It is the speed rating of the tire. In this case "V" is good for 149
MPH. Yeah right in a Hybrid
Here are the rest of the ratings:
M 81
mph 130 km/h
N 87
mph 140km/h Temporary Spare Tires
P 93
mph 150 km/h
Q 99
mph 160 km/h Studless & Studdable Winter Tires
R 106
mph 170 km/h H.D. Light Truck Tires
S 112
mph 180 km/h Family Sedans & Vans
T 118
mph 190 km/h Family Sedans & Vans
U 124
mph 200 km/h
H 130
mph 210 km/h Sport Sedans & Coupes
V 149
mph 240 km/h Sport Sedans, Coupes & Sports Cars