It’s Only Flat on One Side!

Aug 11, 2010

CRASHING SUCKS!!!…as most riders can attest! And to reduce that “suckage” you need to make sure your tire pressure and wear on your tires is correct and at a minimum. Although it may seem obvious that the tire’s purpose is to hold the motorcycle up, tires actually perform several different functions. They help maintain balance of the bike while in motion, they change the steering and handling geometry, they absorb some of the shocks and vibrations from the road surface (without involving the rest of the suspension), and the more obvious transference of energy between the bike and the road (braking, turning forces, acceleration) — as well as handling the disappation of heat from that frictional transaction of energy transference. (Sounds “teckie” huh? We threw that part in to show ya we’ve got some learn’n involved here).

Tires come in different compounds, which is for different intended uses. Softer compounds are designed to give an edge in grip (especially when the bike is leaned over significantly), while harder compounds are designed to promote longer tread life and cooler running (for long-haul riding like we do). Most tire manufacturers now manufacture several different tire compounds from a super-soft tire specifically for track purposes, to a semi-soft street-racing tire, to a only-slightly-soft road touring tire. Additionally, some of the leading manufacturers also use different compounds within a single tire, such as the Metzeler Z-series, which uses a softer compound at the tire’s outer edges and somewhat harder compound in the center, for a design that promotes exceptionally high grip while leaned over and yet still wears slowly in the center (for longer general lifespan).

As we mentioned previously, one of the features of a tire is to handle the friction interface between the vehicle (i.e. motorcycles) and the road, and then deal with the heat from that friction. If you’ve ever seen a semi-truck’s tire tread laying by the side of the road, you’ve seen what happens to a tire that gets too hot (the molecular compounds inside the tire break apart, thus splitting or shredding the tire carcass). As you might imagine, having that happen on a motorcycle you are riding could very easily ruin your beautiful day!

For motorcycle tires, there is a delicate balance going on here, because tire manufacturers want tires to get warm fast (their traction is dependent upon them “coming up to temp,” or reaching a specific operating temperature — and staying there), but at the same time don’t want the tire to get too hot (or the tire material will start to wear out at a very fast pace — or worse yet, delaminate itself as in the truck tire example above). The formulation of the tire compound plays a big part in this equation, since softer materials by their nature flex more (thus come up to “temp” faster, but also run hotter), while harder compounds flex less (thus take longer to get warm, but also run cooler). Since tires used on race tracks need to provide maximum traction, but are not expected to be used for more than a few races normally (a single race at pro levels), they are made of super-sticky materials designed to warm up very fast, and to run a bit hotter than normal street tires (trading life expectancy for superior grip). Touring tires, on the other hand, are expected to be able take a thousand miles or more in a day, for days on end, so they are built to heat much less quickly, and to run at a cooler temperature through-out their use (both for the lifespan of the tire, as well as for the stability of the tire carcass). Typical street tires fall somewhere inbetween these two standards, offering a blend that warms up faster than touring tires but runs slightly hotter than them too.

Your riding style needs to play heavily into tire choices. Running a pure-sports tire, such as a Pirelli Diablo Corsa or Metzeler M3 or M1, without the constant on-brakes & change of direction input it needs in order to be kept in it’s ideal operating temp range will means a seriously loss of traction compared to running a sports-touring tire that doesn’t need that kind of input… In the same sense, running a sports-touring tire if you use the bike solely for track day sessions or are constantly knee-down canyon-carving is insanity. The right tire for the right task makes a huge difference in everything from stopping distances to outright grip-on-demand. BTW, we’ll be having more of these tidbits of info in upcoming posts….so stay tuned! Maybe we all can learn something.

WHAT ELSE TO KNOW:

NARROW VS WIDE: Although wide rear tires are all the rage now, narrower tires handle better under most real world conditions.
TIRE GROWTH: All tires will expand to some degree over time once they are mounted, both due to the pressure on them, and due to heating-cooling cycles. Street tires normally expand 3 to 8%, while race tires can expand up to 22%. Be cautious in mounting a tire that will barely fit your clearances; the tire may easily grow to exceed the available space once it gets up to temp.
UNEVEN TIRE WEAR (#1): Because roads are normally crowned to permit rainwater drainage, and you consistantly ride on the same side of the crown (right side of the road in the most countries; left side in the UK, Japan, and certain former British colonies), under normal street riding, tires wear unevenly to one side across the peak of their center apex.
UNEVEN TIRE WEAR (#2): Depending on a variety of factors, including the size of the land-sea boundaries, the compound composition, the ambient temperature and the road surface temps, tires may wear unevenly from the front to rear of the individual tread blocks. Tire pressure and how it relates to tire surface temperature can have a drastic affect on whether this kind of scalloping/cupping at the land/see boundaries occurs, although certain tires types do it more than others.
HIDDEN LEAKING: Your tires leak. Period. Under pressure, tires leak out some of their pressure directly through the rubber compound of the tire each and every day, very slowly. Check your tire pressure before you ride anywhere for the day (usually referred to as measured “cold”) and add air as required.
PRESSURE DIFFERENCIALS: A ten degree (F) change in the ambient temp will result in a significant pressure change in the tires. If the weather cooled or got hotter since yesterday, check your tire pressure again before you ride.
NAILS, SCREWS, TACKS: If you get a nail, screw or tack in your tire miles from home or the closest shop, you have a few choices. The wisest of them is to call a ride to tow you & the bike to somewhere where you can get a new tire, then pull the object once you get there and hope it didn’t go all the way through. The second is to cut it off flush (if it isn’t already) and ride it to a safe place slowly — very very slowly (think walking pace), ready for a possible leak or blow-out. The third is to pull the item out and pray it didn’t go through — and if it did, you’re not going anywhere without a tow. And the final way is to carry an emergency patch/plug kit, pull the item, plug it as necessary, then proceed directly to somewhere that sells replacement tires.
TIRE AGE: Motorcycle tires should not be used after five years from date of manufacture. Tires contain Volitile Organic Compounds (VOC’s) which help keep the rubber flexible and grippy; as tires age, the VOC’s leach out. Certain conditions can accelerate this process, including extremely hot and excessively humid or dry environments, parking on certain forms of man-made carpeting, certain molds & mildew forms (which may accelerate or even cause what is commonly known as “dry rot”), as well as overheating the tires due to low tire pressure or hard use.