GarageCalc What 245/50R20 means
245 is the section width in millimeters (9.6 in). 50 is the aspect ratio: the sidewall is 50 percent of the width, so 245 × 0.50 = 123 mm (4.8 in). R is radial construction, and 20 is the wheel diameter in inches (508 mm). Stack two sidewalls on the wheel and you get the overall diameter: 508 + 2 × 123 = 753 mm, or 29.6 in.
A full marking adds a load index and speed rating after the size, for example 245/50R20 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 245/50R20
Going up one wheel size, the closest match is 245/45R21 at +0.1% diameter with a 110 mm sidewall instead of 123 mm. Going down one size, 245/55R19 is -0.1% with a taller 135 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 245/50R20 tire?
29.6 inches (753 mm) in overall diameter: the 20-inch wheel (508 mm) plus two 123 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 245/50R20 in inches?
29.6 x 9.6 R20: 29.6 inches tall, 9.6 inches wide, on a 20-inch wheel. The sidewall is 4.8 inches and the circumference is 93.1 inches, so the tire turns 680 times per mile.
What tire sizes are equivalent to 245/50R20?
Within 3 percent of the same diameter on the same 20-inch wheel: 265/45R20 (-0.9%), 255/50R20 (+1.3%), 235/55R20 (+1.8%); on a 21-inch wheel: 245/45R21 (+0.1%), 265/40R21 (-1.0%); on a 19-inch wheel: 245/55R19 (-0.1%), 265/50R19 (-0.7%). The percentage is the diameter change, which is also your speedometer error.
Can I use 255/50R20 instead of 245/50R20?
Dimensionally yes: 255/50R20 is 1.3% taller (+10 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 59.2 mph. The extra width needs about 0.20 in of clearance on each side of the tire and a rim width that suits 255 mm.