Understanding Tire Designations
Deciphering Your Tire — A Method to the Madness
Have you ever looked at a tire and wondered what all of the numbers and letters listed on the sidewall mean? Have you ever thought that all those letters and numbers look kind of random and meaningless? Of course you have!
At first glance, you would be forgiven for thinking that tire information looks like something that a team of drunken monkeys banging away at typewriters would crank out. However, after a little bit of time and effort you will be able to decode all of the wonderful information on your tire yourself … amazing your friends, impressing your co-workers, and mystifying onlookers.
For our examples, the tire that we will be referring to is the rear tire from a 2003 Softail® Deuce® (although the information applies equally well to all tires). The relevant information from the Deuce tire is:
Dunlop K591 160/70 B 17 M/C 73V Max. Load 365 kg (805 lbs) at 290 kpa (42 psi) Cold
Dunlop K591
This series of letters indicates the tire manufacturer and model number. It is important to make sure that your front and rear tires match; that they are the same model made by the same manufacturer.
Tires vary in construction strength, material composition, warm-up requirements, and ride quality. Due to this, most modern tires are designed to be used as a matching set. It is potentially dangerous to ride on mismatched tires, as these tires will behave differently under different road stresses.
160/70
This first set of numbers, the designation 160/70, is a metric description for the size of the tire. 160 is the width of the tire in millimeters. Simple enough, right? The number 70 is a little more complex, however. To understand what it means, you first have to understand how the height of tires is measured.
The height of a tire is not how tall a tire is; instead, the height of a tire is determined by measuring from the inside diameter of the tire (the big hole where the rim fits) to the top of the tire's tread. 70 is the aspect ratio that describes the height of a tire as a ratio of the tire's width. Confused yet? Put simply, the number 70 means that the tire is 70% as tall as it is wide. Thus, if your tire is 160 mm wide, and the number behind the slash is 70, your tire height is 70% of 160, or 112 mm.
What if your tire doesn't have a number that looks like 160/70? What if your tire has something that looks like MT90 instead? This letter designation still tells you the width and height of your tire, just in a slightly different format. In this form, the letter M means that the tire is designed for use on motorcycles. The letter T tells you the tire width code (see table below), which can be used to determine the width of the tire. 90 is the aspect ratio of the height of the tire in terms of the tire's width (see above).
Front Tires Letter Designation Metric Conversion
MH90 80/90
MJ90 90/90
MM90 100/90
MN90 110/90
MR90 120/90
MT90 130/90
Rear Tires Letter Designation Metric Conversion
MN90 110/90
MP85 120/90
MT90 130/90
MU90 140/90
MV85 150/90
Knowing your tire's height and width will tell you a lot about the handling characteristics of a particular tire. For instance, a narrow tire is great for low-speed maneuverability, but its narrow dimensions make it relatively unstable at high speeds. Wider tires are great for high-speed stability, but their width makes them difficult to maneuver in tight spaces (parking lots, city streets, and that pesky driver's license test).
The height of a tire can also tell you a lot about a tire's ride quality. Tires with a high aspect ratio usually translates into a softer, more comfortable ride that is well suited to long-distance hauls. However, because the sidewalls of this type of tire flex a fair amount (this is what gives a tire its cushy feel) they are not well suited to high speed cornering. Tires with a small aspect ratio typically offer a firmer ride and also transmit a lot of feedback from the road. While this translates into a rougher ride, it also means that they are more steady and manageable … especially in high speed turns.
B
This letter tells you a little bit about the process used in the construction of the tire. B means that the tire is a belted bias tire. An R would mean that the tire is a radial tire. While bias tires and radial tires both do a good job of supporting your motorcycle, many of their ride characteristics are radically different. For this reason, bias tires and radial tires should not be used on the same motorcycle unless specifically recommended by the manufacturer.
17
This number tells you the diameter of the rim that the tire fits on, in inches. So the 17 listed here means that the rim the tire fits is 17 inches in diameter.
V
This is the speed rating of the tire (see chart below). The speed rating is the maximum speed a tire should be ridden at under its recommended load capacity. This speed should not be exceeded; doing so will not only dramatically reduce the life of the tire, but can even cause the tire to fail while you are riding.
Tire Speed Ratings Rating Speed
Q Up to 99 mph
S Up to 112 mph
T Up to 118 mph
U Up to 124 mph
H Up to 130 mph
V Up to 149 mph
W Up to 168 mph
Y Up to 186 mph
Z 149 mph and over
Max. Load 365 kg (805 lbs)
This is the maximum weight that the tire is capable of handling when properly inflated, including the weight of the motorcycle, rider, passenger, and gear. Each tire will have a maximum load rating. The combination of these load ratings is the total amount of weight that the tires are capable of supporting.
Keep in mind that this total is likely to be greater than the GVWR of the motorcycle, the total amount of weight that the motorcycle itself can support (including motorcycle, rider, passenger, and gear). The GVWR for a motorcycle can be found in the owner's manual, the service manual, or on a label located on the motorcycle's front frame down tube. Listed with the GVWR will also be listings for the maximum amount of weight that each wheel's axle can support. Make sure that your motorcycle's load is properly balanced so as not to exceed each axle's weight limit or each tire's load rating, and never load your motorcycle with more gear than either the GVWR or tire load rating recommends.
290 kpa (42 psi) Cold
This indicates the maximum amount of air pressure that the tire should hold when the motorcycle is fully loaded. Take note that this is the maximum air pressure for the tire, not the recommended pressure for the tire. It is usually recommended by the manufacturer that a tire is inflated to a few psi less than the maximum pressure rating … how much less will depend on the tire and the manufacturer (see Avon, Bridgestone, Cheng Shin, Continental, Dunlop, Metzler, Michelin, Pirelli, and other tire manufacturers for more information). For instance, the tire in our example has a maximum tire pressure of 42 psi; however, the recommended tire pressure (according to the Dunlop website) is between 36 and 40 psi.
Tire pressure should always be checked when the tire is cold, before you ride your motorcycle. Getting an accurate tire pressure reading is dependant on all the air in the tire exerting the same pressure. Because warm air exerts more air pressure than does cold air, and because a tire will not heat uniformly — the center strip of a tire typically heats the fastest as it has the most contact with the road — all the air inside a warm tire will not exert the same pressure, leading to inaccurate tire pressure readings.
Tire pressure should be checked several times a month to ensure that you have enough air pressure in your tires. You absolutely must check your tire pressure before riding if you have not ridden your motorcycle more than one week. We estimate that between 3 and 7 psi of air pressure can be lost per week when a motorcycle is not ridden.
This is due to the fact that while the tire and rim form an almost air-tight seal, the key word is almost. Cooler temperatures, due to weather or inactivity, cause both the rim and the tire to shrink imperceptibly … leaking small amounts of air in the process.
Over 80% of the motorcycles on the road have markedly underinflated (having 30 psi of air pressure or less). Many have only 5 psi … less than 15% of what they should have. These tires are so underinflated that their lifespans are shortened by several thousand miles, and riding on them is potentially dangerous. Given that new tires are typically several hundred dollars in cost, maintaining the proper air pressure in your tires can save you a lot of money … as well as a trip to the emergency room.
Deciphering Your Tire — A Method to the Madness
Have you ever looked at a tire and wondered what all of the numbers and letters listed on the sidewall mean? Have you ever thought that all those letters and numbers look kind of random and meaningless? Of course you have!
At first glance, you would be forgiven for thinking that tire information looks like something that a team of drunken monkeys banging away at typewriters would crank out. However, after a little bit of time and effort you will be able to decode all of the wonderful information on your tire yourself … amazing your friends, impressing your co-workers, and mystifying onlookers.
For our examples, the tire that we will be referring to is the rear tire from a 2003 Softail® Deuce® (although the information applies equally well to all tires). The relevant information from the Deuce tire is:
Dunlop K591 160/70 B 17 M/C 73V Max. Load 365 kg (805 lbs) at 290 kpa (42 psi) Cold
Dunlop K591
This series of letters indicates the tire manufacturer and model number. It is important to make sure that your front and rear tires match; that they are the same model made by the same manufacturer.
Tires vary in construction strength, material composition, warm-up requirements, and ride quality. Due to this, most modern tires are designed to be used as a matching set. It is potentially dangerous to ride on mismatched tires, as these tires will behave differently under different road stresses.
160/70
This first set of numbers, the designation 160/70, is a metric description for the size of the tire. 160 is the width of the tire in millimeters. Simple enough, right? The number 70 is a little more complex, however. To understand what it means, you first have to understand how the height of tires is measured.
The height of a tire is not how tall a tire is; instead, the height of a tire is determined by measuring from the inside diameter of the tire (the big hole where the rim fits) to the top of the tire's tread. 70 is the aspect ratio that describes the height of a tire as a ratio of the tire's width. Confused yet? Put simply, the number 70 means that the tire is 70% as tall as it is wide. Thus, if your tire is 160 mm wide, and the number behind the slash is 70, your tire height is 70% of 160, or 112 mm.
What if your tire doesn't have a number that looks like 160/70? What if your tire has something that looks like MT90 instead? This letter designation still tells you the width and height of your tire, just in a slightly different format. In this form, the letter M means that the tire is designed for use on motorcycles. The letter T tells you the tire width code (see table below), which can be used to determine the width of the tire. 90 is the aspect ratio of the height of the tire in terms of the tire's width (see above).
Front Tires Letter Designation Metric Conversion
MH90 80/90
MJ90 90/90
MM90 100/90
MN90 110/90
MR90 120/90
MT90 130/90
Rear Tires Letter Designation Metric Conversion
MN90 110/90
MP85 120/90
MT90 130/90
MU90 140/90
MV85 150/90
Knowing your tire's height and width will tell you a lot about the handling characteristics of a particular tire. For instance, a narrow tire is great for low-speed maneuverability, but its narrow dimensions make it relatively unstable at high speeds. Wider tires are great for high-speed stability, but their width makes them difficult to maneuver in tight spaces (parking lots, city streets, and that pesky driver's license test).
The height of a tire can also tell you a lot about a tire's ride quality. Tires with a high aspect ratio usually translates into a softer, more comfortable ride that is well suited to long-distance hauls. However, because the sidewalls of this type of tire flex a fair amount (this is what gives a tire its cushy feel) they are not well suited to high speed cornering. Tires with a small aspect ratio typically offer a firmer ride and also transmit a lot of feedback from the road. While this translates into a rougher ride, it also means that they are more steady and manageable … especially in high speed turns.
B
This letter tells you a little bit about the process used in the construction of the tire. B means that the tire is a belted bias tire. An R would mean that the tire is a radial tire. While bias tires and radial tires both do a good job of supporting your motorcycle, many of their ride characteristics are radically different. For this reason, bias tires and radial tires should not be used on the same motorcycle unless specifically recommended by the manufacturer.
17
This number tells you the diameter of the rim that the tire fits on, in inches. So the 17 listed here means that the rim the tire fits is 17 inches in diameter.
V
This is the speed rating of the tire (see chart below). The speed rating is the maximum speed a tire should be ridden at under its recommended load capacity. This speed should not be exceeded; doing so will not only dramatically reduce the life of the tire, but can even cause the tire to fail while you are riding.
Tire Speed Ratings Rating Speed
Q Up to 99 mph
S Up to 112 mph
T Up to 118 mph
U Up to 124 mph
H Up to 130 mph
V Up to 149 mph
W Up to 168 mph
Y Up to 186 mph
Z 149 mph and over
Max. Load 365 kg (805 lbs)
This is the maximum weight that the tire is capable of handling when properly inflated, including the weight of the motorcycle, rider, passenger, and gear. Each tire will have a maximum load rating. The combination of these load ratings is the total amount of weight that the tires are capable of supporting.
Keep in mind that this total is likely to be greater than the GVWR of the motorcycle, the total amount of weight that the motorcycle itself can support (including motorcycle, rider, passenger, and gear). The GVWR for a motorcycle can be found in the owner's manual, the service manual, or on a label located on the motorcycle's front frame down tube. Listed with the GVWR will also be listings for the maximum amount of weight that each wheel's axle can support. Make sure that your motorcycle's load is properly balanced so as not to exceed each axle's weight limit or each tire's load rating, and never load your motorcycle with more gear than either the GVWR or tire load rating recommends.
290 kpa (42 psi) Cold
This indicates the maximum amount of air pressure that the tire should hold when the motorcycle is fully loaded. Take note that this is the maximum air pressure for the tire, not the recommended pressure for the tire. It is usually recommended by the manufacturer that a tire is inflated to a few psi less than the maximum pressure rating … how much less will depend on the tire and the manufacturer (see Avon, Bridgestone, Cheng Shin, Continental, Dunlop, Metzler, Michelin, Pirelli, and other tire manufacturers for more information). For instance, the tire in our example has a maximum tire pressure of 42 psi; however, the recommended tire pressure (according to the Dunlop website) is between 36 and 40 psi.
Tire pressure should always be checked when the tire is cold, before you ride your motorcycle. Getting an accurate tire pressure reading is dependant on all the air in the tire exerting the same pressure. Because warm air exerts more air pressure than does cold air, and because a tire will not heat uniformly — the center strip of a tire typically heats the fastest as it has the most contact with the road — all the air inside a warm tire will not exert the same pressure, leading to inaccurate tire pressure readings.
Tire pressure should be checked several times a month to ensure that you have enough air pressure in your tires. You absolutely must check your tire pressure before riding if you have not ridden your motorcycle more than one week. We estimate that between 3 and 7 psi of air pressure can be lost per week when a motorcycle is not ridden.
This is due to the fact that while the tire and rim form an almost air-tight seal, the key word is almost. Cooler temperatures, due to weather or inactivity, cause both the rim and the tire to shrink imperceptibly … leaking small amounts of air in the process.
Over 80% of the motorcycles on the road have markedly underinflated (having 30 psi of air pressure or less). Many have only 5 psi … less than 15% of what they should have. These tires are so underinflated that their lifespans are shortened by several thousand miles, and riding on them is potentially dangerous. Given that new tires are typically several hundred dollars in cost, maintaining the proper air pressure in your tires can save you a lot of money … as well as a trip to the emergency room.