Off Road Freedom

Tire Size Comparison: Compare Two Sizes Side by Side

Metric (285/70R17) or flotation (35x12.50R17).

Metric (285/70R17) or flotation (35x12.50R17).

+7.0% diameter change, 285/70R17 to 35x12.50R17

Size A against size B
MeasureABChange
Overall diameter32.7 in35.0 in+2.3 in (+7.0%)
Section width11.2 in12.5 in+1.3 in
Sidewall height7.9 in9.0 in+1.1 in
Circumference102.8 in110.0 in+7.2 in
Revolutions per mile617576-40
Ground clearance at the axle+1.15 in
Speedometer with size B, assuming it was set for size A
AtActual speedDifference
Speedometer reads 30 mph32.1 mph actual+2.1 mph
Speedometer reads 60 mph64.2 mph actual+4.2 mph

Speedometer rows assume the speedometer was calibrated for size A. Ground clearance rises by half the diameter change at the axle only; the lowest point (often the differential) does not move.

Nominal sizes from the formulas. Real tires differ by maker and tread; the maker's spec sheet lists the actual diameter.

Tire A 285/70R17 and tire B 35x12.50R17 drawn to the same scale A 285/70R17: 32.7 in (green)B 35x12.50R17: 35.0 in (orange, dashed)

Worked example

Moving from 245/75R16 to 265/75R16 keeps the 75 aspect ratio and the 16 in rim, so the tire grows only because it is wider: 20 mm of extra width adds 15 mm to each sidewall. That is about 1.2 in of extra diameter, around 4 percent, and the speedometer reads that much low.

+3.9% diameter change, 245/75R16 to 265/75R16

Size A against size B
MeasureABChange
Overall diameter30.5 in31.6 in+1.2 in (+3.9%)
Section width9.6 in10.4 in+0.8 in
Sidewall height7.2 in7.8 in+0.6 in
Circumference95.7 in99.4 in+3.7 in
Revolutions per mile662637-25
Ground clearance at the axle+0.59 in
Speedometer with size B, assuming it was set for size A
AtActual speedDifference
Speedometer reads 30 mph31.2 mph actual+1.2 mph
Speedometer reads 60 mph62.3 mph actual+2.3 mph

Speedometer rows assume the speedometer was calibrated for size A. Ground clearance rises by half the diameter change at the axle only; the lowest point (often the differential) does not move.

Nominal sizes from the formulas. Real tires differ by maker and tread; the maker's spec sheet lists the actual diameter.

How to use this tool

  1. Enter both sizes
    Put the size you run now in A and the new size in B. Metric and flotation sizes can be mixed.
  2. Check the change column
    Diameter change drives speedometer error and gearing. Width change decides how much room the tire needs in the wheel well.
  3. Read the speedometer rows
    They show what the car is really doing when the speedometer reads 30 or 60 mph on size B, assuming it was set for size A.

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How it is calculated

  • Sidewall (mm) = width x aspect / 100. Diameter (in) = rim + 2 x sidewall / 25.4. Section width (in) = width / 25.4.
  • Diameter = first number. Width = second number. Sidewall (in) = (diameter - rim) / 2.
  • Actual speed = indicated speed x new diameter / old diameter.
  • Ground clearance change at the axle = (new diameter - old diameter) / 2.

Results are nominal. Real tires differ by maker and tread, and the maker's spec sheet lists the actual diameter.

A larger tire outlined over a stock one: the height gain, and the axle rising by half of it.
A larger tire outlined over a stock one: the height gain, and the axle rising by half of it.

Frequently asked questions

How is tire size comparison calculated?

Each size is converted to overall diameter, width and sidewall using the size code, then the two are subtracted. The diameter change is shown in inches and as a percent of the original.

Does a bigger tire raise my whole vehicle?

The axle rises by half the diameter change, so a tire 2 in taller lifts the axle about 1 in. Your lowest point is usually the differential or a skid plate, which does not move, so clearance under those parts stays the same.

Why is the speedometer error shown at 30 and 60 mph?

The error is a fixed percentage, so it grows with speed. The two rows show how big the gap is around town and at road speed.

What does a 3 percent diameter change mean?

It is the guideline one tire maker gives for staying close to the original diameter. Past that, expect more noticeable speedometer and odometer error.

Will a wider tire with the same diameter fit?

Not necessarily. A tire of equal diameter can still be wider, which needs more room at full steering lock and on suspension travel. Width and wheel offset both matter, so check offset too.

Can I compare a metric size to a flotation size?

Yes. Both are converted to inches first, so 285/70R17 and 33x12.50R17 can be compared directly.

More tools and guides

Tire size calculator

Diameter, width and sidewall from any size code.

Open the tool

Speedometer calculator

How far off your speedometer is after a tire change.

Open the tool

Gear ratio calculator

RPM at speed, and when bigger tires call for a regear.

Open the tool

Your numbers are saved in the link, so anyone who opens it sees the same result.

Sources

Last checked 2026-11-12. Each link was opened and read on that date.

This guide reflects independent editorial research, not first-hand product testing, professional mechanical training, or rescue certification. Some links on this page are Amazon Associates affiliate links; see our affiliate disclosure.