Hot tires
What is hot tire pickup?
Hot tire pickup is a warm tire softening the coating under it and taking some of the film with it, leaving bare patches the shape of the tread.
The short version
- It shows as patches where the wheels park, not as general wear across the floor.
- Heat plus the plasticizers in the rubber are what work on the film under a tire.
- A thin build has less material between the tire and the concrete than a heavy one.
- A weak bond underneath makes it likelier, because the tire only has to beat the weakest layer in the stack.
What happens under a parked tire
A tire comes home warm. It has been flexing at highway speed and it holds that heat a while after the engine goes off, so for that stretch there is a hot piece of rubber pressed against the floor with the weight of the vehicle behind it. The heat softens the film directly under the contact patch, and nowhere else on the floor.
The rubber is not just sitting there either. Tires carry plasticizers, the ingredients that keep them flexible, and those migrate to the surface and go to work on a warm resin. A softened film, a tacky tire and the weight of the car add up to a bond being pulled on from above at the moment it is weakest.
When the car backs out, some of that film can come away with the tire. What is left is a bare patch the shape of the contact area, sometimes with the tread still readable in it, sitting exactly where the wheels stop every night. That shape is how the trade names the failure from across the garage.
What makes it more likely
Film thickness is the first thing. There is only so much coating between the rubber and the concrete, and a thin build has less of it to lose before the slab is showing. Heat is the second. A vehicle parked straight off a long highway run, into a closed garage in the middle of summer, puts the most heat into the same square foot it uses every day.
The bond underneath is the third and it is the one people skip. A tire pulling up on a film only has to beat the weakest connection in the stack, and on a slab that was never opened up, that connection is at the bottom. Tire patches on a floor like that are usually the first sign of a prep problem rather than a chemistry one.
Where the chemistry comes in
This is why people ask about one chemistry against another before they ask about anything else, and the question is a fair one. Topcoats do differ in how they behave warm. It is also half the picture, because the tire is working on the whole stack and the stack is only as good as the thing holding the bottom of it to the concrete.
So the useful thing to ask about a quote is what the top coat is, how much film is going down, and how the slab gets opened up first. Then ask to see a floor a few winters old that gets parked on daily, rather than one finished last week. Tire patches show up by then if they are going to.