Westlake WESTLAKE SL309 285/70R17/8

The Westlake SL309 in 285/70R17 ships free from ThreePiece.us, with Affirm financing available at checkout and fast delivery from a nationwide warehouse network.

What 285/70R17 means

In the size 285/70R17, 285 is the section width in millimeters (11.22 in), 70 is the aspect ratio — the sidewall stands 70% as tall as the tire is wide, or 199.5 mm (7.85 in) — R denotes radial construction, and 17 is the wheel diameter in inches. That works out to an overall diameter of about 32.71 inches, turning roughly 617 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 17 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 121 — a maximum load of 3,197 lbs per tire, or 118 (2,910 lbs) per tire when mounted as duals. The speed symbol Q corresponds to a maximum sustained speed of 99 mph.

Load Range D corresponds to a 8-ply rating.

Specifications

Frequently asked questions

What does 121/118Q mean on the Westlake SL309?

121/118Q breaks down as load index 121 — rated for 3,197 lbs per tire (118, or 2,910 lbs, in dual fitment) — with a Q speed rating, good for a maximum sustained 99 mph.

What kind of tire is the Westlake SL309?

The Westlake SL309 in 285/70R17 is a high-performance tire.

What warranty does the Westlake SL309 carry?

The manufacturer's warranty on this tire is 40K.

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