[blackedoutharley]

Here is the breakdown on speed ratings for passenger tires.

Keep in mind that some tires have a "P" in front of the size; this is not the speed rating! Also others have it included in the service index which is typically just past the tire size and will look like "92H". The letter is the speed rating, the numbers are the load index.

Speed ratings are based on indoor wheel test with the tire at max psi and load.

J = 62 mph
K = 68 mph
L = 75 mph
M - 81 mph
N = 87 mph
P = 93 mph
Q = 99 mph
R = 106 mph
S = 112 mph
T = 118 mph
U = 124 mph
H = 130 mph
V = 149 mph
W = 168 mph
Y = 186 mph
Z = 150+ mph

J through Q are typically assigned to large truck tires.

Hope this helps.