Okay, I measured the distance between the chainstays at 4.25". This should allow a 4 inch tire with an eighth of an inch on each side for clearance. I completely deflated my tire and re-inflated it. At 10 psi my tire is 4" wide and clears the chainstays. At 15 psi my tire rubs on the right chainstay and measures just shy of 4.25 inches. For comparison I measured the front tire and it is exactly 4" at 15 psi" maybe my rear tire is defective and it is enlarging more than it should.
Roshan said he would either send me a new bike frame when they get their next shipment in a few weeks and have my local bike shop swap all the components or send me the 27.5x3 wheels that will fit my frame. This is the kind of support that makes Biktrix stand out and why I purchased from Biktrix and didn't buy through Alibaba.
That first photo makes the clearance between wheel and chainstay look just as tight as mine.
