(Inner tubes are amazingly compliant and flexible as long as you don't have any thing sharp like spoke holes they can do pretty impressive tricks inside the tyre. I once saw an incorrectly fitted tube that was only fitted to half the tyre and then double backed on itself. Thus only a semi circle of tyre had inner tube in it when deflated. Though when I saw it , the tube had done many months of riding like that having inflated and expanded to fill the full circumference! )
Alien27 wrote:I don't think the tube inside the tyre will stretch away from the valve side that much. especially as the thicker reinforced bit of the tube would have to It's happening with every tube on both wheels. Different brand tubes and different batches of the same brand.
As above, an inner tube can EASILY stretch double its length under pressure. In the above example that is exactly what happened!
Fix the rim tape!