High-Flotation vs Metric Tire Sizes: Which Format

The two sizing systems for light trucks and SUVs

Tire sizes for light trucks, SUVs, and off-road vehicles come in two common formats: metric and high-flotation. The metric format, such as 265/70R17, is the standard on most passenger vehicles and many light trucks. High-flotation sizing, such as 33x12.50R15, is often seen on larger trucks and off-road builds. Both encode the same physical dimensions, but in different units and order.

Understanding both is important because the format determines how you read width, sidewall height, and overall diameter, and that affects whether a tire fits your rims and clears your fenders. It also affects how you compare load ratings and inflation pressures. Refer to the tire size explained page for a broader overview, and tire rim width range for fitment details.

How metric sizes express dimensions

In a metric size like 265/70R17, the first number is the section width in millimeters. The second number is the aspect ratio, a percentage that gives the sidewall height as a fraction of the width. So a 70-series tire has a sidewall height equal to 70 percent of its section width. The letter R indicates radial construction, and the last number is the rim diameter in inches.

Federal regulations define section width as the linear distance between the exteriors of the sidewalls of an inflated tire, excluding labeling and protective ribs. That definition appears in the safety standards for new pneumatic tires, and the standards also specify how load ratings are assigned at various inflation pressures. The overall diameter is not printed on the sidewall; you must calculate it from the width, aspect ratio, and rim diameter.

Metric sizing is precise for width and sidewall height, which makes it easy to compare to an original equipment replacement. Most vehicles are spec'd with a metric size, so staying in metric avoids clearance and speedometer issues. Learn more about aspect ratio on the tire aspect ratio page.

How high-flotation sizes express dimensions

A high-flotation size like 33x12.50R15 tells you the overall diameter in inches first, then the section width in inches, then the rim diameter after the R. In this example, the tire is 33 inches tall, approximately 12.5 inches wide, and fits a 15-inch rim. There is no aspect ratio because the sidewall height is implied by the difference between overall diameter and rim diameter.

This format is popular for off-road and light truck applications because it lets you compare overall diameter at a glance. A 35x12.50R17 tire is simply 35 inches tall and 12.5 inches wide on a 17-inch wheel. The trade-off is that you must verify rim width compatibility and load rating carefully, because the same nominal diameter and width can have different rim width ranges.

While high-flotation sizes are not as common on new vehicles, they appear frequently in the replacement market for trucks and off-road builds. The definition of section width and load rating under federal standards applies equally to these tires, so the same safety principles hold.

Fitment and clearance considerations

Whether you choose metric or high-flotation, the critical numbers are rim diameter, rim width, and overall diameter. The rim diameter must match the wheel exactly, as does the bead seat. Rim width falls in a range specified for each tire size; using too narrow or too wide a rim can cause handling issues and improper bead seating.

Overall diameter changes with the tire size and affects ground clearance, fender clearance, and speedometer accuracy. A high-flotation size makes it easy to compare diameters across sizes, but you still need to ensure the tire does not rub the suspension or body at full steering lock. Metric sizing makes it easier to keep the original diameter because the aspect ratio and width combine to produce a known value.

Before swapping between formats, use a tire size calculator or consult the vehicle's original specifications. Federal standards require that any tire fitted to a vehicle have a load rating sufficient for the axle weight, so check both dimensions and load capacity. See tire size and ground clearance and tire diameter and speedometer accuracy for more detail.

How load ratings work in both systems

Load rating is defined by federal regulations as the maximum load a tire can carry at a given inflation pressure. For vehicles with a gross vehicle weight rating of 10,000 pounds or less, the standard requires that the sum of maximum load ratings on an axle be at least the gross axle weight rating. That applies to both metric and high-flotation tires.

The load index is a numerical code on the sidewall that corresponds to a specific weight capacity at a given pressure. For example, a load index of 115 indicates a capacity of 2,679 pounds at 50 psi for an LT tire, but the actual value depends on the tire's load range and construction. High-flotation tires often use the same load index system as metric tires, so comparison is straightforward.

However, the format does not change the physics. A high-flotation tire with a wider section and larger diameter may have a different load capacity than a metric equivalent. Always verify the load index and inflation pressure on the tire's sidewall and match them to your vehicle's requirements as listed on the door placard. Review the tire load index rating and what is tire load range pages for deeper context.

Choosing the right format for your vehicle

If your vehicle came with a metric size, the safest choice is to replace it with the same metric size or a metric size that meets the original dimensions. This preserves the original ride height, speedometer calibration, and load capacity. For most cars, crossovers, and many SUVs, metric is the correct format.

High-flotation sizing makes sense when you are building a dedicated off-road truck or modifying a vehicle for larger tires. It gives a quick read on overall diameter, which matters for clearance and approach angle. But you must verify rim compatibility and load ratings, and you may need to reprogram the speedometer if the diameter changes.

Whichever format you choose, confirm the tire's load index and speed rating meet or exceed the vehicle's requirements. If you are unsure, consult a tire professional or reference your vehicle's door placard. The tire size interchangeability guide can help you assess whether a different size is safe.

What to pick for your use

Questions

Can I use a high-flotation tire on a vehicle that came with metric tires?

Yes, if the rim diameter matches and the overall width and diameter fall within your vehicle's clearance. You must also confirm that the load rating is sufficient for the axle weight.

How do I calculate the overall diameter of a metric tire?

Multiply the section width by the aspect ratio to get sidewall height in millimeters, convert that to inches, double it, and add the rim diameter. The result gives the overall diameter.

Are high-flotation tires always for off-road use?

No, they are common on trucks and SUVs, but some highway tires use the high-flotation format for sizing. The format itself does not dictate tread design or intended use.

Does the format affect load capacity?

No. Both metric and high-flotation tires use the same load index and load range system. The format only changes how the dimensions are expressed, not how load is rated.

What does the '12.50' mean in a size like 33x12.50R15?

It is the section width in inches, measured at the widest point of the inflated tire, excluding sidewall decorations.

Can I switch between metric and high-flotation without changing wheels?

Only if the rim diameter is identical. You also need to check that the rim width falls within the tire's approved range and that the overall diameter does not cause clearance problems.