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Tire size

315/40R21 tire size: dimensions explained

Factory size on the Porsche Cayenne (9YA facelift). Below are the dimensions calculated from the size marking itself. Your vehicle's correct size, load index and speed rating are on the placard in the driver's door jamb; check it before buying.

MeasurementMetricImperial
Section width315 mm12.4 in
Sidewall height126 mm4.96 in
Overall diameter785.4 mm30.92 in
Wheel diameter533.4 mm21 in
Circumference2466 mm97.1 in
Revolutions per mile652

Calculated values: diameter = wheel + 2 × (width × aspect ratio). Real tires vary slightly by brand and model.

Reading the marking

315 is the section width in millimetres, 40 is the sidewall height as a percentage of that width, R means radial construction, and 21 is the wheel diameter in inches. A passenger (P or Euro-metric) tire and an LT tire in the same size are not interchangeable without checking load requirements.

Compare 315/40R21 with another size →

315/40R21 tires at Tire Rack

All-season

TireLoad/speedPrice per tire
Advanta HPZ-02
Ultra High Performance All-Season		XL 115V$190.86View at Tire Rack
Michelin Primacy Tour A/S
Grand Touring All-Season		111H$404.70View at Tire Rack

Highway / touring

TireLoad/speedPrice per tire
Kumho Crugen GT Pro
Crossover/SUV Touring All-Season		XL 115W$256.24View at Tire Rack
Continental CrossContact LX Sport
Crossover/SUV Touring All-Season		111H$353.75View at Tire Rack

Summer performance

TireLoad/speedPrice per tire
Yokohama ADVAN Sport V107E
Max Performance Summer		XL 115Y$190.71View at Tire Rack
Yokohama ADVAN Sport V107E
Max Performance Summer		XL 115Y$256.94View at Tire Rack

Winter

TireLoad/speedPrice per tire
Vredestein Wintrac Pro+
Performance Winter / Snow		XL 115V$343.76View at Tire Rack
Nokian Hakkapeliitta R5 SUV
Light Truck/SUV Studless Ice & Snow Truck		XL 115T$545.16View at Tire Rack

Showing the lowest-priced in-stock options in each category from 35 315/40R21 tires in Tire Rack's feed, sorted by price only. We don't rank by commission. Match or exceed the load index and speed rating on your placard.

Affiliate links: if you buy through a Tire Rack link, RightTread may earn a commission through CJ. It doesn't change your price. Prices are Tire Rack's per-tire prices from Tire Rack's product feed as of Nov 7, 2026, 9:19 PM PT. Prices change, so confirm on Tire Rack before you buy. Disclosure

Other sizes