Why is the wider tyre faster? It's due to the shorter contact
patch. A wider tyre has a short and wide contact patch compared to
the long and skinny contact patch of a narrow tyre. This results in
the wider tyre deflecting less so hysteresis loss is lower, and
being able to better absorb imperfections that a narrow tyre would
instead transfer into energy moving the bike and rider upwards.
It's not as simple as lobbing on a set of wide tyres though.
Tyre pressure is key to unlocking this potential. Simply put, a
hard tyre has to travel up and over every bump in the road, while a
low-pressure tyre can deform over the bump. That means less energy
is lost moving the bike up and over the bump.
So, the wider the tyre the lower you want to set the pressure. A
25mm tyre at about 90psi will actually provide the same rolling
resistance as a 23mm tyres at 120psi. Go to a wider 28mm tyre and
drop the pressure to 80psi, and again you're looking at the same
level of rolling resistance.
As well as improved rolling resistance, a wide tyre at low
pressure also equals more ride comfort. The tyre is better able to
soak up the vibrations from a poorly surfaced road and that
provides a smoother ride, but also means there is no speed give
away to suspension losses,
As well as the rolling resistance benefits of wide tyres, Tour
magazine also found the wide tyres provided the best comfort.
"The most comfortable ride was achieved with the 28mm tyres at a
pressure of 5.5 bar: the tyre still having plenty of reserve
suspension travel due to its copious volume, while at the same time
being barely at risk of puncture," it says.
After evaluating all data and how the tyres felt, it is clear
that wide tyres are more just than a passing fashion