Tires explained

[KenC]

Can some one please explain to me how tires are measured?

[matt325is]

For any given car tire.

215/40ZR-17

215 = Section width - 215 millimeters the ouside of the sidewall, across the traad, to the other sidewall.

40 = Aspect ratio - The height of the sidewall, pertaining to the percentage of the number (40%) So for a 215mm tire, the sidewall is 86mm or 3.39")

Z = Speed rating (bottom of post)

R = Is Radial tire construction

17 = The height of the wheel, without the tire.

The overall height can be calculated by adding wheel height, 17" + 3.39" + 3.39" = 23.78"

Speed Rating
Q - Up to 100 mph
S - Up to 112 mph
T - Up to 118 mph
U - Up to 124 mph
H - Up to 130 mph
V - Up to 149 mph
W - Up to 168 mph
Y - Up to 186 mph
Z - Up to 149 mph and over

Here is a good tool to find a tire that has the relatively same size as you are running currently. http://www.discounttiredirect.com/di...foTireMath.jsp

matt

[Sean]

Here's an invaluable link pertaining to tire sizes:

http://www.miata.net/garage/tirecalc.html

(Basically helps you find out what size tire will do what depending on the stock tire (changes in speedo readings for example))

Bookmark it! ;)

[bimmerphile]

While we're at it:

Stock E30 Tire size for 14" Basketweaves and Bottlecaps - 195/65-14
Stock E30 M3 Tire Size for 15" Basketweaves - 205/55 -15
Stock E30 325iX Tire size for 15" Basketweaves - 205/55-15

[Rob]

Stock Porsche Carrera GT Front: 265/35 ZR 19
Stock Porsche Carrera GT Rear: 335/30 ZR 20

:eeek:

[randomtask37]

i thought weaves were 6.5 inches wide whereas caps were 6.0.

why do they have the same tire size?

[Rob]

half inch width doesnt make much difference in tire sizing, especially with the fat sidewalls of 14" rubber

[bimmerphile]

half inch width doesnt make much difference in tire sizing, especially with the fat sidewalls of 14" rubber

It is important to note that the actual tread section width will increase by .2" (about) by each inch that the wheel width increases vs the measured width (wheel width tire is designed for, though tires will generally fit .5" smaller and 1" larger, at least, depending on the profile tire, because small profile tires have less sidewall to make fit a larger rim).

For example, a set of Potenza RE950's in 195/65-14 is designed for a rim of 6" (the "measured width" for the tire). However, from sidewall to sidewall (section width) it's actually 7.8". So, it's fair to say that on a 14x6 bottlecap, you have a section width of 7.8". Those same tires will fit on a 6.5" wide basketweave, and will probably have a section width closer to 8".

Note, however, that section width is measured with no weight bearing on the tire (off the car). The amount of weight you have on the tire will increase sidewall flex, and cause a greater "Section width" that touches the ground.

Hope that clears it up.

Kris

[Rob]

i personally cant tell a difference between .2" of rubber on the ground, going from caps to weaves on equal size tires, but kris' facts are straight