Answers to some puzzling automotive questions
What is going on here?
Why are my windows auto-down, but not auto-up?
Why do run-flat tires need TPMS?
Why do the dials just spin around?
Why can’t I go any faster?
Where did the hood light go?
Why so much aluminum?
Why is the dash so flat?
Why does half the fuel gauge move faster?
Why are some mirrors such a weird shape?
Why can’t I start my car without having my foot on the brake?
Why do some cars take premium fuel?
Ever get in your car, look at how something works, and wonder just why it’s the way it is? Well, we do too. From knobs that keeping turning, to lights that aren’t there anymore, here are some of the reasons behind it all.
Auto-down windows open all the way when you press the power window button once, instead of having to hold it the whole time. Auto-up is less common, and that doesn’t seem to make sense: if the motor can go down automatically, why not back up? It’s because an auto-up system must have some way of sensing if a body part is in the way—say, your arm is out the window—and stopping before you get trapped by the glass. That adds complexity and expense, and so it’s less common for windows to go ‘auto-up’ on more moderately-priced cars.
Tire pressure monitoring systems, or TPMS, use tire sensors (shown inside a cutaway wheel above) or, less commonly, the ABS system sensors, to determine air pressure and send a warning if a tire falls 25 per cent below what it should be. TPMS is mandatory on new cars sold in the U.S., but not in Canada. But you will find it if your car has run-flat tires. Since run-flats don’t look any different when they’re deflated, TPMS is required so drivers know when they have a flat tire.
It used to be that dials had detents, and if you turned the knob all the way, you’d reach the point where it would stop. On today’s cars, it’s far more likely that while the stereo or temperature control has an upper limit, the dial itself will just spin endlessly. It’s because there may be a secondary controller, such as a volume toggle on the steering wheel, or voice recognition that will set the temperature you request. You wouldn’t be able to move the wheel controller to 11 if the dash dial was set to 10.
High-performance cars will often have an electronically-controlled top speed limit that won’t let the driver take it above that speed. It’s not because the car can’t take the stress. Instead, it’s the tires. High-performance tires can handle a lot, but they have their limits, and so automakers add the limiter to help ensure driver safety.
It used to be that when you opened the hood, a light would come on to illuminate the engine compartment. These lights have been gone for about ten years, and that’s because they used mercury switches to close the circuit and turn on the light. The mercury wasn’t really a problem when it was in the switch, but it became a health and environmental issue when the car was scrapped, and so the lights were discontinued.
Aluminum is the new steel in many vehicles, showing up in components, frames, and body panels. It’s all because of weight. Automakers are under tremendous pressure from legislators and consumers to improve their fuel economy. It takes more fuel to move a heavier vehicle, but it isn’t always easy to slim down, especially since manufacturers are also stuffing in more options and safety features to satisfy buyers and meet safety requirements. Switching to aluminum produces components that are as strong as steel, but lighter.
The dashes on 1950s and 1960s cars sprouted switches and toggles that became a forest of chrome. They looked cool, but they could cause serious injury in a crash when occupants were thrown against them, and they were one of the major safety flaws that Ralph Nader attacked in his book, “Unsafe at any Speed.” Today, controls have to be designed for safety first, then appearance.
Some cars will seem to stay on the upper quarter or half of the fuel gauge for a long time, while others will empty that first portion quickly and then settle down to a slower rate of consumption. This can be because of the shape of the tank: if it’s narrower at the top, that part will empty faster, and since the gauge measures the level of fuel, rather than volume, it will drop accordingly.
Aerodynamics. How the air moves around a vehicle plays a huge role in fuel economy, and cars spend a lot of time in wind tunnels as engineers tweak them for maximum flow. It’s surprising how a small spoiler or even a tiny raised rib on a body panel, properly placed, can make a huge difference. Mirrors are a real challenge for designers: smaller ones may produce better air flow, but if they’re too small, they’re not useful to the driver. And on top of that, they still have to look good on the car.
You used to be able to reach in and just turn the key to start the engine, but most cars today require that you have your foot on the brake. It’s a safety feature, of course, to prevent the vehicle being started without someone in control of it. You’ll also have to press the brake to put it into Drive for the same reason.
Because premium fuel doesn’t burn as easily as regular fuel. It contains higher levels of octane, and the higher the octane, the less volatile the fuel becomes. Air gets hotter the more it’s compressed, and this can be an issue in higher-compression engines. If you inject regular fuel, this higher temperature can cause it to ignite before the spark plug fires, a condition known as pre-ignition. Since it isn’t as volatile, higher-octane fuel is less likely to do this, and so it’s used in engines where pre-ignition could otherwise be a problem.