What is the "rubbering in" of a track?

[hollus]

Hi all,
My first thread, hopefully I won't look like an idiot. [-o<

I am curious as to what exactly it means when a track "rubbers in". On Fridays the track is green and cars lack grip until enough rubber has been laid in. The rubber is supposed to come off the wheels and stick to the asphalt, acting like a glue from there on, increasing grip and cornering speeds. But in TV, it looks like the line taken by the F1 cars is the cleanest part of all the track, with rubber everywhere else as marbles. Is it supposed to be a microfilm of rubber? Can really so much rubber come off the cars as to cover a patch of track four kilometers long and five meters wide? I also have problems imagining how a bit of rain "washes off" this rubber.
But then, whatever it is, it's effect on lap times is real enough. So what is this "rubbering in" exactly?

[Jersey Tom]

If you put your hand down on a "rubbered in" track, you'll feel its tacky with rubber. Thin film.

[Ray]

Oval racing is cool to watch this happen. If you look closely at a NASCAR race, I know alot here don't care for it, you can see the tracks the tires leave as they bomb around the corners. They are sticking to the rubber that is worn off the tires in a very thin amount on the surface of the track.



You can see it pretty good here too if you zoom in to the left.

[bhall]

Seems to me like you already have a pretty good understanding of the concept, hollus. And welcome to the forum.

It's exactly as you said. As cars circle the track, rubber worn from the tires sticks to the asphalt, forming a thin rubber layer and giving the track more grip. Circuits get "rubbered in" most visibly in areas of heavy braking/turning. And the reason why the racing line always appears cleaner than areas off-line is because almost all cars follow the same, ostensibly fastest, line, clearing it of the rubber "marbles" that are shed from the tires.

In this picture of the hairpin at Circuit Gilles Villeneuve, you can see where the track has been "rubbered in."



As far as rain washing away the rubber, it's easier to wrap your head around when you realize that over 17,000,000 gallons of water is dumped from the sky for every inch of rain that falls over a square mile.

[hollus]

Thanks. I have never been to a track in use, so it is interesting to hear that if feels sticky. And the sharp line from the Nascar is awesome.
I still have problems with the water part, though. Of coulse one inch of rain will wash many things away, that is the kind of rain that makes rivers and parking lots in Interlagos. But a more tipical situation is like a couple of millimeters of rain falling on sunday morning or in between testing sessions, just enough to make everything wet, but no poodles. And somehow, when the track dries 10 minutes later, all that rubber has magically dissapeared.
Rubber is not really supposed to interact with water. Is there anything else than rubber to this rubber?

[Jersey Tom]

But a more tipical situation is like a couple of millimeters of rain falling on sunday morning or in between testing sessions, just enough to make everything wet, but no poodles. And somehow, when the track dries 10 minutes later, all that rubber has magically dissapeared.
Rubber is not really supposed to interact with water. Is there anything else than rubber to this rubber?

Who says that little rain does anything?