Not all tires are the same. But what separates one tire from another? Naturally, your mind immediately goes to the tread pattern, and for a good reason. The tread pattern defines what terrain a tire is capable of handling.
You know that because what's found on an off-road truck is very different from what's on a race car, and the tires on your commuter land somewhere in between. The next thing you'll likely think about is the rubber compounds used. The compound a tire is made of plays a big role in how a tire handles certain elements and plays hand in hand with the tread to determine what conditions the tire can safely tackle.
It sounds to us like you already know quite a bit about tires. What if we told you these factors still aren't all that separates one tire from another?
Thankfully, all of our answers are stamped on each tire. No, we're not talking about the size. We're talking about the tire service description. This simple little stamping can tell us quite a bit about a tire, and we're here to tell you what it means about the capabilities of your tires.
A tire service description is a standardized number that's stamped into the tire right next to the size. Something like 102H is typical. That single, 4-digit code tells us two things. The first part of that, 102, is the load index, while the H is a speed rating.
Believe it or not, that number immediately tells you exactly what a tire is capable of and how it stacks up against other options. That combined with the size, compound, and tread pattern come together to define the overall performance of your tires.
Let’s begin with the bigger part of that number, the load index. Hang on, performance junkies, we'll fill you in on speed rating in a moment.
The load index is essentially the amount of weight that your tire can support. Again, this is a standardized number, so the 102 in our example translates to another weight capacity. In this case, it tells us the tire can support up to 1,874 pounds when fully inflated.
However, 102 is just one of the many different possible weight ratings of your tire. The standardized ratings start at 79 and run to 150, with correlating weight ratings of 963 to 7,385 lbs. The higher your load index number, the more weight the tire can support.
So, you’re now scratching your head and thinking, "my SUV definitely weighs more than 1,874 pounds." That's true. Your SUV probably weighs around 5,000 pounds or more. Not every tire needs to support that kind of weight, though. That weight is distributed across all four tires. Also, the total weight that a set of tires can support is based on a multiple of each tire's load rating.
Since we're talking about a standard vehicle, you have four tires. Therefore, our example tires can collectively support up to 7,496 pounds. That's more than enough for you, your passengers, and some sports equipment.
Load index is an important detail to pay attention to with SUVs and trucks because overloading them can cause the tire to blow out suddenly. For example, let’s say you have a 5,000-pound pickup truck with our example tire on it. Well, the tires can support the truck, but what about a 2,500-pound payload? You're asking for trouble.
Don't worry. You don't necessarily have to familiarize yourself with the standardized numbers. Some tires have the max weight capacity stamped on the side of the tire, near the wheel. That can save you a lot of time when deciding what tire you need to haul the goods.
If you have a need for speed, the speed rating is a massive number to you. Well, it is important for everyone. That's because the speed rating is a number that describes the maximum top speed capabilities of a tire. In other words, it says what speed the tire would be good for.
We get it. We're just as bummed out as you because the speed rating is defined by a standardized series of letters rather than having the rating stamped on the side of a tire.
So while it would be cool to see 186 mph cast in the tire's sidewall, we'll have to settle for the (Y) instead. Probably for the better, though, because something like a wimpy 118 mph is a lot more of a buzzkill than the letter H covering our shame.
While we're cracking jokes, you're busy learning. The wheels are turning, and you're starting to see that the alphabetical code is easy to follow—the later the letter in the alphabet, the higher the speed rating. You're correct, but you're also dead wrong.
Well, you are mostly correct. Most of the standardized speeds do increase with an alphabetical order sequence. However, the letters S, H, V, and Z are all out of series. Why?
Speed ratings were introduced in the 1960s. When they were, S, H, and V were the only three on the chart. Z was then added in and was thought to be the highest speed rating a tire would ever need.
Over the years, other speed ratings were later trickled in in alphabetical order. Since folks were already accustomed to the existing ratings for S, H, V, and Z, they were left untouched, creating some disorder. Of course, Z was surpassed, which is why Y comes next on standard charts.
Unfortunately, you aren't usually given a cheat sheet like you are with load ratings. You will need to familiarize yourself with the correlating speed rating to the alphabetical character on your tire and stick with it— you won't find the actual speed rating stamped anywhere on the tire.
Exceeding speed ratings can be very dangerous. Now, you might have pushed your H tires beyond 118 miles per hour and were just fine. Well, a tire may handle speeds beyond its threshold for short bursts. However, centrifugal force can pose a significant issue to the tire’s structure if those speeds are sustained for a prolonged period.
So, what is a tire service description? In short, it tells you what kind of abuse your tires can take. The first part of the number is your load index, and the alphabetical number that follows is the speed rating. Make no mistake. These are crucial details.
Overlooking these definitive characteristics and pushing your tire beyond its abilities can lead to catastrophic results. You need to make sure you understand the task you need to perform and pick a set of tires that match.
If you're still unsure about tire service descriptions or need help picking out a set of tires that can stand up to the task at hand, give us a call.
Our tire pros will tell you everything you need to know and help you pick out the ultimate set of rubber. Afterward, they can even pre-book an appointment with a trusted local installer who will prep your vehicle to handle anything.
Using a P195/60R15 87S tire size as our example, the 87S at the end of the size represents the tire’s service description. A service description identifies the tire’s load index and speed rating. Service descriptions are required on all speed rated (except for Z-speed rated) tires manufactured since 1991.
The first two digits (87S) represent the tire’s load index and are followed by a single letter (87S) identifying the tire’s speed rating.
P195/60R15 87S – The load index (87) is the tire size’s assigned numerical value used to compare relative load carrying capabilities. In the case of our example, the 87 identifies the tire’s ability to carry approximately 1,201 pounds.
The higher the tire’s load index number, the greater its load carrying capacity.
89 = 1,279 pounds
88 = 1,235 pounds
87 = 1,201 pounds
86 = 1,168 pounds
85 = 1,135 pounds
A tire with a higher load index than that of the Original Equipment tire indicates an increase in load capacity. A tire with a load index equal to that of the Original Equipment tire indicates an equivalent load capacity. A tire with a lower load index than the Original Equipment tire indicates the tire does not equal the load capacity of the original.
Typically, the load indexes of the tires used on passenger cars and light trucks range from 70 to 126.
Load Index Pounds Kilograms 70 739 335 71 761 345 72 783 355 73 805 365 74 827 375 75 853 387 76 882 400 77 908 412 78 937 425 79 963 437 80 992 450 81 1019 462 82 1047 475 83 1074 487 84 1102 500 85 1135 515 86 1168 530 87 1201 545 88 1235 560 Load Index Pounds Kilograms89
1279
580
90
1323
600
91
1356
615
92
1389
630
93
1433
650
94
1477
670
95
1521
690
96
1565
710
97
1609
730
98
1653
750
99
1709
775
100
1764
800
101
1819
825
102
1874
850
103
1929
875
104
1984
900
105
2039
925
106
2094
950
107
2149
975
Load Index Pounds Kilograms108
2205
1000
109
2271
1030
110
2337
1060
111
2403
1090
112
2469
1120
113
2535
1150
114
2601
1180
115
2679
1215
116
2756
1250
117
2833
1285
118
2910
1320
119
2998
1360
120
3086
1400
121
3197
1450
122
3307
1500
123
3417
1550
124
3527
1600
125
3638
1650
126
3748
1700
When looking at light truck (LT) or newer Special Trailer Service (ST) tires, there are two load indexes branded on the sidewall, separated by a forward slash. Using an LT235/75R15 104/101S Load Range C tire as an example, the load index is 104/101. 104 corresponds to 1,984 pounds, and 101 corresponds to 1,819 pounds. So what is the true load carrying capacity of the tire? The answer changes depending on the situation in which the tire is being used.
Since LT tires are commonly used on trucks with dual rear wheels, they are branded with two load indexes. The first number indicates the load carrying capacity if the tire is installed on a truck with a single-wheel rear axle, and the second number applies when the tire is used in a dual rear application.
Though it may seem counterintuitive that a tire is rated to carry less weight when working in tandem with another tire in the dual pair, the purpose is to build in additional reserve capacity should one of the two tires fail, leaving the sole remaining tire to carry the load normally handled by two tires.
In Germany some highways do not have speed limits and high speed driving is permitted. Speed ratings were established to match the speed capability of tires with the top speed capability of the vehicles to which they are applied. Speed ratings are established in kilometers per hour and subsequently converted to miles per hour (which explains why speed ratings appear established at “unusual” mile per hour increments). Despite the tire manufacturers’ ability to manufacture tires capable of high speeds, none of them recommend the use of their products in excess of legal speed limits. The maximum operating speed of a vehicle must be limited to the lowest speed rated tire on the vehicle.
Speed ratings are based on laboratory tests where the tire is pressed against a large diameter metal drum to reflect its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10 minute increments) until the tire’s required speed has been met.
It is important to note that speed ratings only apply to tires that have not been damaged, altered, under-inflated or overloaded. Additionally, most tire manufacturers maintain that a tire that has been cut or punctured no longer retains the tire manufacturer’s original speed rating, even after being repaired because the tire manufacturer can’t control the quality of the repair.
Over the years, tire speed rating symbols have been marked on tires in any of three ways shown in the following examples:
225/50SR16
225/50SR16 89Sor 225/50R16 89S
Each of these was an acceptable method of identifying speed ratings.
Early tires had their speed rating symbol shown “within” the tire size, such as 225/50SR16. Tires using this type of branding were not to have been produced after 1991.
225/50SR16 112 mph, 180 km/h 225/50HR16 130, 210 km/h 225/50VR16 in excess of 130 mph, 210 km/h
Beginning in 1991, the speed symbol denoting a fixed maximum speed capability of new tires must be shown only in the speed rating portion of the tire’s service description, such as 225/50R16 89S. 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 H 130 mph 210 km/h Sport Sedans & Coupes V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars
When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That ultimately caused the automotive industry to add W- and Y-speed ratings to identify the tires that meet the needs of vehicles that have extremely high top-speed capabilities.
W 168 mph 270 km/h Exotic Sports Cars Y 186 mph 300 km/h Exotic Sports Cars
While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire’s 168 mph, 270 km/h maximum speed.
225/50ZR16 in excess of 149 mph, 240 km/h 205/45ZR17 88W 168 mph, 270 km/h 285/35ZR19 99Y 186 mph, 300 km/h
When the Y-speed rating indicated in a service description is enclosed in parentheses, such as 285/35ZR19 (99Y), the top speed of the tire has been tested in excess of 186 mph, 300 km/h indicated by the service description as shown below:
285/35ZR19 99Y 186 mph, 300 km/h 285/35ZR19 (99Y) in excess of 186 mph, 300 km/h
As vehicles have increased their top speeds into Autobahn-only ranges, 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.
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