I got a sudden flat innertube today after pumping up my tyre.
Looking at the puncture and the rim it seems that an access hole of some kind had opened up - see photo - the tube pinch punctured on this when inflated.
What do I need to do to fix this? Do I need to buy some rim tape and apply over the top? Do I need to somehow reseal this hole? Can't go to local bike shop today as it's Sunday and I was going to go out riding...
I would fit a new rim tape that is sized for your rim. That's probably 622mm, and of a width to suit.
You might choose to peel the existing tape off, but there's some chance its stuck down with adhesive. Normal rim tape over the top should be fine, though if you were running tubeless the answer might be different.
If this happened while out on a ride, you'd need to lay something in the valley to cover this hole, then fit a replacement or patched tube and ride home. Such a fix is temporary and will likely fail again within 100 km, maybe much less.
Exactly the same thing happened to me with a brand new pair of DT Swiss ARC 1400 wheels that came as standard on a new bike. Both of them blew out within a few days of each other – thankfully not while I was riding the bike!
The problem is that DT Swiss tubeless rim tape isn't strong enough to handle typical road tyre pressures when applied with a single layer. (This is corroborated by reviews of the tape on a couple of online shops; here and here.)
The solution is either to find some different rim tape that's rated for the pressure you want to run, or to double-wrap it. In your case, I suggest removing the old tape altogether, since it's already compromised. It should come off quite easily.
You might also contact the bike manufacturer and ask for a replacement roll of rim tape if the bike is new-ish, since this defect should be covered under warranty. I did this with my Canyon bike and they were happy to send me a new roll of tape free of charge.
