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Tire size comparison

Enter your current tire size and the one you're considering. See how they differ in height, width and sidewall, drawn to scale, and what your speedometer will read at real speeds after the change.

Show sizes in

Sizes within 3% of 265/70R17 on paper

What the size codes mean

Current: 265/70R17

No letter
A metric (Euro-metric) size. Same dimensions as P-metric, though the load ratings are worked out slightly differently.
265
Section width: 265 mm (10.43 in) from sidewall to sidewall, measured on the tire's measuring rim.
70
Aspect ratio: the sidewall is 70% as tall as the tire is wide, 186 mm (7.3 in).
R
Radial construction, which almost every modern car and truck tire uses.
17
Fits a 17-inch wheel (rim diameter).

New: 285/70R17

No letter
A metric (Euro-metric) size. Same dimensions as P-metric, though the load ratings are worked out slightly differently.
285
Section width: 285 mm (11.22 in) from sidewall to sidewall, measured on the tire's measuring rim.
70
Aspect ratio: the sidewall is 70% as tall as the tire is wide, 200 mm (7.85 in).
R
Radial construction, which almost every modern car and truck tire uses.
17
Fits a 17-inch wheel (rim diameter).
Overall diameter, new vs current
+3.5%
285/70R17 is 1.1 in (28 mm) taller than 265/70R17. When your speedometer reads 60 mph, you're actually going about 62.1 mph.
Current and new tire sizes compared
MeasurementCurrentNewChange
Overall diameter
Overall diameter31.61 in803 mm32.71 in831 mm+1.10 in+3.5%
Section width
Section width10.43 in265 mm11.22 in285 mm+0.79 in+7.5%
Sidewall height
Sidewall height7.3 in186 mm7.85 in200 mm+0.55 in+7.5%
Rim diameter
Rim diameter17 in17 inSame
Circumference
Circumference99.3 in2,522 mm102.8 in2,610 mm+3.46 in+3.5%
Revolutions per mile
Revolutions per mile638617−22−3.4%
Ground clearance
Ground clearance+0.55 in+14.0 mm
That's 3.5% bigger, past the roughly 3% rule of thumb many tire shops use. Expect a bigger speedometer error and changes to gearing, braking and stability systems, and check clearance with a tire professional before you buy.
Wider by 20 mm (0.79 in). Every tire size has an approved range of rim widths, and a wider tire needs room in the wheel well at full steering lock and suspension travel.

Drawn to scale

Side view and tread width, nominal sizes

New7.3 in31.6 in tall10.4 in wide265/70R17CurrentCurrent7.9 in32.7 in tall11.2 in wide285/70R17New

Speedometer with the new size

Speedometer readsActual speedDifference
25 mph25.9 mph+0.9
35 mph36.2 mph+1.2
45 mph46.6 mph+1.6
55 mph56.9 mph+1.9
65 mph67.3 mph+2.3
75 mph77.6 mph+2.6

After 1,000 real miles, the odometer would show about 966. This assumes the speedometer was accurate on the current tires; some vehicles can be recalibrated by a dealer or a tuning tool after a size change.

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How to compare two tire sizes

  1. 1

    Enter your current size from the sidewall or the tire placard in the driver’s door jamb.

  2. 2

    Enter the new size you are thinking of, or pick one of the sizes within 3% of the current diameter.

  3. 3

    Check the change in height, width and sidewall in the table, and see both tires side by side in the scale drawing.

  4. 4

    Read the speedometer table to see how fast you are really going at an indicated 25 to 75 mph.

Features

  • Speedometer and odometer

    Your true speed at six indicated speeds, and what the odometer shows after 1,000 real miles on the new size.

  • Side by side, to scale

    Both tires and wheels drawn at the same scale on one ground line, with the other tire’s height marked.

  • Plus and minus sizing

    One click lists sizes on smaller and bigger wheels that stay within 3% of your current tire’s height.

  • Ride height and width

    See how much the vehicle rises or drops, and how much wider the new tire is, in inches and millimeters.

Reading the comparison

The number that matters most is the overall diameter. Your speedometer and odometer count how often the wheels turn, so a change in diameter changes every speed and distance they report, by the same percentage. The rest of the table tells you what the change will feel like:

  • Section width: a wider tire needs a wheel inside its approved rim-width range and room in the wheel well. A rough rule from the tire industry: each half inch of rim width changes the measured width by about 0.2 inch.
  • Sidewall height: a shorter sidewall usually steers more sharply and rides firmer, and leaves the wheel more exposed to potholes.
  • Ground clearance: the axle rises or drops by half the change in diameter. Going from 265/70R17 to 285/70R17 lifts it about 0.55 in.
  • Revolutions per mile: fewer turns per mile means a taller effective gear, so a much bigger tire can make a vehicle feel slower to accelerate.

Popular comparisons

FromToDiameterAt 60 mph
265/70R17285/70R17+3.5%62.1 mph
265/70R17285/75R17+7.0%64.2 mph
275/55R20275/60R20+3.4%62.0 mph
225/65R17245/55R18+0.3%60.2 mph
205/55R16225/45R17+0.4%60.2 mph
225/65R17235/65R17+1.8%61.1 mph

"At 60 mph" is your true speed when the speedometer shows 60, assuming it was accurate on the original tires. 265/70R17 to 285/75R17 is a common truck upgrade, but at +7.0% it is well past the 3% rule of thumb: after 1,000 real miles the odometer would show only about 934.

Why your speedometer is never exact

The comparison assumes your speedometer was right with the current tires, but even the same size changes as it wears. Many new passenger tires start with about 10/32 to 11/32 inch of tread, and most US states require at least 2/32 inch. Wearing off about 8/32 inch on each side makes a 225/65R17 roughly half an inch shorter, about 1.8%, so a worn set reads slightly faster than a new one. A size change of 1 to 2% is in the same range as the difference between new and worn tires.

Before you change sizes

  1. Start from the size on the tire placard in the driver’s door jamb or in the owner’s manual, not from what happens to be on the car.
  2. Keep the load index and speed rating at least as high as the original’s, especially on SUVs and trucks that tow.
  3. Check the new width against the wheel’s width, and the clearance at full steering lock and with the suspension compressed.
  4. On all-wheel-drive vehicles, follow the maker’s advice: many ask for all four tires to match in size and wear.
  5. Ask a tire professional to confirm the fit before you buy. This page shows the geometry; it can’t see your vehicle.

To look up a single size in detail, with its load index and speed rating explained, use the tire size calculator. A new tire size also skews the miles your odometer records, which matters when you work out fuel economy with the MPG calculator or plan a trip with the gas cost calculator.

Frequently asked questions

How much bigger can my tires be?

Many tire shops use about 3% of the original overall diameter as a rule of thumb for a replacement size. Beyond that, the speedometer error grows and the bigger tire may rub at full lock or over bumps. Lifted trucks go far past it with other changes. Check the placard and owner’s manual, and ask a tire professional.

Will bigger tires make my speedometer read slow?

Yes. A taller tire covers more ground per turn, so you go faster than the speedometer shows. Going from 265/70R17 to 285/70R17 (+3.5%), an indicated 60 mph is really about 62.1 mph. Smaller tires do the opposite.

What is plus sizing?

Fitting a bigger wheel with a lower-profile tire so the overall height stays about the same. Plus one is one inch more wheel: 225/65R17 to 245/55R18 changes the diameter by only +0.3%, and 235/55R18 by −1.2%. The trade-off is a shorter sidewall, which usually rides firmer.

Does a wider tire change the speedometer?

Only if it is taller, and with the same aspect ratio it is: the ratio is a percentage of the width. 225/65R17 to 235/65R17 adds 10 mm of width and +1.8% of diameter. To go wider at about the same height, lower the aspect ratio as well: 245/60R17 is +0.2% against 225/65R17.

Can I recalibrate my speedometer after changing tire size?

On many vehicles, yes: a dealer can often reprogram the tire size, and plug-in tuners do it on many trucks. Recalibrating fixes the odometer as well. Older cars with a mechanical speedometer may need a different drive gear.

Can I run different sizes front and rear?

Only if the vehicle was designed with a staggered setup. Tires on the same axle should always match, and many all-wheel-drive makers ask for all four tires to be the same size and close in tread depth, because different diameters strain the drivetrain.

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