Types of Tire Construction
Bias Ply Definition
Bias ply tires have the cords criss-crossed across the tire from one bead to the other.
The cords make an angle of between 32 and 40 degrees with the centerline of the tread.
Bias ply tires will typically have stiff sidewalls and flexible tread face.
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Radial Ply Definition
A radial tire uses a cord angle of 90 degrees. That is, the cords run from one bead to
the other directly across the tread. In addition, a radial tire has a belt overwrap under
the tread surface, and can be made of various materials including fiberglass and steel
mesh. The belt overwrap of a radial tire causes less tread distortion under load and more
sidewall distortion.
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Belted Bias Definition
Belted Bias tires are a hybrid combining bias plys with the radial belt overwrap under
the tread surface. This type of tire has the excellent feedback of the bias and the
reduced tread distortion of the radial. Most racing radial tires are very close to
this design.
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Cantilever Sidewall
The Cantilever sidewall is very stiff and helps support the tread. This allows us
to use a tread face which is as wide or wider than the rim size. This type of tire
is best suited for cars with Rim width restrictions. EX: We are limited to
a 15 x 7 inch rim. The 23.0 X 9.5-15 Hoosier Road Race tire has a tread width
of 9.2". We would not normally be able to put 9.2 inches of tread on a 7 inch
wide rim. Note: This does not come without a cost, usually the section
width of a cantilever sidewall tire is larger than non-cantilever tires. Also, the
transient response of the cantilever tire is less than non-cantilever tires (provided the
non-cantilever tire is on the proper rim).
Dimensional Terms Defined
All measurements are in
inches.
- Spec. Rim
- This is the rim size used to obtain the measurements in the specification tables. If
your rim size is different, add or subtract .2" from the Section Width for each
1/2" change in the rim width. Example: You're going to mount a P245/45ZR-16 on
a 9" wide rim. The spec. sheet indicates a 10.0" section width on a
8.0" rim. The section width of this tire on a 9" rim would be 10.4"
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- LBS.
- This is the weight we use for shipping purposes. The weight of the tire is rounded
up to the nearest whole pound.
- SUGGESTED RIM WIDTH
- This is the rim width to use on vehicles of reasonable weight. Light cars can use
the low side of the recommendation and occasionally smaller. Heavy cars (most
American iron) and users of bias ply tires should use the widest rim possible.
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A Rim Width
B Tread Width
C DIAmeter
D Section Width
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Rebound
The ability for rubber to retake its shape after being
compressed. Normally low rebound characteristics = high traction.
Heat Curve
The heat curve of a compound can predict how a tire will
react during competition. It is most useful during manufacturing for quality
assurance. We use it to compare different compounds and brands of tires.
Pyrometer
A Pyrometer is a device which measures the temperature of the tire
tread. The two most common designs are the probe and infra-red. The probe
design is inserted just under the surface tread, the infra-red doesn't touch the
tire and reads the surface temperatures.
Durometer
A durometer is a device which measures resistance to compression.
The device is typically used by dirt track racers more than road race/autocross.
Contact Patch
The tire contact patch is the part of the tire that touches the road.
On tall tires the contact patch is longer than wide. On short tires the
opposite is true. The contact patches ratio of length to width is called the aspect
ratio. Aspect ratio is one determining factor of the slip angle.
Slip Angle
The slip angle of a tire is the angular difference between the wheel
direction and the contact patch direction. Design characteristics of tires that
affect slip angles are:
compound
cord bias angle and construction
cord material
side wall height