In the old days fitting 26" mountain bike tyres was so easy. I could usually get the tyre off with one plastic tyre lever and tyres would often mount without a lever at all.
These days people like to run tubeless so tolerances between rim and tyre sizes have become quite small and many people are finding it harder to mount tyres. Personally, I’m still running tubes.
I nearly gave up trying to mount new Schwalbe Big Betty and Magic Mary tyres on the Bontrager Line 30 rims on my Trek Remedy 8. The rims come with a pre-installed Bontrager TLR Rim Strip. This is how the TLR strip looks:
I absolutely could not get the Schwalbe tyres on with the TLR strip. I run Schwalbe tyres on my other bikes so I know the usual trick of pushing the bead right into the centre of the rim but this didn’t work here. I almost snapped a tyre lever which is ridiculous.
In the end I cut out the TLR strip and replaced it with Gorilla Tape and then I was able to mount the tyres using two tyre levers and minimal effort.
I think the issue is that the tyres sit on the part of the TLR strip marked in red in the photo below, and this pushes things just outside of the required tolerance. Gorilla Tape (or real rim tape) sits in the centre of the rim and doesn’t interfere with mounting.
Maybe there’s a trick to getting the bead to sit right in the centre? If not, normal rim tape is an easy fix and Gorilla Tape is apparently compatible with tubeless setups.