How to replace a tube. You can also use this video to show how to replace your tire...
Tubes
US:
Groove = 20x4.0 - Your local bike shop will not likely have this size, so even if you are planning on having a shop replace your tube, you should bring the tube in with you to the shop.
OutCross = 26x4.0 - Your local bike shop may have this size, but I would call them to see before bringing your bike to them to complete the work.
Stride = 26x1.75 - Just about any local bike shop should have this size, just make sure the valve stem is as long as your current tube.
Flex = 26x1.95 - Just about any local bike shop should have this size, just make sure the valve stem is as long as your current tube.
Canada:
Groove = 20x4.0 - Your local bike shop will not likely have this size, so even if you are planning on having a shop replace your tube, you should bring the tube in with you to the shop.
OutCross = 26x4.0 - Your local bike shop may have this size, but I would call them to see before bringing your bike to them to complete the work.
Stride = 26x1.75 - Just about any local bike shop should have this size, just make sure the valve stem is as long as your current tube.
Flex = 26x1.95 - Just about any local bike shop should have this size, just make sure the valve stem is as long as your current tube.
Tires
US:
Groove - CST BFT 20x4.0
OutCross - CST BFT 26x4.0
Stride - CST All Terrain 26x1.75
Flex - CST Jack Rabbit 26x1.95
Canada:
Groove - CST BFT 20x4.0
OutCross - Mohegia 26x4.0 (We could not find a source in Canada for the CST BFT 26x4.0, but these are sold by AliExpress.com and you can have them shipped from China to Canada)
Stride - Swing Penguin (This is a comparable tire to the CST All Terrain 26x1.75)
Flex - CST Jack Rabbit 26x2.0 (We could only find the higher performance folding UST tires on Amazon.ca)

