GarageCalc What 305/35R19 means
305 is the section width in millimeters (12.0 in). 35 is the aspect ratio: the sidewall is 35 percent of the width, so 305 × 0.35 = 107 mm (4.2 in). R is radial construction, and 19 is the wheel diameter in inches (483 mm). Stack two sidewalls on the wheel and you get the overall diameter: 483 + 2 × 107 = 696 mm, or 27.4 in.
A full marking adds a load index and speed rating after the size, for example 305/35R19 91V. Those two codes set how much weight and speed the tire is certified for; look them up in the load index chart and the speed rating chart.
Plus and minus sizing from 305/35R19
Going up one wheel size, the closest match is 315/30R20 at +0.1% diameter with a 95 mm sidewall instead of 107 mm. Going down one size, 285/40R18 is -1.6% with a taller 114 mm sidewall for more comfort and pothole margin. Anything inside 3 percent keeps the speedometer, ABS and gearing effectively stock; the comparison calculator shows the full speedometer table for any pair.
Frequently asked questions
How tall is a 305/35R19 tire?
27.4 inches (696 mm) in overall diameter: the 19-inch wheel (483 mm) plus two 107 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 305/35R19 in inches?
27.4 x 12.0 R19: 27.4 inches tall, 12.0 inches wide, on a 19-inch wheel. The sidewall is 4.2 inches and the circumference is 86.1 inches, so the tire turns 736 times per mile.
What tire sizes are equivalent to 305/35R19?
Within 3 percent of the same diameter on the same 19-inch wheel: 295/35R19 (-1.0%), 285/35R19 (-2.0%), 285/40R19 (+2.1%); on a 20-inch wheel: 315/30R20 (+0.1%), 305/30R20 (-0.7%); on an 18-inch wheel: 285/40R18 (-1.6%). The percentage is the diameter change, which is also your speedometer error.