Motorcycle Forum / General / Sportbikes / April 2005

Not only would you go quicker with a harder compound tire... it would last
longer...

we shall see....I certainly haven't been happy with

Nobody has been happy with SPortecs mileage...

Larry L
94 RC45 #2
Have a wheelie NICE day...
Lean & Mean it in every corner of your life...
If it wasn't for us the fast lane would rust...
V4'S are music to the seat of my pants...
1952 De Havilland Chipmunk...
Yank and bank your brains loose...
http://members.ebay.com/aboutme/-xlax-/
http://home.comcast.net/~netters2/
http://www.fox302.com/index.pl?s=vg&user=netters2

Hey Troy, you should give the Bridgestone 002 front/090 rear combo a try
on the SV.  Just did a day on those and were really pleased with the
performance.

One caveat! Don't let your steel belted Diablo's wear to this point,
else the metal cords will rip through what's left of the tread. This
happened in the middle off my friends 600-mile day ride on his VFR. MY
Rennsport streets did the same thing but not nearly as severe as in
the photo below.

http://extexltd.com/bigrex/191_04-2/191_2-2_.JPG

So were the M1's but they turned out to be turds after a couple
thousand miles (traction suddenly lost in the front above maybe 43
degrees lean angles). And the rears were lucky to get 2500 miles
(street) with just a tad more traction than the stone 010's.

Bob Nixon, Chandler AZ-deer strike recovery-(completed)
01 Sprint ST "RED" 45K miles
03 GSXR 1000 "SILVER" 7K RIP (deer slain)

Keen observations, if a bit pessimistic. Why do we buy the expensive
toilet tissue to pamper our bunghole when we could use yesterday's
newspaper or spring for the expen$ive $ticky bun$ to grab the road when
we could use wooden wheels with iron tires anyway?

Maybe it's ultimately to protect our butts---or is it to feed our egos?

The $pecial problem of motorcycle tire con$truction, or, why your tire$
have to be so $tiff and prohibitively expen$ive and why they don't last
very long.

The special problems :

Motorcycle tires carry approximately *twice* the load per square inch
of contact patch area as a single axle truck tire carries. Motorcycle
tires have to get their traction from softer rubber compounds, at the
expense of quicker wear, since they lack the weight per unit area to
raise the "coefficient of friction" to that enjoyed by the humble truck
tire.

Truck tires often carry 2000 kilograms of weight per contact patch. The
typical ratio of contact patch pressure to inflation pressure is about
0.8  to 1. Motorcycle tires are at the other end of the scale, with a
typical load of around 250 kilograms per contact patch and the ratio of
contact patch pressure to inflation pressure can be 1.4 to 1, almost
twice that of a truck tire.

That's why motorcycle tire pressure is so critical and motorcycle tires
cup and wear funny when you corner hard on a tire with lots of water
channels and unsupported tread blocks. Cornering warps the tread crown
in spite of its planned consistent rigidity. Tread blocks haven't got a
prayer of survival, without support from adjacent rubber.

The horsepower applied to a motorcycle tire's contact patch may be
twice that of the power applied to a passenger car tire's contact patch
per unit area and five times as much as the power applied a truck
tire's contact patch per unit area. And yet the soft blended rubber of
a motorcycle tire is expected to last for some reasonable mileage? Fat
chance.

Cars and trucks tires are generally tilted no more than  5 degrees from
the vertical during cornering. This is called "camber". If a bias ply
car or truck tire is tilted as much as 30 degrees from the vertical,
it's running on the sidewall, which doesn't have a tread. Radial car
tires are a bit better in this regard, they are still running on at
least *part* of the tread, which can be shown in test photographs to
have been warped into a long narrow band of contact patch.

In order to avoid running on the sidewall at all, motorcycle tires
extend the tread from a very short stiff sidewall across a crowned
radius to another very short stiff sidewall. The geometry of the
curvature is often, but not always, planned so that the same contact
patch area will touch the pavement at any angle of lean, and motorcycle
tires corner at lean angles of up to 50 degrees from the vertical. High
performance racing and sport tires will have geometries that increase
the size of the contact patch at greater lean angles, making the center
of the tire "pointier" and the straight up stability of the tire may be
less than confidence inspiring as the motorcycle seems to steer far too
quickly for the tastes of many newbie riders.

When a motorcycle tire is cornering by  camber thrust against the
pavement surface,  it's exerting a force of about 100 kilograms at a
lean angle of 20 degrees. A radial car tire only produces about 50
kilograms of camber thrust at that same lean angle. Fortunately cars
don't lean quite that much. A car leaning at a 20 degree angle probably
has the two inside wheels off the ground, yannow...

The sidewall of a motorcycle tire must be very stiff to withstand 20
degrees of camber thrust. Motorcycle tires need extra hard rubber bead
fillers, one or two  "cap layers" extending down the sidewalls, and
special "chafers" and "flippers" that increase the cost of a radial ply
motorcycle tire to twice that of a bias ply motorcycle tire of the same
size.

The construction of motorcycle tires is basically the same as that of
passenger and light truck tires. The unique difference is,  however,
its shape---the crown area of a motorcycle tire is quite rounded. The
crown area of the tire has to have consistant rigidity at all lean
angles to give the rider the same "feel" at various lean angles. And
belts keep the radial ply tire from growing radially. This radial
growth feels "slippery" to the rider.

Leaning, as the rider reaches the "lip", or the "shoulder" of the
tread, the rigidity of the tire carcass changes. Tire engineers are
tailoring the rigidity of the sidewalls to act as a rubber "spring" at
lean angles where the motorcycle's normal suspension system cannot
react properly to "out of plane" loads...

Construction and expense of manufacture:

The casing of a tire begins on the *inside* and is turned outwards and
upwards around the steel-reinforced beads. Two actual casing plies
correspond to a four ply rating. The plies wrap around the steel wire
beads. The wire beads hold the inflated tire onto the rim. A
reinforcing ply called a "chafer"  protects the plies from damage in
the bead area where they would otherwise rub against the aluminum  or
steel rim. Just above the bead wire is the "bead filler", a triangular
shaped ring of hard rubber that reinforces the bead area, contributing
to the stiffness of the tire's carcass. The "flipper" is triangular
shaped, too, it encloses the bead wire and the bead filler. If the
stiffness of the bead filler is insufficient, motorcycle will be less
stable during cornering and unwanted vibrations may occur.

On the top of the casing and under the rubber tread, the belts or
breakers are applied. Bias ply tires use breakers, so called because
they reinforce the bias ply tire and "break" the impact of road shocks,
protecting the casing from damage. Breakers are normally made of nylon,
while
radial ply tires use steel or aramid fiber belts. Some cheaper bias ply
tires also use cheaper rayon instead of nylon in their construction.
And, inside the breakers or cap belts and the plies that make up the
casings, each tire must have an air tight inner liner made of rubber
that is hopefully soft and remains "gooey" enough to reseal itself when
punctured by a sharp object which is then removed.

Then comes the "black art" of compounding natural rubber, which has
high adhesion to the pavement surface at low speeds but wears quickly,
with high hysteresis synthethic rubber tires which "grip" the road
better at higher speeds, while damping out small surface irregularities
the forks and shocks can't handle. High hysteresis synthetic rubber is
wonderful but is much more expensive than natural rubber. The exact
formulation of such rubber compounds is, and must remain a proprietary
secret if the tire company is to be competitive with other tire
manufacturers.

The "gentleman's sport" of motorcycle racing is a competition between
factories for which they will get market share from a strategy of "race
on Sunday, sell on Monday". Our current heroes arise out of this
gentleman's sport and our mechanical icons continue to evolve. The
motorcycle tire factories are under continual pressure to make their
product evolve as well. Motorcycle tire manufacturing is done in small
lots. The rubber hardens or deteriorates, the motorcycles that use a
certain size tire get used up, retired from service, and new designs of
motorcycles with higher performance engines, different wheel sizes and
widths
become the "norm" for a time. So the limited production top of the line
tire solution to the current traction and wear compromises are very
expensive, and we must pay dearly if we want to play at the desired
level the motorcycle magazines suggest we should want to aspire to...

Cheap is related in Radial tire construction to either a two or three or four
stage building process... cost is also related to the curing steps and the
rejection rates... Rennsports have a higher quality control standard for weight
and trueness...
Rennsports are designed and constructed for the rigors of competition whereas
Diablos are not... Subject a Diablo to competition and it might last 10 laps ...
Rennsports will go about 22 laps... it's the ability of the carcass to go the
distance even though it's thread is a softer compound...

too!

You're right... Chen Shins (Chinese for rim protector) handle like they are made
in a one step process and cured in an oven like cookies...

Larry L
94 RC45 #2
Have a wheelie NICE day...
Lean & Mean it in every corner of your life...
If it wasn't for us the fast lane would rust...
V4'S are music to the seat of my pants...
1952 De Havilland Chipmunk...
Yank and bank your brains loose...
http://members.ebay.com/aboutme/-xlax-/
http://home.comcast.net/~netters2/
http://www.fox302.com/index.pl?s=vg&user=netters2

are so hated? >

You're posting a track toasted rear. Nice try. Mime were street on a
sport tourer feathered to the edge. You couldn't find any public
roads with condition conducive to mine up in that rain forest.
Let's see the some street wear;)