Top 10 Automotive Mechanical Myths and Misconceptions
Let the Truth Shine in
The automotive world is filled with myths and misconceptions. Many are encouraged by carefully worded advertisements. Others originate from Olympic-level leaps of imagination and assumption. And some, particularly those concerning how a car actually works, are created when complex subjects are oversimplified. Here, we'll debunk 10 of the most common mechanical myths.
- Myth: All-wheel drive will help you dodge objects in the road and go faster around corners.
Truth: AWD is great at helping a vehicle accelerate, but even the most advanced systems do little to help a driver avoid road hazards or grip the pavement in corners. How a vehicle responds in emergency or racetrack-type maneuvers is determined mainly by the tires, suspension, vehicle weight and weight location. The bottom line: AWD can help a vehicle climb a snowy hill or accelerate out of a turn, but it can't help it corner or make a turn any quicker.
- Myth: A longer wheelbase — the distance between the centers of the front and rear axles — always makes a vehicle more stable.
Truth: Wheelbase is but one of a long list of factors that determines a vehicle's stability and responsiveness, and it's not even near the top of that list. Formula 1 racecars — the most nimble, ground-based vehicles on the planet — have wheelbases longer than a Lincoln Town Car, a vehicle that is among the least nimble. More important than wheelbase are suspension design and where the vehicle's weight is located. The most nimble vehicles have their weight low to the ground and centered.
- Myth: You must be able to see the flanks of your own car in your outside mirrors in order to have a reference.
Truth: Your outside mirrors are improperly adjusted if you can see the sides of the car. Correctly adjusted, the three mirrors form a panoramic view much like one created with three slightly overlapping photos: The images on the inside edges of the outside mirrors slightly overlap the images on the outboard edges of the inside mirror. Properly adjusted mirrors reduce blind spots and reduce the need to look over your shoulder, which is a lot like closing your eyes while driving.
- Myth: The "ideal" weight distribution is 50/50: The vehicle has the same weight on both the front and rear axles.
Truth: While most sport-oriented cars do have weight distributions close to 50/50, there's much more to proper handling than just distribution. A car with 50/50 weight distribution would handle poorly if most of the weight was at the ends of the car (i.e., ahead of the front axle and behind the rear axle).
Far more important than weight distribution is the location of the center of gravity and polar moment of inertia. (The center of gravity is where a giant could balance the car on one finger. Polar moment of inertia refers to whether the vehicle's weight is concentrated in one location — which makes for a responsive car — or spread throughout the vehicle.) Something else against 50/50 being the ideal weight distribution: Most open-wheel Formula-style racecars, which many people would hold up as being the best-handling type of racecars, have 60 percent or more of their weight on the rear tires.
- Myth: Large-diameter wheels fitted with low-profile tires improve handling.
Truth: Tall wheels with short sidewall tires are more about show than go. The original purpose of large-diameter wheels was to make room for larger brakes. Stylists and motorists liked the look of big wheels with short-sidewall tires and engineers took the opportunity to fit even bigger brakes. Also, low-profile tires tend to provide increased steering response, giving many the illusion of good handling. However, traction is determined largely by the composition of the tread rubber and, to a lesser extent, tire width. Pierre DuPasquier, former head of Michelin's race-tire program, said that if F1 lifted its current mandate of 13-inch diameter wheels, the size would grow to about 18 or 19 inches, "but certainly not 20 or above."
- Myth: All-season tires offer more traction on wet roads.
Truth: A summer tire has more grip, both wet and dry, than an otherwise equivalent all-season tire. "All season" means the tire trades wet and dry grip to gain mobility in snow and below-freezing temperatures. If you live where it never or rarely snows, there's no reason to have an all-season tire.
- Myth: Engine oil must be changed every 3,000 miles.
Truth: Many years ago this myth held some truth, but current improvements in oil change things. Depending on your driving habits, modern engine oil will effectively lubricate your engine for 10,000 or more miles. Stretching beyond the 3,000-mile interval is also environmentally sound. Several automakers are installing systems that determine exactly when your oil needs changing. If your vehicle lacks such a system, check your owner's manual for the recommended change interval. More frequent oil changes are called for if most of your drives are less than 15 minutes or you drive less than 10,000 miles in a year or in dusty conditions.
- Myth: Downshifting a manual transmission car is done to slow down.
Truth: The purpose of downshifting is to be in the proper gear to accelerate out of the next corner. Brakes are much more efficient at slowing a vehicle, and they cost less to replace. Downshifting produces some deceleration force, but it's hard on the transmission, clutch and other components. Also, an improper downshift may cause a rear-drive car to spin out. (An exception: fully loaded 18-wheelers.)
- Myth: The purpose of antilock braking systems (ABS) is to shorten stopping distance.
Truth: ABS was designed to give the driver the ability to steer around danger and not spin out while braking as hard as possible. It's true that most drivers can shorten braking distance with ABS because no skill and little training are needed to get the most from the system: Just stomp on the pedal and steer around the obstacle. A shorter stopping distance is a by-product, not the main purpose of ABS.
- Myth: A tire may explode if you exceed the "max pressure" number on the sidewall.
Truth: The "max pressure" number found on the sidewall of a tire refers to its load-carrying capability, not its burst pressure. The burst pressure of the tire is far beyond the "max pressure" number. When the tire is inflated to its max pressure, it will carry the "max load" weight that appears nearby on the sidewall. Especially for ultralow-profile tires on sport-utility vehicles, the tire may need to be inflated to its max pressure to safely carry the weight of the vehicle and its contents. Always check your owner's manual for the recommended tire pressure for your vehicle.
- Myth: Maximum possible cornering power is one times the force of gravity working sideways against the car and is called 1.0g.
Truth: While it's true that most performance cars top out right around 1.0g, it is possible to exceed this number in a road-going car fitted with the right tires. Production-based racecars exceed 1.5g even in slow turns and winged racecars can exceed 4.0g or more. An Indycar has so much aerodynamic downforce at 200 mph that it could comfortably stick to an upside-down section of racetrack.
- Myth: You're a safe driver. It's the other guy who's the problem.
Truth: OK, so this isn't a mechanical myth, but it is the most pervasive myth of all. Studies show that the overwhelming majority of drivers classify themselves as "safe drivers" or rate themselves in the top 50 percent for their driving skill. It's those other, crazy drivers out there who cause problems, right? But the truth is, those other drivers probably don't classify you as an above-average driver, either. In reality, most of us fall into the below-average category at least some of the time.
Now you can separate fact from fiction in the automotive world.
Copyright Edmunds.com, Inc. All rights reserved. First published on www.edmunds.com and excerpted with permission.