I often shoot Automobile tire. I Use a stamp to clean superfluous inscriptions, a dirt. Can probably make easier.

Cool, I can be the first in reply with a easy method. Let's see.

On this particular case (LOL, I learn that words from Russell Brown's videos ;) )

I just use the magic wand tool with 30% tolerance on one of the picture's dirt

Then in the menu SELECTION/SIMILAR and make a new layer of that selection (command J).

Then the simple's way, I checked on the button PRESERVE TRANSPARENCY and paint all with the center color the non dirt tire.

Then I took a sample of the upper color of the shadow where the new layer contrasts most and use the gradient to the center.

Do the same in the bottom.

It's not perfect, but it's faster ;)

LOL, my history it's in spanish.

Eat tacos!!!

Thanks for answer. I`m trying to use multiplay (invert) layers for indemnifications of a dirt, inscriptions.