I'm worried about my derailleur snapping. The chain isn't running around the bottom pulley, it's running next to it, scraping against the bottom pulley and the frame. When I change gears it makes a horrific noise and the bike has ground to a halt without me touching my brakes. This has happened 3 times.
I am doing the London to Brighton charity bike ride in 29 hours. I don't have time to get it into a shop and I have a 54 mile ride to do and I am worried about my derailleur snapping.
What should I do?