Newsgroups: rec.autos.misc,rec.autos.tech,rec.autos.driving,rec.autos.makers.vw.aircooled,rec.autos.makers.vw.watercooled,rec.autos.makers.chrysler,rec.autos.makers.saturn,rec.autos.makers.honda Subject: rec.autos: Frequently Asked Questions Followup-to: rec.autos.misc Expires: +30days Reply-to: rwelty@suespammers.org Keywords: Monthly Posting From: rwelty@shell.wizvax.net (richard welty) NNTP-Posting-Host: shell.wizvax.net X-Original-NNTP-Posting-Host: shell.wizvax.net Message-ID: <3b85ca79_2@news.wizvax.net> Date: 23 Aug 2001 23:31:05 -0400 X-Trace: 23 Aug 2001 23:31:05 -0400, shell.wizvax.net Lines: 262 XPident: rwelty X-Original-NNTP-Posting-Host: 208.171.236.41 XPident: Unknown Path: senator-bedfellow.mit.edu!bloom-beacon.mit.edu!howland.erols.net!netnews.com!xfer02.netnews.com!newsfeed1.cidera.com!Cidera!news.wizvax.net!shell.wizvax.net!rwelty Xref: senator-bedfellow.mit.edu rec.autos.misc:207202 rec.autos.tech:449246 rec.autos.driving:395753 rec.autos.makers.vw.aircooled:266290 rec.autos.makers.vw.watercooled:302130 rec.autos.makers.chrysler:175326 rec.autos.makers.saturn:113922 rec.autos.makers.honda:313312 [this article is one of a pair of articles containing commonly asked automotive questions; the other article contains questions of general consumer interest, and is broken out to facilitate crossposting to misc.consumers -- rpw] An web index to the FAQ postings, including this one, may be found at http://www.wizvax.net/rwelty/FAQ/ (This file is ftp://ftp.wizvax.net/pub/personal/rwelty/Autos/questions.text) [last change: 6 July 1996: moved to ftp.wizvax.net -- rpw] Radar Questions: Q: Where are radar detectors illegal? A: In the US, currently Virgina and the District of Columbia prohibit all usage of radar detectors. New York prohibits their use in large trucks. In Canada, they are illegal in Manitoba, Ontario, Quebec, Newfoundland, and PEI (Prince Edward Island). They are apparently are illegal through most, if not all, of Europe. Legislation which would make them illegal is pending in many other jurisdictions; chances of such legislation passing varies a great deal. Q: Where are Radar Detector Detectors used? Do they really work? A: Usage is spreading rapidly; initially they were used only in Canada, but now they are appearing in New York and Virginia. It is unsafe to assume that they are not in use in D.C. They work by detecting a certain frequency radiated by many currently available super Het radar detectors; some brands of detector radiate more strongly than others, and are thus more likely to be spotted. New radar detectors are becoming available which may not be detected by the current generation of detector detectors. Note that a detector may only be spotted by one of these devices if it is turned on. Q: What is VASCAR? Is it some kind of Radar? A: VASCAR is nothing more than a fancy stopwatch and time-speed-distance computer. It depends on the operator pressing buttons as the target vehicle passes landmarks. No radar signals are emitted by a VASCAR system. Q: What is Ka band radar? Where is it used? Should a radar detector be able to handle it? A: Ka band has recently been made available by the FCC for use in the US in so-called photo-radar installations. In these installations, a low-powered beam is aimed across the road at a 45 degree angle to the direction of traffic, and a picture is taken of vehicles which the radar unit determines to have been in violation of the speed limit. Tickets are mailed to the owner of the vehicle. Because of the low power and the 45 degree angle, many people believe that a radar detector cannot give reasonable warning of a Ka band radar unit, although some manufacturers of radar detectors have added such capability anyway. The number of locales where photo-radar is in use is limited, and some question the legality of such units. Best advice: learn what photo radar units look like, and keep track of where they are used (or else, don't speed.) Q: Do radar jammers work? Are they legal? A: Quick answer: No, and Not in the USA. Detailed answer: Cheap radar jammers do not work well at all. Jammers that work are expensive and usually the property of the military. Jammers are a major violation of the regulations of the Federal Communications Commission of the USA. Driving technique and Vehicle Dynamics Questions: Q: What are understeer and oversteer? A: Understeer and oversteer are often misunderstood and misused terms. The popular press commonly uses them to describe the behavior of automobiles near the "limit of adhesion", but engineers working in the field of vehicle dynamics prefer to only use the terms for low-g cornering (that is, cornering with lateral accelerations of say, 0.2G, well within the linear or elastic range of tire operation.) These engineers generally prefer to use the term "plow" instead of "understeer" and "spin" instead of "oversteer" when talking about behavior at the limit of adhesion, where performance is controlled by the friction characteristics of the tires. The terms "tight" and "loose" are also used in describing limit behavior. Simply put, these terms describe whether the car wants to go straight in a corner (steer `less', meaning `understeer' or `plow') or it wants to turn more in a corner (`oversteer' or `spin'.) Understeer is commonly designed into most production cars so that untrained drivers, inadvertantly traveling too fast, won't get into trouble. `Plowing' may also be induced by using too much throttle in a corner. Some performance cars, in a corner near the limit, may tend to rotate (which is an incipient spin; the Porsche 356 and earlier Porsche 911s were noted for this); this behavior may induced by lifting on the throttle (sometimes refered to as Trailing Throttle Oversteer, or TTO). Sometimes a genuine spin results. Some technical details: in a corner at speed, the tires on the car will develop what are called `slip angles'; slip angles are the difference between the center line of the tires and the path on which they are actually traveling. In a turn, there will be slip angles at all four tires, and they will generally be different for each corner of the car. Understeer and oversteer are defined in terms of the "rate of change" of the slip angles; in understeer, the front wheels have a greater rate of change in slip angle than the rear wheels, and in oversteer, the reverse will be true. An historical note contributed by Doug Milliken: Folklore has it that the term "plowing" came from Barney Oldfield driving an early Christie Front Drive racer. These cars had huge displacement/slow revving transverse engines with a clutch on each end of the crankshaft. The output from each clutch went direct to the front wheels through Hooke joints (u-joints)! The cars look from pictures to be very front heavy, and with front wheel drive were pretty successful in the days before WW1. When he cornered on a loose dirt track the car did actually plow up furrows!! Walter Christie went on to design some very good battle tanks and other heavy vehicles. Q: What is a rev-matched downshift? A: When downshifting, the engine must be rotating faster in the lower gear than it was in the higher gear. However, during a downshift, normally you declutch and lift your foot from the throttle, so the revs drop rather than increase. In rev-matched downshift, you blip the throttle before re-engaging the clutch so that the engine will already be up to the new speed. This results in a much smoother and faster downshift. Q: What does heel-and-toe mean? A: Heel-and-toe is a technique used to do a rev-matched downshift while braking. This is normally challenging, because you need the right foot for both the brake and throttle. It is called heel-and-toe because you use one end of the foot on the brake, and the other on the throttle to match revs for the downshift. In many modern cars this is a misnomer; often you must use the ball of the foot on the brake and the right side on the throttle. Note that some race car drivers will skip the clutch, and just use the left foot on the brake and the right foot on the throttle, accomplishing the same thing. Q: What is double-clutch downshifting? A: While your right foot is doing the above, your left foot can do one of three things: nothing, declutch once, or declutch twice. The reason for declutching twice is to match the speeds of the two shafts in the transmission to the speed of the engine. This is usually coupled with rev-matching, so that while the engine is in neutral and the clutch engaged, the throttle is blipped and both shafts of the transmission speed up. The procedure is as follows: (0) declutch (1) move gearshift lever to neutral (2) engage clutch (3) match revs (4) declutch (5) move gearshift lever to next lower gear (6) engage clutch This sounds like a lot of work, but with practice it becomes natural. The problem that double-clutching solves is normally the function of the synchronizers within the gearbox. In transmissions without synchros or with very worn synchros, double-clutching makes it much easier to shift. Basically, if you double-clutch well, you are not using the synchros at all. This is generally unnecessary on street cars with synchros in good condition. Q: What do the numbers for acceleration from 0-60, 1/4 mile, skidpad, and slalom times in the Auto Magazines really mean? May they be compared? A: In short, 1) not as much as the magazines want you to believe, and 2) almost never. In more detail: the acceleration numbers (0-60mph and 1/4 mile times in the US) may be vaguely compared as long as they all come from the same source. Testing procedures vary so much from magazine to magazine that comparing a Road & Track number to a Car & Driver number is quite pointless. Keep in mind, too, that the same variation applies from driver to driver on the street; the driver is a major (often *the* major) part of the equation. Skidpads vary, and even if they didn't, skidpad figures are really only tests of the stickiness of the stock tires; they change radically when tire compounds change. DO NOT make any assumptions about the comparative handling of, say, two sports sedans based on skidpad numbers. This is not to suggest that skidpads are without value, however. Skidpads are an excellent educational tool at driving schools. They are simply of limited value in the comparison of anything except tires. Slalom times are slightly more useful; they test some small parts of the automobile's transient response. However, they are also heavily influenced by the stock rubber on the car, and they do not test many corners of the car's envelope. They DO NOT tell you all you need to know before making a buying decision. For example, they don't tell you what the rear end of the car will do on a road which suddenly goes off-camber. When a car has an adjustable suspension, these tests are usually done in the `sport' setting, which may be quite unsuitable for daily driving. The list of caveats could go on for page after page. Q: According to my physics class, you can't ever accelerate or corner at more than 1.0G. Is this true? A: the equations for friction used in freshman physics textbooks presume that the surfaces are smooth, dry and non-deformable, none of which are the case with tires & pavement. Pavement is _never_ smooth; it is always irregular to a greater or lesser extent. Tires, which are not really dry and solid (as rubber is a substance which in its natural form is liquid, and which has only been coerced into a semblance of solidity by chemical magic), deform to match the surface of the pavement which a vehicle is traveling over. The mechanisms by which tires grip pavement are not well understood, but are clearly not those described by the "Introduction to Physics" formula. A better model for tire grip is offered in _Race Car Vehicle Dynamics_, William and Douglas Milliken, Society of Automotive Engineers, 1995. In this model, mu, the constant coefficient of friction, is replaced by a lateral (xy plane) force coefficient, whose value may vary depending on the vertical (z axis) force being applied, and on other conditions. For a modern Formula 1 race tire, the lateral force coefficient may be as high as 1.8 for light loading in the z axis. See chapter two of this fine book for an exhaustive discussion of tire behaviour in extreme conditions. Misc. Questions: Q: What does stand for? A: Here is a list of some of the names which are commonly asked about; be careful in soliciting the meanings of other names as misinformation abounds on the net. In particular, NEVER ask in rec.humor if you want a useful result. Saab: Svenska Aeroplan A. B., or The Swedish Airplane Corporation Alfa: Societa Anonima Lombarda Fabbrica Automobili, or The Lombardy Automobile Manufacturing Company Fiat: Fabbrica Italiana di Automobili Torino, or The Italian Automobile Manufacturers of Turin BMW: Bayerische Motoren Werke, or Bavarian Motor Works MG: Morris Garage Q: Does VW own Porsche? A: No. Porsche is a publicly held company, controlled by the Porsche and Piech families. Porsche has extensive business dealings with VW/Audi, which causes some confusion. Since currently Porsche is in some financial difficulty, there is a possibility that Mercedes or VW may be interested in purchasing the company in the near future, but this is only speculation at this time. -- Richard Welty rwelty@krusty-motorsports.com .