i bought bmx style tensioners (i think thats whay theyre called) tension the chain. the problem is, whenever it look like its the right tension, it turns out to be to tight. i can feel resistance when im pedaling. when i to loosen the tensioner, it seems too loose to me so i make it too tight again. how do i find the sweet spot? also, how do i align the rear wheel so its straight? i currently do i by eye, but i know that everytime i setup the wheel its in a different postions b/c my brake pads are in the wrong postion.