I'll toss in another "leave them off for grass-field operations" vote. I have 3-1/2" wheels that I had used the fiberglass pants witch the model came with (a Kangle S/K 50). Those cracked and gave out in the first season. I installed a set of more flexible plastic pants. Those held up better . . . until last year. I was having a heck of a time getting airborne. I figured I had bad fuel, but the engine ran fine on the ground and the tach showed full RPM. But still I could not get off the ground! I was baffled. Turns out the pants had cracked at the attachment points along the line where the l.g. struts meet the pants. As the grass hit the fronts they bent in - acting like friction brakes on the wheels.

They're gone now.