By Coach Steve
I rode a citizens' bike race last weekend on my tri-bike with 650c
wheels. Five minutes before the start there was a downpour - big
fun! If I had known the race would be on wet roads I certainly would
have brought my road bike with 700c wheels, but I was there with
two options: Race, or don't race. The course is hilly with plenty
of turns, and the last turn is 400 meters from the finish and with
a manhole cover and painted lines right on the apex.
With odds against me I managed to keep the rubber side down; I
made it through the corners upright on my skinny tubulars at 130psi.
In that last corner there were four of us left together in front;
the lead rider slid-out and hit the deck. The rider on his wheel
had to go wide and went up on the sidewalk to avoid him. The rider
in third position went on the inside, as did I. At the line it was
the third rider through the corner that won. Positioning was everything
that day. I went through the last turn ultra conservatively, a bike
length behind which I never made up on the slick road where it was
too slippery to stand up to sprint with full effort.
When the road is wet in a multisport event taking a few precautions
will help you get through with no mishaps. First you must respect
that on a slick road surface your tires won't get as much grip.
Even a little moisture reduces potential friction to perhaps 50%
of a dry surface. Fifty percent less friction limits you to maybe
two-thirds the 'normal' speed on a corner before tire grip is lost.
To add another variable, wet road surfaces offer a wide range of
friction depending on their abrasiveness, residual oil left by cars,
painted lines, and metal surfaces like manhole covers and grates.
When the wet pavement is made of tiny stones with surfaces polished
by many car tires it can be as slippery as ice! If the road surface
is abrasive like sandpaper there will be decent grip even in the
rain. If it hasn't rained in a while there may be a coating of oil
that adds to its slickness when it rains. Painted lines are to be
avoided as they're slicker then most road surfaces. They're also
raised above pavement - a bad thing for grip. Metal surfaces can
be the worst of all and should be avoided as they're always slicker
than the pavement.
There are several precautions you can take to deal with these rainy
race day risks. First, fresh tires will help. Tires with good tread
(ridden at least once on dry roads before race day) will give better
grip in most conditions; the one exception is when the wet surface
is abrasive like sandpaper (which is rare). In that case a slick
tire without tread will give the best grip.
Less air pressure will let your tires flatten out more giving a
larger patch in contact with the road. From my bike racing days
I can remember the shock of a Belgian mechanic putting only 75psi
in my tires for circuit race partly on wet cobblestones with plenty
of corners. It worked, I stayed upright that day. How little pressure
you can afford to use is dependant upon how many corners you'll
contend with, your weight, and how small your tires are. Less pressure
gives better grip but more rolling resistance so some speed potential
is lost. Less pressure will also allow the tires to bottom-out more
easily making pinch flats a possibility. Choosing optimal pressure
for wet roads is always a compromise. With a 700c road tire of 21mm
width or more, I've ridden many of races with less than 100psi.
On narrow 650c tires of 21mm or less 110psi is as low as I'd go.
In the rain your bike handling skills are as important as your
tires. The same rules of good cornering technique apply on wet roads
as dry - the only difference is that technique flaws are amplified
on wet surfaces. With a corner too sharp or fast to pedal through,
shifting some of your weight to the pedal at the outside of the
corner (and in the down position) is critical. This lowers your
center of gravity, which is always a good thing for control and
grip wet or dry.
Perhaps the most important bike-handling consideration of all is
your line through the corner. This has to do with the shape of the
arc you take as you make the turn. A bigger arc will reduce your
chances of slipping as you take the straightest line possible through
the turn. With no road restrictions, begin the turn on the far outside,
cut to the inside curb (apex), then drift to the outside as you
finish the turn. Of course in most races we can't cross the lane
lines and may have to contend with other riders beside us, so that
determines to how you handle each turn. Still, use the entire road
you have access to so you can carry your speed.
On wet roads if you find that you'll need to take a sharper angle
through the corner partway through, you're in trouble. Anytime you
decrease the radius of a turn (make a sharper turn), you'll increase
the amount of lateral acceleration (the force pushing you to the
outside of the turn). When you make this sharper turn part way though
this is when your tire potentially breaks loose and you slide-out.
If you're halfway through a turn and you find you can go wider (make
a bigger arc) - no worries!