My vehicle tires are 245/70 16, is it possible to put on 235/70 16? Can get my hand on a few of them for free, and was wondering if they would even fit. I know that the bigger number is the width, will it leak?

Will what leak? Will the tires leak? If they have wholes or are dry rotted around the bead area they very well might leak.

How old are they... what are the load ratings on them... what are they going on?

Lol, I was just wondering if the tires were thinner, which I believe between the 245 and 235 isn't much than an 1 1/2, will the air leak out between the rim and the tire. The tires are in great condition.

Shouldn't leak if they are good tires. I'd be more curious about load ratings etc. WHat you don't want to do is end up with tired that falls under the minimum requirements for the vehicle. That would be a safety hazard.

I would research what the manufacturer specifies as a minimum required tire size. It may or may not be smaller than what you was running.