By Eric Hagerman

If you want a bike that you can actually ride in the
dirt--even if that dirt comes in the form of an unpaved road--you'll want to spend at least $400 to $450. For about $800 you can get a front-suspension mountain bike that even the most avid riders will respect. As you go into the four-figure range, you'll be paying for dual suspension, lighter weight, greater durability, increased cachet, or some combination thereof.

Suspension
Any good mountain bike will have a suspension fork in the front for shock absorption. So your first real decision is whether you want a dual-suspension bike or a so-called hardtail. The latter, which has only front suspension and thus is typically lighter in weight, has traditionally been the choice for people who want to ride up hills as well as bomb down them. But that's starting to change: Bikes with shocks in the rear as well as the front are getting lighter, making them more suited to climbing. Perhaps the ideal balance of weight versus cushioning is a hardtail supplemented by a suspension seatpost, which gives you a little extra shock absorption for very little weight.

Frame
The frame is what gives a bike its ride quality, so get the best one your budget will allow. With aluminum and steel (often "cromoly") frames, this means making sure the tubes are "butted"--thin at the middle to save weight and thick at the joints for the requisite strength. Don't let anyone tell you that an aluminum frame is by definition lighter and stronger than steel--both can offer light, resilient rides, though all things being equal, aluminum is stiffer and cromoly more lively. Titanium, the metal of choice among connoisseurs, is lighter and stiffer than both and will never rust, but will put a heftier dent in your pocketbook. Finally, there's carbon fiber, which really deserves a category unto itself. It can be even lighter than titanium, stiffer than aluminum, and more comfortable than steel. But it's also superexpensive and essentially a glorified form of plastic, making it somewhat less durable than the other alternatives.

Wheels
Consider this: A rear wheel outfitted with a cassette (for shifting gears), inner tube, and tire weighs as much as an entire bike frame. So to keep it as svelte as possible, make sure your prospective purchase has aluminum rims, aluminum spoke nipples, and double-butted spokes. Also, ask if the hubs are of the same caliber as the rest of the parts--some manufacturers skimp on the hubs becuase it's hard to tell that they're doing so.

Shifters
Shimano or Grip Shift? Most riders have a strong opinion, so be wary of pushy salesfolk, since it truly is a matter of personal preference. (Full disclosure: I use Grip Shift for my front derailleur, and Shimano XT Rapidfire for the rear.) Grip Shift works like a motorcycle throttle: You twist through a series of clicks by cocking your wrist. It's lighter than Shimano but unquestionably less durable because it's made of plastic. Shimano Rapidfire shifters have two aluminum triggers that you operate with your index finger and thumb. They're comfortable, intuitive, and require very little effort. Both systems work equally well when tuned up, but I think the Shimano system requires less ride-to-ride fiddling.

The Extras
Make sure the shop will exchange the bike's seat if it's not comfortable and the stem if it doesn't give you the right fit. They should do this for free before you leave the shop. Also, make 'em throw in a couple of water-bottle cages--they're like the floormats for a new car.

Eric Hagerman is senior editor of Outside magazine.