There are two common reasons to mark a tire: If you are repairing a flat, you will want to mark the area around the leak; then, when rotating tires, you may wish to mark where the tire was, or where it is going. This helps keep all four wheels straight when repositioning them on the car. The easiest way to mark the tires is using a specially made tire marker or crayon. They write well on a rubber tire, even in wet conditions, and the marking is typically waterproof and long-lasting.
Locate the leak on the tire when marking a tire for repair. If an offending object cannot be located, then spray the tire with soapy water. A bubbling or frothy area will indicate where the leak is.
Wipe the soapy mixture away from the area, without losing the location of the leak. Circle the leak with the tire crayon, which will write smoothly on the rubber. Make sure that the mark is dark enough to be easily seen. A well-made tire crayon may still write on a wet tire, but often works better if the rubber is wiped dry first.
Decide whether you are writing the new placement or the current location for tires that you are rotating. Make sure that you consistently mark on each tire, to avoid confusion. These marks are difficult to remove, so mark the tires discreetly. Make sure that you pay attention to the tread direction on directional tires, so that you don't mount them against their tread. (A directional tire will have an arrow on the sidewall to indicate which direction it should turn.)
