McLaren P1 tire size
The most common factory tire size for the McLaren P1 is 245/35R19 front, 315/30R20 rear, on 5 of the 5 year and trim fits listed. The table lists every year from 2013 to 2015 and the size each trim was built with. Pick your year and trim to see the tires that fit.
Check your own tire
A trim can be sold with more than one wheel size. The size printed on the sidewall of your current tire, or on the placard in the driver's door jamb, is the one your vehicle has.