Black Ice, that thin layer of ice covering roads, perhaps only in shadowed area, can be
one of the most insidious winter risks to deal with. You can be riding along on bare
pavement one minute and sliding down the road the next instant.
Black Ice is called Black, because it takes on the color of the underlying pavement.
It is very thin, and often gives the impression of having some surface
irregularity, and therefore appears to supply some traction. These looks can be
deceiving, because as soon as you apply brakes (or make significant turning movements) you
start to slide.
Turns
Turns on Black Ice are best accomplished by keeping the bike as upright as possible.
This may involve offsetting your upper body to the side (toward the direction you
want to turn) while at the same time keeping the bike upright.
The principal reason to keep the bike upright is NOT to keep more of your tire tread
(or studs) in contact with the road, but more simply, that a leaning bike necessarily puts
lateral forces on the tire at the contact patch. The contact patch (where the rubber
meets the ice) is that preciously small area providing all the traction. Black Ice
frequently does not supply enough traction to counteract this lateral force, the tire
slips out from under you, and down you go.
Turns with the bike mostly vertical also imply slow turns. That, more than
anything is the name of the game.
Braking
Braking on black ice will cause a slight melting of the surface layer of the ice,
producing a very thin layer of water. Water on ice is a lot more slippery than just
ice. (See: How Slippery Is It).
Braking must be done with great care, and principally with the back brake. The
front brake of a bicycle supplies way more braking power than the back brake. The
more it works, the more weight is transferred to the front wheel, and the more the braking
force applied to the contact patch.
The problem in winter is that you will quickly break traction with the front wheel.
Once you do, your chances of remaining upright are minimal. Reserve the
limited traction of the front wheel solely for steering. Brake with the back wheel.
Transfer weight rearward, (stick your butt out behind the seat), to keep as much
weight over the braking tire.
As long as you can steer you have a good chance of remaining upright. This is why
if you only have one studded tire it belongs on the front. It is also why you want
to avoid braking with the front wheel on black ice. Even with a locked up rear
brake, and the rear wheel skidding, as long as you stay off the front brake, you can steer
all the way down icy hills too slippery to walk.
Ride the Grit or Fresh Snow
At the side of the road, there is usually an area covered with sand and other debris
swept there by car tires. Sometimes there is just fresh untracked snow there.
In Black Ice conditions this grit becomes "glued down" by the same ice that
is covering the road. Its like riding on sandpaper. There is far more traction
in the girt than on the Black Ice itself.
Similarly, when there is some snow around, the snow will often provide more traction
than the ice. Even light snow directly on top of Black Ice may provide better
traction than just the Black Ice. This is because snow is angular, and the angular
particles catch and bind on on another, your tires, and the ice below.
Once melting starts, snow can add to the slipperiness of the underlying ice, so
occasional tests with the rear brake give you a good idea of the traction below.
Studs
Studded tires are great on Black Ice. In fact, this, and hardpack are the best
areas for stud use, they are largely wasted in deep snow.
Studs will provide amazing traction in black ice, and the more studs the better.
In fact, you can get down right cocky with the amount of traction you get, and that's when
you find out that all good things have limitations. You still need to be careful
with turns and braking. But you can at least consider using just a little front
brake.
Techniques
As mentioned above, look for the traction, stay off the front brake, and wear your
studs.
Test Black Ice conditions when going straight, by slowly applying the rear brake till
you get a feel for how slippery it is. As soon as the back wheel skids, let up on
the brake. Its best to do this early in the ride, so you will have an idea of how
long it will take you to stop. Watch hills. Especially watch sharp corners,
slow down, drag the foot that is on the inside of the turn. DO NOT BRAKE in the
TURN. Your back wheel will spin out if you do.
Finally, watch it when you come to a stop. Bike tires, with or without studs,
always seem to have more traction than shoes. Its embarrassing to blithely handle 10
miles of black ice and fall on your butt at the front door.
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