R (radial construction)

How to read it

FMVSS 139 defines a radial ply tire as one whose ply cords, running to the beads, are laid at substantially 90 degrees to the centerline of the tread, and a bias ply tire as one whose cords are laid at alternate angles substantially less than 90 degrees. USTMA says a radial tire must also show the word RADIAL on the sidewall, which FMVSS 139 requires. NHTSA’s booklet says radial construction has been the industry standard for the past 30 years.

Also searched as: radial tire, R in tire size.

D and B in place of R

A D in the same place means diagonal, or bias ply, construction: Ford’s example temporary spare is T145/80D16, and Carlisle’s trailer tire ST175/80D13C. Carlisle describes the cords of a bias tire running at about 45 degrees and those of a radial at 90. Australia’s design rule for passenger tyres lists three construction symbols: D for diagonal ply, B for bias-belted and R for radial ply. Yokohama says D is rare on passenger and light truck tires.

ZR and RF

ZR in place of R also means a radial tire, marked for speeds above 240 km/h (149 mph). Yokohama notes that ETRTO lets makers add an F to the size to mark a self-supporting Run-flat markings (RFT, ROF, ZP, SSR) tire.