Tubular tyre construction
Rolling resistance measurements
for two of Continental's high-end tyres show the Competition tubular
has lower rolling resistance than the Grand Prix 300 clincher
Tyre rolling resistance decreases
as tyres become fatter, according to Continental's measurements.
Figures from an SRM power
meter show that at 50km/h a narrow tyre requires less power than
a fatter one. Rolling resistance may be lower for the fat tyre,
but the narrow rubber's superior aerodynamics more than makes up
Continental used Paris-Roubaix to introduce a new 'Competition' model
tubular: a 25mm tyre with a double layer of Vectran, a hi-tech material
that is said to offer significantly better puncture resistance than Kevlar
and other materials.
The thin Vectran layer resides between the tyre casing and the outer
tread. The German company recognised Vectran's strengths, but producing
it so it could be used in lightweight bicycle tyres required over two
years R&D, resulting in a secret and patented process.
The first tyres to use this layer were used by the professionals in the
2005 Paris-Roubaix, and the day before by a group of journalists who all
survived their cobbles experience (see
Like many bicycle components (or anything performance-oriented, for that
matter) the production of a tyre is a compromise of weight over strength.
Yes, tyre companies could make a tyre that would be virtually impervious
to punctures, but it would be heavy and slow.
But what do we mean by "slow"? How can a tyre be "slow" - isn't it the
rider? Well yes and yes; a tyre casing that would be puncture-proof would
either be solid or so thick as to have the responsiveness of a gumboot.
A tyre still changes its shape when it rolls down the road - regardless
of the inflation - and the energy that is required to make the tyre change
its shape is determined by its thickness. Therefore, a thick tyre casing
requires more energy than a light casing. More energy absorbed = slower
The challenge, therefore, is to make a tyre capable of handling high
pressure, but still be light and puncture resistant. There are
other requirements like longevity and grip, but a racing bicycle tyre's
intrinsic shape and weight mean those qualities are almost always sacrificed
in the name of performance. We're not talking Moto GP here. Tyres don't
go off or get shredded by 180hp engines. (Of course if you can
have grip without compromising weight and speed, then that's a bonus,
and tyre development in the last 20 years has seen substantial improvements
in rubber compounds.)
After wind resistance, a tyre's rolling resistance is the cyclist's next
best enemy, and Continental presented some research results that explode
some myths about tyres and rolling resistance.
Conti's figures further demonstrate how tyre design and construction
- even at the high-end - is still a compromise of conflicting objectives.
Continental's numbers support the widespread belief that tubular tyres
are faster than clinchers, but most surprising was research that showed
how wider tyres have less rolling resistance. For example, a 25mm tubular
offers less rolling resistance than 22mm and 19mm tyres (see graph).
But when a bicycle and rider build up velocity, resistance is not as
important as aerodynamics, and wind resistance becomes the all-important
factor. For this reason, Continental found that - conversely - a thinner
tyre requires less energy than a fatter tyre to travel at 50kmh, principally
due to aerodynamics (see graph).
For this reason, Continental believes the fastest combination of tyres
is to have a 19mm front and 22m (reflected in its Grand Prix Attack/Force
combination that use a 22mm front/23mm rear combination - see
review). But this combination was proven on the velodrome in Buttgen,
Germany. In the real world, there are factors such as comfort, grip and
not the least, puncture resistance.
What is Vectran?
Which brings us to improving a tyre's puncture resistance without impacting
its performance. Continental clearly believes it has the edge with the
use of Vectran, and while it is only available in the 25mm "Competition"
tubular, executives hinted at its likely introduction into other tyres
in the range.
Vectran is - for the chemists out there - a "wholly aromatic, liquid
crystal polymer, derived from polyester" that's five times stronger than
steel. As a puncture-prevention layer in a tyre, Vectran is said to have
the edge over materials like Kevlar because of its near-zero moisture
absorption and fatigue performance. It is also said to have better resistance
to folding and buckling - essential if it is going to be used in high-pressure
Conti believes the material is also superior as a 'breaker' material
because it is more cut resistant (see table) but still light and thin
so it can be used in bicycle tyres without adversely affecting the tyre's
weight, rolling resistance and overall performance. In short, it is something
of a breakthrough that is likely to be featured in more products, but
only for the road. Special track and time trial models are unlikely to
feature the new material.
Time will tell if it is more than a marketing gimmick, but given Continental's
background in bicycle tyres, it is something the company believes will
give it the edge for years to come.
See also: All
stitched up - Inside Conti's tyre factory