Tire Sizes

I’m fed up with not having a good reference for tire specs. So here it is, all in one. I have: 195/50 Z R16 84W currently. On the Mercedes I have 195/70 H R14

Let’s say you have a tire with the measurements 245/45 Z R19 98W and Uniform Quality Tire Grade (UQTG) specs of 440 AA A.

Here’s a nice picture taken from here to get us started:

245 is the tire width, in millimeters
45 is the ratio of sidewall height to tire width, expressed as a percentage. So 245*.45 = 110.25mm of sidewall height
Z is the MAXIMUM speed rating. Not to be exceeded under penalty of death!!
R is the tire construction method. R means there are cords of fabric that run perpendicular to the tire’s circumference, that is, radially. The other option is the letter “D” which stands for diagonal, meaning a biased ply. This ply has overlapping layers that alternate ply directions. The nice picture from Michelin shows the plies at about a 45 degree angle. Maybe that’s the reasoning for calling it bias ply.

Here’s radial:

And here’s bias:

19 is the wheel diameter in inches (of course). Think of it as tire inside diameter
94 is the load rating. How much weight the tire is designed to handle. Here’s a nice chart to explain it:

W is the typical speed rating the tire is rated for when properly installed and inflated. The letters are designated as follows:

440 is the treadwear grade. It provides a rough estimate of how long the tire will last. If a tire lasts for 7,200 miles,it gets a grade of 100. Think of it as a percentage. A tire with the grade of 200 will last for 200% of 7,200 miles, or 14,400 miles. Likewise, 440 is 31,680 miles. Since this is a lot of marketing hype, a better estimate is 10,000 miles per 200 of grade.

AA The first grade is the traction grade, also a bit of marketing fluff. Says how well the tire does on wet concrete with locked brakes
A The second grade is the temperature grade. It tells you how hot the tire can get/how well it dissipates heat. Kind of like speed rating, but less informative. A means the tire can go over 115 mph, B is under 115 mph, and C is under 100 mph.