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The Mechanics of Leaf-Drop Dictate How You Maneuver Behind The Wheel

Posted: November 11, 2022 - 3:09PM
Author: Marc Stern
The other day Torque News ran a piece about fall leaf drop and how it affected drivers. Today we decided to expand on the idea and explain the mechanics of leaf-drop and its effect on driving. Believe it or not, the mechanics of leaf drop on road surfaces can be very interesting.


A couple of days ago, Torque News ran a piece about fall driving. The premise was that as the seasons change, you have to expect changes in the driving environment. The story mentioned snowstorms that have already blanketed much of the country's Northwest and Central states areas with not inches but feet of the white stuff. You can read the first story here

Late Fall Has Many Driver Hazard

At the same time, Torque News discussed problems drivers in areas of the country face that aren't staring at many inches or feet of snow. Primarily, these areas are plagued with another late fall, early winter problem, leaves.

Indeed, leaf-drop is a dangerous time of year for drivers in the Northeast, Southeast, South Central, and Southwestern states. The reason is simple, leaves.

Yes, it does sound weird when you put it out there. After all, how can leaves be a problem? It's easy when you think about it. Indeed, the Torque News story discussed wet leaves, but it was an overview of the dangers wet leaves present, and we thought you might like to know a bit more about what happens when leaves fall from the trees.

So, without further ado, let's look at leaf-drop mechanics as they apply to vehicles.

In most of the country, leaf-peeping season (when motorists drive the backroads of an area staring at the gorgeous montage presented by nature – at least for part of the fall season) is between early October, as the color wave swells and the end of the month. By early November, the leaf-looking season is gone, usually the victim of autumn storms where wind and rain conspire to rip the colorful leaves from the trees they have adorned for half a year.

Geography Has A Lot To Do With Leaf-Drop Problems

This is when leaves become dangerous to drivers. Let's look at a stretch of road somewhere in leaf-peeping country to see why.

At first, leaf-drop is a nuisance as the leaves fall from the trees and are blown around by mid-autumn winds. The leaves, you see, are dry at this point. Indeed, you probably have noticed them when you walk near your homes. The leaves are just things blowing in the wind. However, things change when the first rains – or snows – hit the leaves.

It's at this point that the mechanics of leaf-drop change. As Torque News noted in its first story about fall driving hazards, seasonal rains (which usually start to increase late in October and continue through December) make the leaves sodden masses of leaf junk on the ground. The once-pretty leaves are now just seasonal detritus. (At one time, the fallen leaves enriched the soil of forests as there were few paved surfaces. As areas developed, they became paved, and the chances for leaves to fall o the ground, where they would eventually disintegrate into the soil, dropped to about zero. Soggy leaf junk lining local roads can be lethal to drivers.)

This is the way it works – and why it is dangerous. At first, the leaf junk is very haphazard. Roads are not fully covered by dropping leaves, leaving many road surfaces for vehicle tires to bite into so vehicles can stop.

How Many Trees Are Out There?

As the fall of leaves continues, many trees drop their leaves, with some estimates equating the number of trees with those areas before the Civil War when farms dotted the local landscapes.

The combination of an added number of trees and less forest floor – yes, it is a paradox, but it is true – quickly spells a deadly combination as the leaves fall on the road surface, the stack up on the layers below them. By the time the fall season advances as far as the snow, most roads are leaf-covered to quite a depth.

The residue is quite soggy unless the municipality sends its equipment to scoop up or blow the leaves to the side. What happens next is not unique, but this is where the rubber doesn't touch the road. Leaf detritus of even less than an inch – in leaf terms, it may be seven or eight generations of leaf-drop piling up and making a real mess.

With seven or eight layers – more or less – wet leaves on the road, there is minimal road surface left for the tires to bit into. Even brand-new tires with great tread will "float" on the top layer of leaves and bite into the leaf detritus to a limited degree.

Things Become Dicey As Leaves Act Differently

At this point, things become really dicey as the leaves act like "snow" or "ice" in that the top leaves slide over the bottom layers that have been on the road surface for some time. Many experienced drivers know that this occurs over time in the fall, and they adjust for it. However, drivers who are inexperienced or who have never experienced leaf-drop can be fooled by a "normal-looking" road with a few leaves on it.

As the leaves slide and vehicle wheels are kept from touching the road surface, vehicles can quickly go into skids, which can often lead to harmful consequences for drivers as there is nothing for the tires to bite into, and wheels can lock up quickly. Even with today's modern "smart" anti-lock systems that "watch" things with cameras can be fooled as the car loses its traction.

As noted, the soggy leaves slide over the layers below, and problems can occur, often causing drivers to panic as they "stand" on the brakes. With no road surface to bit into wheels, it just keeps flailing, leaving drivers with issues.

If drivers run into this problem, the best thing to do is get off the gas and stay off the brakes. Yes, it is tempting to jump on the brakes because the road ahead looks okay when it isn't. As we have noted, there are likely several layers of leaf detritus on the road that can hinder safe stopping. As with ice or snow skidding – or even wet-weather problems on open roads – the best way to control things is to get off the accelerator and stay away from the brake pedal until the vehicle slows way down and you are assured of control again.

How Do You Control A Skid?

It would help if you remembered to steer toward the skid. It doesn't matter if you are driving a Ford Bronco or F-150 4X4 or an all-wheel-drive model like the Maverick (many of these new compact pickups are all-wheel-drive models with CVS transmission systems that rely on accelerator pressure to move ahead or slow down). CV transmissions – continuously variable – can help you with the leaf-drop problems even though you may not realize it, as you can see.

That pretty much wraps up the mechanics of leaf-drop and leaf-drop driving. In this situation, the key is to remain as calm as possible. And, then, getting off the accelerator as you let the vehicles slow down. Once it has slowed sufficiently, you can lightly apply the brakes to slow the vehicle further. Also, remember if the vehicle does skid, steer in the direction of the skid as the vehicle slows. It would help if you quickly regained control.

Once you have control, keep your vehicle's speed down until you get back to clear roads where you can get back to highway speeds.

Also, remember that even if the leaves look dry, they are only dry on top. The layers below are still soggy and can cause you all kinds of headaches.

Ford Motor Photo

Marc Stern has been an automotive writer since 1971 when an otherwise normal news editor said, "You're our new car editor," and dumped about 27 pounds of auto stuff on my desk. I was in heaven as I have been a gearhead from my early days. As a teen, I spent the usual number of misspent hours hanging out at gas stations Shell and Texaco (a big thing in my youth) and working on cars. From there on, it was a straight line to my first column for the paper, "You Auto Know," an enterprise I handled faithfully for 32 years. Not many people know that I also handled computer documentation for a good part of my living while writing YAN. My best writing, though, was always in cars. My work has appeared in Popular Mechanics, Mechanix Illustrated, AutoWeek, SuperStock, Trailer Life, Old Cars Weekly, Special Interest Autos, etc. You can follow me on: Twitter or Facebook.