(I figured i'd post this up to help anyone that may be new to wheels+tires.)

Alot of people can be confused when it comes to the sizes of tires. P###/##R-##

It'll take 1 minute for me to explain to you

The best way to explain is to use an example. For this example, i'll use my tire size:

P215/35R-18 ( simplified as--> 215/35-18 )



P-----> The P denotes the tire as being a Passenger vehicle tire

215--> The 215 denotes the measurment of the WIDTH of the tire (in milimeters, 215mm)

35-->35 denotes the Height-to-Width Ratio. That aspect ratio of height to width here in our example is 35 The height of the tire (aka--> Profile or sidewell) is 35% the width of the tire. So if the width of the tire was 100mm, then the height of the tire would be 35mm. Or if the width was 200mm, the height of the sidewell, or profile, would be 70mm, and so on.

R---> R identifies Radial Construction.

18---> The last number, in our case 18, is the diameter from bead to bead on our tire. The 18 denotes that this particular tire fits, and ONLY fits an 18" rim







Simple huh?



Next i'll explain the speed designation of tires: The speed rating of a tire is really nothing more than an expression of how well the tire will withstand the temperatures of high speed. Also, this does not necessarily mean that a high speed rated tire will perform better at low speeds than a lower rated tire.

Lower rated tires are usually made from a harder rubber and last longer than softer high speed rated tires. So my advice is that if you don't plan on going 100+mph then don't buy such a tire, they'll only wear more quickly!



Speed ratings:


F / 50mph
G / 56mph
J / 62mph
K / 68mph
L / 75mph
M / 81mph
N / 87mph
P / 93mph
Q / 100mph
R / 106mph
S / 112mph
T / 118mph
U / 124mph
H / 130mph
V / 149mph
Z / 149+mph



Sticky?

 

added this with the FAQ thanks! DJXT

 

You might want to add this link too. It is a tire size calculator that can tell you how changing the tires alters things like speed and distance traveled...

http://www.csgnetwork.com/tireinfo4calc.html

 

/\/\ that's an excellent tool!

 

Helpful hint when calculating height.......215mm =21.5 cm...........and, 2.54cm = 1 inch. So 2.54 is your conversion factor to get it in inches.

21.5*.35=7.525/2.54=2.96(that the height of the sidewall in inches.)*2=5.93+18=23.93 inches.

The overall height of a 215/35/18 is 23.93".

 

The "R" after the aspect ratio means it's a radial tire. Those of us who grew up when most tires were bias-ply (old farts) will know that.

 

Ahh! That is absoutely correct! Wow, my mistake!

1st post has been editied. Thanx for pointing that out to me