Hi, I just noticed some of my once a week lawns are tuning brown from where the tires are rolling not from the blades. Does anyone have a clue why this is happing? It happened to all five lawns in one neighborhood!

If I had to guess. I would think you were leaking something from your tires. Do you have tire sealant in them? Or did you spray roundup before you mowed? That is all I can think of.

couple of potential causes. I have had this happen before and most likely your fuel tanks are located over your tires, and the cap was loose. It would only have to happen on one sidesince you probably overlap your passes alternating direction.
I have also had this happen during an extremely dry, hot period here in S Texas when the sheer weight of my gravely 34z crushed the grass.
Hope this helps!

Change the direction that you are going. like up and down, to side to side. Hope it helps!