Tire Tech 101

Okay you guys, so its time for another of Mr. Philthy's seminars.



Students, we are here to talk about tires.

Now we all use tires but many of us don't understand exactly what those little numbers on the side of your tires mean right?

It's okay to admit it, I remember when I learned what they meant, and it wasn't that long ago.

So you look on the side of your Volk TE37's and see the numbers P245/40R17, what the hell does that mean?



Well lets start from the beginning
P = P-Metric; generally apply to passenger vehicles, but basically means the type of measurement on this type of vehicle.

There is also
LT = Light Truck
T = Spare
ST = Specialized Trailer Service

If it ends with LT designates that it is a Numeric, Wide Base, or Flotation for Light trucks that carry heavy loads.
And, if it ends in a C it basically means its for commercial use.

Now the 245 designation is the width of the tire in millimeters. So 245 means 245mm across.

Most of us know that, but what about the next number? 245/40

That 40 does NOT mean that the sidewall of the tire is 40mm like most people think, rather it means that the side wall is 40% of the width.
So the exact size of the sidewall on a 245/40 would be:
245 * 40% = 98mm

The R in the formula of 245/40R17 means the type of construction of the tire, the R designates RADIAL. Now there is also D which means diagonal, usually for light truck and spare tires. There is also a B meaning belted but this type of tire is basically discontinued amongst all manufacturers.

And lets not forget the 245/40ZR17 that we see often. This ZR basically gives the speed rating of Z and the type of design, R. Below are the designated speed ratings.

M 81 mph 130 km/h
N 87 mph 140km/h
P 93 mph 150 km/h
Q 99 mph 160 km/h
R 106 mph 170 km/h
S 112 mph 180 km/h
T 118 mph 190 km/h
U 124 mph 200 km/h
H 130 mph 210 km/h
V 149 mph 240 km/h
W 168 mph 270 km/h
Y 186 mph 300 km/h
ZR 99Y 186 mph, 300 km/h
ZR19 (99Y) in excess of 186 mph, 300 km/h

And lastly the final number designated the wheel diameter in inches. Interesting that the rest is metric, and this is standard, but thats the way it is.

Now you know the basics!

So a review:
245/40ZR17

means the width of the tire is 245mm, with a sidewall of 40% of the total width, the ZR designates the speed and the type of construction, Z-rated and Radial design, and finally it is on a 17" rim.

So have fun schooling other people on what you know about tires.