Originally Posted by NJ-Brett
Dirt bikes or street bikes?
Its hard to get 12 inches of travel out of the dual shock setup.
On the street, twin shocks make it easy to adjust for added load, and the shocks keep bags out of the rear wheel, otherwise the single shock setup likely has some performance advantages but uses up space.
I have a 1984 Husqvarna 500xc that uses two shocks in the rear. The bike is stock and has 13.8 inches of rear wheel travel.