Motorcycle Tires 101 – All About Motorcycle Tires

Motorcycle Tire Components and Anatomy

Each part of a motorcycle tire is engineered to influence every aspect of its performance.

• Tread: The part of the tire that touches the ground. On street tires, the main function of tread is to disperse water so traction is maintained when the pavement is wet. Racing motorcycles may use “slicks” with no tread, but only in dry conditions. Off-road tires have more aggressive tread designed to bite into an unpaved surface. Between racing slicks and the most-aggressive off-road “knobbies” are a variety of tread patterns designed for specific situations, or just for cosmetic appeal.
• Bead: The part of the tire that contacts the inside of the wheel rim. The bead both grips the wheel and, in the case of a tubeless tire, seals air within the tire.
• Sidewall: This is the portion of the tire between the outer edge of the tread and the bead. The height, shape and construction of the sidewall plays a major role in how the tire handles, and its load rating.
• Carcass: Usually refers to the construction of the tire under the tread. Motorcycle tires may bias-ply or radial construction.

WHAT ARE THE DIFFERENT Types of Motorcycle Tires?

Motorcycle tires are designed to perform on a specific type of motorcycle and surface.

• Street Tires: For daily use on paved roads, typically made with a harder rubber compound to provide longer tread life.
• Performance Tires: Generally have a lower aspect ratio, minimal tread, are designed to provide traction when the motorcycle is ridden aggressively, and will have a high speed rating. They may have a softer tread compound that grips well but also will wear more quickly than other street or touring tires.
• Touring Tires: Engineered to carry the anticipated load of a heavier motorcycle, a passenger and luggage, and designed for long wear and a smooth ride.
• Off-Road Tires: So-called “knobbies” have a very aggressive, blocked tread designed to dig into dirt and sand. Within this category are tires designed for casual trail riding and for different types of off-road competition. Most can be used on the road, but may not handle well on a paved surface.
• Dual-Purpose Tires: These tires split the difference between a street tire and an off-road tire, and are intended for dual-purpose bikes that may be ridden on or off the pavement. The tread may be more aggressive than a street tire, but not nearly as blocky as a pure off-road tire. Within this category are a variety of tread patterns that may skew more towards off- or on-road use.
• Tubeless Tires: These tires do not use an inner tube.
• Tube-Type Tires: These tires require an inner tube, and are common on bikes with wire-spoke wheels, which in most cases will not hold air without a tube.
• Bias-Ply Tires: Refers to the way the tire is constructed, with its inner reinforcing belts or cords running at a 30 to 40 degree angle to the tire bead.
• Radial Tires: Refers to the way the tire is constructed, with its inner reinforcing belts or cords running directly across the tire from bead to bead.
• Slicks: Tires with no tread for use in road or drag racing. Slicks maximize traction in dry conditions and are designed with a very soft rubber compound that needs high temperatures to grip the pavement. They are not safe (or legal) for use on the road.

WHAT’S THE DIFFERENCE BETWEEN Big Tires vs Small Tires?

Tires are selected by the motorcycle manufacturer as a component of the chassis, and in many cases the motorcycle and tire manufacturer work together to engineer a tire for a specific motorcycle. Changing tire size can upset this equation. Trying to install a larger tire, for example, could result in interference with other parts of the motorcycle. A tire that has a taller or shorter aspect ratio may change the ride height and have a negative effect on steering geometry of the chassis. Changing to wider tires may also affect the way the motorcycle responds to steering input, and those tires may not fit properly on the motorcycle rims. For all of these reasons, Harley-Davidson recommends that replacement tires should always be of the same size and tire model as supplied on Original Equipment.

When is it Time to Replace Motorcycle Tires?

There are a few telltale signs that can indicate when to replace a motorcycle’s tires. Riding on worn, damaged or old motorcycle tires can compromise your safety. Here are some indications of when to replace your motorcycle tires.

• If Your Tires are Worn: Worn tires provide reduced traction, adversely impact stability and handling, and may be more easily damaged, potentially leading to tire failure. It’s time to consider installing new tires when tread depth reaches 2/32 inch, and tires should be considered worn out and unsafe when tread depth is 1/32 inch or less. Most tires have wear bars molded into the grooves of the tire tread. There may be a small triangular indicator on the tire sidewall that points to the location of the wear bars. Tires should be replaced before the tread wears down to the level of the wear bars. The traction of off-road tires will diminish as the tread wears, and the rear tire usually wears out at twice the rate of the front.
  
  It can sometimes be challenging to see the wear bars. Harley-Davidson offers three tire pressure gauges that feature a tool for measuring tire tread depth.
• If Your Tires are Old: Professionals recommend replacing motorcycle tires every six years, as indicated by the date-of-manufacture code on the sidewall. Even if older tires appear to be in good shape, the rubber compound can begin to dry out over time, and the internal construction can deteriorate.
  
• If the Sidewalls are Weathered: Inspect the tire sidewalls for small cracks that make the tire appear to be drying out. The UV in bright sun can age the tires in this manner if the bike is usually parked outdoors.
  
• If Your Tire is Damaged: Consider the repair of a punctured tire or tube a temporary “get home” procedure. A repaired tire loses its speed rating and should be replaced. Harley-Davidson recommends that when riding on a repaired tire, speed should not exceed 50 mph for the first 24 hours after repair, and the repaired tire should never be used over 80 mph.
  
• If There’s Cupping or Uneven Wear of the Tread: Tread that is wearing unevenly can affect handling and cause uncomfortable vibration. It may also be an indication of another problem, such as an unbalanced wheel, a bent or mis-aligned axle, a damaged wheel rim, or a bad wheel bearing. A professional technician can often diagnose other problems by looking at uneven tread wear. 
  

How to Break in Motorcycle Tires

Riding on a new set of motorcycle tires can be like walking in a new pair of shoes – it can take a little while for either to become broken in and comfortable. Follow these tips to learn how to break in motorcycle tires and get off to a good start.

• Take it Easy – Some, but not all, new motorcycle tires may have a light coating of a substance called mold release that allows the tire to pop cleanly out of its mold. Does your new tire look shiny and feel a little slippery? That’s mold release. It will quickly wear off as you ride, but it can also make the tire feel a little slick, especially if the road is wet. It’s best to avoid any aggressive moves until the entire tread area looks normally scuffed up.
• Feel Your Way – Even if your new tires are the same size and brand as your old tires, they might feel a little different on the bike. As tires wear, the tread profile and tread depth change, which can impact how the motorcycle handles. Take it easy on your new tires while you feel out any changes in handling.
• Count Your Miles – Ride in a variety of situations – around town, down the freeway and on curvy backroads – for the first 100 miles on new tires to break them in before you try pushing the limits of traction.

Tire size can be expressed in three different ways: Metric (the most common), alpha-numeric, and inches.  

Metric Example: 180/55B18 80H BW (the code on the sidewall)

o   180: Width of the tire tread in millimeters.

o   55: The aspect ratio; the profile of a tire in cross-section.

o   B: Construction type. B indicates this is a bias-ply tire. The letter R would indicate a radial tire. If there is no letter, the tire is bias-ply.

o   18: The size of the wheel rim the tire will fit, in this case 18 inches.

o   80: This is the tire load rating. 80 indicates a load rating of 992 pounds. The rating scale goes from 33 to 90, and the higher the number the higher the load rating.

o   H: The speed rating, in this case the H indicates a rating of 130 mph.

o   BW: Indicates this tire has black sidewalls. WW would indicate white wall tires.
 

Alpha-Numeric Example: MT90B16 72H WW (the code on the sidewall)

o   MT: This code indicates the tire width. In this case MT indicates a width of 130mm.

o   90: The aspect ratio; the profile of a tire in cross-section.

o   B: Construction type. B indicates this is a bias-ply tire. The letter R would indicate a radial tire. If there is no letter, the tire is bias-ply.

o   16: The size of the wheel rim the tire will fit, in this case 16 inches.

o   72: This is the tire load rating. 72 indicates a load rating of 782 pounds. The rating scale goes from 33 to 90, and the higher the number, the higher the load rating.

o   H: The speed rating, in this case the H, indicates a rating of 130 mph.

o   WW: This is a white wall tire.
 

Numeric Example: 4.00x18 64S (the code on the sidewall) 

This code is expressed in inches and is usually seen on reproduction vintage tires. It will not have a construction type because these tires are always bias ply. 

o  4.00: Tire tread width in inches. 

o  17: The size of the wheel rim the tire will fit in inches. 

o  64: The load rating, in this case 64 indicates a maximum load rating of 617 pounds. 

o  S: The speed rating, in this case the S indicates a rating of 112 mph. 

What is Tire Aspect Ratio?

The aspect ratio indicates the profile of a tire in cross-section as a ratio of the tread width to the height of the tire, measured from the bead to the center of the tread. Aspect ratio is part of the tire size code on the sidewall. For example, a tire with 180mm tread width and an aspect ratio of 55 will have a sidewall that is 99mm high, or 55 percent of the tread width. The lower the ratio, the wider the tread in comparison to the sidewall. A tire with a low aspect ratio usually has a stiffer sidewall. This is the type of tire seen on a performance motorcycle that places a premium on handling. In a tire with a taller aspect ratio the sidewall will flex more and offer a smoother ride, preferred for commuting and touring. 

Motorcycle Tire Date Code

Every motorcycle tire has a date code on the sidewall that indicates when the tire was manufactured. The code is preceded by DOT (Department of Transportation), followed by a series of numbers. The last four digits are the date code – the first two numbers represent a week, and the second pair indicates a year. For example, a tire with a code of 3522 was manufactured in the 35th week of 2022. Tire manufacturers generally recommend replacing any tire that is more than six years old, even if it appears to be in good condition. Checking this code is important if you are buying a used motorcycle to determine if the tires should be replaced.

Tire Pressure

Maintaining correct tire pressure is critical for both safety and long tire life. Over or under inflating tires can cause them to wear unevenly, and can also affect motorcycle handling. Riding with low tire pressure can cause the tire to over-heat, which can lead to dangerous tire failure. Harley-Davidson recommends checking tire pressure before every ride. Tires will normally lose two pounds of air pressure in about 30 days. If you see tire pressure has dropped suddenly, you could have a damaged tire, a damaged rim or a faulty tire air valve, and should have the tire and wheel inspected by a professional technician.  Quality Harley-Davidson® Tire Pressure Gauge tools offer dependable accuracy. The Harley-Davidson® Compact Air Compressor with Light is a great accessory to add to your travel gear.

Check your motorcycle’s operator’s manual for your bike’s recommended pressure. Tire pressure should be checked when the tires are cold, after the motorcycle has not been ridden for two hours. As the tires warm from riding, the pressure will go up a little. Ambient air pressure will also affect tire pressure. A Harley-Davidson® operator’s manual has a chart to help you determine the best tire pressure depending on ambient temperature, and if the motorcycle has recently been ridden. If you add air to warm tires, Harley-Davidson recommends checking and adjusting the tire pressure after the tires have been allowed to cool.

Check your motorcycle’s operator’s manual for your bike’s recommended pressure. Tire pressure should be checked when the tires are cold, after the motorcycle has not been ridden for two hours. As the tires warm from riding, the pressure will go up a little. Ambient air pressure will also affect tire pressure. A Harley-Davidson® operator’s manual has a chart to help you determine the best tire pressure depending on ambient temperature, and if the motorcycle has recently been ridden. If you add air to warm tires, Harley-Davidson recommends checking and adjusting the tire pressure after the tires have been allowed to cool.

Tire Speed Ratings

The speed rating indicates the maximum speed at which a tire can be used based on maximum load and inflation pressure. The sidewall code will indicate the speed rating, from “J” (62 mph) to “Y” for 186 mph. A “Z” or “ZR” rating has no maximum speed. When replacing tires, make sure the new tires have the speed rating specified by the motorcycle manufacturer.