Rear tire grabs when turning

[suntreemcanic]

My B7800 new to me. When on gravel or dirt and turning sharp the inside rear tire jumps and spins a little. The differential lock is not engaged. Is this normal?

 

[Mat4644]

It's normal on gravel. Does it more on my new small tractor vs one much bigger. If you lock the rear it's much worse. Did this to check mine.