p15 bumper is a periodic colour-preserving glider reflector with Karel's p15 providing the necessary spark. The minimum repeat time is 45 ticks. For an equivalent colour-changing periodic glider reflector see p15 bouncer. A stable Snark reflector can be substituted for any bumper. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams. A p3 bumper or p5 bumper can also be substituted for a p15 bumper if that allows for a better fit with nearby circuitry.