I know I probably should be posting this in a different forum, but I'm having problems changing my 700x38c tubes and tires on my 29'' rims. The tires are folding tires, but for some reason, both tires and tubes seem too big. The tires bead keeps coming out and the tubes want to bunch up in the tire. I'm just wondering if I'm missing a trick to getting them on. It doesn't seem to have been a problem for me before

I don't have an answer on the bead but are you putting a little air in the tube first? Doing so makes getting it in cleanly a lot easier. And the really simple trick to getting the right amount of air - don't use a pump or inflator. Blow the tube up with your lungs. (Sadly, this only works with presta valves, not Schrader unless you can figure out how to depress the spring. It's such a useful trick that it is a reason to consider presta it you aren't already using it. You will need a sleeve to reduce the rim valve hole. Any bike shop.)

In any case, just enough air to inflate the tube, no more, will make the job easier with much less chance of pinching the tube as you work the bead over the rim. (Sometimes I have to let a little air out to get that last bit of bead. That's OK. It did its job.)

If any part of the tube gets under the bead of the tire, it'll push the tire bead off the rim when you inflate. You've gotta try and situate the tube inside the tire as evenly as you can with your fingers when you install.

I doubt the tire is too big, if you are mounting one side of the tire on and it fits, then the tire is fine, so put some air into the tube by blowing into it as hard as you can with your lips, this will give the tube enough air to give it some form.