How To Find Tire Size, Load Index, And Speed Rating On Your Tire

How To Find Tire Size, Load Index, And Speed Rating On Your Tire

How do you find the right tire

Determining what size of tire you need is quite simple if you know where to look. The letters and numbers on the side of your tire will tell you everything you need to know. The 3 measurements needed to look up a tire for your vehicle are:

1. Tire Width
2. Aspect Ratio
3. Rim Diameter

Once you have those 3 numbers, click here to search our tire prices.

If you are unable to find the tire size yourself simply call us and we will be more than happy to look up the tire size specified by the manufacturer of you vehicle.

 

Tire Width (Width of Tread)

tire width

The first set of numbers in the tire size code represent the tire width (in millimeters). This number is measured from the widest point of its outer sidewall to the widest point of its inner sidewall when mounted and inflated.

 

Aspect Ratio (Height of Tire Sidewall)

aspect ratio

The second set of numbers in the tire size code represent the tire height (in percent) starting from the rim to the tread. This number identifies the tire’s profile and is a percentage of the tire width.

Ex: The size 205/55/16 has an aspect ratio of 55%. The height of the sidewall is calculated as follows:

205 millimeters x 55% = 112.75 millimeters

The larger the aspect ratio number the taller the sidewall profile (height), and the small the number the lower the sidewall profile.

 

Tire Construction

tire construction

R = Radial construction. This classification implies that the tire’s body plies “radiate” out from the imaginary center of the wheel. Radial tires are by far the most popular type of tire today representing virtually all tires installed.

D = Diagonal construction. This classification implies that the tire’s body plies crisscross. Tires of this sort are for light truck and spare tires.

Note: The Tire Construction is always written on the sidewall, but does not have to appear in the tire size code. Ex: You may see 225/50/17 or 225/50/R17 – both of these are the exact same.

 

Rim Diameter

The final number in the tire size code represents the rim diameter (in inches). The most common personal vehicle rim sizes are: 8”, 10”, 12”, 13”, 14”, 15”, 17”, 18”, 19”, 20”, 22”, 23”, 24”, 26” and 28” and can be found on cars, minivans, vans, sport utility vehicles and light duty light trucks.

In rare cases some vehicles have rim diameter expressed in half-inches (ex: 15.5) or in millimeters (ex: 415). It is absolutely crucial that the correct tire size is installed on rims with these rare diameters.

 

Other Important Markings

Tire Class

tire class

P = When a tire size begins with a “P,” it signifies the tire was designed to be fitted on vehicles that are primarily used as passenger vehicles. The “P-Metric” size applies to cars, minivans, sport utility vehicles and light duty pickup trucks (typically 1/4- and 1/2-ton load capacity).

LT = If a tire size begins with “LT,” it signifies the tire was designed to be used on vehicles that are capable of carrying heavy cargo or towing large trailers. The “Light Truck-Metric” size applies to medium and heavy-duty (typically 3/4- and 1-ton load capacity) pickup trucks, sport utility vehicles and full-size vans. “LT Metric” tires have more heavy-duty internal components designed for heavier vehicles which carry large loads.

The absence of a letter preceding the three-digit numeric portion of a tire size, signifies the tire is a “Euro-Metric”. “Euro-Metric” tire sizes have identical dimensions as “P-Metric” tires but have minor variations in load carrying capabilities.

 

Load Index

The first number after the tire size code indicates the tire’s Load Index. Generally, the numbers on passenger cars and light trucks range from 70 to 110. The Load Index specifies the maximum amount of weight a tire can safely carry. It is very important to maintain the proper load index for your vehicle when replacing your tires.

Load Index Lb Kg Load Index Lb Kg
71 761 345 111 2,403 1,090
72 783 355 112 2,469 1,120
73 805 365 113 2,535 1,150
74 827 375 114 2,601 1,180
75 853 387 115 2,679 1,215
76 882 400 116 2,756 1,250
77 908 412 117 2,833 1,285
78 937 425 118 2,910 1,320
79 963 437 119 2,998 1,360
80 992 450 120 3,086 1,400
81 1,019 462 121 3,197 1,450
82 1,047 475 122 3,307 1,500
83 1,074 487 123 3,417 1,550
84 1,102 500 124 3,527 1,600
85 1,135 515 125 3,638 1,650
86 1,168 530 126 3,748 1,700
87 1,201 545 127 3,858 1,750
88 1,235 560 128 3,968 1,800
89 1,279 580 129 4,079 1,850
90 1,323 600 130 4,189 1,900
91 1,356 615 131 4,289 1,945
92 1,389 630 132 4,409 2,000
93 1,433 650 133 4,541 2,060
94 1,477 670 134 4,674 2,120
95 1,521 690 135 4,806 2,180
96 1,565 710 136 4,938 2,240
97 1,609 730 137 5,071 2,300
98 1,653 750 138 5,203 2,360
99 1,709 775 139 5,357 2,430
100 1,764 800 140 5,512 2,500
101 1,819 825 141 5,677 2,575
102 1,874 850 142 5,842 2,650
103 1,929 875 143 6,008 2,725
104 1,984 900 144 6,173 2,800
105 2,039 925 145 6,393 2,900
106 2,094 950 146 6,614 3,000
107 2,149 975 147 6,779 3,075
108 2,205 1,000 148 6,844 3,104
109 2,271 1,030 149 7,165 3,250
110 2,337 1,060 150 7,385 3,350

 

Ply Rating

Much like a passenger tire has the load rating written after the tire size code, light truck tires specify the load range after the tire size code as well.

LT-metric, LT-flotation and LT-numeric tires are branded with their load range using letters. The further along the letter in the alphabet, the higher the ply rating, and maximum inflation pressure and load.

LT-Metric, LT-Flotation and LT-Numeric Light Truck Tires
Load Range Ply Rating Abbreviated Maximum Load Pressure
B 4 B 35 psi (240 kPa)*
C 6 C 50 psi (350 kPa)*
D 8 D 65 psi (450 kPa)*
E 10 E 80 psi (550 kPa)*
F 12 F 95 psi (650 kPa)*
*Selected large LT sizes are designed with reduced maximum load pressures

Speed Rating

The letter after the number indicates the Speed Index. Tires are issued a speed rating by the federal government for meeting safety standards at a specified speed. In general, a higher speed rating will result in better vehicle handling. The maximum driving speed of a vehicle must be limited to the speed rating of the tires installed.

As advances in technology have increased vehicle top speeds, the tire speed ratings have evolved to better identify the tire’s capability, allowing drivers to match the speed of their tires with the top speed of their vehicle. Despite their high speed capabilities, no vehicle should be driven on public roads in excess of the legal speed limit.

Caution should be used when tires have been damaged, altered, under-inflated or overloaded as the speed rating has been compromised under such circumstances. Additionally, most tire manufacturers state that a tire that has been cut or punctured no longer retains the original speed rating after repair because the tire manufacturer can’t control the quality of the repair.

The most common tire speed rating symbols, maximum speeds and typical applications are shown below:

L 75 mph 120 km/h Off-Road & Light Truck Tires
M 81 mph 130 km/h Temporary Spare Tires
N 87 mph 140km/h
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 Sport Sedans & Coupes
H 130 mph 210 km/h Sport Sedans & Coupes
V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars
W 168 mph 270 km/h Exotic Sports Cars
Y 186 mph 300 km/h Exotic Sports Cars
Z >149 mph 240 km/h (obsolete, replaced by W and Y)