What Is Considered a Low-Profile Tire on Commercial Trucks and Buses?

On commercial trucks and buses, a low-profile tire is a tire whose sidewall height is a smaller percentage of its section width than a conventional truck tire's. You can identify one from the size on the sidewall. A metric size such as 295/75R22.5 includes an aspect ratio, which is the second number (75). Tires in the 80, 75 and 70 series are commonly called low profile. Inch-only sizes such as 11R22.5 or 11R24.5 are called conventional sizes. Tires at 65 series and below, such as 385/65R22.5 or 445/50R22.5, are usually described as super low profile or wide-base tires.

No single regulation sets an exact cutoff. Manufacturers and fleets use these groupings by convention, and some catalogues label them slightly differently. The aspect ratio is the number that decides the label, so the sidewall markings are the place to start.

What Is Considered a Low-Profile Tire on Trucks and Buses?

A commercial tire is considered low profile when its size designation shows an aspect ratio, typically 80 or lower, and its sidewall is therefore lower relative to its width than a conventional inch-sized truck tire. The table below shows how the size markings usually map to the profile groups used in the commercial tire industry.

Many low-floor city buses, for example, run 70-series sizes such as 275/70R22.5 or 305/70R22.5. Line-haul tractors and trailers commonly use 75- and 80-series sizes in place of conventional 11R22.5 and 11R24.5 tires.

How to Read the Numbers on a Commercial Tire Sidewall

A commercial tire size designation gives the tire's nominal width, its construction, the rim diameter and, for metric sizes, its aspect ratio. Separate markings give load and speed capability. Only the size designation tells you whether a tire is low profile.

Reading a metric size: 295/75R22.5

1. 295 is the nominal section width in millimetres. Section width is the width of the inflated tire from sidewall to sidewall, not counting raised lettering or protective ribs. 295 mm is about 11.6 inches.
2. 75 is the aspect ratio. The sidewall height is 75 percent of the section width. This number is what makes the tire a low-profile size.
3. R means radial construction.
4. 22.5 is the rim diameter in inches. Truck rim diameters ending in .5, such as 17.5, 19.5, 22.5 and 24.5, are used with tubeless tires on 15-degree drop-centre rims.

Reading a conventional inch size: 11R22.5

In a conventional truck size such as 11R22.5, 11 is the nominal section width in inches, R means radial and 22.5 is the rim diameter in inches. No aspect ratio is printed. Because of that, you cannot calculate the sidewall height from the marking alone. You need the manufacturer's published overall diameter. Conventional sizes have a sidewall height that is a large share of the width, which is why the 75- and 80-series metric sizes that replaced them are called low profile. Older tube-type sizes written with a decimal, such as 11.00R20, are also conventional sizes and mount on 20-inch rims.

Load and speed markings do not define the profile

Commercial tires carry performance ratings next to the size. These ratings describe capability, not dimensions:

• Load index pair, for example 144/141. The first number is the maximum load per tire in single fitment and the second is the maximum load per tire in dual fitment. Load index 144 corresponds to 2,800 kg and 141 to 2,575 kg, each at the specified inflation pressure.
• Speed symbol, for example L, which corresponds to 120 km/h (75 mph), or M, which corresponds to 130 km/h (81 mph).
• Load range, for example G or H, which indicates the tire's strength and inflation capability.

A low-profile tire and a conventional tire can share the same load range or speed symbol. These ratings tell you nothing about sidewall height.

What Makes a Tire Low Profile?

The aspect ratio is what makes a tire low profile. The aspect ratio is the sidewall height divided by the section width, expressed as a percentage. A lower number means the sidewall is shorter relative to the tire's width.

The aspect ratio is a proportion, not a height. A low-profile tire does not necessarily have a short sidewall or a small overall diameter. A wide tire with a low aspect ratio can have the same sidewall height as a narrower tire with a higher ratio. For example, the calculated sidewall height of a 445/50R22.5 is about 8.8 inches. A 295/75R22.5 has a calculated sidewall height of about 8.7 inches, almost the same. The calculation for each tire is:

• 445/50R22.5: 445 mm × 0.50 = 222.5 mm, or about 8.76 inches.
• 295/75R22.5: 295 mm × 0.75 = 221.25 mm, or about 8.71 inches.

What Size Tires Are Low Profile?

Common low-profile commercial sizes include 275/80R22.5, 295/75R22.5 and 285/75R24.5 for heavy trucks and trailers, 275/70R22.5 and 305/70R22.5 for many city buses, and 245/70R19.5 and 265/70R19.5 for medium-duty trucks and some trailers. The table shows calculated sidewall heights and overall diameters. These are geometric values from the size marking, not manufacturer measurements.

The table shows two useful patterns. First, 385/65R22.5 is a super-low-profile size but is calculated to be taller overall than 295/75R22.5, because it is much wider. Second, a smaller rim diameter has a bigger effect on overall height than a lower aspect ratio. This is why 19.5-inch low-profile sizes are used where a low vehicle or deck height is needed.

How Width, Aspect Ratio and Rim Diameter Change Tire Size

Sidewall height depends on both section width and aspect ratio. Overall diameter depends on sidewall height and rim diameter. Circumference follows directly from diameter. You can calculate all three for any metric size with the following steps.

1. Sidewall height (mm) = section width (mm) × aspect ratio ÷ 100.
2. Sidewall height (inches) = sidewall height (mm) ÷ 25.4.
3. Overall diameter (inches) = rim diameter (inches) + 2 × sidewall height (inches). The sidewall counts twice because it sits above and below the rim.
4. Circumference (inches) = overall diameter × 3.1416.
5. Revolutions per mile = 63,360 ÷ circumference in inches, because a mile is 63,360 inches.

Each value has its own effect:

• Width: at the same aspect ratio, a wider tire has a taller sidewall. At 75 series, every additional 10 mm of width adds 7.5 mm of sidewall height and 15 mm of overall diameter.
• Aspect ratio: at the same width, each 5-point drop in aspect ratio on a 295 mm tire removes about 14.75 mm (0.58 in) of sidewall height and about 1.16 in of overall diameter.
• Rim diameter: moving from a 22.5-inch to a 24.5-inch rim adds 2 inches to overall diameter if the sidewall stays the same.

Worked example: 11R22.5 compared with 295/75R22.5

The 295/75R22.5 is the low-profile size most often compared with the conventional 11R22.5. The metric size gives a calculated overall diameter of about 39.9 inches and a calculated circumference of about 125.4 inches, or about 505 revolutions per mile.

The 11R22.5 has no printed aspect ratio, so its diameter has to come from manufacturer data. Published overall diameters for 11R22.5 tires commonly fall around 41 to 42 inches, depending on the tread design. The following calculation uses an illustrative 41.5 inches:

• Sidewall height ≈ (41.5 − 22.5) ÷ 2 = 9.5 inches.
• Implied ratio ≈ 9.5 ÷ 11 ≈ 0.86, so the sidewall is roughly 86 percent of the nominal width.
• Circumference ≈ 41.5 × 3.1416 ≈ 130.4 inches, or about 486 revolutions per mile.

On these figures, the 295/75R22.5 is slightly wider, about 0.8 inch lower in sidewall height per side and about 1.5 inches smaller in overall diameter. Its circumference is roughly 5 inches, or about 4 percent, shorter. The low-profile tire turns more times per mile, which affects speedometer and odometer readings and effective gearing. Use the exact published figures for the tire models you are comparing, because the 41.5-inch value is only an example.

Same rim, different series

On a 22.5-inch rim with the same 275 mm width, moving from 275/80R22.5 to 275/70R22.5 lowers the calculated overall diameter from about 39.8 to about 37.7 inches. That 10-point drop in aspect ratio removes about 2.2 inches of overall height, which is a large change for a commercial vehicle.

Calculated Geometry vs Actual Tire Dimensions

The numbers calculated from a tire size designation are nominal geometry. They are not the measured dimensions of a specific tire. Actual dimensions differ for several reasons:

• Section width depends on the rim. The nominal width applies on a specified measuring rim. Mounting the tire on a wider or narrower approved rim changes the measured width slightly.
• Tread design and depth matter. Drive tires with deep tread usually have a larger new diameter than rib or trailer tires of the same size. Diameter falls as the tread wears.
• Inflation and load change the shape. The tire grows slightly when inflated and flattens under load. The static loaded radius is smaller than half the unloaded diameter.
• Rolling revolutions are measured, not calculated. Manufacturers publish revolutions per mile or per kilometre measured under load. These figures differ from the simple circumference calculation and are the ones to use for speed calibration.

Calculated values are useful for understanding why one size is taller, wider or lower than another. Data-sheet values should be used whenever an exact dimension matters.

Why Similar Dimensions Do Not Guarantee Fitment

Two tire sizes with similar calculated diameters are not automatically interchangeable on a truck or bus. Fitment compatibility depends on more than the size geometry:

• Approved rim width. Each size has a range of approved rim widths. For example, 11R22.5 and 295/75R22.5 are both commonly approved on 8.25-inch-wide 22.5 rims, but this must be confirmed for the specific tire.
• Load capacity. The load index and inflation pressure must meet the axle's requirements. A lower-profile size does not carry the same load by default.
• Clearance and dual spacing. Section width and the tire's loaded bulge must clear suspension, body and brake parts, and must leave adequate spacing between dual tires.
• Matched diameters on duals and drive axles. Tires paired on a dual assembly or across drive axles should be closely matched in diameter, following the manufacturer's guidance.
• Vehicle calibration and height. A change in circumference affects speedometer readings and engine control settings. A change in diameter affects ride height, trailer deck height and coupling height.

The size markings tell you whether a tire is low profile and how its geometry compares with another size. Whether a size is suitable for a particular vehicle depends on the vehicle and tire manufacturers' specifications.