Conference terri::cars_uk

    
    I've just read note 1120.18, re the new Vauxhall which will do 170+mph
    and thought I'd renew an old topic - 
    
    Just what is the point in this type of top speed? especially to the
    average motorist? Yes you can go to Germany and play on the autobahns,
    _but_ to handle this sort of speed requires considerable driving
    skills, you can't just decide to pop over to Germany to play with your
    new toy! I've driven in Germany, and yes, the road/weather/traffic
    conditions sometimes do allow you to 'put your foot down'  - but even
    at 125mph - (the fastest I've driven) you have to be _so_ vigilant if
    there is _any_ other traffic on the road. What is the stopping distance
    at 170 mph? can you judge what the cars that far away are likely to do?
    
     

    re .10,
    
    Yep, Elaine the police have put forward similiar worries...
    
    The article I read said if you were doing 70/80 and you looked in your
    rear view to pull out, you would see nothing, however if this Vauxhall
    was hammering down the outside lane at 170mph then it would suddenly
    appear up your backside in next to no time!!
    
    Greg

170 MPH = 83 yards per second.

IE: The distance you travel while looking in your mirror at this speed
exceeds the total stopping distance of a car travelling at 70mph.

This sort of speed is for race tracks only.  Manufacturers are being stupid and
irresponsible making road cars with this performance.

The "shortest stopping distance" at 170mph is 1615 feet, or 538 yards, or
about 1/3 of a mile.

The "two second rule" would mean leaving a gap of 166 yards between cars on a
motorway, not the 166 inches normally seen today.

I am in favour of "performance" cars to give quick acceleration for overtaking,
but this is going a bit too far...

Scott

    I remember reading about an idiot in some in big american muscle
    car caught doing 140mph down the M1 in the papers.
    
    They worked out that if all the conditions were good and the driver
    was good, he could still only stop the car in � mile!
    
    Thats a long way, if something happens right in front of you (ie
    if someone pulls out into the fast lane doing 70/80ish.

    How many years has the Lambourghini Countach been available?
    Hasn't it always had a top speed of 170mph+
    
    What about the F40, 959? If 170mph is that dangerous, why were these
    200mph cars allowed.
    
    Should the new Jaguar Sportscar be shelved, as it has a rumored top speed
    of 220mph?
    
    chris 
    
    

I remember reading a test report that found that Lambos can't go at 170+,
and was sceptical of other high-speed claims.  Do you have documented proof of
a Countach clocked at over 170 on a public road, or for an F40 at over 200?

Scott

PS In the test report, they had to spend about three days going up and down
autobahns to find conditions safe enough to do 150 in the lambo, and this was
as fast as they could make it go.  Further "proof" that anything faster isn't
safe or necessary.

    Also like .12 says, to get very fast acceleration on large heavy cars,
    you have to have a very large high speed.
    
    I am much more in favour of the characteristics of lighter
    vehicles eg  kit cars,hatches,bikes ; where to varying degrees, you
    get performance more biased towards acceleration,
    
    Chris

    re 15, I was trying to remember an article I read in Motor a few years
    ago, where they were testing the Lambourghini against the top Ferrari
    of the time. They found both cars to be well down on the top speeds
    claimed. I can't remember the figures. 
    
    I do remember that they were advised to  remove the wiper mechanism
    on the Lamb. for maximum aerodynamics!
    
    Also, I thought the original top speed claimed for the Countach was
    190mph?
    
    Re documentation.  I don't about cars, but I know that most
    of the large jap bikes speed claims *are* valid, and have been
    tested fairly reliably using timing lights, for instance.
    I was reading a test in Motorcycle International only yesterday,
    where a tester wrote that he saw 170mph+ on a speedo, which
    he knew to be a genuine 160ish (timed).
    
    A lot of the Motorcycle press are concerned about the top speed
    of the large bikes. Hopefully the *voluntary* 125hp limit will
    eventually be fully obeyed.
    
    Chris

    
    Re High Speed = Fast Acceleration.
    
    Is this true? Surely even on heavy cars the main restriction on
    acceleration is torque and/or gearing.
    
    I always thought that a good rule of thumb was that High Power = High
    speed and High Torque = Fast Acceleration.
    
    Mark

    
    
    What people keep forgetting (conveniently maybe) is that on a motorway,
    one rarely has to slow to 0.
    
    One usually only has to loose the difference between your own speed and
    the speed of the "obstruction"...
    
    Travelling at 90, this is usually only about 10-20 mph, and I don't
    know about the rest of you, but I can loose those 10 miles an hour, in
    a matter of a few yards, just by taking my foot off the accelerator !
    
    Elaine asks what is the obsession with top speeds...I can't answer that
    one, but I would certainly like to know what this obsession is with
    the distance it takes to slow from X mph to 0 mph...
    
    This is rarely required on motorways, and when it is, there is usually
    a fair amount of warning...

    
>>    Should the new Jaguar Sportscar be shelved, as it has a rumored top speed
>>    of 220mph?
    
     I don't know.....  you could say that all cars should be 'governed' to
    the top speed of the country they are in, but then come the
    'accelerate out of trouble' arguments, so you say ok, there is no need
    to do more than 10 miles over the speed limit.......
    
    If you banned the new high speed cars than you would have to work down
    until someone decided what a 'safe' maximum was - impossible to do
    
    You may end up with a ban on 'dual purpose' vehicles on the road -eg
    the 23 - a road legal racing car, quite capable of high top speeds, but
    which is as capable as any other car of being driven within the
    confines of the highway code, and which (as Derek mentioned) has brakes
    which are far more efective than your average car.  
    

    RE .21 coefficient of Drag will also play a large part in the stopping
    distance.  A not so aerodynamic vehicle will slow a lot quicker from
    100 to 70 MPH than it will from 71 to 0 Mph.  You'll also find that
    the engine tends to back-off from the higher revs a lot quicker than
    backing off from lower revs.
    
    Dave.
    

   re .18

   There is a direct relationship between Power and Torque, the relationship
being to do with REVS (I have never found out the actual formula.), so it is
so that high top speed and fast acceleration are linked.

    As to gearing, really it is a matter of economy, top speed, and acceleration
with the best economy coming from a higher gearing, which will also give a 
higher top speed, but slower acceleration, whereas a lower gearing, and thus 
better acceleration, will give poorer economy. The ultimate top speed isn't 
found simply by putting the highest gearing that you can find on to the car
though !!!

   ANyway, hope that that answers your question, even though reading it I doubt
it. Glad I didn't ever think of becoming a teacher !!!!!!

	 ALAN
	~~~~~~

    re .15
    
    I did a lot of kilometres at speeds above 250kph in a Countach (mostly
    on Swiss and Italian motorways). I dont trust the Countach can do
    300kph, but I've done 280 myself.
    
    Of course to be able to do that requires very low (if not zero)
    traffic and a lot of warning when approaching isolated cars
    (headlamps).
    
    The Countach is a good example because of its excellent balance
    and braking power. I would not do that sort of things in many cars.
    I believe a Porsche 959 or a Ferrari F40 are designed to cope with
    such speeds.
    
    Finally the driver him(her)self is the key factor. I'm used to do
    that and I feel safe (otherwise I would never do it, or I would never
    travel with anyone driving at those speeds). I'm concerned about the 
    jerk who just bought a F40 and has never driven at 200kph ? 
                               

So Patrick, did you notice your watch was a few 10ths of second slow when you
emerged from the Countach??  :-)

Dave

I suppose the "theoretical" top speed of a car oinly depends on:

- the maximum sustainable speed of the engine: about 6000 rpm on your
  common-or-garden Ford, higher on engines built for racing.
- the highest gearbox ratio (1:1 for 4th, about 0.82:1 for 5th)
- the diff ratio (usually in between 3:1 and 4:1)
- tyre and wheel size

The engine power / torque just determine how quickly you get there, and also
whether there is enough "power" to overcome all the drag forces at that speed.

Having looked at acceleration / power / torque figures, it seems that
acceleration and power are linked (ie more BHP => quicker acceleration).
Torque doesn't really come into accelearation.

Remember that power is rate of energy change: simplistically energy is �mv�, so
power determines the change in v, ie acceleration.

Torque has the same dimensions as power (both are ML�T��), but measures
something different.  A useful analogy might be: Geoff Capes has lots of 
torque, but Linford Christie has lots of power.

But don't take my word for it...

Scott

 Re .28

	Theoretical top speed is determined by maximum power and the drag 
factor mainly, the gear ratio only comes into it in so far as that you
need to get max power and theoretical max speed to coincide.

	 Alan
	~~~~~~

    
    I believe the obsession for speed is quite normal for those
    of you who can afford to pay the excessive amounts for performance
    cars which exceed 170 mph. I guess the question needs to be asked
    'Why would you buy a car which exceeds 170 mph ?' I'm sure there
    are many answers...
    
    One of the reasons why manufactuers quote things like 0-60 and
    max speed is to promote the sale of the car etc. Some people look
    for comfort, while other just go for raw speed ...
    
    The performance of any car is managed by the driver. Naturally
    there are many factors which will determine if/how/why excessive
    speed should be applied.
    
    The police are on the look-out more and more for would be F1 drivers
    on the roads.
    
    If you feel the need for speed, then be careful when you apply it.
    
    Just my opinion.....
                                        
    Later.
    
    -fv

    
    
    Most of this is from my dealing with bikes, but here is power and
    torque as I see them :
    
    An engine has 3 'characteristics' ( for want of a better word )
    power, torque, and the power band ( a sort of misnomer used to describe
    a rev range ). typically this may be the case :
                            
      join your own dots !
    
      |                + +   +
      |                    +  +
      |              +  ..      * *
      |            +   .  .   * +   *                    
   ^  |           +   .    .*     +   *
   |  |       + +     .    * .     +   *
kg/m? |     +       .   *    .      +   *
      |   +   . . .   *       .      +    *
      | + . . *   *            
      | .  *
      +------------------------------------------------------
                 |  'power band'   |               RPM ----->
                                
      + = 'envelope'  . = power   * = torque
     
      This 'envelope' is composed of the added factors of torque and
    power. And it's shape represents roughly the performance you can
    expect from the engine. Engines can be tuned to give torque and 
    power at different points of the midrange. An engine in a 'high' 
    state of tune will have torque and power as coincident as poss, 
    giving poor performance outside the 'power band', but monstrously 
    quick acceleration and ( gearing considered ) max top speed. 
    Conversely, an engine in a 'low' state of tune will have max torque 
    and max power fairly far apart, smooth acceleration, power throughout 
    most of the rev range and a smoother , more consistent 'envelope'.
    
    Power, I believe gives you the top speed; and torque the acceleration
    and the sustained 'pulling power' but only to a certain extent. 
    
    In an ideal situation, engine force would only need to be applied
    to accelerate the car, then it would cruise with no engine assistance.
    However, Friction within the engine,wheels,aerodynamics etc causes
    a negative acceleration upon the car. Force is therefore required
    to overcome the 'resistance to motion' of the vehicle. As you go
    faster, the resistance to motion increases until you reach a stage
    where the acceleration produced by the engine equals the resistance
    to motion - terminal velocity ( or maximum speed ) is then reached.
    
    So, using smaller rato gears will give quicker acceleration, only if
    you have the torque to pull them ( F=ma ). Using larger ratio gears
    will only give a higher speed to the point where the engine is only
    able to equal the resistance to motion of the vehicle. power.
    
    I'm not a good explainer, but I hope you understand.
                                                          
    regards.
                            Nik.
    
                 

  Nik, is your key for the graph correct, do bikes have peak torque higher up 
the rev range than peak power ???

  I can't actually think of a reason for this, so I am willing to beleive you,
just slightly confused as it is the other way round on cars.

	 Alan
	~~~~~~

    
    Alan, I drew it entirely from memory, but I'll check it out if I
    can find some mag articles at home.
    
    Nik.

    other key points about high speeds
                    
    - aerodynamics, especially the balance between front and rear, assuming
      the shape of the car produces some amount of lift
    
    - attitude of the car under strong braking
    
    I found the high performance saloons (tuned engines, turbo extra,
    etc) very tricky to handle at high speeds mostly because the
    suspension, steering and general weight distribution have NOT been
    designed for such speeds.
    
    Typical examples of cars designed for 200kph+ : Porsche 911, Countach,
    with an excellent weight distribution : low centre of gravity and
    proper centre of roll.
    
    Counter examples: Ferrari BB which has a disastrously high centre
    of gravity and terrible roll characteristics

    Nik,
    
    if torque gives acceleration why is it that diesels dont have mind
    blowing acceleration. Don't they have lots of torque?
    
    I always thought (at least for the last few minutes) that power was
    what really counted. If your car is consuming a set ammount of energy
    at its current speed then acceleration will be determined by the power
    available to give it the extra energy to get to and maintain a faster
    speed.
    
    Torque, I supposed, was like having a big flywheel in the car. With
    lots of torque you could maintain your current speed but might not be
    able to significantly change it. 
    
    I remain totaly confused on the subject and the more I try to
    understand it, the more confused I get.
    
    Peter

>>                      <<< Note 238.35 by BONNET::HARDY >>>
    
>>    if torque gives acceleration why is it that diesels dont have mind
>>    blowing acceleration. Don't they have lots of torque?
    
    
    Ordinary diesels, generally don't have 'lots' of torque, but have a
    flatter more even torque band. They also have a very limited rev range
    (4500RPM about max).
    
    Turbo diesels with lots of torque do have superb acceleration!!! 
    
    Richard

         <<< Note 238.36 by UKCSSE::RDAVIES "Live long and prosper" >>>

>    Turbo diesels with lots of torque do have superb acceleration!!! 
    


I do hope so (Citroen BX TD due October) !!!!!!!!!!!!111


BX GTI    125 f/p torque at 3,5000
BX TD     134 f/p torque at 2,5000


(from memory...)

As I understand in torque is the turning, twisting, or rotational force.
Therefore in a high torque engine it is much easier for the engine to overcome
such elements as gearbox, diff, wheels, road drag etc.If you have a lot of 
torque it makes these wheels spins that you see easier to do.

My landy has a Perkins 4203 diesel engine. This beast is 3.3 Lt. has a low rev
count and just about makes must other cars look like tonka toys when it comes 
torque.

In fact the engine has so much torque, if you are in DEC park you are quite
welcome to come over and see the effect! I have two of the gearbox gears on my
desk sans several teeth. 

Mind you it does have its uses. Have you ever seen a 'car' do a four wheel
wheel spin (on gravel of course). Or pull cars from under fallen trees, or 
drive across thick mud that you would have difficulty walking across.

Simon.

Is this some new high-revving diesel engine? ;-)

    
    
    re. a few back.
    
    My mistake, torque is usually generated slightly lower down the
    rev range than power - just swap the legend on the graph, the peaks
    can be tuned to coincide tho'. Perhaps a reason for generating torque
    lower is that it is needed to overcome the inertia of a stationary
    vehicle to start it moving. ( Could be BS tho' and it's just a side
    effect of combustion engines ;-) )
    
    Torque, measured in foot-pounds or kilogram-meters is the ability
    of the engine to overcome resistances to motion. The more torque,
    the more quickly resistance may be overcome when acclerating and
    the greater your rate of acceleration is.                    
    
    Power, measured in bhp, represents work done at a constant rate
    of exertion ( in turn measured in watts or joules ). Maximum
    power is therefore loosely translatable as maximum constant work
    done. When you have reached your terminal velocity ( where the
    engine is only able to meet the resistance to motion not exceed
    it ), the engine will be working constantly at max power.
                                                 
    re. wheelspins - These are caused when the torsional rotation of
    the wheel ( amount of torque trying to create an amount of linear
    acceleration ) exceeds the coefficient of friction between the tyre 
    and the road, and traction is broken. The wheel then spins. Wheelies
    are created in a similar manner. So much torque is applied at the 
    back wheel,but not enough to cause the rubber to break contact, 
    that a bike will rotate around the back wheel, thus lifting the front
    off the floor ( not always a good idea as the entire weight of the
    bike is then supported through the chain and gearbox.
     
    Remember, torque is a measure of 'torsional rotation' , not linear 
    force. ie - it makes things go round, not along.
    
    Remember ,changing wheel and tyre sises will affect your gear ratios, 
    and your ability to accelerate, top speed, consumption, and ultimately
    engine life.
    
    It took me ages to get these concepts sussed in my own mind, will
    you please stop confusing me ;-)
    
    Nik.
    

    
    re: Landrover with Perkins motor .... have you ever seen one of these
    overtaken by an invalid carriage??
    
    Regards,
    	   Ray.

� 	Perhaps a reason for generating torque lower is that it is needed to 
�	overcome the inertia of a stationary vehicle to start it moving. 
�	(Could be BS tho' and it's just a side effect of combustion engines)

Could be BS, but probably not: note that off road 4WD vehicles usually produce 
their peak torque at lower revs by design than normal road vehicles (ie my
Espace appears to produce peak torque at about 4000 rpm, whereas a Land Rover
diesel does so at between 1500 and 1800 rpm)

/. Ian .\

    Re: .40
    
    > Torque, measured in foot-pounds or kilogram-meters 
    
    Think you'll find it's Newton-metres.  A Kilogram is a mass.
    
    Jeff.

    
                                                  
    Well slap my wrists ;^)
    
    Only 5 years out of the education system, and forgetting the basics.
    Oh the shamelessness of the youth of today ;-)
    
    Nik.

	We've been through all of this before power/torque/revs etc.

	Summary -

	Acceleration is mainly a factor of Power and Weight.

	Top Speed is a factor of Power and Drag Resistance.

	By the way, there's a 70mph speed limit in the UK, in case
	some haven't noticed.

	I think this generation of 200mph, or whatever, supercars will
	be a short lived fad, the last expression of 80s type attitudes.
	Soon the new era of environmentally friendly, cheap to run cars
	will be taking over.

	-John

>>	Soon the new era of environmentally friendly, cheap to run cars
>>	will be taking over.

Complete Garbage!!!

NO car is environmentally friendly.

Mark.

    Mark,
    
    shame on you, no HUMAN is environmentally friendly.
    
    R.