Re-Tirement Guide | MC Garage

The right rubber for the job

By Jerry Smith, Photography by Kevin Wing, Dunlop

Tires, and the technology that underpins them, have developed dramatically in the past few years. Of course, tires are a compromise. Their carcass designs, compounds, and tread patterns are all built for specific duties and embody various tradeoffs. As a general rule, the gripper a tire is, the lower its life expectancy. A trackday tire's sole lot in life is to cling limpet-like to the asphalt—wear is not a primary or even secondary issue—and it's not expected to work well in wet conditions. Relatively speaking, it's easy to build a trackday tire: Whip out the stickiest compound you have, eliminate all but a few grooves, slap on an eye-widening price tag, and there you are.

Most sport riders appreciate that trackday tires are now too specialized for everyday street riding; they need to operate at temperatures nearly impossible to achieve on the street, and they are not the best choice for mixed conditions, such as a slightly wet or dirty road. The next step "down" is a class of tire called sport or supersport. Construction and compounds vary by manufacturer and by class overlap within each tire maker's line—that is, some brands have more specialized models while others have one tire to fill the range from occasional trackdays to long-life sporting use. But, generally speaking, these are tires with slightly harder compounds intended to be effective at lower temperatures, more rubber and tread depth for durability, and more grooves to improve performance in wet weather. It's fair to say that from the standpoint of pure grip, supersport tires of today are as good as trackday tires of five to eight years ago, yet suitable for the street. This is something we accept as a natural progression of tire development. As a general rule, performance has increased while longevity has held steady or improved slightly; in this class, grip is still more important than wear.

But here's the real surprise: Today's sport-touring tires grip as good as hard-core sport tires of just a few seasons ago but pack a lot more durability and weather capability. Advances in compounds, and the widespread use of multi-compound rear tires, are largely responsible for this fortuitous situation. Their performance level is so high that few riders will ever run out of grip on the street, and they'll still be roadworthy thousands of miles after pure sport tires turn into pitbull chew toys. What's not to like?

Sport-touring tires are also a great option for large ADV machines. In fact, the original-equipment tires that come on most of these machines really are sport-touring in basic construction and compound, though usually with a slightly more open tread pattern to accommodate the odd dirt road. If your favorite roads are often wet or dirty, tires like the Continental TrailAttack, Dunlop Trailmax, Michelin Anakee III, or Pirelli Scorpion are good alternatives to straight-up ST rubber. Worried that your powerful bike will eat them alive? Forget it—these tires come stock on 150-hp high-performance ADVs all day long.

Floorboard-sparking lean angles don't top the list of attributes tourers and cruiser riders look for in their bikes. They typically care more about mileage than cornering performance, so the choices in this category will probably come down to which brand of tire to buy. A lot of the available rubber is bias-ply, but before you scoff at the notion of putting prehistoric tires on your bike instead of cutting-edge radials, remember that mileage is the one area where bias-plies often leave radials by the roadside. Radials run cooler than bias-plies, so they can use a thinner layer of tread, while bias-plies need thicker tread to act as a heat sink. The average sport radial, for example, has about 5/32 of an inch of tread depth on the front and about 8/32 on the rear. Some bias-plies have 10/32 front and rear; the thicker tread means longer tire life.

No matter what you get, the further you stray from the norm in terms of size or construction, the more you're on your own. Tire manufacturers can't test every possible combination of bike and tire, and they'll recommend against mixing bias-plies and radials or fitting a much wider or narrower tire than what's standard. They're not specifically saying it won't work, but because they can't promise it will they err on the side of caution. Something you might want to do, too, before you spoon a pair of road-racing slicks on your spoke-wheel Mach III or mount a car tire on the back wheel of your Gold Wing.

Save the Knobbies

Owners of dual-sport and ADV machines are often tempted into a set of real knobby tires for their far-ranging ad-ventures. And while it’s true that genuine open-tread knobbies are superior in the roughest off-road conditions, they pay a big price in terms of noise, handling, and wear qualities. You need to truly do more than 75 percent of your riding off road for full knobbies to make sense.

Sidewall Secrets

Breaking The Code

WORDS: Jerry Smith PHOTO: Marc Cook

Trying to make sense of the markings on a tire sidewall is enough to convince you they were proposed by the US Department of Needless Confusion and subcontracted to a monkey with a typewriter. But once you break the code, those mysterious numbers and letters tell you a lot about the tires you have now and the ones you'll replace them with later.

The most common sizing method is metric. Take a 180/55ZR-17 as an example: It's 180mm wide when mounted and inflated. Its aspect ratio is 55, so it's 55 percent as tall as it is wide­—or 99mm. Its speed rating is Z, so at maximum load and inflation it can be run at speeds of 149 mph and higher. The R designates radial construction, and the 17 is the diameter in inches of the wheel it fits. If there's no R, the tire is a bias-ply. A "B" means it's bias-belted—with added belts for strength and extra load capacity—but not all bias-belted tires have the B in the size.

Incidentally, not all tires measure exactly like their specs. Some models are a little bigger and some smaller because of design choices to tailor steering response or bump compliance. Normally, tires never leave their range—that is, a tire said to be a 180 won't actually be 190mm across—but there is definitely model-to-model variation.

Many touring tires use an alphanumeric size designation like MT90S-16, where M means motorcycle, T is the width (it's "T" wide? Does anyone else smell a monkey?), 90 is the aspect ratio, S is the speed rating, 16 is the wheel size in inches, and no R means it's a bias-ply. Metric-sized tires can be substituted for alphanumerics (MT90 is the same as a 130/90). Refer to tire manufacturers' and dealers' websites for conversion charts.

Other bits of useful information on the sidewall include the date of manufacture (2313 indicates it was made in the 23rd week of 2013), whether it's tube-type or tubeless, its direction of rotation, whether it's a front or rear, its load rating (the maximum weight allowed on the tire at max inflation), and the maximum inflation (not the same as the recommended tire pressure for riding). The raised letters TWI are important, too, because they show where the tread-wear indicators are; find them on the sidewall, then look in the grooves in the adjacent tread for a small raised bump; when the surrounding tread wears down even with the bump, the tire's toast.

By Jerry Smith
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