Off-Road vs Highway Tread Depth: What to Expect

Tread depth basics: How it's measured and what the law says

Tire tread depth is the vertical distance between the top of the tread and the bottom of the main grooves. It is expressed in fractions of an inch, typically in 32nds. The U.S. federal motor vehicle safety standards require every new tire to include treadwear indicators that visually show when the tread has worn down to 1/16 inch (per 49 CFR 571.129). That depth is the legal minimum for safe highway use in most states, although many experts recommend replacing tires before that point. The tread depth directly affects traction, hydroplaning resistance, and how the tire performs in mud, snow, and wet conditions.

Separately, the regulations draw a line for light truck tires. Under 49 CFR 571.139, a light truck tire with a tread depth of 18/32 inch or greater is not covered by the standard for ordinary light vehicle tires; instead, it falls under 49 CFR 571.119, which has additional endurance, strength, and high-speed performance tests. This 18/32-inch threshold is a useful reference when comparing off-road and highway tires, because deep-tread off-road tires often approach or exceed it. These tests ensure that tires with such deep tread can handle the stresses of highway speeds without failing, as the tall tread blocks may be more prone to flexing and heat buildup.

Understanding these standards helps you interpret the numbers you see on a tire spec sheet. For most passenger cars, the tread depth at purchase is typically around 10/32 to 12/32 for highway tires, but we are not quoting those numbers here because they are not from our sources. Instead, focus on the relative depth categories: highway tires have the shallowest tread, all-terrain tires are deeper, and mud-terrain tires are deepest. The 18/32-inch line is a legal and engineering threshold that you may come across when reading about light truck tires.

Highway tires: Shallow tread for quiet and efficiency

Highway tires, sometimes called street or all-season tires, are designed for paved roads. Their tread blocks are small and tightly spaced, which keeps noise and rolling resistance low. The tread depth is usually modest, staying well below the 18/32-inch LT threshold for most models. Because the tread is shallower, the tire runs cooler and more efficiently on the highway. This translates to better fuel economy and a quieter ride, which are priorities for daily commuters and long-distance drivers. However, the shallow tread means less bite on loose surfaces like gravel or mud, so if you venture off-road, you will quickly feel the limits.

For drivers who spend at least 95% of their time on pavement, a highway tire is the right choice. They wear evenly, provide good dry and wet traction, and are often lighter, which reduces unsprung weight. If you own a car or SUV and rarely leave the road, consult the best car and SUV tires guide to see current options. Highway tires are also available in light truck sizes, but those models may have slightly deeper tread to handle heavier loads, though they typically remain below the 18/32-inch line unless they are an off-road variant.

All-terrain tires: A balance for mixed use

All-terrain tires fill the gap between highway and mud-terrain designs. They typically have larger tread blocks and deeper grooves than highway tires, giving them improved grip on gravel, dirt, and light mud. However, they are not as aggressive as mud-terrain tires. Many all-terrain LT models stay under the 18/32-inch threshold, but some feature deeper treads that approach it. The trade-off is a modest increase in road noise and rolling resistance. For drivers who split time between pavement and unpaved trails, an all-terrain tire is often the best compromise.

The deeper tread on all-terrain tires helps in snow as well, as the larger voids allow snow to be packed into the tread, which can actually improve traction on packed snow. They also offer more resistance to punctures because the rubber is often thicker and the tread is more robust. However, on wet highways, the larger tread blocks can sometimes lead to less water evacuation than a dedicated highway tire, so you should always check the tire's traction rating. See the best all-terrain tires guide for a range of options from mild to aggressive. If you tow or carry heavy loads, you may want a light truck version, which can have a higher load range and possibly deeper tread.

Mud-terrain tires: Deep tread for extreme traction

Mud-terrain tires are the extreme end of the spectrum. Their tread blocks are tall, widely spaced, and designed to self-clean in mud and soft soil. Many of these tires have tread depths that reach or exceed the 18/32-inch threshold set by federal standards. As a result, they are subject to the stricter requirements of FMVSS 119, which includes additional endurance and strength testing. The deep tread provides great off-road grip, but it also generates more noise and wears faster on pavement. For occasional off-road use, the extra depth is a liability on the highway, as the tall blocks squirm and generate heat.

If you regularly drive through deep mud, rock trails, or soft sand, the aggressive tread is essential. The ability to eject mud and maintain traction is far more important than on-road comfort. However, you should be prepared for a rougher ride and shorter tread life. Some mud-terrain tires use harder compounds to extend wear, but that can reduce off-road grip. When you do drive on pavement, keep your speeds moderate and check tire pressure regularly, as under-inflation can cause rapid overheating. Explore the best mud terrain tires guide for models that strike a balance. For those who also rock crawl, there are even more specialized options covered in our mud-terrain vs rock-crawling tires article.

Choosing the right depth for your driving

When you compare tires, focus on where you spend most of your driving time. If you rarely leave the pavement, a highway or touring tire with a shallower tread will give you lower noise, better fuel economy, and longer wear. If you need to tackle gravel or light trails, an all-terrain tire offers more tread depth without going overboard. Only choose a mud-terrain tire when you genuinely need the extra traction in deep mud or soft soil.

The depth also affects how the tire performs in wet and winter conditions. Deeper treads generally channel water better, reducing hydroplaning risk, but they also tend to have more flex, which can hurt cornering stability. In snow, a moderate depth with good siping is often more effective than extreme depth. For more on tread depth in specific situations, see our guides on tire tread depth new and tire tread depth for winter driving. Also, remember that federal law requires treadwear indicators to appear at 1/16 inch, and replacing a tire before it reaches that point is always safer. If you are unsure about the condition of your current tires, learn how to measure tread depth.

What to pick for your use

Questions

What does the 18/32-inch tread depth threshold mean?

Under U.S. federal standards, a light truck tire with a tread depth of 18/32 inch or greater is exempt from the standard light vehicle tire requirements and must meet the more stringent testing in FMVSS 119. This threshold is often seen in deep-tread off-road and mud-terrain tires.

At what tread depth should I replace my tires?

Federal regulations require treadwear indicators that show when the tread is down to 1/16 inch. For safe driving, most experts recommend replacing tires before that point, especially for highway use. Many drivers replace at 2/32 inch for wet traction, but you can use a tread depth gauge to check.

Do all-terrain tires have deeper tread than highway tires?

Generally yes, all-terrain tires have larger tread blocks and often deeper grooves than highway tires, but they typically stay below the 18/32-inch LT threshold unless they are very aggressive. The exact depth varies by brand and model, so always check the spec sheet.

Why do mud-terrain tires wear faster on the highway?

The deep, flexible tread blocks generate more heat and movement on pavement, leading to faster wear and increased road noise. The trade-off is necessary for serious off-road traction, so many owners rotate them more frequently and avoid long highway trips when possible.

How can I measure my tire's tread depth at home?

Use a tread depth gauge, a penny, or a quarter. Insert the gauge into the main grooves and read the measurement. For the penny test, insert the penny into the tread with Lincoln's head upside down; if you can see the top of his head, the tread is below 2/32 inch. Alternatively, you can use the wear indicators built into the tire, which are visible when the tread is at 1/16 inch.