How important is inner tube sizing to your tire profile ? Specifically, would it be safe to use a tube sized for 110/90-18 on a tire that is 110/80-18?
Not likely to be a problem. Bridgestone tubes we used to sell at the bike shop had a half a dozen sizes the 18" would fit, from the 4.00-4.60 inch sizes to the 100-110 mm sizes, still true. click I will say if it will fit an 80 profile it will fit the 90 profile too. After all, they are stretchy rubber. Just don't run too big a tube, it can wrinkle and chafe causing a flat.
By the way, there is no dumb question when it comes to inner tubes. It can get crazy the way they size them. Key point, do not go too big, better to be a shade under than over, to avoid the wrinkling of too big a tube. If you ever put air into a tube looking for a leak you would see just how big they can go!
