companies just use stages to make it easier to differentiate different size wheels, think about it like this, say stage 2, 3, and 5 for example... You could also say small medium and large... or 50mm, 60mm, 70mm.... those numbers are inaccurate, im just tryin to give you an example... Its just something more common, so people can relate to it as oppose to people having to pull out a ruler to try to calculate sizes... Im sure there is a better explanation for it, but for someone like me who simplifies everything, thats just how I look at it... My 76 trim is slightly larger than a stage 5, so sometimes, I call it a stage 5 just to make things easier.... Although I still think 76 trim has a LOT more sack....