"Other Peoples Rubber" (OPR) is what people refer to as any extra rubber that adhears and becomes bonded to your tire. In autocross and TT applications, you will want to remove this rubber before you start a session. To do this, you'll need an oscillating multi-tool. This post describes the best blades for this application.
I have tested several blades and keep coming back to the FEIN 2 inch blades. Not all blades are equal. Many will dig into the tire, are not sharp enough, or wander uncontrollably. I have not found anything even close to these blades. Unfortunately, these are no longer sold in big box stores. Here is where you can find them.
Key Features
Width: 2" - Wide enough for typical treads, but not too wide. (tested on 315s and 225s)
Edge: Sharp with teeth, but flat. The flatness is important, otherwise the tool will wander uncontrollably.
Construction: Wide and thick center section provides good control and supports the outer edges of the blade.
Product Details:
Brand: FEIN
Part number: 6 35 02 221 26 0
Price: $37.55 (for 3, updated 8/29/2023)
Below is an example of OPR. Even this amount is worth removing if you have time. You can also let the tires cool, then drive the car in the smallest circle possible and scrub the tires; this will remove most of the OPR very quickly. If you can hose the pavement, it will work even better. Don't do this while the tires are hot.
8/29 update: the M18 FUEL Oscillating Multi-Tool (not pictured above) seems to be the best oscillating tool on the market. When they advertise low vibration they aren't lying. Definitely worth the price.