Hi all, okay your looking for a racing bike something cheap just to get you fit or gets you to work, maybe you want something just to hack around on while on holiday.
Before we go into detail my advice for all buyers (doesn't really apply to racing bikes so much) is never buy a bike from a Toy store or Supermarket or online store from Germany, it may look like a great buy but there is a reason why it is so cheap, yep you guessed all the parts are made cheaply, don't last very long & made by some poorly paid person in China or other Asian country...just think of the carbon footprint :-))
Okay lets start at the basics.
If you haven't ridden for a long while don't go & buy that carbon fibre bike looking the bollox in the window at your local bike shop 'cos more than likely you'll come a cropper in more ways than one. You want something that can ease you back onto the road.
If you had an old bike that fitted you take the measurements of the frame (centre of bottom bracket to centre of top tube) this will give you a fair idea of size. Here is a place that will help you find the ideal fit for you, jimlangley.net/crank/bikefit/html
As a rough guide 20" fits about 5ft 5 to 5ft 7, 21" frame fits 5ft 6 to 5ft 8 22" fits 5ft8 to 5ft 10, 23" fits 5ft10 to 6ft 1 but these are just rough guides.
Okay so you now have an idea as to the size: So lets start looking, there are a multitude of bikes out there not just on ebay, try and go for a manufacturer you've heard of or see a lot of here on ebay like Raleigh, Peugeot, Claud Butler, Carlton, Dawes, etc. Start with a steel frame this will feel more comfortable than an aluminium frame though a little heavier it will outlast an ally frame. Anything with a Reynolds sticker on it is a good sign of good steel tubes used for the main part of the frame & for the purpose of buying a starter bike 500, 501 is fine. Also other manufacturers will have good steel frames some marked Cro-molloy or Cro-mo this means steel too.
Ask the seller if there are any significant dents to the bike, small dents are fine but bigger ones may have weakened the frame structurally. Ask if there are any cracks near the welds especially the bottom bracket shell or if there is any bad rust. Superficial surface rust shouldn't be a problem but bikes that have been left outside for years especially if they are near the coast may have rust that has affected the integrity of the frame. Another good thing to ask is if the seatpost is moving freely because if its stuck you can't adjust the height and they are a bugger to free if you haven't got the tools.
At the end of the day ask for close ups of any damage/rust. If your not sure or the seller wont send extra pics...don't bid there are hundreds more bikes out there.
Right the rest of the components on the bike will come in varying qualities, if the seller hasn't listed them ask the name and numbers of the parts. Shimano/Campagnolo parts are all on the internet and come in specific levels, then there are older parts like weinmann, Suntour(SR) etc. Don't be put of by these as they often made great components. Wheels will vary from a set of chromed steel ones to alloy quick release. If they are reasonably straight and don't have busted spokes don't worry too much about who makes them. Generally unless you buy quite an old bike these will come in 700C or 28" as referred to by Europeans. The older size is bigger which is a 27" wheel(A long complicated story behind sizes could ensue just take it that the 27" wheel IS bigger than a 700C/28" wheel) A 27" tyre will NOT fit a 700C wheel. You can buy new 27" tyres at halfords & Wilkinsons as well as your local bike shop.
Other components include the crank, look out for well worn ones were the teeth have been worn down badly they look like claws or sharp points, these are knackered and the rings would need changing, check the bottom bracket to see if it rotates reasonably okay, if there is a lot of side to side movement or it feels wobbly the bearings or whole bottom bracket may need renewing. Bikes up to the early 90's will have Freewheel cogs at the back these are different to a freehub which is a cassette on a newer bike, check to see if the cogs are well worn in the same way as the crank teeth. With a badly worn worn drivetrain the chain will slip when you put any sort of pressure on the pedals.
Gears and brakes should operate okay, if the gears are indexed(SIS) the gears should click into place, if there is a bit of grating of the chain or the gear doesn't go into place this may just mean a tightening or loosening of a cable. With brake levers they sometimes stick just squeeze the brakes really hard to see if the levers return okay, the cables can be rusted/stuck inside the outer cable which is just a cable renewal or greasing job. Sometimes the brake calipers are stiff and need maintenance, so manually squeeze the brake calipers themselves if they don't return back away from the wheel rim the springs have had it so this will cost you more money.
Pedals should move round freely otherwise they may need stripping and the bearings renewed/regreasing
All in all there are thousands of bikes out there, use some common sense, if its an old bike but looks reasonably clean then you are likely to have a bike that doesn't need much doing to it. Something that has been neglected, left outside or just looks unloved then maybe the cost of getting it back to roadworthiness just isn't worth it.
If you have any doubts just walk away.
Good luck hunting!!!!