TireMath

Tire size calculator: compare any two tire sizes

Enter your stock tire size and the size you're considering. You'll get the diameter difference, speedometer error, revs per mile, ground-clearance change, and a straight answer on whether the swap stays within the ±3% guideline. Free, no signup.

Theoretical values based on standard tire math. Always verify physical clearance and load rating with a tire professional — this tool makes no fitment guarantees.

Tire size comparison calculator

Metric (265/70R17, LT285/75R16) or flotation (33x12.5R17). The leading P/LT is optional.

Plus / minus sizing finder

Want a bigger wheel without messing up your speedometer? Enter your stock metric size and we'll suggest −1/+1/+2 alternatives that keep overall diameter within ±1.5%.

What minus and plus sizing mean

The trick in every case: as wheel diameter goes up, aspect ratio comes down so total diameter barely moves. Rim width must still suit the tire — confirm the approved rim-width range on the tire spec sheet.

Where to price the sizes above

Once you've picked a size, compare installed pricing (mounting, balancing, alignment) — not just the per-tire price:

Tire size questions, answered

What does 265/70R17 mean?

265 = section width in millimetres. 70 = aspect ratio: the sidewall height is 70% of the width (185.5 mm). R = radial construction. 17 = wheel diameter in inches. Full breakdown in our how to read a tire size guide.

What is the 3% rule?

Keep the replacement tire's overall diameter within ±3% of stock. Beyond that, speedometer error grows past ~2 mph at 60, effective gearing changes enough to notice, and you risk rubbing plus ABS, traction-control, and transmission shift complaints.

Will bigger tires make my speedometer read wrong?

Yes. Taller tires travel farther per revolution, so with the stock calibration your speedometer reads low — you're going faster than it shows. The calculator above shows the exact error at 30, 60, and 80 mph. More detail: bigger tires, speedometer & gearing.

Do bigger tires hurt MPG?

Usually. More weight, more rolling resistance, more aerodynamic drag, and taller effective gearing that can lug the engine. Expect roughly 1–2 mpg less going up one truck tire step, sometimes more with aggressive tread.

Can I put wider tires on my stock wheels?

Sometimes — every size has an approved rim-width range (a 285/70R17 is typically 7.5–9.5"). Exceeding it is unsafe and can void the tire warranty. Check the manufacturer's spec sheet, not just the diameter math.

What is plus sizing?

Fitting a larger wheel with a lower-profile tire so overall diameter stays the same: +1 means wheel up 1", aspect ratio down. Use the sizing finder above to get options that keep your speedometer honest.

Guides