On a 1'1 type, rear sprocket is better as the engine-tranny pack is at the rear and not prone to damage by HE strikes. Also, the double pin chevron track is designed to shed mud and debris before it gets over the sprocket....hence the "backward" appearance of a track which looks like it should be a scoop design to dig in, but has the outer chevrons or cleats pointing up.. The Merkava has everything up front but that is the only tank in the world that was ever designed as a defensive tank = tanks are offensive weapons. Many Sherman and Lee based tanks were put out of action by HE rounds on the transmission casing, damaging the gear box, so the M-26 and beyond moved the tranny to the rear.