ATV Tire Chain Size Chart: Reading Tire Sizes for Chain Fitment

ATV tire chains are sized by the tire size printed on the sidewall, mainly the overall tire diameter, the tire width and the rim diameter. On a size such as 25x8-12, the first number is the approximate overall diameter in inches, the second is the approximate width in inches, and the last is the rim diameter in inches. A chain must be long enough to wrap the tire's circumference and wide enough to span its tread. Find your tire size, convert it to diameter and width if it is written in metric, then compare it with the tire sizes the chain manufacturer lists for each chain. The chart below shows the calculated geometry of common ATV and UTV tire sizes, so you can see how sizes relate to each other before you check chain fitment and clearance on your vehicle.

How do you read the numbers on an ATV tire sidewall?

ATV and UTV tire sizes appear in two main formats: the inch-based flotation format, such as 25x8-12, and the metric format, such as 205/80R12. Both describe the same three things, which are overall size, width and rim diameter. They describe them in different units and in a different order.

Inch (flotation) format: 25x8-12

In the flotation format, every number is in inches:

• 25 is the nominal overall tire diameter, the height of the tire standing upright, in inches.
• 8 is the nominal tire width, measured across the widest part of the tire, in inches.
• 12 is the rim diameter, the wheel size the tire mounts on, in inches.

A dash before the rim size, as in 25x8-12, usually means bias-ply construction. An R, as in 25x8R12, means radial construction. Some tires add a prefix such as AT, as in AT25x8-12, to show the tire is intended for all-terrain vehicles. For chain sizing, the first two numbers matter most, because they give the diameter and width directly.

Metric format: 205/80R12

In the metric format, the numbers mix millimetres, a percentage and inches:

• 205 is the section width in millimetres.
• 80 is the aspect ratio. This means the sidewall height equals 80% of the width.
• R means radial construction.
• 12 is the rim diameter in inches.

A metric size does not state the overall diameter. You have to calculate it, as shown below, before you can compare it with a chain listing written in inches.

Markings that describe performance, not size

Other sidewall markings describe strength and speed capability, not dimensions. They do not change which chain size fits:

• Ply rating (for example, 6-ply rated or 6PR) describes carcass strength relative to a traditional ply standard. It is not necessarily the actual number of layers.
• Load index is a number that corresponds to the maximum load per tire on a standard table.
• Speed symbol is a letter that corresponds to a maximum rated speed. For example, F means 80 km/h (50 mph) and J means 100 km/h (62 mph).
• Maximum inflation pressure is the highest pressure the tire may hold. It is not the recommended operating pressure, which comes from the vehicle maker.

These ratings matter when you choose tires. When you choose chains, use the dimensional numbers.

ATV tire chain size chart: calculated dimensions of common tire sizes

The chart below lists common ATV and UTV tire sizes with their calculated sidewall height, implied aspect ratio and circumference. All values come from the nominal sidewall numbers. They are not measurements of any specific tire. Use the chart to group tire sizes by diameter and width, then confirm the exact chain against the manufacturer's fitment list.

Tire size	Nominal diameter (in)	Nominal width (in)	Rim (in)	Sidewall height (in)	Implied aspect ratio	Calculated circumference (in)
22x7-10	22	7	10	6.0	86%	69.1
22x11-9	22	11	9	6.5	59%	69.1
24x8-12	24	8	12	6.0	75%	75.4
25x8-12	25	8	12	6.5	81%	78.5
25x10-12	25	10	12	6.5	65%	78.5
26x9-12	26	9	12	7.0	78%	81.7
26x11-12	26	11	12	7.0	64%	81.7
27x9-14	27	9	14	6.5	72%	84.8
27x11-14	27	11	14	6.5	59%	84.8
28x10-14	28	10	14	7.0	70%	88.0
30x10-14	30	10	14	8.0	80%	94.2
32x10-15	32	10	15	8.5	85%	100.5

Two patterns stand out. First, tires with the same diameter, such as 25x8-12 and 25x10-12, share the same calculated circumference, so chain length is similar, but they need different chain widths. Second, tires with the same width but different diameters, such as 28x10-14 and 30x10-14, need chains of different lengths, even though the cross-chain span is similar.

How do you calculate tire diameter, sidewall height and circumference?

Tire geometry can be calculated from the sidewall numbers with simple arithmetic. The formula depends on the size format.

For inch sizes (example: 25x8-12)

1. Sidewall height = (overall diameter − rim diameter) ÷ 2 = (25 − 12) ÷ 2 = 6.5 in.
2. Implied aspect ratio = sidewall height ÷ width = 6.5 ÷ 8 ≈ 81%.
3. Circumference = π × overall diameter = 3.1416 × 25 ≈ 78.5 in.

For metric sizes (example: 205/80R12)

1. Width in inches = 205 mm ÷ 25.4 ≈ 8.07 in.
2. Sidewall height = 205 mm × 0.80 = 164 mm ≈ 6.46 in.
3. Overall diameter = rim diameter + 2 × sidewall height = 12 + 2 × 6.46 ≈ 24.9 in.
4. Circumference = π × 24.9 ≈ 78.3 in.

The calculated result shows that a 205/80R12 is geometrically very close to a 25x8-12. On paper, it falls in the same chain size group. The same method works for any metric size. For example, a 255/80R12 works out to roughly 10.0 in wide and 28.1 in in diameter.

How do width, aspect ratio and rim diameter affect chain fitment?

Each part of the tire size controls a different dimension that a tire chain depends on.

• Overall diameter controls chain length. Each 1 in of extra diameter adds about 3.14 in of circumference (π × 1 in). Going from 25x8-12 to 26x9-12 adds about 3.1 in of circumference. That can exceed the adjustment range of a chain sized for the smaller tire.
• Tire width controls cross-chain span. A chain made for an 8 in wide tire may not span a 10 in or 11 in tire correctly. A chain made for a wide tire can sit loose or shift on a narrow one.
• Aspect ratio controls sidewall height. On metric sizes, a higher aspect ratio at the same width and rim gives a taller sidewall and a larger overall diameter. For example, a 205/80R12 has a 164 mm sidewall, while a hypothetical 205/70R12 would have about 143.5 mm. That is roughly 1.6 in less overall diameter.
• Rim diameter affects diameter only together with sidewall height. A 27x9-12 and a 27x9-14 have the same nominal outer diameter, but the 12 in rim version has a 7.5 in sidewall instead of 6.5 in. The outer chain dimensions are similar, but sidewall shape and where the side chains sit can differ.

Practical comparison: one size step up

Change	25x8-12	26x9-12	Difference
Overall diameter	25 in	26 in	+1 in
Width	8 in	9 in	+1 in
Sidewall height	6.5 in	7.0 in	+0.5 in
Circumference	78.5 in	81.7 in	+3.1 in

This small step in tire size changes both the chain length and the chain width needed. For this reason, a chain listed for one tire size should not be assumed to fit the next size up.

Why can calculated tire size differ from the actual tire?

Calculated geometry describes the nominal size, not the tire on your vehicle. The actual mounted dimensions often differ from the nominal numbers. Several factors cause this:

• Manufacturer variation: two tires marked 25x8-12 from different brands or tread designs can measure differently in diameter and width.
• Low inflation pressure: ATV tires run at low pressures, so pressure noticeably affects shape, width and diameter.
• Rim width: a wider or narrower rim changes how far the tire spreads, which changes the measured width.
• Tread design and wear: tall mud lugs add to the outer diameter, and worn tread reduces it. Lug shape also affects how a chain sits.

For chain fitment, the useful numbers are the tire diameter and tire width measured on the vehicle at normal operating pressure. Use the sidewall size to find the right chain group, then check the measured size if your tire sits near the edge of a chain's listed range.

How do you choose the right chain size for an ATV or UTV tire?

Choose an ATV or UTV tire chain by matching your exact tire size to the chain manufacturer's fitment list, then confirming clearance on the vehicle.

1. Read the size on each tire. Front and rear tires on many ATVs and UTVs are different sizes, for example 25x8-12 front and 25x10-12 rear, and may need different chains.
2. Identify the format. Decide whether the size is in inches (25x8-12) or metric (205/80R12).
3. Convert to diameter and width in inches if the size is metric, using the formulas above.
4. Measure the mounted tire at normal operating pressure. Measure the height from ground to top of tread and the width across the widest point.
5. Compare with the chain manufacturer's list. Chain makers specify which tire sizes each chain fits, and their ranges differ, so a generic size chart cannot replace the maker's own fitment data.
6. Check clearance before driving, as described below.
7. Install and tension the chain following the chain maker's instructions, then recheck tension after a short distance.

How much clearance do ATV tire chains need?

ATV and UTV tire chains need enough clearance around the tire so that the chain does not touch the vehicle anywhere in the wheel's movement. Chains add thickness to the tread and sidewall area. They also add some movement, because a chain can lift slightly away from the tire at speed.

Check clearance between the tire and these parts:

• Fenders, mud flaps and body panels above the tire
• Suspension arms, shocks and springs on the inner side
• CV boots, axles and brake components
• Steering parts, checked at full lock in both directions

Check each of these with the suspension compressed as well as at rest. The required gap is not universal. Follow the chain maker's and vehicle maker's guidance. Larger or wider aftermarket tires leave less room for chains, so a tire upgrade can make chains unusable even when the chain itself is sized correctly.

What are the limits of a tire chain size chart?

A tire chain size chart is a comparison tool, not a fitment guarantee. It shows how tire sizes relate by nominal diameter, width and circumference. It does not account for brand-specific measurements, tread pattern, rim width, inflation pressure or the space available on a particular vehicle. Two tires with nearly identical calculated geometry, such as 25x8-12 and 205/80R12, usually fall in the same chain group. Even so, the final check is always the chain maker's listed tire sizes and a test fit on the vehicle with clearance confirmed.