Could someone pleeeze tell me the real reason why we don't research a problem at all?
Ofc it's just I love
the chain tensioner - I install them on non-motorized bikes alla time just for kicks
The sad fact is many bikes need them for a few reasons, not least of which is chainstay clearance. Were I do as you suggest - the chain would saw through my Schwinn's chainstay in about twenty feet of use, my Rollfast - the same problem, but it'd last a quarter mile or so 'cause it's at least steel. As for a "quality 415 chain" - good luck with that, it's far easier to get a quality 410, but unless you change those sprockets too you'll be amazed how much that chain will still "stretch".
Hey - if ya can get away w/o a tensioner - awesome! Do remember that motorcycles, motorbikes & mini bikes were designed
with an engine in mind, complete with horizontal drop outs - another thing many bicycles no longer have.