Cooper Discoverer STT Pro LT305/70R18/10 126/123Q - 170125034

The Cooper Discoverer STT Pro in 305/70R18 ships free from ThreePiece.us, with Affirm financing available at checkout and fast delivery from a nationwide warehouse network.

What 305/70R18 means

In the size 305/70R18, 305 is the section width in millimeters (12.01 in), 70 is the aspect ratio — the sidewall stands 70% as tall as the tire is wide, or 213.5 mm (8.41 in) — R denotes radial construction, and 18 is the wheel diameter in inches. That works out to an overall diameter of about 34.81 inches, turning roughly 579 revolutions per mile. Overall diameter is what matters for speedometer accuracy and clearance when you change sizes, so compare it — not just the width — against your current tire.

The manufacturer lists the overall diameter of this specific tire as 35.08 inches — when clearance is tight, go by the published figure rather than the nominal size math.

The service description on this tire decodes to a load index of 126 — a maximum load of 3,748 lbs per tire, or 123 (3,417 lbs) per tire when mounted as duals. The speed symbol Q corresponds to a maximum sustained speed of 99 mph.

Specifications

Frequently asked questions

What does 126/123Q mean on the Cooper Discoverer STT Pro?

126/123Q breaks down as load index 126 — rated for 3,748 lbs per tire (123, or 3,417 lbs, in dual fitment) — with a Q speed rating, good for a maximum sustained 99 mph.

What kind of tire is the Cooper Discoverer STT Pro?

The Cooper Discoverer STT Pro in 305/70R18 is a all season tire.

Will 305/70R18 tires fit my vehicle?

Check the size molded into your current tire's sidewall or the tire placard inside the driver's door jamb — if it reads 305/70R18, this tire matches your vehicle's fitment. If you're changing sizes, compare overall diameter to keep your speedometer and clearances right.

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