MOUNTAIN bikes - those fat-tired cousins of the darlings of the '70s, the 10-speeds - are crossing creeks, reducing mountains to molehills, prevailing over urban potholes, and taking the entire bicycle industry along for the ride. Last year, over 50 percent of all bicycle sales in the US were of mountain bikes. And a 1988 buyers' guide lists more than twice as many models as were listed last year. Interest is also on the rise overseas, particularly in France, where 60,000 mountain bikes are in use.
Exactly what is a mountain bike? Originally designed for going up and down mountains, specifically Mt. Tamalpais in California's Marin County, the bikes are now designed to handle a wide variety of terrain, hence one of their other names - ATBs (all-terrain bicycles).
Costing anywhere from $99 to $4,100, these bikes have 10 to 18 speeds, strong but responsive frames, and high-quality components, setting them apart from the 60-pound monsters of the 1930s and decades following.
With names such as Super Grizzly, Rockhopper, Prairie Breaker, and Annapurna, these bikes are not for setting in the garage behind the lawn mower. Even the uninitiated can recognize mountain bikes by their thick, nobby tires, upright handlebars, and motorcycle-type brake levers.
If those unusual features don't give it away, the mud all over the frame and grass clogging the derailleurs probably will.
Environmentalists, however, such as Sally Reid, would prefer that the mud and grass be left where they are. Ms. Reid, vice-president of the Sierra Club, says, ``Steep trails and trails with certain soil characteristics are subject to tremendous erosion from the use of mountain bicycles. This has been proved over and over again. We have trail maintenance workers [who] put in weeks of work on a trail and have the water bars and the other safeguards for erosion wiped out by mountain bikes in a weekend of heavy use.''
According to Reid, large logs or rocks, used as water bars, have been intentionally removed by cyclists who see them as nothing more than ``speed bumps.''
The club is pressing the United States Forest Service to determine which areas are ``appropriate'' for mountain bike use and then enforce the rules laid down.
Christopher Ross, director of the National Off-Road Bicycle Association, tends to agree that there are places too fragile for mountain bikes. ``We don't want to ride everywhere,'' Mr. Ross explains. ``We realize that there are areas that shouldn't be ridden on, and we're not trying to push to get into those areas.''
Mountain bikers, many of whom consider their environmental credentials to be perfectly intact, object to the image sometimes painted of them. ``We're not a bunch of crazy guys out to wreak havoc on the environment,'' says Ross. ``We're willing to work on trails, attend meetings, and represent ourselves.''
In perhaps the only study on the compatibility of mountain bikers and other trail users, an environmental studies professor at the University of California at Santa Barbara, Calif., had 66 of his students interview 1,400 trail users to determine whether mountain bikes were a problem.
They found that 67 percent of hikers and equestrians didn't consider mountain bikes to be a safety hazard. Eighty-nine percent described the cyclists they had encountered as ``polite.''
In addition, only 11 percent of the respondents thought of cyclists as a major source of dissatisfaction, whereas 25 percent cited litter as such a source. The survey revealed that there were 15 hazardous encounters between hikers and bikers, with none involving horses.
Ironically, about 80 percent of mountain bikes are purchased for use in urban areas, according to Ross. This is mostly attributable to the tires, which are excellent for negotiating railroad tracks, potholes, curbs, broken glass, and other road debris. They can make excellent commuting bikes, particularly for shorter routes with the above-mentioned hazards. Nevertheless, the city bike, similar to a mountain bike but designed more for urban and utility use, might be a better choice.
Doug Mink, an astronomer at Harvard University, for example, has used his mountain bike for his 10-mile commute during periods of road reconstruction, but normally opts for his road bike, which shaves about 10 minutes off his commuting time.
Why the current boom in mountain bike sales? Most of the reasons are to be found in the marketplace. For the first time, manufacturers have been offering bikes, both on- and off-road, with high-quality frames at a price the public can afford. Usually made of chromium-molybdenum (``chrome-moly,'' or ``chro-mo''), the frames, together with alloy rims, provide the necessary strength without adding a lot of weight. The result is a surprisingly light bike that is responsive to the rider's handling.
If you go
Two helpful books on mountain biking are: ``Eugene A. Sloane's Complete Book of All-Terrain Bicycles,'' by Eugene A. Sloane. New York: Simon & Schuster, 1985, $12.95, paperbound, and ``The Mountain Bike Book,'' by Rob Van der Plas, Mill Valley, Calif., Bicycle Books Inc., 1988, $8.95, paperbound.
A useful buyer's guide is 1988 Mountain Biking Magazine's Buyer's Guide. Order from Challenge Publications Inc., 7950 Deering Ave., Canoga Park, CA 91304. $5.50 postage paid.
A list of 63 clubs in the US, Canada, and England appears in the May issue of Mountain Biking magazine: 10968 Via Frontera, San Diego, CA 92127.