How to evaluate a used bike

I really need a beater bike that I can lock up without worry. So I'm looking at used bikes.

I can judge the obvious -- if the brakes work, if it shifts, etc., and I can get help with DIY if a bike needs basic tune-up work. I expect to spend some money and time on a used bike.

What I'm worried about is the frame and wheels. Will problems be obvious to my naive eye? Do I need to remove the tire to evaluate the wheel?

I'd appreciate any advice. I don't care about cosmetics -- in fact, for locking up in NYC, the worse it looks, the better.

Hi Pam
wheels are pretty easy. Give it a spin - if it wobbles, it's crooked. If a bike is really really well used, as in the wheels are used up, you will see a considerable valley in the rims. I'm going to have to get photos of my husband's rims, come to think of it, why hasn't he gotten new wheels yet? hm.
ok, what else.
What is fun to do is to get a bike and then take it to a bike shop. If it's a good bike (not a walmart bike) they will happily adjust the brakes, true your wheels and change your chain... for less than $200.

ok, back to the frame. Yes, you can see cracks in frames. you can eyeball and see things that are bent.
good luck on your hunt..

Check the headset and bottom bracket bearings.

Stand over the bike, apply both brakes, plant the front tire and push the handlebars backwards and forwards. Can you feel any movement in the headset? Now, pick the front end of the bike up off the ground by the frame, so that the frame and fork are perpendicular to the ground. Give the bars a nudge and see that the fork turns smoothly to the side with no binding (other than what the cables might cause), grinding or rough spots. Do the same thing on the other side. (Or do it on a workstand if you have one handy.)

Put the bike back down on the ground, grab both crankarms and see if you can feel any side/side or up/down movement in the bottom bracket. Then pull the chain off the chainring - let it rest against the BB if there's room, or just hold it in one hand - and spin the cranks. Again, they should turn smoothly with no binding.

If it's a carbon frame, any defect in the paint is cause for concern. It doesn't necessarily indicate a weak spot or crack in the frame, but it could, so I'd either have a trusted bike shop check it over or just pass on it. With a metal frame, if it's cracked, you'd see it on careful inspection, and chips in the paint are just cosmetic.

I've noticed that the craig's list bikes section (at least in the PNW) has a number of self appointed "safety police" who will call out any of the sellers who are trying to sell a bike that has been crashed or misrepresented in some way or that is grossly over priced, so it seems to me to be a pretty good way to buy a used bike.

Check the hubs by trying to move the rim side to side in the bike frame to see if there is play. Also good to pull the wheels off and turn the hub bearings by hand to see how they feel, either smooth or tight or with crunchy spots. While you have the rear wheel off, spin the cassette or freewheel to see that it works properly.

Some of what's on this list re-states what has already been said, but I like it because it's pretty comprehensive but not overwhelming...I printed out a shorter version of it to take with me as a reminder the last time I looked at a used bike.

The main page of the guide also has tips on buying/selling a used bike.

Thanks, everyone. This is exactly what I needed.