Well, a little bit to go with at first. The thing is, there are three different "genres " of riding, if you may. Racing, Flatland, and Abusive. Personally, that's how I see it, and "Abusive" encompasses street, skatepark, and trails. This article will focus only on abusive riding, since that's where most people will be using their bikes.
Another type of riding style you might be interested in is commuter. Yes, I have seen people buy 20" bikes for commuter bikes for their compact size and the fact that they are fit for adults, being that small (more on that later). This article won't focus too much on that. That is mostly comfort with a little bit of quality, so that will be touched upon a little bit but is not the main focus.
Well, let's get right to it. The first thing you need to know is what to look for in the bike. But when you break it down, you can't look for "thing A" on "Bike B" and be satisfied. A bike is a multitude of parts organized into a quite complex machine. So we'll break it down.
The first, and probably most prominent part in a bike is the frame:
What you should be looking for in the frame is important. After all, the frame is holding everything. If the frame feels like crap, the entire build will feel like crap because of it. So, to keep it basic you want to look for a Chromoly (CrMo) frame. The other version you might see is Hi-Tensile strength Steel. Avoid that. You want a frame that is completely CrMo. You might run into some parts that are "Hydroformed" or "Sanko Chromoly", they're pretty names for Chromoly. Keep it CrMo, and you'll be good.
You might realize that a new aftermarket frame can cost as much as a bike that has a completely CrMo frame, and wonder how that can work. Well, aftermarket (AM) frames are higher quality than the generic frames used for stock bikes. However, you shouldn't worry. Stock frames are basically just generic versions of those AM frames, and can take the abuse.
Now the next bit. You have the frame material, how are you going to assemble it is an issue. The general shape of a frame is simple, but the specifics aren't all that simple. This is where the commuter biker has to pay attention.
The "Geometry" of a frame are the specifics, such as the angle of the headtube, the angle of the seattube, the length of the chainstays, etc. This geometry combines together to make the feel you want. The most important dimensions to look at when buying a complete bike, though, is the top tube length. This is what will make a bike sized differently. This is what makes a bike fit a 5'11" rider, having the same size wheels as a bike that is fit for a 5'1" rider (me and a local rider in my town, for example).
When people see you riding a BMX bike, they'll call it a kid's bike. In reality, it is not. My wheels are the same size as a 10 year old's bike, but if he were to ride mine, he would be hunched over the bars and would feel very uncomfortable. My bike is a small bike, but sized for me (5'11"). The thing that does this is the top tube length.
The top tube is what spaces the seat tube and head tube, and to close out the triangle, the cranks. With the geometry being fiddled around here, you can be comfortable on your bike. The problem with completes is that they don't always give all that much freedom when it comes to specific geometry, but you can look for your specific sized top-tube length. Having a longer top-tube will give you more room on the bike. The measurement you should have is mostly dependent on your height, but also a little bit of personal preference. I personally prefer a longer top tube than I am fitted for, but only by a quarter inch or so. In a complete bike, choosing the toptube length is all that you really need. beyond that, the frames are all very, very similar.
Danscomp mail-order website has a decent chart about the size of a bike compared to your size:
There are a lot more sizes than just the top-tube length on there, but we'll get to those later.
The forks and bars are actually fairly important. If you get cheap bars, they can snap and trust me, ragged metal can do some damage when you fall on it. Also cheap forks can bend quite easily. When you're looking at a complete bike, you want to look for CrMo bars and forks*. Hi-Ten just simple will not do for the bars, and I would highly suggest against it on the forks.
*When it comes to the forks, there may be two pieces listed. Hi-Ten forks with a CrMo steerer tube. The steerer tube is the piece that goes up through the headtube of the frame. You want BOTH to be CrMo. You need to watch for this, because some companies will claim a CrMo Steerer tube, but not mention for the forks (or vice versa).
For now, let's ignore axle size.
As far as bars go, you'll want to look again to the chart from Danscomp for the sizing. The height and width depend on your height and your shoulder width. Shoulder width bars are what I think are the most comfortable. I'm 5'11 and run 8" rise bars. I love those dimensions, but bars are mostly rider preference. Just don't overdo it on getting bigger bars.
A headset is the assembly of bearings and fittings that keep the forks turning in the frame. Most bikes have what is called an integrated headset. In these, the bearings rest in the frame itself, and not bearing cups that are pressed into the frame. You want your headset to be sealed. As a matter of fact, I would say that a headset is a part where sealed bearings are a necessity. From one bike to the next, headsets are pretty much the same. Just look for integrated and you'll be all set.
Cranks, Bottom Bracket
Cranks - The arms that your pedals go into
Bottom bracket - The "headset" for the cranks. It's the bearings, fittings, washers, etc that go into the frame so that the cranks can spin.
Once again we get back to our old friend CrMo. Your cranks should be tubular CrMo*. There are two types, 48 spline and pinch-bolt. A 48 spline crank has little tiny ridges that correspond to the spindle, and the arms are literally pressed straight on. They are held on by press-fitting, and are held at their angles by the splines. A Pinch bolt crank uses a similar principle in keeping the angle, but instead of depending on press-fit, the cranks are held on using a bolt that pinches the spindle boss (the part of the crank arm that the spindle goes into) to the spindle. One is not better than the other, but 48-spline cranks look cleaner and are usually a little bit more expensive.
*There is a second 'family' of crank, if you may. They have solid aluminum crank arms and are held on with pinch bolts. I personally use these cranks on my bike, they're my preferred setup. I don't know if any completes use them though. So, if you see aluminum crank arms, don't think that it's a typo. They exist.
A side note about cranks. There are 1pc, 2pc, and 3pc cranks. 1 pc are just...horrendous. I actually will not talk about them other than this mention to tell you to stay away. 3pc cranks have the spindle going through the frame, and the arms attach on each side. In a 2-pc style crank, the arm is permanently attached on one side (the side with the sprocket).
Now the bottom bracket. This is simple. You want sealed. No, actually, you NEED sealed. If you are going to use your bike more than just to go to the corner store every weekend, a sealed bottom bracket (BB) is a necessity. They are much easier to maintain, are more durable, and feel much smoother. Plus, unsealed BB's only exist for 1-pc cranks* and are cheap and annoying to deal with.
There are two types of sealed BBs that you will run into. Mid and Spanish. The only difference is the diameter in the frame. Spanish is a little smaller. There are two other types that you may run into, Euro and American. Avoid Euro, the bearings are far too small (you have a very small chance of actually running into this for a BMX bike outside of racing). American isn't a problem as long as it's sealed, but the only difference between mid and american is simple. Mid bearings press directly into the frame. American bearings rest in cups, the cups are pressed into the frame.
*There IS an unsealed mid BB in existence. I haven't seen it much. I saw it a couple years ago, and that was the end of it (as far as I know). However, if you come across this, avoid it. Keep the bearings sealed.
A small mention only. Pedals are simple. I won't get into plastic vs. metal in this article, I may in the future in a different article on its own. At this point, choose what you want. Most completes come with plastics nowadays. Another thing about pedals is sealed vs. unsealed. Pedals are probably the ONLY part of your bike that unsealed bearings are just fine. I have unsealed pedals, have had the same ones for 4 years and they're running just fine still. You may want to clean them from time to time though.
Wheels and Tires
Ohhhh boy. You might think this is a small part, but honestly I think my wheels and tires combined are the most expensive 'piece' on my bike. So where do I even start with this.
Let's work from the inside out, starting on the front wheel. Now, when looking at specs, the forks will have an axle dimension as well. I never mentioned this before because for the forks, it's not important, and I didn't want to get into wheels on a tangent. So here we are. The axle sizes you will run into a 14mm and 3/8". 3/8 axles are approximately 10mm (a little less, but just giving context for the sizes). In the front, you'll run into what is called a "female" axle (and sometimes in the rear, but more on that later). The difference between a male and female axle is how they are held onto the forks (and frame for the rear). A male axle has a long threaded rod that rests in the dropouts, and the hardware on the rod will thread in together to grab onto the dropout. In a female axle setup, though, the hub has a rod that goes through it and stops when it meets the forks. There are then bolts that thread into the hub, and hold onto the forks. It's confusing to explain in words, if you have a problem differentiating the two, google "BMX Female axle" and "BMX Male axle" and look at the images, it shouldn't be too hard to figure out. I will be making an x-ray of both eventually, so I will link those when I finish them.
If you have a 3/8" axle, you'll want female. 3/8" male axles aren't strong enough to deal with the beatings you can give it. Especially if you run pegs.
Also you'll want a sealed hub. Unsealed hubs just get mucked up way too fast to be worth saving some money on.
Moving out you run into the spokes. On a complete bike, the spokes are all just about the same, the difference being in the amount of spokes you have. The popular sizes are 36 and 48. I haven't seen many 48H (the "H" stands for "Holes", meaning the hole the spoke runs to) wheels on completes lately. In the front, 36H is fine.
Moving out further you get to the rim. You want a double walled rim. Single walled rims are acceptable on the front, but very much so not preferred. Ignoring the strength factor, single walled rims are usually produced to be a rim to say it's a rim. They're very cheap, and probably won't hold up. There are cheap double wall rims, but not as many.
Sorry if I confused you, the "walls" are basically layers of the rim on the outside. The additional wall adds a tremendous amount of strength.
Moving out further we get to the tires, which I will deal with combined after talking about the rear wheel.
Moving back to the rear wheel, let's start at the hub. Now this may just be the most intricate and complicated simple part on your bike. I hope that doesn't make sense to you either.
So the rear hub can be either a freewheel or a cassette. Avoid freewheels. Much like single walled rims, a freewheel hub is cheap, so the quality probably is lacking. Along with that, the freewheel itself is pretty cheap most of the time, so avoid them for that reason.
Now onto cassettes. A cassette has two main pieces: The hub, and the driver. The driver has the springs and pawls that grab onto the teeth of the hub to make it spin. You'll want to look for a sealed hub and driver, again saving some money is just not worth it when it comes to hubs.
Moving out we reach the spokes again, but this time you may actually run into 48H wheels. Don't let the 36H vs. 48H be the difference in which bike you buy. Nowadays there really isn't a dramatic difference in the two. Unless you plan to be brutally abusing your rear wheel, don't worry about running 36H.
Note about what spokes do: Spokes don't add that much strength to the rim vertically. They add strength, yes, but the amount of strength they add isn't huge. The strength that the spokes give to the rim is the sideways impacts, such as when you land mid-spin on a 360, your wheels will get a side-impact-load. The spokes help to distribute that load and absorb the impact.
Moving on out we get to the rim. In the rear, you DEFINITELY want to have a double wall rim.
Quick note: I'll be writing an article about this probably by the end of the month, but if you plan to be running brakes, you'll want to look for a chrome plated rim. If you don't plan to run brakes, then the color doesn't matter. Also you shouldn't limit your selection to only those with chrome plated rear rims. That will cut out a lot of options. More on that in the article, but thought I would mention it quickly here.
Like I said, the wheels are probably the most important part on a bike, and you would not even think it before you start riding or looking into bikes.
About tires: Most stock tires are going to be un-impressive. The thing that sucks is that most stock tires are rated for 60Psi, while you want to be running about 85-90 Psi (more on that in another article maybe). 60 just feels way too low. So, just a note on that. Look for tires that are rated for up to 110 Psi, but like looking for a chrome rim, don't limit your search to this.
Brakes (and gyro).
If you want brakes, then read this bit. If you want to ride brakeless, skip right on over it.
If you're looking for a straight cable setup, then one brake setup to the next is about the same. More on that later, but you won't see a marginal difference.
As far as gyros go though, there is a bit more to look at. Gyros are the part on your bike that allows the bars to spin around without the cables getting tangled up. I run one, and personally would never run brakes without it on a BMX bike. Gyro systems also have less cable flex in them, so there is more power directed to the brakes themselves.
What you want to look for is a dual-lower cable setup. A splitter-cable lower cable setup is the most annoying thing to deal with in setting up gyros, they're inefficient, they're just....stay away, please. Dual lower cables are much easier to set up and maintain. Trust me.
However, a splitter on your upper cables is just fine. I run dual upper cables, but you really don't need to. Not to mention that if you plan to set up a dual upper cable setup, some brake levers will not work with them.
Also you may want to look for removable gyro tabs on your frame. In frames with an integrated headset, removable tabs on the side of the headtube have replaced the lower plate that goes on with the headset. Some frames have tabs welded straight on to the frame. These aren't horrible, but I just prefer removable tabs, they're also easier to deal with. removable tabs are trivial though, and a bike having them should not turn you away from it.
Now that bit about one brake being the same as the next. Most brakes that come on complete bikes are generic brake setups. They're actually just fine. Generic brake arms are great even for professional riders. They're cheap and simple, and most brakes aren't different from each other.
The levers on complete bikes will be non-hinged though, mostly. The issue is that to remove the lever, you need to remove the grip. A hinged lever can be un-hinged form the bars and taken off with the grip remaining on.
Well, that's it. You have read all there is to buying a new bike. There are a few more notes, but nothing major. So, if you want to go with that and get a new bike, go for it!
Well, a note about generic parts. There are some parts on a bike that make no difference and are generic. Seats, grips, chains, brakes, etc. Chains are important, and buying a new chain on its own is something worth talking about, but a chain on a complete is going to be the same from one bike to the next.
I never talked about chainwheels and gearing. Chainwheels will also be similar from one bike to the next. Gearing size is usually 25/9 on completes nowadays.
Note: If you see 9,10,or 11t, you should instantly know that the hub will be a cassette. Freewheels only go down to 12t, and even then, the 12t freewheels are weak, and most run only as low as a 13t.
These guidelines I wrote are what I would use if I were looking for a bike. Now, obviously I can't make you choose a bike, but I can help you out. When it comes to buying bikes, some compromises might have to be made. Maybe you can't get a chrome plated rim because you can't afford that bike. But there are some things that should not be compromised:
- CrMo Frame, forks, bars. Don't get Hi-Ten steel, it will not last.
-Sealed BB and headset. Unsealed hubs are acceptable if you need to cut down your budget. I wouldn't suggest running an un-sealed cassette though.
-Cassettes. Do not run a freewheel hub, they just are not worth the movey savings. They will not last long, and will need to be replaced anyway. Most of them are produced cheaply. They have their price tag for a reason, and their durability is not that reason.
-1Pc cranks. DO NOT EVER DO THIS. EVER. PLEASE FOR THE LOVE OF ALL THAT IS GOOD DO NOT GET A BIKE WITH ONE PIECE CRANKS!
If you have any questions, leave them in the comments and I will get back to you ASAP.
Happy shopping, and I hope you are happy with your bike!
Note: all of these tips are about buying NEW bikes, not a used bike. I will probably work on an article about buying used bikes soon, but that is a different game in itself.