Motorcycle Tire Basics
Unless you're a professional or amateur motorcycle racer, rider, enthusiast, or are otherwise ultra-conscious of your bike's tires, a safe guess says that round and black is most of what many motorcyclists know - or care to know - about the tires mounted to the wheels of their trusty two-wheeled steed.
Yet, ignorance of tire knowledge is understandable to a point. Once the tires are purchased, mounted to the wheels and inflated, their presence is easy to forget: tires produce only a small amount of noise when rolling at speed, are difficult to see while riding, and the only routine care necessary in most cases is checking for proper inflation.
Many tires are designed to last for thousands of miles of trouble-free service with very little upkeep. Understanding some basic tire knowledge will help you better care for your rubber and make you an informed consumer when the time comes to get some new round, black hoops.
The simplest route to choosing new tires is to install tires identical to those you're replacing. This is fairly easy if you're riding a motorcycle manufactured within the past 10 to 15 years.
Many motorcycle tire companies today still produce tires that are either identical to those you're replacing, or are suitable replacements designed to work with your specific model of motorcycle. At the very least, if an identical replacement isn't available, tire manufacturers will offer a number of tires that will work in the broader category of your type of motorcycle, i.e. the 600cc sportbike class or the heavyweight touring motorcycle segment.
However, best practice is to select replacement tires identical to those currently on the motorcycle.
A fact too infrequently mentioned is that motorcycle manufacturers will go to great lengths to develop a motorcycle's handling performance around a tire of particular construction.
Motorcycle companies will work directly with one, perhaps two, tire manufacturers to produce a tire set that will allow the motorcycle to perform exactly how the bike maker intended. Selecting a tire with different dimensions, even marginally different than the tire fitted as original equipment, can dramatically alter the way a motorcycle steers, stops or accelerates.
A large touring motorcycle requires tires capable of handling the combined weight of the motorcycle, rider, passenger, and whatever items the rider and passenger bring along. The motorcyclist should remain diligent in keeping the bike's total load within the load capacity maximums listed on the tire, as well as in the motorcycle owner's manual.
Often these changes in the bike's performance are for the worse, although there are instances where handling improves when a tire slightly different than the original is used. Knowing your motorcycle intimately will help you determine if the motorcycle manufacturer intended a specific tire for your machine.
The primary piece of data needed to begin your tire search is the exact model and year of your motorcycle. With this seemingly trivial bit of information we can immediately offer you a number of tire choices from a variety of tire makers. At that point you might choose to select the least expensive tire, and call your job done.
On the other hand you might want to choose between longer wearing tires for increased mileage, or those that provide mileage similar, or slightly less, to your original tire, but offer increased grip performance. Tire makers also design tires claimed to provide a smoother ride, quicker warm up time, or any number of other features that enhance tire quality.
The next step in better knowing the tires that will work on your ride is understanding tire size dimensions. Modern street tires have size data embossed on the tire's sidewall. Metric sizes generally consist of three numbers arranged in this manner: XXX/XX x XX.
The first number is the tire's width expressed in millimeters, though the mm designation isn't printed next to the number. The second number following the slash mark is what's known as the tire's aspect ratio. This is the height of the tire's sidewall expressed as a percentage of the tire's width - put simply, it's a ratio of height to width. The final number refers to the wheel diameter (also the inner circle of the tire) expressed in inches.
For the sake of easily understanding how to read a tire's metric size dimensions, we'll use a common rear tire size found on modern sportbikes: 180/55 x 17.
The number 180 tells us the tire is 180mm at its widest point, while the second number, 55, says that the tire's sidewall height is 55-percent (roughly 99mm) of the width of the tire. Finally, 17 tells us that this tire is for a wheel measuring 17 inches in diameter. The front tire will use the same sizing convention, but unlike most automobile tires that have matching sizes front and rear, the front tire on a motorcycle is almost always narrower than the rear, even if the particular bike uses identical diameter wheels for front and back.
Of course, a simple look at a motorcycle's tires will reveal the disparity in widths of the front and rear tires. But in our ever-litigious society tire makers want to ensure consumers, and even professional motorcycle mechanics, know which tire is for the front and rear, so it's not uncommon to see Front or F embossed on a front tire, and Rear or R embossed on a rear tire.
You'll often also see a rotational direction indicator to prevent you or the shop from mounting the tire backwards for lack of a better term since most tread patterns are designed to work in one direction in order to effectively disperse water from the tire.
Along with the tire's dimension numbers, you might also see a letter or two mixed in. The first letter is the tire's speed rating and indicates the maximum speed for which the tire was designed. A second letter may follow the first, indicating the type of construction: "R" (radial), "B" (bias belted) or "_" (bias).
If you ride an older motorcycle, particularly some makes of cruisers, your tires might use an alphanumeric convention to relay size info. For example, you might see MT90-16 on the rear tire.
Converted to the metric tire dimension system the above rear tire's dimensions would roughly read: 130/90 x 16. However, many current model cruisers, including those from Victory Motorcycles® and Harley-Davidson®, now display tire dimensions on bike model spec charts using the metric reading. Your local shop shouldn't have any trouble helping you find a metric equivalent if your current tires use the alphanumeric system.
Note that the speed index letter (W) next to the load index number (58) is different than the tire's Z speed rating designation in the dimensions area. This load/speed index (58W) tells us that when the maximum listed inflation pressure is used the tire may be safely ridden to a maximum speed of 168 mph so long as the tire's load doesn't exceed 520 pounds.
The obvious thing to take away from this is that while the tire is rated for speeds in excess of 149 mph, it isn't designed to do so when burdened to its maximum load capacity, hence the load/speed index indicator.
Other important tire information that falls into that all-too-infrequently-mentioned category relates to the type of tire construction, and new/old tire combos.
Referring to our earlier note about how motorcycle manufacturers design their motorcycles with a specific tire in mind, we need to point out that a tire's construction, whether radial, belted-bias, bias, etc., plays a huge role in a motorcycle's handling performance. What you need to know here is that, generally, you shouldn't use a mix of a bias-ply tire and a radial construction tire on the same bike if the bike didn't come originally equipped as such. Doing so may adversely affect the motorcycle's handling.
Nearly as important as avoiding mixing tire construction types is installing one new tire instead of two - specifically replacing a new front tire while still using a worn rear. This cheapskate mixing of new versus worn could potentially cause instability in the bike's handling.
Since a motorcycle's rear wheel is the driven wheel, it's not uncommon that the rear tire wears sooner than the front, leaving the front tire with many more good miles. Replacing a rear tire without replacing a front tire that's still serviceable may be moderately less risky than doing the opposite. But again, employing best practices says replace tires in pairs if you can.
Another component of tire construction involves construction materials (the chemistry of ingredients that make up the tread area) and their arrangements.
A recently popular type of construction is to use two different rubber compounds in the same tire - a longer-wearing center section with a grippier compound in the shoulders of the tire for better cornering performance.
Of course, using some logic and a little simplification says that if one material is softer then it's probably going to wear sooner than the harder material, but a motorcycle almost always spends more time in a straight line - on the center of the tire - than it does on its edges, and tire manufacturers endeavor to provide dual-compound tires that wear as evenly as possible from side to side, thereby avoiding what seems like the obvious trade-off of having two different tread materials on one tire.
Like anything for sale on the open market, every tire maker producing dual-compound tires, or any tire for that matter, claims it has a unique concoction that makes its tire stand apart from the rest. And some tire makers are currently bucking the dual-compound trend, and instead using a proprietary construction that allows the tire to use a single compound but mimics the performance of a dual-compound tire.
Most dual-compound tires are marketed to the sport and sport-oriented motorcycle segment, including sport-tourers. However, some d-c tires are finding their way on to larger, touring type motorcycles.
Motorcycle tires vary in their type of construction. The tire in this graphic, Dunlop's Sportmax Roadsmart II, is of radial construction, and also uses a dual-compound tread. The center section on the rear tire is harder, therefore longer wearing, while the edges of the tread use a softer compound to enhance tire grip while cornering.
Safety Tips for Off-Road and Dual-Sport Motorcyclists
1. Air pressure: Always maintain the recommended tire pressure for the type of terrain on which the motorcycle is being ridden; check the owner's manual. Underinflated tires may cause wheel damage when ridden on rocky, rough terrain and allow the motorcycle to squirm or wander on smooth, hard terrain. Overinflation may damage the tires and cause an unnecessarily harsh ride. To accurately measure tire pressure, use a standard tire-pressure gauge.
2. Condition: Check for cuts and gouges that may cause air leakage. Also, check the tires for missing knobs and excessive wear.
3. Wheels: To avoid loss of control or injury, make sure axle nuts are tight and secure. Grasp each tire at the front and rear and try to rock it on its axle to detect worn-out bearings or loose nuts. There should be no free play or slip as you rock the wheel. Inspect wheels for broken or loose spokes and for cracks on the hub or rim.
Motorcycle tires vary in their type of construction. The tire in this graphic, Dunlop's Sportmax Roadsmart II, is of radial construction, and also uses a dual-compound tread. The center section on the rear tire is harder, therefore longer wearing, while the edges of the tread use a softer compound to enhance tire grip while cornering.
Tires Are Maintenance-free, Right?
Out of sight, out of mind is the attitude most of us have toward tire care. Yet a few simple precautions and checks is all that most tires require. Chief among those checks is your tire's inflation pressure.
Tires typically don't shed pounds of air overnight. Nevertheless, a weekly check (if not before every ride) of the tire's air pressure with a good-quality air gauge will only take seconds, and the benefits of keeping the tire within its proper inflation range are numerous.
Other basic upkeep, while not necessary, includes cleaning. A clean tire sidewall can really jazz up the bike, but stick to water and mild soap for cleaning.
Stay away from heavy duty tire cleaning products if you can, and for heaven's sake don't spritz on products designed to make your tire look shiny and new - you risk getting the tire dressing product on the tread. By using tire dressing you might have just made your tires ultra-slippery, but you likely won't realize this until after you and your motorcycle are once again upright.
In this same vein, do everything you can to prevent your tires from prolonged contact with oil and gasoline. Not only are these fluids slick as snot, they eventually cause degradation of the tire material.
If you live in a region of climate extremes, or otherwise don't ride your motorcycle for an extended period, you'll want to consider treating the tires on your motorcycle just like a motorcycle shop or large tire retailer would treat tires they store as part of their stock. Proper storage includes avoiding exposure to direct sunlight, extreme hot/cold temperatures, as well as keeping clear of ozone generating sources such as electric motors, battery chargers, generators or welding equipment.
An ideal storage area is clean, dry, well ventilated, and has consistently moderate ambient temperatures. Although you may not use the motorcycle for weeks or months, you should occasionally make a check of the tire pressure for proper inflation levels.
Here are some more important tips on tire inflation and general tire care from the Dunlop tire company:
Keep The Rubber Side Down (And In Good Condition)
Motorcycle tires have a dual nature: They perform the complex and paramount task of keeping your bike connected to the road, sometimes at silly speeds, yet they demand just a little more routine attention than a pet rock.
Hopefully you've come to better appreciate some of the aspects of the tires that keep you happily enjoying your two-wheeled lifestyle. From this brief tire education you should realize that motorcycle tires are more than just a part of the bike, but rather are a crucial component, and though expensive in some cases, represent an investment of the highest order in you and your machine.
Take care of your motorcycle's tires and they'll take care of you whenever you ride.