It's not optimal, but it'll work fine. I wouldn't worry about it. Tubes for wide tires in a narrow tire are more problematic, in my experience.
this post was submitted on 05 Jul 2026
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Because the rubber is being stretched, a puncture can tear open like a balloon being pinpricked. A puncture in a fitting inner tube leaks slower.
You can slow down air leakage further by sticky-taping the wheel's spoke holes airtight. It helps by letting you ride to a more comfortable place for patching after noticing you have a leak.
I don't think that the width is an issue, because when you pump it up, it will expand
It expands, but also thins out. I really don't think it's going a be a big problem in this exact case, since it's only slightly undersized, but there is a limit.
As an example, many years ago I was in a small group ride with 32mm tires and had flat. My spare was also flat, and the closest tube another rider had was for 25mm max. It worked fine for about a mile and then loudly popped.
Or explode! If it hasn't then it's probably fine.