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Tire size comparison calculator

Enter your current tire size and the size you are considering to see the difference in every dimension, drawn to scale, plus how your speedometer will read.

Your numbers

Results

Check before you buy. Results are calculated from size codes and standard formulas; real tires vary by brand and model. Always check your vehicle placard and owner’s manual for approved sizes and load ratings, and ask a tire professional about fitment and clearance.

What this comparison shows

Changing tire size affects more than looks. A taller tire raises the vehicle slightly, makes the speedometer read low, and makes the engine work a little harder at a given speed. A wider tire can rub on suspension parts or the fender liner. This tool calculates each dimension for both sizes and shows the difference, so you can see the trade-offs before you buy.

How the differences are calculated

Diameter = 2 × (width × aspect ÷ 100) ÷ 25.4 + rim Diameter change (%) = (diameter B ÷ diameter A − 1) × 100 Actual speed = speedometer reading × diameter B ÷ diameter A Ground clearance change ≈ (diameter B − diameter A) ÷ 2

Ground clearance under the axle only rises by half of the diameter increase, because the axle sits at the center of the tire.

Worked example: 265/70R17 vs 285/70R17

A 265/70R17 is 31.61 in tall; a 285/70R17 is 32.71 in tall. The new tire is 1.10 in (3.5%) taller and 20 mm (0.79 in) wider, and it raises the axle by about 0.55 in.

With the 285s fitted, when your speedometer shows 60 mph you are actually doing about 62.1 mph. Revolutions per mile fall from about 638 to 617.

See our popular tire size comparisons for precomputed tables of common upgrades.

The ±3% guideline

Many tire retailers recommend keeping a replacement tire within about 3% of the original diameter. Staying close keeps speedometer and odometer error small and avoids large changes to gearing and to how anti-lock braking and stability systems see wheel speed. It is a rule of thumb, not a law: many trucks run larger tires successfully with a lift, recalibration and sometimes regearing. Going beyond 3% is a reason to check carefully, not an automatic "no".

Fitment checklist

  • Clearance: check at full steering lock and with the suspension compressed. A larger tire may contact the upper control arm, frame, mud flaps or fender liner.
  • Wheel width: every tire size has an approved rim-width range from the tire maker. A much wider tire on a narrow wheel can bulge and wear unevenly.
  • Load rating: the new tire's load index (and LT load range, if any) must meet or exceed the requirement on your door placard.
  • Speedometer and gearing: large changes may call for speedometer recalibration and, on trucks, a numerically higher axle ratio. Try the gear ratio calculator.
  • Spare tire: make sure the new size still fits the spare carrier, and that a mismatched spare is acceptable for your four-wheel-drive system.

Reading the drawing

The drawing shows both tires to the same scale. On the left is the side view with the wheel drawn to the rim diameter; on the right is the tread (front) view showing section width. The dashed line marks the top of the taller tire. Real tires, especially aggressive off-road treads, can look larger or squarer than these idealized shapes.

Popular comparisons

All popular comparisons, grouped by wheel size →

Frequently asked questions

How much bigger can I go without problems?

A common guideline is within about 3% of the original diameter. Beyond that, check clearance, speedometer error and gearing, and consider recalibrating the speedometer.

Will bigger tires make my speedometer read wrong?

Yes. A taller tire covers more ground per turn, so the speedometer reads lower than your real speed. A 3.5% taller tire means about 62 mph when it shows 60.

Do bigger tires hurt fuel economy?

Usually somewhat, because larger tires are typically heavier and the effective gearing becomes taller. Also, the trip computer under-reports miles driven, so measured MPG looks worse than it really is unless the speedometer is recalibrated.

Can I compare metric and inch tire sizes?

Yes. Enter any combination, for example 285/75R16 against 33x12.50R15.

Can I share a comparison?

Yes. Add the sizes to the page address, for example /tire-size-comparison/?a=265/70R17&b=285/70R17, and the calculator will open with them filled in.

Last reviewed November 2026. Spotted an error? Tell us.