During the holidays and winter ski months, many San Francisco residents take to the road to hit the ski slopes. Veteran Tahoe travelers know that tire chains, or more accurately, tire cables or traction devices, are sometimes necessary when crossing the mountains in winter. In Northern California, chain requirements are most often enforced on Interstate 80 over Donner Pass, U.S. Highway 50 over Echo Summit, and Interstate 5 north of Redding.
Tire cables are sold by the pair and help car or truck tires get more traction in conditions where snow or ice have accumulated on the road. Although four-wheel drive and all-wheel drive vehicles with snow tires used to be exempt from chain control areas, currently there is no exemption and all vehicles are required to have chains in these weather conditions.
Cable chains usually feature tough carbon steel rollers that provide traction and long wear and are galvanized for rust prevention. The low-profile steel rollers allow increased tire-to-road contact, resulting in better stability and considerable reduction in noise and vibration.
Many hardware retailers and tire stores stock the most popular-sized cables for cars and passenger trucks. You will need your specific tire size as set forth by the ISO metric tire code. Virtually all tires have this information molded into the sidewalls, or you can use the factory spec for your tires if they have not been changed since you purchased your car. At most retailers, tire cables are not returnable even if they are unused, so it is important that you purchase the correct size.
HOW TO READ YOUR TIRE SIZE
The tire code consists of a leading letter and a string of numbers, for example, P285/40R15. The leading letter “P” correlates to a passenger car; “LT” signifies a light truck. (European car models may not have a letter.)
Following the letter (or lack of one), there is a three-digit number (285 in the example below), which is the NSW, or tire width in millimeters.
After the slash are two or three additional numbers. In the example below, 40 represents the aspect ratio 40 percent, or the percentage of the total width of the tire that the sidewall would cover if placed directly over it.
Following the last series of numbers, there may also be an additional letter indicating the construction of the tire carcass: “B,” (bias belt), “D” (diagonal) or “R” (radial, which is the standard on most vehicles).
Finally, the tire size will terminate with another two-digit number, 15 in the example, which is the wheel diameter the tires are designed to fit.
If you buy a pair of tire chains, you often must buy a pair of tensioners with them. These are essentially six small rubber bungee-type cords, bound by a circular rubber piece in the center and come two to a bag. This is an integral part of the several popular systems and may not be omitted.
If you are required to put chains on your tires, you must pull completely off the roadway. Independently employed chain installers are usually available if you don’t wish to install them yourself. These folks do not sell or rent chains, and they do not work for Caltrans. Be sure to have cash for their services, get a receipt, and note the installer’s badge number.
Be prepared — don’t get caught on a mountain pass without snow cables!