I am running stock size tires on my truck (according to the door sticker) and my speedometer reads 5 mph faster than what I'm actually doing. I know its actually a percentage that it reads off, but basically 5 mph faster.
My only guess as to why is that a previous owner ran bigger tires and had the speedometer recalculated for those tires
I plan on my next tires going up to 285 or maybe 295 somewhere in there as i think they look good on a stock lift truck, and im hoping that will correct my speedometer.
My buddy runs 285's on his stock PSD and his spedo reads about 5 mph slower than what he is actually running.