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Tire size

305/30R21 tire size: dimensions explained

Factory size on the Porsche 911 Carrera (992), Porsche Taycan. 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 width305 mm12.01 in
Sidewall height91.5 mm3.6 in
Overall diameter716.4 mm28.2 in
Wheel diameter533.4 mm21 in
Circumference2250 mm88.6 in
Revolutions per mile715

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

Reading the marking

305 is the section width in millimetres, 30 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 305/30R21 with another size →

305/30R21 tires at Tire Rack

All-season

TireLoad/speedPrice per tire
Continental ExtremeContact DWS 06 Plus
Ultra High Performance All-Season		XL 104Y$451.99View at Tire Rack
Goodyear Eagle Touring
Grand Touring All-Season		XL 104H$492.99View at Tire Rack

Summer performance

TireLoad/speedPrice per tire
Pirelli P Zero R
Max Performance Summer		XL 104Y$261.61View at Tire Rack
Pirelli P Zero (PZ4)
Max Performance Summer		XL 104Y$302.37View at Tire Rack

Winter

TireLoad/speedPrice per tire
Goodyear Ultra Grip Performance Gen-1
Performance Winter / Snow		XL 104V$235.11View at Tire Rack
Pirelli Winter Sottozero Serie II
Performance Winter / Snow		XL 104W$312.56View at Tire Rack

Showing the lowest-priced in-stock options in each category from 18 305/30R21 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