Cycling provides a unique way to see Yellowstone  up close. Unfortunately, park roads have narrow shoulders and traffic is heavy, making for dangerous conditions. These problems are exacerbated early in the year by high snowbanks, so bikes are not allowed on certain roads.
Call 307/344-7381 for current road conditions.
The Park Service produces a helpful Bicycling in Yellowstone National Park  brochure with details on bicycle routes and safety, plus a map showing road conditions; get it from visitor centers or download a copy at www.nps.gov/yell .
If you’re planning a cycling trip through Yellowstone, be sure to wear a helmet and high-visibility clothing. A bike mirror also helps.
If you want to avoid some of the hassles and don’t mind spring conditions, visit the park between late March and the third Friday in April, when motorized vehicles are usually prohibited from entering the park (except for park administrative vehicles). During this period, cyclists are allowed to ride only on the stretch between the West Entrance  and Mammoth Hot Springs ; other roads are closed to cycling because they’re being plowed. Fall is also a good time to ride because traffic is much lighter than in summer.
The best times to ride in summer are in the morning before traffic thickens or late in the afternoon before the light begins to fade and you become less visible to motorists. Special hiker/biker campsites are available at most park campgrounds for just $5.
The best main park roads to ride (less traffic or better visibility and shoulders) are the following sections: Mammoth to Tower, Tower to Cooke City, Canyon to Lake, and Lake to Grant Village . Bikes are not allowed on backcountry trails or boardwalks inside Yellowstone. Several relatively short but fun mountain-bike rides are available around the park, including:
Of these routes, cars are allowed only on the Old Gardiner Road and Blacktail Plateau Drive, but traffic is light on these two.
Rent bikes inside Yellowstone at Old Faithful Snow Lodge (307/545-4825, $8 per hour or $35 for 24 hours) and in the surrounding towns of West Yellowstone, Jackson , and Cody. Backroads (800/462-2848, www.backroads.com ) has six-day multi-sport trips into Yellowstone  and Grand Teton  that include biking, hiking, rafting, and kayaking. These are offered as either camping trips ($2,000-2,300 per person including meals) or trips on which you stay at local inns ($2,900-3,300 per person including meals). Trips take place weekly June-August.
Teton Mountain Bike Tours (307/733-0712 or 800/733-0788, www.wybike.com ) leads all-day tours of the Old Faithful area for $150. The park website (www.nps.gov/yell ) has a list of other permitted bicycle-tour operators.