OK, foolproof tips for "your mate" 😉 on making sure he doesn't nip the tubes when putting the tyres back on:
1. Follow twohats' advice. Oh, and make sure he's running the tyres at a high enough pressure.
2. Use decent tyre levers – my favourites are some old Kona ones I've had for years (though discovered yesterday that I've lost them… boo). Leave one bead of the tyre on the rim.
3. Pump up the tube so that it maintains its shape before putting on the rim. Err on the side of a little bit too much air, than too little. This step is essential..!
3. Put the vale through the hole, but don't put the lockring on.
4. Starting at the valve, gently push the tube up onto the rim. Work all the way round the tyre doing this.
5. Once the tube is seated on the rim, start gently pushing the remaining bead onto the rim. I start at the valve and work both sides evenly. Plenty of tyres won't need levers to finish off the last but (but a bit of a push), though some might need one lever to do the last bit.
6. Result – installed tyre without pinching the tube..!
🙂 🙂