22.5 Flotation Tires: How to Read the Size and What It Means

The short answer

A 22.5 flotation tire is a wide, low-profile tire that mounts on a 22.5-inch rim. The 22.5 figure is the rim diameter in inches. "Flotation" means the tire spreads its load over a broad footprint so it can ride over loose or soft ground instead of sinking in. Tire retail guidance on high-speed flotation tires for spreader trucks and trailers names 550/45R22.5 and 560/45R22.5 as two of the most common sizes.

An important condition: in the 22.5 category, "flotation" usually describes the tire's purpose and shape, not a separate way of writing the size. Common 22.5 flotation sizes are written in the standard metric format. The inch-based flotation format, which lists overall diameter first, is a different convention and is more often associated with light-truck and off-road tires.

What "flotation" means

Flotation describes a tire's ability to stay on top of soft surfaces such as loose dirt, mud, sand or tilled ground. A wider footprint at a given load lowers the pressure the tire puts on the ground. That reduces sinking and rutting. This is why the term comes up with spreader trucks and trailers that travel on fields as well as roads.

"Flotation" also has a second meaning. Some sources use it for an alternate tire-sizing format based on overall dimensions in inches. Knowing which meaning a seller or article intends will prevent confusion when comparing sizes.

Reading a metric 22.5 flotation size

Take 550/45R22.5 as an example. Each part means the following:

• 550: nominal section width in millimeters, measured from sidewall to sidewall.
• 45: aspect ratio, meaning the sidewall height is about 45 percent of the section width.
• R: radial construction.
• 22.5: rim diameter in inches.

The format mixes millimeters for width with inches for rim diameter. That is normal for metric-designated tires.

Converting a metric size to approximate inches

You can estimate the dimensions in inches from the size code. Use the steps below. The results are nominal calculations only. Actual measured dimensions vary by manufacturer, tread design, rim width and inflation, so use the manufacturer's published specifications for anything that depends on clearance or fit.

Section width (in)   = width_mm / 25.4
Sidewall height (in) = (width_mm x aspect_ratio / 100) / 25.4
Overall diameter (in) = rim_in + 2 x sidewall height

Size | Nominal width | Nominal sidewall height | Nominal overall diameter

550/45R22.5 | about 21.7 in (550 mm) | about 9.7 in (247.5 mm) | about 42.0 in

560/45R22.5 | about 22.0 in (560 mm) | about 9.9 in (252 mm) | about 42.3 in

How inch-based flotation sizes differ

Inch-based flotation sizing lists three measurements: overall tire diameter, section width and rim diameter. A light-truck example is 33x12.50R15. That size describes a tire roughly 33 inches tall and 12.5 inches wide on a 15-inch rim. Because the overall diameter is stated directly, no aspect-ratio calculation is needed.

Look at the position of the numbers to tell the two formats apart. A metric size begins with a three-digit millimeter width and a slash, as in 560/45R22.5. An inch flotation size begins with the overall diameter and an "x", as in 33x12.50R15.

Trucks, trailers and other uses

The available material links 22.5 flotation tires to spreader trucks and trailers, including high-speed versions intended for road travel as well as field use. It does not establish whether a given flotation tire suits a dump truck, a semi truck tractor, or a particular trailer axle. Suitability depends on the vehicle's axle ratings, wheel specifications, intended speeds and operating surfaces. Confirm it with the vehicle or equipment manufacturer and the tire manufacturer, not from the size alone.

What to check before choosing

Two tires with the same size code can still differ in ways that matter. Before treating a tire as a match, check these points against the manufacturer's data and your vehicle documentation:

• Load capacity and load index for single or dual fitment, as published by the tire maker.
• Speed rating, especially if the tire will spend time on highways. "High-speed flotation" is a description, not a rating.
• Approved rim width and wheel specification for the size.
• Required inflation pressure for the load carried.
• Clearance for the full width and diameter, including fenders, suspension and brake components.
• Overall-width limits for road use, which depend on jurisdiction and are not covered here.

Limits of this guide

This guide explains size notation and the meaning of "flotation." It is not fitment approval for any vehicle. It does not cover current availability, prices, brand comparisons, or legal width and load rules. The dimension figures above come from the size codes, not from manufacturer measurements. Rely on the tire maker's data book, the vehicle or trailer manufacturer, and applicable regulations for final decisions.