once again, i say. isnt the speed picked up via wheel speed sensor. aka not in the driveline. so tire size should not matter.My 2 cents if I may:
overall diameter of these various tire sizes.
OE: 255/35/19 overall diameter = 26.00 inches
275/30/19 overall diameter = 25.50 inches
275/35/19 overall diameter = 26.50 inches
About a 1/2 inch difference in O.D. either size from factory. Divide that 1/2 by 2 since it's a round tire and you end up with about a 1/4" difference top and bottom from factory spec. Not really enough to make significant difference in the speedo IMO. Probably would be off be 2-4 mph.