When it comes to off-road rubber, bigger is better. Right? You want taller tires to climb over obstacles and wider ones for the most traction; everybody knows that. Except, like so many other common-sense rules, it’s far more complicated. We break it down to help you pick squat over skinny. Narrow versus wide.
Taller Is Better Off-Road
When it comes to taller versus shorter, it’s simple. Moving to a taller tire, say from a 31-inch tire to a 33, gives you about half of the difference in extra ground clearance. That 33-inch measurement is the diameter, so half is above the axle and half is below.
A taller tire also lets you hit a taller rock or log and still climb over it. There are other benefits and drawbacks, like how it alters your gear ratio, but we’re talking about width here, so we’ll get back to it.
Wider Means More Contact, Right?
If you use a wider tire, it will give you a bigger contact patch for traction on rocks and ice and float over sand and snow compared with a narrow one. Or will it?
The width of your tire actually has very little to do with how much tread touches the pavement, what’s called the contact patch. The contact patch between your tire and the ground is almost entirely based on two things: load and pressure.
The mathematical formula to determine the contact patch of a tire has three variables: load, pressure, and that answer. Raise the load on the tire through more weight on that corner, and the patch expands. It’s why drag racers want weight to shift to the rear at launch. A bigger contact patch means more grip.
Pressure works in the opposite direction. Lower the tire pressure, and the patch expands. It’s more intuitive than it sounds if you remember that load is pounds and pressure is pounds per square inch. Divide the weight on that tire by pressure, and you get square inches — area.
So really, it makes no difference how wide your tire is, since load and pressure decide how much contact it has with the ground. It’s an open-and-shut case, right? Of course not.
Then, Why Do Sports Cars Have Wide Tires?
If width truly had no influence on traction, then the high-power sports cars of the world wouldn’t have rear tire widths that start with a 3.
Changing your tire width and the diameter of your tire might not affect the size of your contact patch, but those changes greatly affect its shape. Contact patch shape plays an important part in how your vehicle performs. A wider tire delivers a wider contact patch side to side. More of the face of the tread is touching the ground at any point. A narrower tire has a longer contact patch.
Are the Engineers Really Right?
Every mechanic knows that the engineering is perfect right up until the moment a part goes into service, and that’s no different here. There are other variables that change the actual patch between any two tires, including the width of the wheel, the sidewall profile — more sidewall equals more squish — and the tread block pattern itself.
The differences between individual makes and models of tires are smaller and almost impossible to account for, but despite that, the basic math tells most of the story.
When Wider Is Better
Wider tires are better for acceleration. More front edge is exposed to grip the surface, helping it gain traction to move forward. This applies to pavement and gravel, and it should apply to larger rocks.
It’s not all gain, though. Wider tires have higher aero resistance because of the width, and that can add up. They’re usually heavier, too, which cuts into acceleration, hurts braking, and uses more fuel. Use wider tires when you have big power and don’t care about weight or fuel consumption, and most of your off-roading is on rocks, gravel, or similar surfaces. Think RAM TRX, here, for example.
What about paddle tires in sand, mud, or deep snow? Those are wide, right? The reason you see ultra-wide tires on sand rails and mud drag races isn’t because of more ground pressure; it’s because they don’t act like traditional tires.
They’re called paddle tires because they’re closer to paddle wheels (think riverboat casino). Massive full-width rubber paddles push through the sand and mud like pulling your arms through water. Tread friction isn’t a factor.
How about those cool Arctic trucks with the giant balloon tires? They’re designed for incredible amounts of flex at near-zero pressures. The huge size is about flattening out the tread and reducing the amount of pressure your vehicle exerts on the surface, allowing you to float over snow. Of course, the downside to this design is all the squirming and movement that the tires allow, making these useless on pavement or rocks, for example.
When Narrow Is Better
Narrow tires aren’t as good at forward acceleration, but they are better in other conditions. In the snow, the narrower leading tread pushes snow out of the way for the rest of the contact patch to, well, make contact. The same goes for when there’s water on the road, where a longer, narrower patch improves resistance to hydroplaning.
Wider tires don’t deliver any more surface area, so how could they float on top of a loose surface? They can’t. If you want more proof, look at desert racers like you’ll find in the SCORE Baja events.
Last year’s Baja 1000 winner used a Ford trophy truck with 13.5-inch-wide Toyo Open Country M/T-R tires. 13.5 inches is only about half an inch wider than the road-going F-150 Raptor’s, despite having more than double the horsepower.
You’ll see similar tire choices across the off-road spectrum, where the winners don’t always use the biggest or widest tires they can find. Plenty of recent Dakar winners have used a tire just 245mm (10 inches) wide, and they race through deep sand dunes.
On snow and ice, the fastest cars are in the World Rally Championship (WRC). Those 500-horsepower cars run 205/65R15 tires. That’s a compact car size from 20 years ago, not a big modern tire. Yet they can go incredibly quickly on snow and ice, studded or not. Part of that comes down to the tire compound, but a lot of it is physics based on tire size.
What Really Drives Your Decision
Here’s the thing, though, and it’s probably what really matters to most people when shopping for tires for their rig: aesthetics. For many people, wider tires look better than skinny ones. A rig that looks like it skipped leg day might look silly to you, but if you’re building a traditional overlander in the South African or Australian style, narrow tires might be the look you’re after.
Plus, those narrow tires will generally offer better tire life with increased fuel economy, something that’s more important when you’re trying to cross a continent on dirt, rather than blasting down a desert trail with buddies.
Just make sure you get the right tread design and compound for how you drive. Don’t waste your money on chunky mud terrain tires if all you do is pavement driving, and don’t expect a cheap all-terrain tire to do a dedicated winter tire’s job. We get the appeal of one do-it-all tire, especially given how much tires cost these days, but a jack-of-all-trades is a master of none.
