Confused about what that letter means right after your tire size? Ever had someone at a tire shop ask what your speed rating was and didn't know what the person meant? Don't know whether you need the more expensive V- or ZR-rated tires that the car came with? Fear not, mighty consumer, for the information here will edify you.

Definition of Tire Speed Ratings

A tire's speed rating is an indication, expressed as a letter code on the tire sidewall, of a speed the manufacturer expects the tire to be able to sustain over a long period of time without coming apart. This is good information to have for a number of reasons, some of which actually include the likelihood of you ever being able to sustain even the lowest of speeds that passenger car tires are rated for.

The speed rating code is semi-alphabetic and goes like this:

B: 50 kph 31 mph

C: 60 kph 37 mph

D: 65 kph 40 mph

E: 70 kph 43 mph

F: 80 kph 50 mph

G: 90 kph 56 mph

J: 100 kph 62 mph

K: 110 kph 68 mph

L: 120 kph 75 mph

M: 130 kph 81 mph

N: 140 kph 87 mph

P: 150 kph 93 mph

Q: 160 kph 99 mph

R: 170 kph 106 mph

S: 180 kph 112 mph

T: 190 kph 118 mph

U: 200 kph 124 mph

H: 210 kph 130 mph

V: 240 kph 149 mph

After V, all ratings begin with ZR and end with either W, Y or (Y). There is probably some entirely rational reason for this which completely escapes everyone else in the entire world. S, H, and V were the original three developed and is why H is out of alpha order.

ZRW: 270 kph 168 mph

ZRY: 300 kph 186 mph

ZR(Y): 300+ kph 186+ mph

Obviously, most of these ratings are for tires that do not go on passenger cars. The lowest speed rating you will probably ever see on a passenger car or truck tire is either S or T, which appear most often on dedicated snow tires. You can see that there is quite a safety cushion built into the system–how long do you think you're going to sustain 112 miles per hour on snow tires? How many times do you think you might even reach 112 miles per hour on snow tires?

How to Use Tire Speed Ratings When Buying

However, there is another use for this information–it gives you an idea of how well the tires are built for speed. In general, speed ratings of V or above mean that the tire has extra cap plies or even multiple steel belts to provide extra stability at very high speeds. It's built better to perform better. If you're looking for a tire to run on the Autobahn in your M3, you probably want something in the ZR range. Likewise, if you're looking to put inexpensive shoes on a minivan, you probably don't need V-rated tires, even if they were the original equipment manufacturer (OEM) choice.

It's hard to understate the importance of knowing what the speed ratings really mean. If for example, the manufacturer did put V-rated tires on that minivan, it can be difficult to convince many tire places to put an H-rated on as a replacement. This is less about selling more expensive tires, although that ends up being the functional consequence, and more about fears of liability. The “official line” that tire sellers generally get is, “Don't ever put on a lower speed rating than what was already on the car.”

This, although good advice in general, has to be balanced against the car manufacturers' predilection for putting increasingly over-rated tires onto new cars. This is something that you as a consumer should be aware of. Do you need the more expensive, better-built tire that will perform beautifully at 90 mph, or will you be better off with the cheaper one that works just fine at 65–75 mph but maybe doesn't do as well at 90–100 mph and might fail at 150 mph? That's ultimately a choice for you, not the tire seller.

A caveat: The speed ratings are based on lab conditions and don't take into consideration an extra-heavy load in the vehicle or the heat and condition of the pavement. Maybe your tires aren't perfectly aligned or inflated, which will also affect their performance. The rating does not represent exactly the maximum speed that you can drive on them in real-world conditions. Consult your owner's manual for other warnings or advice related to your specific vehicle.