Mobility Scooter Tire Size Chart: Reading the Numbers on the Sidewall

A mobility scooter tire size is the code moulded into the tire sidewall, such as 3.00-4, 4.10/3.50-4, 13x5.00-6, 260x85 or 62-203. Each format describes some combination of three dimensions: tire width, rim diameter and overall diameter. In the most common inch format, 3.00-4 means a tire about 3.00 inches wide that mounts on a 4-inch rim. A metric code such as 260x85 instead gives an overall diameter of about 260 mm and a width of about 85 mm. To find the right replacement, first work out which format your tire uses. Then compare the rim diameter exactly and the other dimensions closely.

What the numbers on a mobility scooter tire sidewall mean

The size marking on a mobility scooter tire is a set of nominal dimensions. Nominal means they are the manufacturer's stated sizes, not measurements of your individual tire. The size is usually the largest set of numbers on the sidewall. Other markings sit nearby, including maximum pressure, ply rating, load information and construction type. Those other markings describe performance and construction, not size.

• Tire width (section width): how wide the tire is from sidewall to sidewall. In inch codes like 3.00-4 it is in inches. In codes like 120/70-10 it is in millimetres.
• Rim diameter: the diameter of the wheel rim the tire mounts on, almost always in inches. The number after the hyphen (the 4 in 3.00-4) is the rim diameter.
• Overall diameter: the outside diameter of the inflated or solid tire. It appears first in codes like 13x5.00-6 (13 inches) and 260x85 (260 mm).
• Aspect ratio: sidewall height as a percentage of width. It is shown directly only in metric codes like 120/70-10, where 70 means the sidewall is 70% of the width.

The separator matters. A hyphen usually points to the rim diameter. An x usually separates overall diameter from width. A slash separates either two alternative width designations (4.10/3.50) or width from aspect ratio (120/70).

Mobility scooter tire size chart

The chart below lists size designations commonly seen on mobility scooters and similar small wheels. It shows what each number stands for and a calculated overall diameter. The calculated values come from the nominal numbers on the tire, so they are not a manufacturer's measured size. The method is explained in the next sections. Where the code does not state the overall diameter, the estimate assumes the sidewall height roughly equals the width.

Sidewall marking	Format	Width	Rim diameter	Overall diameter (stated or calculated)	Notes
2.80/2.50-4	Inch, dual width	2.80 or 2.50 in	4 in	About 9.0–9.6 in (calculated)	Two width designations; small wheels
3.00-4	Inch width-rim	3.00 in	4 in	About 10.0 in / 254 mm (calculated)	Often cross-referenced with 260x85 and 10x3
4.10/3.50-4	Inch, dual width	4.10 or 3.50 in	4 in	About 11.0–12.2 in (calculated upper range)	Real diameter is often smaller than this simple estimate
3.50-5	Inch width-rim	3.50 in	5 in	About 12.0 in / 305 mm (calculated)	5-inch rim only
4.00-5	Inch width-rim	4.00 in	5 in	About 13.0 in / 330 mm (calculated)	Commonly cross-listed as 330x100
3.00-8	Inch width-rim	3.00 in	8 in	About 14.0 in / 356 mm (calculated)	Commonly cross-listed as 14x3
3.50-8	Inch width-rim	3.50 in	8 in	About 15.0 in / 381 mm (calculated)	Same rim as 3.00-8, larger tire
9x3.50-4	Diameter x width-rim	3.50 in	4 in	9 in (stated)	Lower profile than 3.00-4
13x5.00-6	Diameter x width-rim	5.00 in	6 in	13 in (stated)	Wide, relatively low profile
260x85	Metric diameter x width	85 mm (about 3.3 in)	Not stated	260 mm / about 10.2 in (stated)	Rim must be confirmed separately
200x50	Metric diameter x width	50 mm (about 2 in)	Not stated	200 mm / about 7.9 in (stated)	Often called 8x2; common on small front wheels
12½ x 2¼ (62-203)	Inch nominal / ISO	62 mm (about 2.25 in)	203 mm bead seat (about 8 in)	12½ in nominal / about 318 mm	ISO number gives the most precise rim fit

Cross-references such as 3.00-4 and 260x85 are widely used as equivalents. They describe a similar nominal size, but a given tire from a given maker can still differ slightly in actual width and diameter.

Mobility scooter tyre sizes explained: the main notation formats

Mobility scooter tyres use several sizing systems because they borrow from wheelchair, small-wheel, industrial, bicycle and motorcycle conventions. These are the formats you are most likely to find.

Inch width-rim notation (for example 3.00-4, 3.00-8)

In inch width-rim notation, the first number is the nominal tire width in inches and the number after the hyphen is the rim diameter in inches. A 3.00-8 tire is about 3 inches wide and fits an 8-inch rim. This format does not state the aspect ratio. Many tires in this style have a sidewall roughly as tall as the tire is wide, so overall diameter is often estimated as rim diameter plus two times the width. For 3.00-8 that gives 8 + 2 × 3.00 = 14 inches. This is why 3.00-8 is commonly listed alongside 14x3.

Dual-width notation (for example 4.10/3.50-4)

A dual-width marking like 4.10/3.50-4 means the tire is designated to serve both the 4.10-4 and the 3.50-4 size. Both share a 4-inch rim diameter. The two numbers are alternative width designations, not width and height. The width you actually get depends partly on the rim width it is mounted on. The simple diameter estimate gives a range: 4 + 2 × 3.50 = 11.0 inches and 4 + 2 × 4.10 = 12.2 inches. Many tires of this size have a sidewall shorter than their width, so the real overall diameter is often below that range. For this size, check the manufacturer's stated diameter or measure the tire.

Overall diameter x width-rim notation (for example 13x5.00-6, 9x3.50-4)

In this format all three dimensions are given in inches: overall diameter, then width, then rim diameter. A 13x5.00-6 tire is about 13 inches tall and 5 inches wide, and it fits a 6-inch rim. Because the overall diameter is stated, you can work out the sidewall height and an effective aspect ratio:

• 13x5.00-6: sidewall = (13 − 6) ÷ 2 = 3.5 in; aspect ratio ≈ 3.5 ÷ 5.00 = 70%.
• 9x3.50-4: sidewall = (9 − 4) ÷ 2 = 2.5 in; aspect ratio ≈ 2.5 ÷ 3.50 ≈ 71%.

Overall diameter x width without a rim size (for example 260x85, 200x50, 10x3)

Some mobility scooter tire size markings give only overall diameter and width. They may be in millimetres (260x85, 200x50) or inches (10x3, 8x2). The first number is the overall diameter and the second is the width. These codes do not tell you the rim diameter. Two tires with the same overall size can mount on different rims, so confirm the rim size from the wheel or another marking before buying. To convert, divide millimetres by 25.4 to get inches: 260 mm ÷ 25.4 ≈ 10.2 in.

Metric width/aspect ratio-rim notation (for example 120/70-10)

Larger road-going mobility scooters may use motorcycle-style metric sizes. In 120/70-10, 120 is the width in millimetres, 70 is the aspect ratio in percent, and 10 is the rim diameter in inches. This is the only common format that states the aspect ratio directly. That makes it the easiest format for calculating sidewall height and overall diameter, shown in the worked example below.

ISO/ETRTO notation (for example 62-203)

An ISO (ETRTO) marking such as 62-203 gives the tire width in millimetres (62) and the rim bead seat diameter in millimetres (203). It is often printed beside an inch size such as 12½ x 2¼. The bead seat diameter is the precise rim dimension, so the second number is the most reliable way to match a tire to a rim. Two tires with different inch labels but the same bead seat number fit the same rim diameter.

Other mobility scooter tire markings: ratings and construction

Besides the size code, mobility scooter tire markings describe how the tire is built and what it is rated to carry. These numbers do not change the tire's dimensions. They tell you whether a replacement meets the same performance limits.

• Ply rating (for example 4PR): a strength rating for the tire casing. It is an index of load capacity, not a literal count of fabric layers. A replacement should generally match or exceed the original rating.
• Load index and speed symbol: some tires carry a number followed by a letter. The number is a code for maximum load per tire, read from a standard table. The letter is a code for the maximum rated speed. Neither is the weight or speed itself.
• Maximum load: sometimes printed directly in kilograms or pounds per tire.
• Maximum inflation pressure: shown in PSI, kPa or bar on pneumatic tires. This is the highest pressure the tire may be inflated to, not the recommended running pressure. The recommended pressure comes from the scooter's manual or the scooter maker.
• TT / TL: tube type (needs an inner tube) or tubeless.
• Construction: a hyphen in the size usually indicates bias-ply construction. Solid or puncture-proof tires use the same size codes as pneumatic tires, but they are often sold fitted to a wheel.
• Rotation arrow: a directional tread must be mounted so the arrow points in the forward rolling direction.

How width, aspect ratio and rim diameter change the wheel size

Overall wheel size depends on two things: rim diameter plus two sidewall heights. The sidewall height in turn depends on width and aspect ratio. Change any of these and the tire's diameter, circumference and axle height change too.

Sidewall height

Sidewall height is the distance from the rim edge to the tread surface. It equals width × aspect ratio ÷ 100. In a 120/70-10 tire, the sidewall is 120 × 0.70 = 84 mm. In inch width-rim sizes without a stated aspect ratio, a sidewall roughly equal to the width is the usual working assumption. Treat this assumption as an approximation.

Overall diameter and circumference

These are the two formulas used for the calculated values in this article:

• Overall diameter = rim diameter + 2 × sidewall height. Use the same unit throughout. A 10-inch rim is 254 mm.
• Circumference = π × overall diameter, using π ≈ 3.1416. Circumference is the distance the tire rolls in one full turn.

Worked example for 120/70-10: 254 mm + 2 × 84 mm = 422 mm overall diameter (about 16.6 in). The circumference is 3.1416 × 422 ≈ 1,326 mm.

Worked example for 3.00-4, assuming sidewall ≈ width: 4 + 2 × 3.00 = 10.0 in (254 mm). The circumference is 3.1416 × 10.0 ≈ 31.4 in (about 798 mm).

Comparing two sizes: what the difference means

Comparing calculated dimensions shows how much larger or smaller one tire is than another on paper. The table compares sizes that share a rim diameter, because only tires with the same rim diameter can be mounted on the same rim.

Comparison	Overall diameter (calculated)	Circumference (calculated)	Difference
3.00-8 vs 3.50-8	14.0 in vs 15.0 in	44.0 in vs 47.1 in	+1.0 in diameter (about +7.1%); axle about 0.5 in higher; about 3.1 in more travel per turn; about 0.5 in wider
3.00-4 vs 4.10/3.50-4 (using 3.50)	10.0 in vs 11.0 in	31.4 in vs 34.6 in	+1.0 in diameter on paper; at least 0.5 in wider. The real tire is often smaller than the estimate
3.00-4 vs 9x3.50-4	10.0 in vs 9 in (stated)	31.4 in vs 28.3 in	About 1 in smaller diameter but 0.5 in wider; lower profile

In practical terms, a larger overall diameter raises the scooter slightly and changes the distance covered per wheel revolution. On a driven wheel, the scooter travels a little farther per motor revolution, so any speed or distance reading based on wheel rotation shifts by roughly the same percentage. A wider tire needs more side clearance to the frame, mudguard and body panels. A smaller or lower-profile tire reduces ground clearance and leaves less sidewall to absorb bumps.

Mobility scooter wheel sizes: calculated geometry vs real dimensions

Calculated mobility scooter wheel sizes are estimates based on nominal markings. The real width and diameter of a tire can differ from the calculation for several reasons:

• Assumed aspect ratio: inch width-rim codes do not state sidewall height, so the rim + 2 × width estimate can overstate or understate the real diameter.
• Rim width: the same tire mounted on a wider rim usually measures wider and slightly lower. On a narrower rim it measures narrower and slightly taller.
• Tread design and maker tolerances: two tires with the same marking can differ slightly between brands and tread patterns.
• Inflation and load: a pneumatic tire grows a little with pressure and flattens under the rider's weight, so its loaded height is less than its free diameter.
• Wear: a worn tread reduces overall diameter.
• Nominal labels: names like 10x3 or 12½ x 2¼ are rounded trade sizes. For example, 62-203 calculated with sidewall ≈ width gives about 327 mm, while the nominal 12½ in is about 318 mm.

Use calculations to compare sizes and judge whether a difference is small or large. Use a manufacturer's published dimensions, or a measurement of the actual tire, when exact size matters.

How to read the size on your mobility scooter tire

Reading a mobility scooter tire size takes a few minutes and works for any of the formats above.

1. Find the largest number group on the sidewall. Check both sides of the tire, because the size may be printed on only one side.
2. Identify the format from the separators. A hyphen followed by a small number (4, 5, 6, 8, 10) is the rim diameter in inches. An x after the first number means that number is the overall diameter. A two-part number like 62-203 is an ISO width and bead seat diameter in millimetres.
3. Write down the full code exactly, including both numbers in a dual size such as 4.10/3.50-4.
4. Note the nearby ratings: ply rating or load marking, maximum pressure, and TT/TL.
5. If the code does not give a rim diameter (such as 260x85), find the rim size from another marking on the tire or wheel, or from the scooter's documentation.
6. If the markings are worn away, measure the inflated tire. Measure overall diameter across the centre of the wheel from tread to tread, and width at the widest point of the sidewalls. Treat these as approximate, because load and inflation affect the numbers.
7. Compare the result with the chart above to see equivalent designations and calculated dimensions.

Replacement tire sizing: what a matching size does and does not guarantee

For replacement tire sizing, the rim diameter must match exactly. A tire marked for a 4-inch rim will not mount on a 5-inch rim, and an ISO 203 mm bead seat will not fit a different bead seat diameter. A matching full size code, or a recognised equivalent such as 3.00-4 and 260x85, means the replacement has the same nominal dimensions. That is the starting point for a correct match.

A matching size does not by itself confirm that a tire fits a particular scooter. Other factors also decide fitment:

• rim width and wheel design, such as split rims or one-piece wheels;
• hub, bearing and axle arrangement when a complete wheel is replaced;
• clearance to the frame, forks and body panels, especially when choosing a wider or larger tire;
• tube type or tubeless construction;
• load and pressure ratings that meet or exceed the original.

Changing to a different size, even one with the same rim diameter, changes the geometry described above: overall diameter, circumference, width and ride height. The scooter maker's specified tire size remains the reference for what the vehicle was designed to use.