These wheel are often misused on John Deere and other equipment that are designed to have the deck "hang" from the frame of the lawn tractor to achieve the proper height adjustment. Their are some companies that actually use the gauge wheel to adjust the height of the cut, but John Deere isn't one of those companies. So reading any further will just be for your knowledge.
The gauge wheels on a John Deere and like designed mower decks are intended to guide the deck up and over a hump or obstacles that may be in the mowing path. These wheels are intended to be a 1/4" to 3/8" above the bottom of the deck. The wheel should never ride on the ground. This can be seen when the gauge wheel becomes flattened from the weight of the deck over time.
John Deere designs their tractor so that the weight of the deck is supported by the frame of the tractor rather than by the ground. These are not to set the height of the cut. JD has a knob and adjuster that stops the lift mechanism to achieve cutting height. Also, the anti-scalping wheel is the roller directly at the front of the deck. It is intended to lift the deck over items to insure the middle blade doesn't cut the grass too low.