carbon-fibre frame with alloy lugs, head tube, forks, and stainless steel drop outs, which has a comparatively cheap retail price.
CARBON-FIBRE
This is anistropic — strong and stiff along the axis of the fibres (right). These can be formed into any shape, with the strength placed where needed. Carbon-fibre offers the ultimate in light weight, feel and comfort. With the onset of
mass production, carbon-fibre frames
are becoming inexpensive — less bike and more performance than ever before.
A fter the frame, wheels are the most vital ...element in bike performance. Two factors in wheel design are critical: weight and shape. As the wheel spins, angular momentum creates a gyroscopic effect: the heavier the wheel and the faster it turns, the greater the momentum and the greater the amount of force you need to accelerate or brake it. To save weight, wheels are made with spokes. However, as the wheels spin, the spokes churn the air, generating aero- dynamic drag that increases proportionately faster than ground speed. The solution is to design wheels that smooth the flow of air: even though they may be heavier than spoked wheels, these require less energy at high speeds.
COMPOSITE The Specialized
Du Pont Composite
wheel (above) is made
from fibres of carbon, aramid, and glass, over a foam core, bonded to a 6061 T6 aluminium rim. An open-side area
of about 50 per cent reduces vulnerability to cross-winds and makes the wheel safe to use both front and rear. Each spoke acts as an aerofoil that generates forward lift in a cross-wind, like a sailboat tacking into the wind. Despite being almost 50 per cent heavier than a standard 1 kg (2 lb) spoked wheel, at speeds over 10.5 km/h (17 mph) the Du Pont has faster acceleration. In a 40-km (25-mile) time trial, they claim to save 2 to 3 minutes.
36-SPOKE WHEEL
Set in a "crow's foot" pattern (left) with one-third of the spokes radial and two-thirds crossed, this is an
unusual combination; most wheels are either
one or the other. Radial spokes traverse the shortest possible distance between hub
and rim, thereby reducing weight, but they are poor for transmitting torque from acceleration or
braking. The crossed spokes leave the hub at a tangent, thus creating a lever that allows the spoke to transmit torque with less stress than a radial spoke. Each, arguably, has its own particular merits. However, the size and hardness of the tyre, and the weight and strength of the rim, have a greater effect on wheel stiffness and on shock absorption. Radially spoked wheels have a slight aerodynamic advantage worth one second per kilometre (2/3mile) over three-cross pattern wheels. They are often fitted to ultra-lightweight time-trial bikes.
THE RACING BIKE