Things to check:
1.) Axle. now these are built strong but enough of a force will slightly bend it oblonging the bushings.
2.) bushings.. there sould be a little bit of play when the nut is loose, but when you tighten the nut there should be no play what so ever. so the bushings are tight against the swingarm.
Spokes. take the axle and tire, put it back on the bike w/o bushings and spin it. see if it wobbles or bounces on the axle. if it does i would recomend taking it to a shop and get the tire trued.
and as for your chain tension. way too tight..... sould have a .5" play in both directions so an inch total. approx. |