Guide

The 3% tire size rule

Many tire shops treat a replacement size as close enough if its overall diameter is within about ±3% of the original. For example, 265/70R17 to 285/70R17 is +3.5%. It's a rule of thumb, not a manufacturer or legal limit, and it says nothing about whether a size physically fits or is approved for your vehicle.

What it covers and what it doesn't

Staying near the original diameter keeps speedometer error, gearing and ride height close to stock. It does not check wheel width or offset, clearance at full steering lock and over bumps, load index, speed rating, or systems such as ABS and AWD that your vehicle maker may have specific rules for.

Check a change

1

Your current size

e.g. 265/70R17, 2657017 or 33x12.50R20

Where do I find my size?

It's on the tire sidewall, e.g. P265/70R17 115T, and on the tire placard sticker on the driver's door jamb (also in the owner's manual). If your current tires aren't the original size, the placard shows what the vehicle came with. Digits are enough here: 2657017 or 33125020.

2

Size you're considering

 

More guides

How to read a tire size · Nominal vs actual diameter · AWD and mismatched tires · Load index & speed rating · Revs per mile chart · Tire size chart

Important: These are calculated (nominal) dimensions, not a fitment recommendation. Real tires of the same size differ by brand and model (makers allow about ±3% of section height), and width changes with the rim it is mounted on. The math can't see wheel width and offset, clearance at full steering lock and suspension travel, load index, speed rating, or what your vehicle maker approves. Before changing size, check your door-jamb placard and owner's manual and ask a tire professional. A replacement tire must meet or exceed the load index and speed rating on the placard.