2005 Honda 500 Canadian trail problem

[dooby]

I have 700km on my unit. My front tires were worn much more than the back and I decided to replace them. Backs looked like 10% wear. Installed identicle tires and serviced diffs (80W90 hypoid) and performed aligment check as per service manual.
Here is the issue. In two wheel drive all is well, when I put it in 4WD the rear of the quad will elevate to the limit of the shocks. Drive train appears to be under stress and is forcing the suspension upward. Raised the quad so all 4 wheels were off the ground and no signs of problems or noises in 2 or 4WD.
Talked to several dealers and they are at a loss. Any ideas ?

 

[Summiteer]

Right size tires front and back? Different diameter tires would stress the drive train I would think.

 

[dooby]

Stock tires were put on, confirmed in service manual.

 

[dooby]

After several checks ends up the Dunlop 25-8-12's are not 25's. When measured I got around 23.75's. These were brand new take offs still with the t*t's on them. Over inflated the tires and problem was gone.