Carcass
The load-bearing fabric skeleton inside the tyre: cord plies running from bead to bead that carry load and air pressure. Their arrangement defines the construction – cross-ply or radial.
The carcass (also casing) is the tyre's load-bearing skeleton: several plies of rubberised cord fabric – once cotton, later rayon, nylon or steel – stretched from bead to bead. It contains the air pressure, carries the vehicle load, transmits driving, braking and cornering forces and gives the tyre its shape. The number of plies is traditionally stated as a ply rating, for example 4PR.
The arrangement of the cords defines the construction: if the plies cross diagonally to the direction of travel, the result is the cross-ply tyre; if the cords run at 90 degrees from bead to bead with a belt stabilising the tread above them, it is a radial tyre. The carcass is thus the component where the two worlds of historic and modern tyres part ways technically.
Especially important for classics: the carcass ages even without mileage. Plasticisers escape, the fabric fatigues and fine cracks in the sidewall and bead area are warning signs – a tyre with good tread can therefore still be finished. As a rule of thumb, replace tyres about ten years after the date of manufacture (DOT code) – on little-used cars that stand for long periods, rather sooner. Those who drive historic cars therefore check the carcass more regularly than the tread.
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Related terms
Tripmeter
A precise supplementary instrument for measuring the distance driven – more accurate than the standard odometer. The co-driver's key tool, often called a tripmaster.
Rotes Kennzeichen
Umbrella term for Germany's red recurring-use plates – depending on the leading digits 05 (inspection), 06 (dealer) or 07 (historic vehicles).
Matching numbers
Collector term for a vehicle whose major components (engine, gearbox, axle, frame) still carry the original numbers that match one another and the factory records – an indicator of originality, not of identity.