Unraveling Automotive Mysteries
The facts behind five things that make weary road warriors go hmmmm.
My kids expect me to have all the answers. But when my 10-year-old daughter asked me the other day how the gas pump nozzle shut itself off while I was over there washing the windshield, I was stumped.
And I can't stand being stumped — it's a guy thing.
So I set out to find the answer to that question, and to some other little mysteries of our driving culture that have had me scratching my head for years.
Here's what I found, so now you, too, can impress that inquisitive and somewhat precocious 10-year-old in your life.
How does the gas pump nozzle turn itself off?
The basic concept of the automatic shut-off system has been around for 50 years, says Brad Baker of Husky Corp., a leading manufacturer of fuel delivery equipment. The next time you fill up, turn the gas nozzle over and look for a small hole at the tip of the spout. Now look inside the spout and notice there's a tube inside leading from that hole. This tube connects the "sensing hole" at the nozzle tip to a diaphragm near a shut-off valve within the nozzle.
When you squeeze the nozzle handle, gasoline pours through the spout and creates a vacuum in the small tube. This vacuum holds the diaphragm in a neutral position. When the fuel tank is nearly full, gasoline in the fill pipe rises and covers the nozzle-sensing hole. Air can no longer rush into the sensing hole to bleed off the vacuum, and the higher atmospheric pressure pushes the diaphragm up from the neutral position. This flips a switch in the automatic shut-off device and, ker-thunk, the pump cuts off.
What are those huge tire chunks you often see on major highways?
Truckers call them "gators." They are usually, but not always, from large 18-wheelers. These are tread sections that have separated from the carcass of the tire, and they are frequently associated with the retreaded tires used on many semi-trailers. However, says Kyle Jensen of Bridgestone Bandag Tire Solutions (the nation's biggest manufacturer of retreaded tires), the tire debris we see along the road is not always from retreaded tires.
"Just as with auto tires, truck tires usually fail due to underinflation, which causes them to overheat and then literally fall apart," Jensen says. "About 40 percent of the truck tires are retreads, and studies show that they fail at the same rate as original-tread tires." He adds that if you can see wires or cords in the gator, the tire was not a delaminating retread, but a standard tire that had come apart.
Because a lot of trucks are on the road, and each of them covers many miles under a heavy load, tires that fail are predominantly truck tires. Each truck has up to 18 tires, or 4.5 more opportunities for tire failure than a car or light truck. Jensen says the tires that fail are usually on the trailer because an owner-operator often does not own the trailer and thus is less vigilant about maintaining it. When a semi blows a tire, it usually has enough good rubber on the road to come to a safe stop or limp to a service area for a repair.
If a large tire section is in your vehicle's path, the best course of action is to drive around it without making any erratic maneuvers. If you're suddenly confronted with a tire chunk, it's probably better to drive over it rather than make a rash maneuver and risk an accident. It's unlikely to damage your car. However, tire treads can be a serious hazard for motorcyclists.
What is the purpose of those deep grooves cut into the pavement, except to annoy?
Grooves cut in concrete pavement work like tire treads — they channel water away from the contact patch under each wheel and minimize hydroplaning, says Kevin McMullen, president of the Wisconsin Concrete Paving Association. Hydroplaning occurs when a layer of water is trapped between the tire and road surface, causing the tire to lose traction, which may lead to a loss of braking and steering control.
Those grooves, which are 1/8-inch wide, 1/8-inch deep and 3/4-inch apart, provide an escape route for water captured under the tires. When a new section of road is paved, a "macro-texture" is created in the still-soft concrete with a special steel-wire broom that has the same effect as cut grooves. McMullen says grooves are usually cut into a road surface that is 25 to 30 years old as part of general repairs and upgrading. By then, the surface is often worn smooth and traction is reduced.