NB: This guide is based around buying second hand racing bicycles however I'm sure would be useful for buying other types of bicycles too. It has been written explaining everything, so should be useful both to beginners and those that already have good knowledge of bicycles.
Over the past three years I have bought or sold a total of 7 different bicycles. Some of them I found useful for a while, and then sold when I bought a new bicycle, and some of them I have bought and then sold again for a few reasons: they have had mechanical problems, have been poorly looked after, are the wrong size or just total trash.
Through these experiences I have developed a check list to ensure you get a good bicycle and don't loose any money or get ripped off, something that would have been extremely useful to me had I had it 3 years ago, and I hope you will find useful too.
1. Check the stem and seat-post move freely
This is a quick check that can be done using an allen key multi-tool. The stem is the part attaching the handlebars to the rest of the bicycle and can be loosened by turning the centre top bolt anti-clockwise. When it is sufficiently loose check the stem can move up and down freely within the frame.
After you have done this re-tighten and loosen the seat pin where the seat-post goes into the frame and check the seat-post moves up and down.
This is probably the most important check. It is important that you can move the stem and seat-post in order to beable to alter the bicycle so that it will fit you properly and be a comfortable ride. The stem and seat post must both be oiled regularly in order to keep them from becoming stuck. If either are stuck this also means that other parts of the bicycle are rusted together and and when you want to repair, service, or change a part on it, it will take a great deal of work. You may even end up with an immovable seat post such as the one pictured below
As you can see a beautiful hand made Mercian frame that is pretty much useless due to the seat post, stem and bottom bracket being totally stuck, and being so far stuck in they are impossible to cut out.
2. Check the Wheels are True
This is another quick check you can do which could save you a lot of time and money. If you hold the bike firstly so the front wheel is off the floor, and spin the wheel whilst looking at the profile of the wheel, (as below) and watch the wheel to see if it appears to wobble from side to side whilst it is spinning. If it wobbles noticeably, the wheels is either buckled or damaged
If it is buckled, the wheel will wobble both ways as the wheel spins, (left and then right). If the wheel is buckled it can be fixed, by either a bicycle mechanic (which will cost between £10 and £15) or can be fixed by yourself using an adjustable spanner. It is a common misconception that truing wheels yourself is very difficult and you need a spoke spanner. This is not true and you can easily fix small buckles yourself with a little practice using an adjustable spanner, although it does take a little more time! If you have this problem and wish to try reparing it yourself this video can tell you how :)
If the wheel wobbles but not side to side, just to one side then this means your rim is probably damaged and you will need to replace your wheel. Which brings me to my next point....
3. Check the Bicycle Components and Compatibility
This may sound slightly OTT, but can definitely be a problem if you need to replace any parts. Whilst most bicycles are fine, some companies such as Raleigh and Peaugot make parts to manufacturer specific sizes. So if you are buying a bike that you feel may need some reparing at some point, check for compatible parts by asking the seller or doing a quick web search.
4. Frame Size
Obviously you can tell quite easily if the bicycle fits you by by sitting on it, but if you have to travel a long way or pay postage for the bicycle, then it is worth checking if it will fit you before. The easiest way to measure a bicycle is by asking the seller to measure the length from the centre of the bottom bracket, or bottom bracket axle (see picture) to the top of the seat tube. For adult size racing bikes, this will be somewhere between 49cm and 62cm.
To check your own size, measure your inside leg, in centimetres. Then take away 27cm from this measurement, and you will have the approximate size of bicycle you need.
5. Check the Drive Train Works Smoothly
It is very important to check the gears change smoothly, as this is a common area for problems and can be expensive and time consuming to fix. The best way to do this is to take the bicycle for a short ride, and gently click through all the gears, checking that the gears change smoothly.
If the seller is uncomfortable with you taking the bicycle for a short ride, you can turn the bicycle upside-down so that it's resting on the handlebars and the seat, and click through the gears, using your hands to turn the cranks.
If all the gears change smoothly you are on to a winner.
6. Check the Brakes
Obviously just as important as the gears are the brakes, however these are more likely to be easier and cheaper to fix. These can easily be checked, by checking you can stop abruptly on a short ride or checking from standing that the brakes can stop the wheels from turning. The brakes should be smooth and not get stuck, or slow down the bicycle at all when you are not pulling them.
Should you need to tighten or loosen your brakes at all, you can do this easily by loosening the nut which grips your brake cable on your brake caliper. To tighten your brakes, loosen the nut and squeeze you brake calipers together. While still holding your calipers in the position, tighten the nut back up. To loosen your brakes, repeat the process, while holding your brake calipers so that they spring apart slightly.
7. Check for Rust Spots
Check your bicycle for rust spots. You are bound to find some pitting on the bicycle in some places especially if it has chrome parts on it. Otherwise, if there are rust spots on the bicycle, there is a good chance it has not been not looked after. Especially if it has large rust spots on it, then you definitely shouldn't buy it!
8. Check for Impact Marks
Impact marks appear when a bicycle has been crashed badly and indicate that a bicycle definitely should not be purchased as it is unsafe to ride. You can easily recognise them as they are rings of rust or flaked paint around the tubes of the frame.
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