If you’ve ever started digging deep into tire comparisons, especially while shopping for off-road tires, you might have seen the term speed rating. Here’s everything you need to know about that single letter you can find on any road tire.
If you go outside right now and look at the tires on your car, you’ll find the service indicator. This code, made up of a number and a letter, includes two pieces of information. A common service indicator is 94V. The 94 is for load index, which indicates the weight category the tire can carry at its factory recommended PSI. But V is for the speed rating.
You probably already put this together, but speed rating refers to a tire’s safe top speed, sustainable for a reasonable length of time. The US Department of Transportation specifies no fewer than 32 different tire speed ratings.
Since this system is borrowed from the Euro standard, each speed rating increases by 5 or 10 kilometers per hour. So while the numbers may seem random in miles per hour, the global standard chart looks nice and neat. Speed ratings A1—A8, B, C, D, and E each increase by 5 kph per rating, while F through Y each increase by 10 kph.
Most road-going, automotive tire speed ratings start with M. The M speed rating guarantees a tire’s safety up to 81 mph with safe tread depth, while inflated to the factory mandated PSI. N is 87 mph, P is 93 mph, and so on. The highest rating is Y, which is 186 mph, or 300 kph. Tires designed to go faster than this are sometimes marked as “(Y)” and sometimes as “Z.”
M — Up to 81 mph
N — Up to 87 mph
P — Up to 93 mph
Q — Up to 99 mph
R — Up to 106 mph
S — Up to 112 mph
T — Up to 118 mph
H — Up to 130 mph
V — Up to 149 mph
W — Up to 168 mph
(W) — Over 168 mph
Y — Up to 186 mph
(Y) — Over 186 mph
Your owner’s manual will let you know what speed rating you need for your vehicle. Many performance cars require Z-rated tires, even though they might not be capable of 187 mph. The 2020 Ford Mustang Shelby GT350R, for example, is factory limited to 180 mph. Even the 2019 Mazda MX-5 Miata, which is only capable of 135 mph, is supposed to get Z-rated tires.
It’s not just sports and performance cars, though. Luxury cars are also capable of huge top speeds these days, compared to their ancestors. Z tends to be the go-to choice for manufacturers, who’ve adopted a strategy of “better safe than sorry.”
This ceiling won’t likely be tested on American highways. Not legally, anyway. Our fastest speed limit is 85 mph, on a stretch of highway outside Austin, Texas. But manufacturers know that some customers don’t always adhere to these speed limits. More importantly, many vehicles are now global, meaning that we Americans get the same cars everyone else does. And since the same model might end up on a German autobahn, the car actually needs to be safe at much higher speeds than it will see here.
Speed ratings really come into play with custom tires— specifically off-road tires on Jeeps, trucks, and SUVs. Tires are heavy, and the Newtonian mechanics of centrifugal force dictate that the faster they spin, the more force they’ll exert on their own structure. Off-road tires tend to be bigger, chunkier, and heavier than their on-road counterparts, and can sometimes be so big and heavy that they’re no longer safe to operate at high speeds.
Some off-road tires aren’t intended for highway use at all. Many have an R, S, or T rating, which means they’re fine at most highway speeds, but no good for a spin on the unrestricted autobahn. This is something to be aware of when you’re shopping for new tires for your off-road beast.
If you look carefully at the speed rating chart above, you’ll notice that H is out of place, alphabetically. When the European standards were first developed in the 1960s, S, H, and V were the only speed ratings. They still hold their designated ratings, but other ratings have since filled in around them, and H is the only one out of alphabetical order.
What about the sub-M tires? Why start in the middle of the alphabet? Lower speed tires are used for other machines. A8 tires, for example, are common on large tractors. It’s not a problem that they’re only designed to go 25 mph, because that’s about as fast as some tractors go. A3-rated tires are for even slower machines like lawn mowers.
Fun fact: The Michelin XDR2 E-4 59/80R63 is one of the largest tires in the world. It contains more than one ton of steel, and each one costs about $40,000. It has a speed rating of B, so it can safely travel at 31 mph when riding under what was once the world’s largest dump truck: The Caterpillar 797B. Yet the truck’s massive double V-12 diesel engines, producing 3,370 total horsepower, can move it along at a brisk 42 mph unloaded.
What about the slowest tire, the A1? What vehicle could possibly use a tire that can’t go faster than 3 mph? Remember, a tire’s speed rating is only half of the service indicator. The other half is the load index, which determines how much weight a tire can safely carry. The two figures are paired. The speed rating is designated around the load index. If you have a V-rated tire, it’s safe to drive at 149 mph under its full weight rating.
So what vehicle travels at extremely slow speeds while carrying a great deal of weight? One of the oldest vehicles in the world: the wheelbarrow. A common, single-wheel barrow can hold up to 400 lbs of rock or cement, and if you’re pushing it with that much weight, you probably won’t be going much faster than 3 mph anyway. And certainly not for an hour straight. A1 is the tire you need.
Unfortunately, we don’t service wheelbarrows, but this A1 wheelbarrow tire is actually made by Carlisle, one of our excellent suppliers.
Both wheelbarrows and ginormous dump trucks are two examples of why speed rating matters. You’d better believe that under its full load of 380 tons, the Caterpillar 787B would damage its tires at its top speed of 42 mph, if it drove at that speed for any sustained period of time.
The same goes for your big Jeep mudders with a sub-M speed rating. You might be able to reach 81 mph just fine, but if you want to cruise at that speed, with a full load of people and gear, for an entire road trip, you could damage your tires and put yourself in an unsafe situation.
If you have questions about speed rating, or tires specs are best for your vehicle, chat with one of our tire tech experts now.
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