Hi all,

I'm looking for advice following a puncture on a new inner tube. Short version - new (one 20 mile ride) inner tube puncture from 2cm slit near the valve. What is the likely cause?

I had a thorn cause a small puncture. I'm pretty confident I removed all of it so I don't think there was any sharp material inside the tyre.
I decided to try replacing the old inner tube with a new slime filled one. A couple of days after I went for a 20 mile ride mixed tarmac and gravel.
I went to ride today and found it flat.

The new inner tube had a 2cm slit on the outside of the tube just near to the valve.
I know you can get pinching punctures if you incorrectly replace the inner tube, but I thought they were two small holes rather than a slit.
My thoughts are either a pinching puncture then the inner tube failed between the two holes or the bead of the tyre has gone so it didn't support the tube.
Any other suggestions?

Thanks