The rim I have is very sharp around the hole for the value and when using two different inner tubes with rubber valve stems it has cut and and caused a hole/flat.
I have an inner tube suitable for 2.5" and it has a metal valve. Could I just use this do you think?
I think first off I would eliminate that sharp edge with a Dremel or some emery paper wrapped around a cylindrical object until it is rounded off and smooth. Not sure on the tube but I have used the tube from a 1.75 tire in a 2.25 tire without issues , I feel it will stretch without to much stress.
Short answer: Yes.
Slightly longer answer: What @Bug72 says, you should fix the issue at the valve hole.
Tubes are stretchy, you can run a slightly thinner tube without much issues in my experience. (Maybe it looses slightly more air when it’s sitting and pinch flats a tiny bit easier, but really only by a minimal amount.)
+1 to what others have said about the hole, sharp edges and tubes don’t go well together.
I run a 2.5" $5 tube from decathlon on my 29" x 3.0 build and it hasn’t had any issues. Benefit is that it saves a bit of weight too.
The conventional wisdom is that it will stretch the tube a bit but if you’re not doing really aggressive muni it should be fine
quite possible that he holds. However, the lifespan is often shortened. The information provided by the manufacturer is not printed for fun. I stick to the rules myself. You can find good (and light) 3" tubes from Schwalbe in all sizes, 20 + 24" only as a downhill version, 26", 27.5" and 29" also as a light freeride version
As someone who worked in a bike shop I will agree with this. Best practices are there for a reason so expect that things can happen. It might run for a bit but it’s not optimal.
Thanks all! I will have a look at filling away those sharp edges. I also went ahead and ordered a more suitable inner tube, which supports 3" wide tyres and has a metal vavle stem and can be screwed down (thus less likely to move and stronger if it does).
In the mean time the weather has turned in my favour. Last week it was pretty snowy and I was using my 26er with a 3 inch (lightly) self studded, Duro Wildlife Leapard, which worked pretty nicely for the conditions actually (before the failure). This week however it has warmed up and now ice is more of a problem, so actually my 29er with a heavily studded (402 studs in fact), Schwalbe Ice Spiker Pro tyre is better suited anyway. And by the time the snow starts falling heavily again, I will have my inner tube. 