by C. O. Jones
I love it when friends forward emails filled with information and caveats that I’ve have never heard before…..especially when there’s no documentation! Among our favorites are driving tips.
Twenty years ago I attended a dinner party with about thirty middle-aged, well-educated people, split between sexes. Something came up, and one of the men announced: “Oh yes, you should NEVER use your emergency brake for normal driving because it could put you through the windshield.” It’s hard to imagine braking that could rip seatbelts from their mounts; but nonetheless, several men nodded and grunted concurrence. Since it was the host who said this, none but your intrepid reporter had the gall to question this bit of wisdom. I had heard it before.
In the early days of motoring, mechanical problems occurred often. Before the advent of safety glass, head-on collisions were frequently fatal because going through the windshield produced severe lacerations. Even in minor accidents, motorists often bled to death. Braking systems were inefficient, often faulty. In the event of brake failure, the “emergency” brake, if there was one, was so poor that generally the vehicle could not be stopped. This is perhaps the source of this connection between use of the emergency brake and going through windshields.
It really seemed that the brake to use in an emergency would be the “emergency” brake. Surely that would produce the shortest stopping distance. The problem with this illogic is that the only emergency for which this mechanism is designed is failure of the normal braking system. So in the face of this myth gathering steam, about 30 years ago auto makers stopped calling the auxiliary brake an “emergency” brake. The unit became called a “parking” brake, and usually came with the caveat of never being used while driving…not because it would put motorists through the windshield, but because the crash resulting from the unit’s poor performance might actually produce this result.
Parking, or “emergency” brakes, usually use mechanical linkage to the back wheels only. The back wheels produce less than 25% of braking performance because the units are smaller and during heavy braking the great majority of the vehicle weight is thrown to the front tires. There are no anti-skid systems linked to parking brakes and they easily lock up, which reduces braking even more.
OK, next: A couple of times in the last few years we have seen emails circulating with warnings about using cruise control on slippery pavement. According to an unnamed Highway Patrolman, “Driving on wet pavement using the cruise control risks runaway acceleration if the vehicle hydroplanes and exits the pavement.” Really!!? I’m afraid this fails the Robbinsense Bull#@&t test.
Let’s consider:
1) Modern highways are crowned to prevent water accumulation, and grooved for added traction. The grooves in the pavement act the same as tread on tires, channeling water, which prevents hydroplaning. At “normal” speeds this will not occur.
2) Most of the data accumulated to study hydroplaning is for aviation, where takeoff and landing speeds are necessarily high. Formulas center around air pressure in the tires, which is critical because aviation tires are rounded like on a motorcycle. Rounded tires help prevent hydroplaning, but are poor for cornering traction, which airplanes don’t need. For automobile tires that have flat surface area at the road, the most significant factor is speed.
For most drivers, accustomed to tooling along at 70+ miles per hour, driving on a rural highway, which may not be crowned or grooved, may easily present a challenge in speed control. On wet roads the absolute best thing you can do is keep your speed down! There is no better tool for this than a cruise control. A cruise control set at 52 will not waver from that speed, unlike a momentarily distracted driver on foot control, for whom 52 mph feels like standing still. Clearly, under circumstances where road conditions are rapidly changing, greater caution is required, and in this case the driver will probably be attentive to his task and the cruise control is a nuisance anyway. For every driver who (may, conceivably) encounter the aforementioned bout with hydroplaning and uncontrolled acceleration, there are probably ten who would stay on the road because they’re not driving too fast!
3) Let’s look at the operation of a modern cruise control, which does not monitor vehicle speed. In the alleged scenario above, a vehicle loses traction, which causes the vehicle to slow, which causes the cruise control to increase the throttle. An antiquated throttle lock, or “throttle friction” would do this. Instead, a modern cruise control monitors drive train speed. When the tires lose traction, the wheels speed up, while the vehicle may or may not be slowing down. As the drive train speeds up, the cruise control will decrease throttle, and if engine speed increases fast enough, will disconnect, perhaps sooner than a distracted driver would release the throttle.
4) Modern vehicles respond to irregularities in the road much faster even than the cruise control can intervene. Most expensive cars are equipped with an “active handling” system. This measures traction at each tire and applies braking and throttle inputs that are individual and beyond the scope and awareness of the driver. Active handling would intervene to disconnect a cruise control. In addition to that, basic “traction control,” standard on almost all newer cars, would do the same.
So there it is, friends! Merit or Myth? You choose. To stay on the road, keep your speed down! Meanwhile, be skeptical of the stuff you get on the internet. Most of the people writing these tracts have an ax to grind, or just want to propagate their opinions.
C. O. Jones is a Robbinsense staff writer
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