Where the Rubber Meets the Road – Understanding Tires

No matter how hot your bike’s engine is, no matter how many performance upgrades you’ve made or if everything is still stock, there’s only one thing that keeps your motorcycle planted on the road, and that’s the tires. Worn or incorrect riding tires can quickly turn a great day of riding into a life-and-death disaster. 

Whether you are replacing a set of worn-out tires or upgrading to improve performance, it is important to know what the specifications of the tires are for your specific bike and how to match the specifications against those of the tires you are considering. 

Anatomy of a Tire

No matter the brand, all tires share similar basic components:

• Tread – where the rubber meets the road, the tread is what gives you grip. There is a wide variety of tread designs depending on the type of tire and the type of motorcycle.
  
• Carcass – the skeleton (so to speak) of the tire, made of steel or fiber cords that run from bead to bead. Every tire is either a bias ply or radial ply. Bias plies are laid at an angle (bias) from bead to bead, and as a result, these tires are stiffer. As a result, they’re often found on heavy touring bikes designed to carry passengers and luggage. In contrast, radial plies are laid directly from side to side. Radial tires dissipate heat better (which increases tire life) and they’re less stiff, allowing them to contour to the road better.
• Bead – where the tire mounts to the wheel. Multiple steel cords are placed in these areas to ensure a snug fit against the wheel and ensure that there’s no leakage in a tubeless tire.
  Sidewall – besides being the place where all the vital tire information is displayed, the sidewall is vitally important, as virtually all the load support and much of the handling is determined by the sidewall design.

Now that we’re familiar with the tire construction, the next step is learning how to decode the sidewall information. Most of what you need to know is molded right into the tire’s sidewall in either metric or alphanumeric. Let’s dissect a typical metric sidewall designation example: 130/90 R 16 67 H (shown here).

• The first number refers to the tire width: 130 indicates the tire is 130mm wide at its widest point when installed and ready to ride. This is referred to as “section width.”
• The second number refers to tire height: 90 indicates the tire’s sidewall aspect ratio; which is 90 percent as tall as measured as it is wide, or 117mm in this example. The lower the aspect ratio, the shorter the sidewall if section width remains unchanged.
• The Letter designation refers to tire construction: For this example, R stands for radial ply. If the carcass design was bias, it would be indicated as “B”.
• The third number is the wheel size: 16 indicates the wheel diameter in inches the tire is designed to fit. In this case a 16-inch wheel.
• The last number refers to the load index: In this case, 67 is the load index designation. In this example 67 informs the consumer that the tire’s maximum load capacity is 661 lbs. (see chart)
• The last letter refers to the load index: In our case, H is the designated rating, which means the tire is suitable for speeds up to 130 MPH.

Alphanumeric tire information is very similar to metric. Let’s use the following example:MT 90 – 16 Load Range B (shown above)

• In this case, the first letter always is M, for “Motorcycle.” However the second letter is important which represents the width or section. Like metric, the number following the section width is the aspect ratio. Like metric again, the next number is wheel size followed by load rating.

Know the Signs of Aging

It’s tempting to look at your tread and think there’s a ton of life left in the rubber. In reality, there’s more to it than simple tread depth, and your tires don’t have to bald, to be out of commission. Here are a couple of things to inspect if it’s been a while between fresh hoops:

• Tread Depth – manufactures incorporate wear bars that run across the tread, and once the wear bars are flush with the tread, it’s time to replace. Another easy trick is use the old penny technique. Place a penny in the tread, and if Honest Abe’s head is covered in some degree, your tires likely have some life in them. In any event, there should be at least 2/32” of tread in any area.
• Age – as a rule of thumb, you should never ride on tires older than five years.
• Cracking – like most things, tires are susceptible to breakdown from sunlight exposure. If your tires have been exposed for long periods of time to direct sunlight, they can experience cracking on the tread or along the sidewalls.
• Cuts and Punctures – frequently check for any kind of damage.
• Losing Pressure – if you notice that a tire is frequently losing air pressure, it’s a sign that you may have a faulty valve stem or bad tire bead. Replace the tire immediately if this is the case.
• Feeling Odd – if when riding the bike feels sloppy, is vibrating, pushing, pulsating or exhibiting any unnatural sensation, it could be your tires.
  
• Bad Tire Pressure – both under-inflation and over-inflation can lead to uneven wear. You will find excessive wear in the center or sides of the tire if not aired up properly. 

When it comes to tire pressure, follow these tips: 

• Always use the suggested air pressure as indicated on the tire’s side wall. If you are going to carry lots of luggage or a passenger, check your bike’s owner’s manual for the recommended increases, but never exceed the maximum tire pressure indicated on the tire’s sidewall.
• Purchase a good tire gauge, as cheap gauges don’t always properly reflect the true tire pressure.
• Check pressure frequently—at least once a week.

While an entire book could be written about motorcycle tires, these basics should help you understand your machine’s rubber a little bit better. Follow these tips, let the tires warm up before really hitting the throttle, and above all, have fun on the road!