Winter Biking’s Invisible Hazard
by Tad Staley
One of winter cycling’s greatest hazards is black ice—a thin layer of ice that freezes without bubbles or other visible imperfections, making it nearly invisible or easily mistaken for water. In either case, when riding over black ice you will have far less traction than you might have expected.
Traction is key to bicycling, whether accelerating, turning or stopping. Black ice dramatically reduces your bike’s traction, and compromises your control.
One of the insidious characteristics of black ice is that it is often difficult or impossible to see. It is sometimes visible in the form of a dark patch on the road or, if you’re lucky, you may catch some glare off the surface that signals that the pavement is covered. But black ice is often disguised, so it’s best to be alert to conditions that can create it.
When does black ice form?
Any time the road surface drops below the freezing point, it can turn water into ice.
Just because the air temperature has risen above freezing, it doesn’t mean that you won’t encounter black ice on the road. Ice can form on the road even when the air temperature is above freezing, as long as the road surface remains below freezing. This can happen if the air warms quickly after an extended cold spell that leaves the surface of the roadway below 32°F, or on a clear night when the road surface radiates its heat to the night sky.
The loss of traction on ice is created when friction from your tires melts the very top layer of the ice, and the resulting water reduces friction. At lower temperatures, the top of the ice melts more slowly so the surface actually becomes less slippery as the temperature drops further below 32°F. This means that the most slippery conditions occur at temperatures right around freezing.
Where are you most likely to encounter black ice?
Black ice can occur any time a thin layer of water freezes on the road surface:
- Snow banks on the side of the road that melt during the day, often in direct sunlight, can create a thin layer of water by the roadside that can turn to ice as the temperature drops later in the afternoon. On a hill or curve, the black ice can extend across the entire roadway.
- When plowing has left a layer of snow between tire tracks on the road surface, runoff can turn to black ice with a drop in temperature. Sidewalks and bike paths may have snow on the uphill side, which melts across them and refreezes.
- Bridges and overpasses are prime territory for black ice, because air temperature beneath the bridge can drop lower than the ground temperature normally beneath the road. Highway departments are often reluctant to deposit salt on bridges to avoid the corrosive effects on the bridge’s metal, making bridges even more treacherous.
- Underpasses can also be prone to black ice, because they generally get no sunlight. If the underpass is at the base of a descent, water will naturally pool there.
- Water can also come in the form of condensation from a car’s tailpipe. Watch for black ice where cars have been idling, for example, at traffic lights or in driveways.
Because traction is harder to come by on ice (black or otherwise), you will need to modify your riding style.
First, be aware of where black ice can form, and under what conditions, so you can avoid potential trouble spots.
If you find yourself on ice, stay calm. If possible, coast in a straight line (no braking, turning, or accelerating) until you’ve reached dry pavement.
If you must turn on ice, take it slowly so you can stay as upright as possible. Leaning into a turn requires a lot of lateral traction to keep your tires connected to the road. Without that traction on ice, your tires will quickly lose their grip and you may find yourself having a direct encounter with the ice. If you must brake, use your rear brakes only. This will keep your front tire rolling and in the best possible contact with the road surface, and will help maximize your steering traction.
If you use a single studded tire, mount it on the front wheel because that will ensure better traction where you need it most—for steering. One strategy is to have a spare tire with studs that you can mount if you anticipate ice on a ride.
The possible presence of black ice need not stop your winter bike rides. Proper attention to the conditions that create black ice, avoiding turning or braking (when you can), and using the turning/braking techniques discussed above (when you must), will help ensure that your bike doesn’t slide out from under you.