Tire-**** marks come off almost instantly with HONDA SPRAY CLEANER-WAX in the pink and black can. Miracle stuff. Cheep too. Many, many touch-up uses.
Marbles are a function of volume of cars, how often the track is swept, and DO YOU DRIVE THE CLEAN RACING LINE ? !!! There are pace-car weekends when I have to take breaks to clean the marbles! (Pace Cars dont get to use the race line...we ride track center, ever notice that? We get a SPITLOAD of marbles.)
Marbles slough-off the tire as it corners, and can GREATLY minimize your ability to corner safely.
The BEST way to clean them off is on a concrete (not asphalt) skid-pad (deserted parking lot?) You have to drive in fast, medium-tight circles, as fast as you can, til the car begins to slip. Then drive 4-5 more circles to warm the marbles even further. Keep circling. Try to corner in such a way as to force the front to plow-push-understeer. By circle # 10 or so, they come FLYING off like shrapnel-cigars.....rattling in the wheel wells...Keep your windows closed or you can actually collect them inside while tight cornering!
Spinning-out does NOT clean marbles as well as weighted, hard cornering, on the VERGE of loss of traction. "Threshold Spinouts"
Then, dont slow down, do more circles the OTHER direction, half as many, since the tires will be warmed. NOTE: I am usually DIZZY afterwards, as are my passengers. This scuffs off 80% of em..... and if you have a flat-bladed putty knife you can then easily "peel" off the fronts while still hot.
A lot of the rear marbles will have come off, but can also be "burnout cleaned" off, again rougher concrete works better than smoothe asphalt.