| Aspect Ratio |
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The ratio between the tyre's section height (height of the sidewall) and it's
section width (the width of the tyre, sidewall to sidewall). A tyre with a 6
inch sidewall and a 10-inch section width would be a 60 series tyre. Expressed
as a percentage, aspect ratio influences the tyre's profile, or the distance
between the tread and the rim. Lower profile tyres have a lower aspect ratio.
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| Bead |
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The area that mates the tyre to the wheel. This area is a critical part of the
tyre's construction and consists of a hoop of high tensile steel wires to which
the belts are attached. This anchors the belts as well as providing a firm grip
on the rim.
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| Bead Seat |
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This is the smooth face on the bead area of the tyre that seals against the
rim to hold air.
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| Belts |
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Rubberized woven fabric that runs around the circumference of the tyre under
the tread. Polyester and steel in combination is the most common construction
material these days, but many experts regard kevlar (or Aramid fiber) as the
best.
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| Casing |
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The body of the tyre built up from cords and belts of material. Also known as
the carcass.
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| Compound |
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The mixture of material that is the "rubber" part of the tyre. There are 5
basic ingredients: rubber, carbon black, plastisizers, a curing ingredient
and an ozone retardant.
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| Contact Patch |
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The tyre "footprint", the tread material that actually has contact with
the ground.
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| Cord |
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The stranded material incorporated into the belts and plies that are made
into the casing or the tyres.
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| Crown |
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The center of the tyre tread.
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| Deflection |
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The amount the tyre "gives" under load. Essentially, the difference between
it's free and unloaded radius and it's fully-loaded radius.
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| Directional Stability |
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The ability (or lack thereof) of a tyre to maintain a straight line rather
than following irregularities in the road.
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| Hoop Strength |
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The inherent strength of the material in the belt to hold it's circular shape.
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| Hydroplaning |
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A condition that occurs when the tyre floats above water encountered due
to speed or tread design and loses traction. The tyre actually rides up on
the water like a speedboat on a lake, losing contact with the road surface.
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| Kerf |
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A cut or slit built into the tyre and used to enhace traction. A kerf is
similar to a sipe, but is molded into the tyre rather than cut in. Kerfs
enhance wet and icy traction.
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| Liner |
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A fairly thin layer of dense rubber on the inside of tubeless tyres designed
to hold air.
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| Plies |
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The layers of corded material that provide the structural "building blocks"
of tyre construction.
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| Rollover |
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When the tyre gives in to the g-forces of hard cornering. The inside edge of
the tyre tread may lift and the sidewall may actually contact the road. In
extreme conditions, it may pop the bead and suddenly deflate the tyre.
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| Rubber |
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A common term for the material of the tyres. In the old days, this was
actually rubber from the rubber tree, but now it's a synthetic material
derived from petroleum products.
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| Section Width |
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The sidewall-to-sidewall width of the tyre. Not to be confused with tread width.
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| Shoulder |
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The area of the tyre where the tread joins with the sidewall.
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| Siping |
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Slits or cuts in the tread blocks that allow the blocks to move and grip.
Sipes can be built into the tyre by the manufacturer or added later. Siping
usually enhances the wet and icy performance of the tyre.
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| Void Ratio |
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The ratio of open areas in a tyre tread vs. the parts that actually contact
the ground.
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