I just bought my first mountain bike worth owning, and my second MTB of all time, and I can tell you now that there are certain other things you should really know when you're buying a bike. Here's some of the big hints:
Know What Kind of Bike You Want. This depends on what kind of riding you're doing. There are different kinds of mountain bikes including:
These bikes are listed in order of lightest to heaviest.
- Cross Bikes (Cross-Country Bikes): Light mountain bikes which are designed to be run for long distances on mostly flat ground.
- All-Mountain Bikes: Designed to climb and descend hills, they usually have five to six inches of suspension travel and are designed to cross any terrain you'll normally experience on a day's ride without beating you up.
- Freeride bike: Meant for the rough terrain and big drop-offs, they usually have seven or eight inches of travel and a bit more weight than an all-mountain. They're usually not that pleasant to pedal uphill, but will go anywhere.
- Downhill: The heaviest, beefiest bikes, usually with the most pedal bob. They're painful to ride up hills, but the longest and most "plush" (stable and comfortable) of all mountain bikes. By far these are the heaviest bikes, but the added weight provides much-needed durability. Long suspension travel enables them to float over large obstacles and handle very large dropoffs.
Mountain bikes also come in hard tail and soft tail models, the latter having a floating rear suspension. Realistically, with today's technology all credible "all-mountain" and heavier bikes are "soft tail". This almost always takes the form of a triangular swing arm with the pivot near the cranks. This adds significant weight but both results in a more durable bicycle (less likely to bend something in the back) and in something you can ride over more serious obstacles. A good full suspension is the key to rapidly traversing rock gardens and other lumpy obstacles and both helps you go faster downhill and pedal over lumpy obstacles going uphill, provided you keep enough momentum. It also lets you "pump" the bike on downhills (pushing down on the front and back with all your weight in a surge) which makes the bike take on speed rapidly without pedaling; this lets you make less gear changes and yet go fast.
- Take an expert with you. Take the person that you know who is most knowledgeable about the kind of bicycle you want to buy. Having someone along to tell you what works and doesn't work on their bike and other bikes they've ridden is immensely valuable. And if you do this, you can also:
- Look at used bikes. There are usually tons of bicycles available for sale all the time, not least because mountain bikers are upgrading theirs. I paid $1000 for a $3500 all-mountain bike that needs under $300 in work. This is not a project for the uninitiated, which is why it's so important to take someone knowledgeable with you until you know what you're doing. The most important things to look for are frame damage and shock damage. An aluminum frame can go from "tiny crack" to "full separation" disturbingly quickly and repaired frames have to be heat treated before use. A carbon frame can practically explode under you, starting with just one little scratch. Steel frames are by far the most durable and repairable, but they've gone almost completely out of production because aluminum is cheaper, easier to work, and lighter than a quality steel. Try shifting the bike back and forth, shifting both ends at the same time and such to look for problems. Anyone with a clue will have adjusted the bike before you get your hands on it, so if it's still not working right it's probably broken. That might just mean a $55 dérailleur. It might not.
- Read Reviews. When I was looking at the listings of used bikes, I read literally dozens to hundreds of reviews of the bicycles and their components. The forks, shock (when present) and the rear dérailleur are the things to look at most closely, not least because they are generally the most expensive items. It is not and never has been enough to just buy a brand name, because Shimano makes complete garbage too, and they occasionally change the names. Pay careful attention to the year-models of the components; things change fast in mountain biking and the difference between for example a 2003 and a 2006 model is gigantic. With that said, you will learn that there are certain brands to be universally avoided (like Rock Shox) and that some models from some manufacturers are worlds away from other kit they build.
- The Bike Must Fit (or else you must quit): Bicycles have different angles; the head tube and seat tube in particular are at a variety of angles depending on the bicycle. A greater head tube angle increases caster which improves centering, but increases the wheelbase and makes the bike harder to turn. It also stretches the bike out for people with a long torso. A greater seat tube angle places the rider further over the back wheel, which improves traction and makes the bike turn easier, but which can cause wheelies on hill climbs. The rider's knees should be directly over the pedal while pedaling, and there should be three inches between your crotch ("inseam") and the top tube ("standover height") for mountain riding. Many people go down a size from road biking when it comes to mountain biking, to make the bike easier to handle. The "jump vigorously" advice is just going to get you too-small a bike, which is going to hurt you (physically) on the uphills. It might have worked for BMX, but if you get into trouble on a mountain bike you're going to get off the bike. Just let it go, and worry more about where you're going. You can survive if the bike goes off a cliff or gets wrapped around a tree, but it's harder to survive if you go off a cliff. You want to be ready to jump off the pedals, and "throw" the bike away (hopefully into something soft, like a big fluffy bush.)
- Tires are Key. Odds are, if you do choose to buy a new bike it will come with inadequate rubber. It ought to be fine if you're just starting out and don't plan on hitting any technical trails right away. I did, so I was very glad to have some very aggressive rubber up front. It doesn't matter if we're talking about a car, or a bicycle, or a motorcycle; the rubber is the interface to the trail and if it isn't good you're going to regret it. Again, like any other vehicle riding on rubber, if you don't have good tires the rest of your vehicle is useless. If you don't need big knobbies, you don't need a mountain bike either! Buy a hardtail cross bike with some combination tires and just know that you're not going to be able to ride offroad at speed.
- Brakes are Important too. Pretty much every mountain bike today is going to have disc brakes. If it doesn't, back away slowly. Disc brakes have more grab, are more consistent, and are better in wet conditions than the traditional "pinch" type V-Brakes. In particular you can make shallow stream and puddle crossings without even getting them wet; just make the crossing slowly. Even if you get an incredible deal, you shouldn't even consider buying a bike that doesn't at least have the mounting points to accommodate discs. They're important in the front AND the rear; making very tight turns can require sliding the back wheel. Hydraulically-operated brakes are a little more responsive, but require significantly more maintenance.
Anecdotally, I went out with a long-time MTB riding friend to pick up a bike; he was also on a mission to purchase a bicycle for his brother. We picked up bikes found on Craigslist; both 2006 models (which we purchased in April of 2009) for $1000. The bicycle I got was heavily upgraded and needs under $300 in work if I take it to a shop — less since I am a mechanic. My pal spent the same for a bike of the same year which was bone-stock but had very good components and had practically never been ridden, even being clean. Mine, on the other hand, came with free dirt. Both bikes have now been to Boggs Mountain and accounted for themselves well.
Back to the subject of selecting the bike for you: I wanted an All-Mountain bike with full suspension (again, there really isn't any other kind by today's standards) because I live in the hills and the terrain is rough, but I also see the bicycle as fitness equipment so I ride up hills, not just down them. That puts me on an all-mountain. If you're only riding broad foot paths which don't really qualify as dirt at all, and they're not particularly lumpy, then you might consider just getting a front-suspension bicycle. If you're asking yourself "do I need any suspension at all" then the question you should really be asking is do I really need a mountain bike? You could get away a lot cheaper and a lot lighter by getting a road bike. Downhill riding is probably best saved for experts and the bikes are by far the most expensive, so odds are a DH bike won't be your first MTB unless you buy it by accident (or it was just too cheap to pass up.)
Finally, don't worry if a bike is a couple pounds heavier than you dreamed. It's usually not too hard to shave two pounds off of you, or put on a pound of muscle to make up the difference... but cutting those couple of pounds off the bike could literally cost you hundreds of dollars. If you get a bike with good frame geometry, you can keep it for a long time and upgrade everything around it.