What is it there for?
 

I've had my xtx for 7 years but there is one part on it that I still don't get. So can anyone please explain why there is a black roller attached to the frame which is described as a tensioner, yet it is nowhere near the chain itself. It's on the near side and seems to have no function whatsoever? It's not a spare either as it's not the same as the lower chain tensioner....

When the rear suspention gets near full compression the chain becomes
quite slack as the rear sprocket has moved foward as the rear wheel arcs forward... the chain hits the roller makeing what would be the straight length
between the rear & engine sprocket longer thus useing up the extra overly free chain..

Thanks Pete, it would take some serious travel I suppose. Can't say that my one has ever been used and I've done 46000mls