Ag Tire Size Chart | Read Sizes Right

Farm tire markings show width, sidewall profile, construction, and rim size, so the right match starts with reading the full sidewall code.

An Ag Tire Size Chart gets useful the moment you stop reading only the big numbers and start reading the full code. Width, profile, construction, and rim diameter all live in that short string on the sidewall. Miss one piece and you can end up with a tire that rubs, throws off axle timing, or will not fit the rim you already own.

That is why the smartest way to use an Ag Tire Size Chart is to match three things at once: the code on the tire, the rim it fits, and the rolling size your tractor expects. A chart can point you to the right family fast. It cannot turn every same-looking size into a safe swap. That gap is where most mistakes start.

If you are replacing one worn tire, updating an older inch-marked size, or trying to decode a metric radial, this article will help you read the chart with less guesswork. You will see what each size format means, where old and newer sizes overlap, and what must match before you place an order.

Ag Tire Size Chart Basics For Real-World Fit

The first thing to know is simple: farm tire size codes are not random. They tell you the section width, the sidewall shape, the tire build, and the rim diameter. Once you know that pattern, a chart stops looking like a wall of numbers and starts acting like a sorting tool.

Take 480/80R42. The 480 is the width in millimeters. The 80 is the aspect ratio, which tells you the sidewall height as a share of width. The R means radial. The 42 is the rim diameter in inches. An older size like 16.9R38 uses inches for width, still shows radial build, and still ends with rim diameter.

What The Sidewall Code Actually Means

Most growers get tripped up in one of two places. They either compare width alone, or they treat an older inch size and a newer metric size as if they speak the same language. They do not. One code may tell you width in inches. Another may tell you width and profile in metric form. Both can fit the same sort of job, yet they are not read the same way.

Michelin’s tire-marking explainer lays out the usual order clearly: width, series, construction, and rim diameter, with tags such as IF and VF added ahead of the size when the casing has flex features. That matters because IF and VF are not decoration. They tell you the tire can carry load differently from a standard casing.

Why Old Farm Sizes And Metric Sizes Both Show Up

Older tractors and older replacement habits are the main reason. A machine may have left the yard years ago on 18.4R34 or 20.8R38. A newer catalog may list metric sizes that land in the same rolling family. On paper, those pairs do not look close. On a chart, they can sit right beside each other.

That is where rolling circumference and outside diameter earn their keep. Titan’s RCI chart groups ag tire sizes by rolling family, not by width alone. That helps when you are trying to keep front and rear tire timing in line or when you want a modern size that stays close to the tractor’s working height.

Size Marking	How To Read It	What It Usually Tells You
11.2-24	11.2-inch width, bias build, 24-inch rim	Older numeric farm size often seen on older tractors and implements
16.9R38	16.9-inch width, radial build, 38-inch rim	Older inch-based radial format still common in farm listings
480/80R42	480 mm width, 80-series sidewall, radial, 42-inch rim	Modern metric radial size used in many replacement searches
420/85R34	420 mm width, 85-series sidewall, radial, 34-inch rim	Tall metric radial often chosen where height matters as much as width
17.5L-24	17.5-inch section width, flotation-type section, bias, 24-inch rim	Common on loader, wagon, and implement positions
IF650/65R38	IF casing, 650 mm width, 65-series, radial, 38-inch rim	Flex casing that can carry the same load at lower inflation, or more load at the same inflation
VF380/90R46	VF casing, 380 mm width, 90-series, radial, 46-inch rim	Tall sprayer-style size with a flex casing
IF800/70R38 CFO	IF casing, 800 mm width, 70-series, radial, 38-inch rim, CFO tag	Harvest-oriented marking used on some cyclic high-load jobs

The table above is the fastest way to calm the confusion. Some codes start with inches. Some start with millimeters. Some carry extra letters before the size. Once you know where the width sits, where the build letter sits, and where the rim size ends, a chart becomes easier to trust.

How To Use The Chart Without Picking The Wrong Tire

Start with the rim. If the rim diameter does not match, you are done. A 42-inch tire does not belong on a 38-inch rim, no matter how close the width looks. Then check the approved rim width range for the tire family you are buying. Two tires can share a rim diameter and still want different rim widths.

Next, match the working height of the tire, not just the section width. This is where charts save you from bad guesses. A wider tire can be shorter. A narrower tire can be taller. If you run a mechanical front-wheel-drive tractor, that difference can change how the front and rear axles pull together.

Why Width Alone Gets People In Trouble

A lot of buyers shop by width because width jumps off the sidewall first. That is only one slice of fit. The series number matters too. A 480/70R30 and a 480/85R30 have the same width and the same rim diameter. They do not stand the same height, and they will not act the same on the tractor.

The same trap shows up when people swap an older inch size for a metric size without checking rolling family. The tire may bolt on and still be wrong for clearance, stance, or axle timing. That is why good charts sort tires by more than one dimension.

Front And Rear Pairs Need Extra Care

On MFWD and 4WD tractors, front and rear tires work as a pair. Change one end too much and you can push the lead ratio out of the window your tractor was built around. That can show up as tire scrub, driveline strain, or odd wear that feels hard to pin down at first.

If you are replacing all four, the chart helps you stay inside the right family. If you are replacing only one axle, go slower. Match the current rolling family, load rating, and approved rim fit before you chase a lower price or a wider footprint.

Common Same-RCI Size Families

The chart below shows why charts matter so much when old inch-marked sizes and newer metric sizes meet. These groupings come from the same rolling families shown in Titan’s row-crop RCI chart. Treat them as cross-check clues, not as automatic swap approval.

RCI Family	Common Sizes In That Family	What That Usually Means
46	20.8R38, 520/85R38, 480/80R42	Similar rolling size family; rim fit and load still need a separate check
44	16.9R38, 420/85R38, 18.4R34, 480/85R34	Older inch sizes and metric radials can land in the same height group
43	380/80R38, 420/85R34, 540/65R34	Different widths can still share a close rolling family
42	320/85R38, 380/85R34, 420/85R30, 480/70R30	Profile changes can keep overall working height near the same
41	290/95R34, 320/85R34, 380/85R30, 420/85R28	A strong reminder that size families are built around rolling fit, not width alone

These pairings clear up a lot of head-scratching. A 420/85R30 and a 480/70R30 do not look close at a glance. Yet they sit in the same rolling family. That tells you their working height is in the same neighborhood. It does not tell you they share the same rim, load table, or clearance needs.

Mistakes That Cost Time In The Field

Most bad ag tire orders come from the same few habits. None of them look dramatic when you place the order. All of them get loud once the tire shows up.

• Buying by width only. Width is easy to spot, so people lean on it too hard. Height, build, and rim fit matter just as much.
• Skipping the rim-width check. The tire may mount on a rim and still be a poor match for shape, bead seat, or tread wear.
• Treating same-family sizes as direct swaps. Same RCI helps with rolling match. It does not wipe out load, speed, or clearance checks.
• Mixing tire types on a driven pair. A radial and a bias tire can behave differently under load, even if the sidewall numbers seem close.
• Ignoring the job the tractor does. Loader work, road travel, row-crop work, and harvest loads can push the same size in different ways.

There is also the money side. A wrong-size order burns more than shipping. It can steal field time, throw off a planting or hay window, and turn a one-evening fix into a week of phone calls.

A Simple Fit Check Before You Order

If you want a clean way to shop, use this order and stick to it:

1. Read the full sidewall code from the tire already on the machine.
2. Write down rim diameter and approved rim width.
3. Match the rolling family if the tractor uses paired front and rear drive tires.
4. Check load and speed tables for the work the tractor actually does.
5. Measure clearance at fenders, steps, hubs, and row spacing if you are changing width or profile.

That short list keeps the chart in its proper lane. It is a strong sorting tool. It is not the whole answer by itself. Pair the chart with your current sidewall code and the maker’s fit data, and you are far less likely to buy a tire that looks right on paper and acts wrong on the machine.

A clear size chart saves time because it lets you rule out bad matches early. That is the real win. You stop chasing width alone, start reading the whole code, and get closer to a tire that fits your rim, your tractor, and the work waiting in the field.