If you've popped your tube or looking to carry one is a spare, we stock a range of quality 27.5" mountain bike tubes for a wide range of widths in both valve types. If you're on the hunt for 650b bike tubes, take a look at our range below. When browsing for tubes, it's important to know the valve type and the width of your existing tyre. Your 27.5" tube will either be a presta or schrader valve and the width will be printed on the side of your tyre.