Originally Posted by
wphamilton
One thing about the cassettes is puzzling. The two end combinations (19-41 and 41-19) wrap a total of 60 combined teeth. All of the others wrap 58 teeth. It seems goofy to add that extra bit at the ends when leaving it at 39 would keep the same chain length for all combinations, reducing or eliminating a DR-like tensioner.
It is still a chain. In order to be shiftable, a chain always requires extra slack and a tensioner. "Keeping it the same length in all gears" would not in any way eliminate the need for that.
A belt can take this kind of advantage of "constant length" gearing. A chain cannot.