So I was installing a new rear tire and checking the bearings today for a race this weekend and it got me to thinking about this post. Some of the more experienced mechanics on here can confirm if my thoughts are correct. An over tightened rear axle nut and or rear axle bearings that are going bad making the decelleration is greater? I guess the front bearings and axle nut could also do that? Maybe a dragging rear brake?
I have an 08 YZ450 and the engine breaking doesn't seen extreme.
An over tightened axle nut... likely not a problem. If you look at how all the pieces of the rear wheel go together you will notice that all the pieces (axle head, swing arm, spacer, inner race of wheel bearing, inner spacer, second inner race, second spacer, other side of swing arm, and nut) basically form a solid piece that does not move within the mounted assembly if all is in proper working order. Basically once you begin to over torque the nut you will need to deform a piece before it will cause a binding issue.
Failing wheel bearings could certainly be a problem, but they would need to be drastic before you would notice it while riding or on deceleration.
A dragging rear brake could certainly be a problem. If there is not enough free play for the master cylinder to allow the fluid to return you will have an issue. A failing caliper could induce excessive heat from excessive drag and therefore heat. This could also cause a non-return issue with the fluid and resulting brake drag.
All this you would notice during pushing the motorcycle, which he did not mention.