Compare Tire Size Calculator

Common questions

How do I compare two tire sizes?

Type the size the car is on now in the first field and the size you are considering in the second. The two panes show every derived dimension for each, and the strip under the new size carries the diameter difference as a percentage. Sizes can be written any way the sidewall does: 225/45R17, 225/45 R17, P225/45R17 or 225/45r17 all read the same, and Swap turns the comparison around.

What does going up a size actually change?

Three things you can measure: the overall diameter, which changes ride height and gearing; the circumference, which changes revolutions per mile; and the section width, which changes how much rubber is across the wheel. A wider tire on a lower profile can come out shorter than the tire it replaces, which is why the percentage matters more than the numbers looking bigger. 225/45R17 to 235/40R18 is wider and a larger rim, and still only 1.72 percent taller.

Does the speedometer error work the same in kilometres per hour?

Yes. The error is a ratio of diameters, so it is the same percentage at every speed and in every unit. A size that reads 58.99 at a true 60 mph reads 98.31 at a true 100 km/h. The page states the percentage as well as the reading at 60 so you can apply it to whatever your dash shows.

Which size should I put in which field?

The size on the car now goes in the current field, because the speedometer and the odometer were calibrated for it. That order is what makes the reading at 60 and the odometer figure mean anything: they are what the instruments will do once the new size is fitted. Putting the same code in both fields gives a zero difference and a speedometer reading of exactly 60, which is a quick way to check you have typed what you meant.

Will a difference this small cause a problem?

That is a question about your car rather than about arithmetic, and this page will not answer it. Clearance, suspension travel and how the electronics were calibrated decide it, and none of them can be seen from a sidewall code. The comparison gives you the exact figure to take to your vehicle's documentation or to a fitter.

Does a size change affect fuel economy figures?

The figures your car shows, yes. The odometer and the trip computer count distance in wheel turns, so after a size change the miles they record, and any mpg worked out from those miles, are out by the same percentage as the odometer line on this page. Fitting a taller tire makes the car under-record miles, so a fuel economy figure worked from the odometer comes out lower than the real one. That is a measuring error, separate from any real change in consumption, which a sidewall code cannot tell you.

How much does a bigger tire raise the vehicle?

At the axle, by half the diameter change, because the tire grows equally above and below the hub. 265/70R17 to 33x12.50R17 adds 1.39 inches of diameter, so the axle centre and everything hung from it sits about 0.70 of an inch higher. The page shows this as the axle height change. Whether the body clears the larger tire is a different question that depends on the vehicle and is not answered here.

Can I compare staggered front and rear sizes?

Yes. Put the front size in one field and the rear size in the other, and the diameter percentage is the difference between the two axles, with revolutions per mile for each so you can see how far apart the wheel speeds are. Whether a given gap suits a particular all-wheel-drive or traction system is set by the vehicle maker, and this page does not judge it.

How do I check a plus size or an up size?

Type the size on the car now as the current size and the candidate as the new one. Plus sizing keeps the overall diameter close while the rim grows, so the figure to watch is the diameter percentage: 205/55R16 to 225/45R17 is only 0.38 percent. The page does the arithmetic for any pair you type and does not produce a list of sizes for you.