rec.autos: Frequently Asked Questions

[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]

[last change: 19 September 1995; oversteer/understeer Q&A substantially
   revised to reflect comments from Doug Milliken -- rpw]

                Commonly Asked Questions

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

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

    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

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"

   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 <name or acronym> 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.
 ``All who have raced there know that the earth is flat and ends in the
   sand at turn 2.  The emotional rewards of driving this turn flat out
   are just as intense as the physical consequences of blowing it''
     -- Bruce MacInnes on Bridgehampton Race Circuit (1957-1995?)