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Motorcycle Tire Tips
1/30/2004
By Ken "Hawkeye" Glassman
The most crucial yet overlooked and misunderstood component of
any motorcycle is the tires. Tires affect handling, comfort,
ride quality, and of course, safety.
I recently had the pleasure of spending some time with Mike
Manning, of Dunlop Tires. Dunlop is the largest motorcycle tire
manufacturer in the world, and Mike knows pretty much everything
there is to know about tires. He was gracious enough to answer
all my questions so that I could bring his knowledge to you.
First the basics; there are two types of tire construction:
bias-ply and radial. A safe generalization is that most cruisers
use bias ply tires, and sportbikes use radials. (Spoke wheels
require a tube to maintain tire pressure, while cast wheels
allow for a tubeless tire). A bias-ply tire has a round profile,
and tall sidewalls. A radial tire has a flatter profile, and
shorter sidewalls.
In a bias-ply tire, the carcass (the material beneath the tires
tread) is made up of overlapping layers of nylon or rayon cords.
Each of the several layers stretch across the tire at opposite
angles forming an X pattern, hence the term "bias." Some tires
add another layer on top of the plies, called belts, and those
run in the direction of the tire rotation. As a tire rotates,
the small portion of the tire that meets the pavement, the
"contact patch," flattens out for a split second. So as the tire
rotates, it is constantly flattening out, and rebounding into
shape. That constant flexing action generates heat, which is
good for grip. But too much heat is the enemy, as it decreases
performance and accelerates tire wear.
A radial tire has its plies running "radially" at a 90ø angle to
the direction of the rotation. This design reduces heat
generation, so the tires run cooler. The downside is that the
sidewalls flex easier, so they are given a shorter profile. The
lower profile means that they can't handle heavier loads that a
large heavy cruiser, with a passenger and baggage, requires. A
cruiser's suspension design and cornering needs are better
suited to bias ply tires, so always check to make sure a tire is
approved for your particular bike before buying.
Tread pattern grooves, or "sipes," greatly differ between bias
ply and radial tires and are based upon their intended use. The
grooves are designed to channel away water from the tire's
contact patch, so the tire won't ride up on the water, or
hydroplane. The more sipes, the better the tire will handle that
duty. Cruisers and touring bikes are meant to ride in the rain,
so handling wet pavement is an important characteristic of the
tire. Sportbikes, by comparison, are not designed to ride in the
rain. So, the less sipes a tire has, the more rubber meets the
road for greater traction on dry pavement.
Tire wear is an important factor when choosing tires. Softer
compounds produce more traction but wear out quicker. Harder
compounds wear better, but aren't as grippy. Manufacturers have
to juggle many different factors when designing their tires for
the street that can combine effective grip with longer mileage.
But the most important factors affecting tire life is
controllable by the rider. The number-one factor that leads to
premature tire wear is underinflation. Mike Manning travels to
motorcycle events around the country with the Dunlop Tire
Inspection Crew. They provide tire care and free tire
inspections to all motorcycles. He tells me that 85% of all
tires that they check are underinflated. Not only is that
dangerous for the bikes handling, but it can shave 20 to 40% off
the tires life. Mike recommends that you look at the tire
manufacturers suggested tire inflation pressure rather than the
number the motorcycle manufacturer puts in the owners manual, to
get the optimum performance from the tire. You can safely
inflate the tire up to the maximum tire pressure shown on the
sidewall of every tire, so it offers more load capacity when you
are riding with a passenger and luggage.
Riding style can also affect tire wear. Cruiser bikes normally
wear out the rear tire first, because there is more weight on
the rear tire, and it's the tire that bears all the traction and
braking forces because most cruiser riders use more rear brake
than front brake. More aggressive riders, however, will often
wear out the front tire first. I tend to brake late into corners
with mostly the front brake, then dive into the corner at a
higher speed before accelerating out of the turn. So I put more
grip and braking forces on the front tire than the rear. Tire
manufacturers usually put more tread depth on the rear tire, so
that the set wears out close to the same time. It is best to
change both tires at the same time so that traction is equal at
both ends of the bike. It is also a good idea to install new
valve stems when you put new tires on your bike.
A lot of riders would like to put fatter or larger diameter
tires on their bike, but that usually isn't a good idea. First,
you must be concerned with clearance of the fenders and
suspension components. And the motorcycle manufacturers spend
hundreds of hours designing and testing tires and wheels to
bring you the optimum sizes to compliment the suspension system.
Changing the size will usually adversely affect how the bike
rides and handles, and in many cases can result in an unsafe
motorcycle.
Always change your tires when the tread depth reaches 1/32 of an
inch. When in doubt, use the "penny test". That means if you put
a penny into a tire groove with Lincoln's head pointing down,
and can see the top of his head, it's time to change the tire.
If you are unfortunate enough to get a flat tire, the safest
thing to do is replace the tire. The tire may be repaired if the
puncture is in the center of the tread, but never if it's near
the sidewall. A proper repair must be done with the tire off the
bike, and only by a trained tire repair specialist. The tire
repair kits that plug a tire from the outside are only meant to
repair the tire so you can get to your destination. However,
tire makers strongly suggest you do not use those types of kits,
since you may not be able to see damage inside the tire, and the
tire could go flat even if you are just limping home slowly.
Remember a tire failure at speed can cost you your life, so
don't try to save a few bucks with a questionable repair.
One of the questions I've always had about motorcycle tires was
why they are so darned expensive, in many cases more expensive
than much larger heavier car tires. According to Mike Manning of
Dunlop, there is no simple answer to that question. There are a
myriad of factors that contribute. First, there is a lot more
engineering requirements in a motorcycle tire, because there is
much more horsepower per square inch of contact patch, and many
more stress forces between cornering and braking, than is put on
a car tire.
Motorcycle tires can have as many as nine different compounds in
its makeup, whereas a car tire might have just two or three.
There is also much more development testing because a motorcycle
tire is designed to fit a lot of different models of
motorcycles, and work effectively for all of them. Another cost
factor is that they don't manufacture nearly as many motorcycle
tires as car tires, so the economies of scale aren't there.
Since manufacturers only schedule a manufacturing run on some
tire sizes for a week or a month each year, more tires have to
be stocked in inventory, which raises the cost.
There is a ton of information that riders should know about
their tires. No matter what brand of motorcycle you ride or what
brand of tires is on your bike, you can access vital information
by going to
Dunlopmotorcycle.com.
The more you know about your tires, the better you will handle
buying decisions and maintenance procedures, for safe, fun
riding.
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