Wanna guess his weight and I read it all ! Bugger lugs !well i'm with baxter on the ?? maybe going the same place maybe not....could be tires...more likely suspension....all that speed puts some interseting forces on the quad...If you're going fast enough and your suspension preload/valvling is set too soft for you and the quad the forces excerted by the air your moving against may be torquing the entire quad and causing your suspension to wallow back and forth....first thing I would do is tighten up the preload a significant amount (the rear) and do another straight line trial run....if you notice an improvement....you now know where your problem lies...note that this is only to diagnose....try to go by the book when setting ride height and preload....our quads have limited suspension and maybe ....worst case need to have the shocks resprung and revalved... but chances are the preload front/rear is set all the way soft as it was on all of our quads from the dealer...play with this a bit...also....(Baxter: STOP READING HERE) another thing that can counter act this sort of motion is to stiffen the sway bar in back...Kyle Laton makes an excellent product at a resonable price...or if you know someone with one....try it out. The first thing to check is the suspension...you are on an IRS quad now and don't have the inherant torque countering SRA to keep these forces at bay...hope this helps
No I am not employed by nor do I recieve incentives for the sway bar...It helps in exact scenarios like this...if suspension adjustment fails...???? Ask!