I've see people have these on their bikes, it stops the chain bouncing all over the place ect.
How much is one of these? Can it be used on a 21 Speed bike? three cogs on the front. And 7 on the rear. I would like these as i do quite abit of jumping ect on my bike, and the chain bouncing is so annoying, and i think that's why i have rear mech problems.
Can someone assist me please?