In my case, I wash my car seldom going on never, this is the best way to tell. While it is true that rear discs also throw some dust, the difference is obvious enough that you just know which tires go where. And 3-5K miles is more than enough for wheels to clean themselves that you are not seeing the dust from the last rotation.
Many shops have a large window seeing into the garage on the waiting area. I find this a great sign on a shop, much like an open kitchen in a restaurant. I am sure that the fact that the mechanics see me sitting there waiting for my truck helps to ensure I get the right service. I have never had a missed rotation. It also helps if you buy the tires from them and purchase the insurance (it sounds like a rip off, but in my case it has paid off handsomely). Then they want those tires to last.
I can tell because when I drive a car thats had its tires rotated it feels different in a very obvious way. Its like how the car feels and handles after getting new tires. The wheel feels completely different. Am I the only one who has experienced this?
I am not saying this is your case, but a friend normally mentioned that until I figured that he was letting his tire pressure get so low that the difference he felt was just the fact that the shop brought the tires up to pressure.
I admit this is nitpicky, but your conclusion here doesn’t actually follow from the premise. (And I know you know how it works, but some might not. Lecture is for them.)
Almost no cars on the road have identical grip levels on the front and back. Virtually every car on the road, then, will lose grip on one axle first. Passenger cars are usually designed to lose grip at the front first, so they understeer (because people’s instinct is to brake when the car refuses to turn, which is the right thing to do).
Uneven wear could change your handling enough to induce oversteer, but that seems unlikely, though it might be an issue at speed in the wet.
On the other hand, in conditions other than extreme wet or ice, legal/safe driving won’t take a car even close to its grip limits, unless the car is hydroplaning. Thus, I would say that tread depth is only really important for water pumping for a normal driver.
A lot of that has to do with the aging and heat cycling of the tires as they wear to that point though. Most of the guys that I track with that bring non-slick, track-specific tires have them shaved to reduce tread depth. Full height tread can squirm and deform, leading to slightly reduced traction and more specifically, poor feel. Your best grip, assuming rubber in good condition, is with no tread at all. That’s why the fast guys and the pros run slicks.
It is interesting, though, how many people don’t realize that the tread on their tires is there specifically to deal with wet roads. I’ve come across plenty of people who believe that, even on perfectly dry surfaces, the tread is what keeps the car from skidding off the road whenever they take a corner.