Do chains stretch, or do they wear? Hmmm a modern conundrum!The 5g is bikeberry junk with 2 chains made of unknown material that stretch. It's barely better than the crappy single chain TC. The 4g is much better quality, and belt drive (belts don't stretch). Don't fall for the higher numbers, its a sales tactic. Look at the gasbike/kingsmotorbike garbage quality knockoff of the grubee 4g, they named it the 7g to make it seem better, because of the higher number.