If the tube is physicaly larger than the tire its supposed to fit inside, you 'll likely end up with folds in the inner tube, which might affect ride quality, but will definately increase the risk of a flat. In an emergency, if it might save me walking 50km to the next bike store - I'd do it anyway.
Rans Enduro Sport, Hase Kettweisel Tandem, Merin Bear Valley beater bike
That small of a difference probably won't have much effect.
One thing to be careful of is not catching a fold of inner tube under the tire bead while you are installing the tire. The bigger the inner tube, the more likely that is to happen. In an emergency I'll use a slightly too large inner tube to get me home. Given the choice however, I'd prefer to use a slightly too small inner tube.
One thing to be careful of is not catching a fold of inner tube under the tire bead while you are installing the tire.
Yes, that's really the problem - installation can be trickier if the tube is too large and you may have a blowout if part of the tube gets pinched between the tire and the rim. But I've sometimes used tubes that were way too large without any ill effects. That includes using a tube for a 27" tire in a 20". It had to be folded over on itself but the wheel rode fine and was in daily use for a long time before I got around to getting a tube of the proper size.
assuming the larger size does not cause folds or pinches in the tube during install -skill can help a lot here
Then the most noticable difference i've seen is that it takes much much longer for the tube to naturally lose air.
Since the oversized tube is not being stretched as much, the pores in the rubber aren't as wide it seems.
-based on observations of 26x2.1 tube in 26x1.5 tire.
once at work a hand truck dolly got a flat. Didn't have any tubes for the tiny 8" wheels. Took a 24" bike tube, looped it 3 times (same way you fold a tire). 24/3=~8 At only 30psi used on those wheels, it worked great.