(Updated January 2020)Speaking from experience, you know some information to avoid getting ripped off, avoid buying a bike that gives you knee problems, and to spot an amazing deal.When I was much younger, a teammate on my Master's swim team took pity on me and, seeing that I was entering my first triathlon, offered to sell me his road bike for $300. I thought that was a lot of money, but it was the right size and I needed a real bike. It turns out he sold me an Italian bike with Italian gears and brakes and it's still my trusty backup bike 20 years later, even though I now have a carbon fiber, triathlon-specific bike that I purchased and swapped out the components for SRAM red (and sold the Shimano parts it came with at a profit). I probably should have paid him $1,000 for that road bike.So here we are 20 years later, trying to help the next triathlete find something that will work, for not very much money.
The best way is to begin your search for a road bike or triathlon bike is to pay money for a professional bike fit BEFORE you go shopping, even for a used bike, so that you know what you need. This step used to be prohibitively expensive for new triathletes, but thanks to improvements in technology, you can often walk into a bike shop and get a virtual fitting in a few minutes for free. At the end of the fitting, you should receive a printout of measurements, including the frame size and "reach" recommended for you. There are better and more specific fittings that can be done while riding on a stationary bike trainer that will better take into account your own flexibility and mobility. Often this costs more than $100, and realistically someone looking to get started is just not going to make that investment. If you are investing in an expensive bike, you MUST do this step first. If you are looking for something used, keep reading.
Repeat after me: The frame is the most important item. ("The frame is the most important item.")If your frame size is right, you can change the gearing, change the pedals, change the seat, change the stem, change the handlebars. If your frame size is wrong, as soon as you start buying new things for your bike, you are going to realize that you need to start over with the correct frame.You can always replace components on a frame. If you replace the frame, you can't always take all your components with you, if they don't fit the new bike, so if you are on a limited budget, get the right frame first. Then you can add items bit by bit with your birthday money, a tax refund, etc.If you can afford carbon instead of metal, you won't regret it. If you can't, don't worry about it. Just don't ever test-ride a carbon bike until you think you can afford it, or you will hate yourself until you get one.OK, let's start with the assumption that you don't have the money for a professional fitting by a certified bike fitter, and you are looking for a used bike and just want to make sure you get something that fits.
Ideally, you would have your measurements from the bike store, or you would go on YouTube and search for a video about how to measure your inseam for a bike frame. If you don't do that because it's a hassle, you can use something called "Stand-over height." Swing your leg over the bike you are looking at. Put your feet flat on the ground. There should be a couple inches between your crotch and the bike frame. (This part of the bike frame between your legs is called the Top Tube. Because it's on top.)Now obviously you can only test the standover height in person. That's why it's better to get a measurement, so you can shop on Craigslist and eBay and BT's classifieds forum and know what size frame you need. Most frames are measured in centimeters. 60cm is for a very tall person. 50cm is pretty small. Mine is 48 cm. 46 cm is possible, but VERY hard to find.
It's great that you found a bike that is the right height, but it still may never fit right if you are reaching too far in front of you. When in aero bars, your wrists should be directly below your eyes, and your arms should form an "L" at the elbow, like this:If your top tube is too long, you end up having problems and your elbows will be too far out in front of you. It is common to see people riding in this position, particular people with a more compact frame, and women who have a different proportion of limb length to total height. You don't want to look like this: (elbows almost out under your face and wrists way ahead of your head)If your reach is too long, you will find that you get tired faster, can't breathe correctly, and end up sitting up a lot and getting out of the aero position because it's too uncomfortable. This occurs because, when your elbows are directly below your shoulders, you're using your skeleton to hold you up. If you move your elbows out in front of your shoulders, you are using your core muscles, which will tire. To understand this better in 20 seconds, assume the plank position and move your elbows farther and farther forward to gain an appreciation of how much more work is required to hold the position.If you are a small person, especially if you are female, you want to be careful about top tube length. Many standard brand bikes have too long of a reach. This is not universal, but most women, compared to men, have shorter torsos and longer legs. Most women can stand next to a man of the same height and will find that their legs are longer and torsos shorter. Therefore a woman and man who would ride the same sized frame would need two different top tube lengths. Rarely do bike manufacturers make the same sized frame in two different top tube lengths.This becomes a big problem when trying to find a bike that won't make you too stretched out. Check geometry tables for bikes you are looking at. A shorter top tube will be less than 500mm. Or look for a bike with TWO SEAT POSITIONS on the seat post. The two on the left (Cervelo and Felt) have two spots where you can put the seat - forward or back. See? It's easiest to see on the Cervelo, because it has two big holes. You put the seat in either one.Being able to put the seat forward allows you to get closer to the handlebars.Also when you are looking at brands, look at Top Tube lengths. Cervelo and Felt have the shortest Top Tube lengths, because of the movable seat position. That's why I have a Felt!Of course the seats are adjustable a little bit. You can slide them forward by loosening a bolt, sliding the seat on its rails, and tightening it again. But you want to be able to adjust your seat as your abilities change. You don't want to be stuck in the all-the-way-forward position starting out, and have no room for adjustment.
Most pieces on a bike are adjustable and replaceable. Well, everything except the gears and brakes, commonly called "Components." If you are shopping, you can ask what brand the Components are. The listing below is going to seem boring and you may be tempted to skip over it, but the key to buying a used bike is figuring out if you are getting a steal or getting ripped off. The components are the most or one of the most expensive parts of the bike. If you find someone has listed an older bike on eBay for a few hundred dollars, but it has top-end components on it, you know you've found a good deal and the bike will be reliable and easy for a mechanic to work on.We could describe these in detail, such as which are carbon fiber and which are aluminum, but these characteristics change over time and you are buying a USED bike, which means you would have to know the manufacture year in order to determine the specifics. Here's a summary just so you can spot a really good deal online.
Brand name: Shimano (Japanese. This is the most common set you will see on bikes for sale)Shimano Dura-Ace = top-of-the-line. Best, lightest, shifts smoothest; available with electric shifters or without.Shimano Ultegra = Also good, not quite as light; available with electric shifters or without.Shimano 105 = lowest of the premium quality Shimano components. Still works reliably.Shimano Tiagra = the best components you'll find on a "leisure" bike.Shimano Sora = a step down from TiagraShimano Claris = a step down from Sora
Brand name: Campagnolo (Italian. Somewhat rare)Campagnolo Super Record = luxuryCampagnolo Record = top end. Quite pricey. WONDERFUL. Well engineered.Campagnolo Chorus = mid range of Campagnolo, but still VERY VERY nice.Campagnolo Athena/Potenza = a step down from ChorusCampagnolo Veloce/Centaur = a step down from Athena
Brand name: SRAM (American. Extremely good.)SRAM Red = top end.SRAM Force = Very good.SRAM Rival = Good.SRAM Apex = A step down from Rival
If you should find a bike with the right size frame and it has Campagnolo ("Campy") or SRAM components, snap that thing up! There's nothing wrong with Shimano, though. Except it's just not as good. (Others will disagree here.)
Everything else is on a case by case basis, and doesn't cost nearly as much. You can go get a saddle that works fine on clearance at a bike shop for $30. Wheels are important, but you'll always have a chance to get nice wheels down the road sometime. Of course if you find a used bike comes with amazing, expensive wheels, that's something to consider.Be sure to buy a helmet if you don't have one, and the other critical items that can be purchased or moved from your old bike, such as a toolbag, a spare tube, a tire pump, water bottle cages, etc.One last thing: As you are shopping you might skip over bikes being sold with no pedals, figuring that seems complicated to correct, or downright weird that someone would sell a bike with no pedals. The fact is, most people have a system of bike shoes, cleats and pedals that work together. And since detaching the pedals requires no more than a simple wrench, they are likely to keep their pedals to put on their next bike. So don't worry if you are buying a bike that has no pedals. It's easy to buy pedals, and even easy to put them on.