When are tires unrideable? How many nicks are too many? I'm asking because I'm a student who commutes by bike, who spends ALL his money paying through university. A friend of mine who rides a lot has a box of old tires he said I can have and I'm just trying to figure out which I can use and which I can't.

Your friend probably stopped using them for a reason. Ask him what kind of defects they have. It's hard to tell from the tyre surface without really careful inspection. A nick on the surface can have a small piece of glass in the bottom, so when you put the tyre on a tube and inflate it causes a slow leak.

--J

How pessimistic, Juha! I ride a lot and I have a number of perfectly good tires that I wouldn't hesitate to donate to a poor friend in need.

Careful inspection is the key here. Obviously, feeling the inside of the tire for pieces of glass, metal, or other sharp things is a start. Try to find spots where the fabric inside the tire is showing through the rubber - those are bad. So are large cuts; small puncture holes aren't so bad.

When you mount the tire, inflate it to maximum pressure and look for any bulges - if there are, throw that tire away.

I'm sure your friend can help you inspect the tires he has to give you... Read what Sheldon Brown has to say about tires. And good luck!

The tire is usable as long as the threads in the casing are not cut.

I realise the word "defect" was a bit strong in my post, and I certainly don't think OP's friend is somehow setting him up here. But I'm not pessimistic either, I just don't have the time or inclination myself to change a perfectly good tyre. You seem to suggest you change tyres for no other reason than just for the fun of it?

--J

Well I have some friends who start out each season with a new set of tires. They don't look at them to see how much tread is left or if there are any issues. For them it is part of the Spring tune up process and I would imagine those have some life left.

Kenny - I think we need more information. Got pictures? Are all the used tires the correct size for your bike? Does your bike even need to have it's tires replaced? If your current tires have plenty of tread left and they don't look like trash, then your friend can keep his box of hazardous waste ...

HOWEVER, if he frequently replaces his tires then you might have a box of gold! Look for a sweet pair that match!