Wide versus narrow wheels

Do wider tires get better traction? I keep getting in a debate with people and my position is that they don’t. A wider tire has more surface area in contact with the ground but an objects weight is distributed over a wider area.

Am I correct in this assertion?

You’re right but wrong.

If the road was perfectly smooth you would be right. A wider tire has a larger contact patch, but less weight per square inch.

However, the road is not smooth. It has all kinds of little dips and ridges. The tire will deform around these imperfections and this increases traction. Since the wider tire has a larger contact patch it will have better grip than a narrow tire.

A soft tire will further increase the effect.

Also, the larger the diameter, the larger the contact patch which is why dragster tires have such a large diameter as well as width.

Over slick surfaces (water/snow/slush) wider tires ARE at a disadvantage and have less grip vs a similar narrow tire (or one that has more weight per sq inch).

Wider tires used to suffer greatly from hydroplaning and can lose all ability to handle snow and be scary in rain. Traction control and major advances in tread design and rubber compounds have helped make even wider tires available.

Wider tires have a contact patch that works better when the tire corners hard, leaving more tire in contact with the road versus a taller or narrower tire that has the same standing contact patch area before cornering.

Wider tires also tend to ‘borrow’ rubber from the sidewall, and are generally more ‘squat’ resulting in stiffer sidewall that further helps a wider tire maintain a good contact patch when cornering, especially aggressively.

(It is sometimes recommended that one use a narrower tire when switching to snow tires for the winter driving season, for more bite in the snow via the concentrated weight per inch)

Wider tires work better in mud and sand. The lower contact pressure reduces the amount the vehicle sinks into the soft surface.

To some extent this works on snow, so it is a balancing act between this and the point above. Unlike mud and sand, snow packs when the vehicle sinks, becoming a firmer surface.

Not coincidently, the contact pressure is the same as the inflation pressure of the tire. You can temporarily obtain much of the benefit of wide tires by reducing the tire pressure. It is not uncommon for off-road enthusiasts to exploit this fact, “airing down” when the pavement ends. Note that this can make flat tires much more likely when carried to extremes, and bead locks will be required at very low inflation pressures.

The downside of wider tires:
Hydroplaning: A tire can hydroplane when the hydrodynamic pressure equals the inflation pressure. Wide, low pressure tires will hydroplane at much lower speeds than narrow high pressure tires, and under inflated tires are more likely to hydroplane. Ask the hot rodder with the wide slicks on the rear how that car handles in the wet!

Finally: When wide tires are retrofitted to a vehicle, increased offset wheels are often used. This moves the contact patch outward from the designer’s intent. This can lead to evil handling due to changes in steering geometry, as the steering axis is normally designed to intersect the road near the center of the tire contact patch. In addition, moving the contact patch outward increases the stress on wheel bearings, ball joints and rear axles, and may substantially shorten the life and/or increase the likelihood of failure of these components.

As Kevbo said, wider tires are better if you are on a soft surface and don’t want to sink in, such as sand or deep mud. However, if you’re driving through mud or snow that’s not terribly deep and you want to have contact with the ground for better traction, skinny tires are the way to go.

Anecdotally I offer my cycling experience. On snow or ice it is easier to lose control with my road bike, with its skinny tires, than with my “hybrid” bike with its fatter wheels. Yes the hybrid is a pound or two heavier, but on the scale of my weight I cannot imagine it is too significant to the issue. Of course the tires are also smoother on the road bike.

I found this which explains some about tire traction:

(Bolding mine.)

I also think that the issue gets confounded by the subject of rolling resistance.

My 1500 pound car was terrifying on wet roads until I got tires made of softer rubber.

Now it is only scary. It just doesn’t have enough weight. I should put tricycle wheels on it.