Tyres 
Canberra Hot Rod Association (CHRA)
Tyre Hieroglyphics
Here are what the numbers on the side of tires mean:
For example I
am going to use a 235/70 R 15 94 H
The 235 (or 9.25 inches) is the Nominal Section Width of the tire in millimetres. The section width of the tire is the overall width of the tire from outer sidewall to outer sidewall with the tire inflated but not loaded, and does not include raised letters or sidewall ribs or any sidewall protrusions. This is sometimes termed the "Fat" of the tire.
The 70 is the Aspect Ratio, which is the relationship of the Nominal Section Height (which is the height of the tire section, from the outer tread surface to the tire bead where it makes contact with the rim, with the tire inflated but not loaded, or commonly called Sidewall Height) to the section width. So in simple terms: 70 means 70% of the section width or the 235mm (9.25 inches). So 70% of 235 is 164.5mm or 6.48 inches - the sidewall height. The R is for the Construction Type, which is a Radial. The 15 is the Wheel Diameter, which is not the overall wheel diameter measured from the outer rim lip, but the diameter of the wheel's rim that supports the tire bead.
You can figure the Diameter of the tire with the above information as well, and I will convert to inches for this. 235mm divided by 25.4 = a section width of 9.25", 9.25" multiplied by a aspect ratio of 70% or .70 = a sidewall height of 6.48", 6.48" multiplied by 2 (two sidewall heights) = 12.96" added to the wheel diameter of 15 equals a total tire diameter of 27.96"
The 94 is the load index number of the tire, that goes as follows:
(rated in
pounds)
75=852lbs
76=882
77=908
78=937
79=963
80=992
81=1019
82=1047
83=1074
84=1102
85=1135
86=1168
87=1201
88=1235
89=1279
90=1323
91=1356
92=1389
93=1433
94=1477
95=1521
96=1565
97=1609
98=1653
99=1709
100=1764
101=1819
102=1874
103=1929
104=1984
105=2039
Then the H is the speed rating, that goes as
follows:
S=112
T=118
U=124
H=129
V=149
W=168
V*=unlimited
Z=over
149
Z*=unlimited
Tread wear, traction, and temperature numbers are listed in little print on the tire. Tread wear numbers really are only manufacturer specific, a tread wear number of 180 for a Cooper tire is not equivalent to a 180 in a Goodyear, so only compare that number within the same manufacturer. Tread wear numbers can range from as low as 60 to over 500 - the lower the number the shorter the life of the tire or the "stickier" the tire is. Traction numbers are A, B, and C with A being the highest, based on wet braking traction.
Temperature resistance rating is also rated A, B and C with A again being the highest. That means the tires resistance to building heat during use. That is really the most useful information on the tire, the rest is really irrelevant so to speak.
If you want to go old school and go the Alpha-numeric tire sizes, some of the most popular sizes equate as follows: Abbreviations are as follows: TW=tread width, SW=section width, OD=overall diameter
D70-14 TW=6.2", SW=7.9", OD=25.4"
E70-14 TW=6.4", SW=8.0",
OD=25.7"
F70-14 TW=6.7", SW=8.3", OD=26.2"
G70-14 TW=6.9", SW=8.8",
OD=26.8"
E70-15 TW=6.0", SW=8.3", OD=26.6"
F70-15 TW=6.5", SW=8.3",
OD=26.9"
G70-15 TW=6.7", SW=8.5", OD=27.5"
F60-15 TW=8.8", SW=9.2",
OD=25.9"