Weight and per Person Fuel Consumption
1
It's been a while since I've written in, and I
think for the first time, I'm not going to complain...Well, I don't think
I am anyway! Just read Driving Emotion - Weight and per person fuel consumption,
and it's certainly a different way of looking at motoring. In regards to the
closing few paragraphs, you put forward the question as to why there aren't any
single person vehicles other than bikes (pedal and motor). I put it down to
two things, impracticality and price. Obviously, if all you're going to do
is commute to and from work, then a single seater car would be great, but that's
pretty much the only use it would have. Even with small cars these days, if
you're on your way home and get a call from you kids or friends, etc, you
can divert and go and pick them up, or carry a sizeable load (bulk wise at
least) if there's no one else in the car. A single seater is just too
limited.
Price is the next thing. I'd imagine it'd cost a lot to develop
a single seater car. Look at Smart cars. Admitedly, they are built by Mercedes,
but they're still well over $20,000 for a two seater. The ForTwo, with 45kw
weighs just 730kg empty. A boosted turbo could surely bring the power up a bit,
but still, the sales just aren't there to justify more models like this.
Even motorbikes can cost over $30,000 these days. I think if a single
seater came out, it'd have to be well under $10,000 to have a chance of
decent sales, remembering that the low end (and tiny) 4 seaters like Yaris,
Barina and Getz start from around $14,000. I just think that a single
seater is way too unjustified in todays market. Might as well just buy a
scooter or motorbike in my opinion.
Evan Smith
Australia
Weight and per Person Fuel Consumption
2
Re - Driving Emotion 2/6/7 I'm sure you'll get a few emails on
this one but you ask the question "Where are the two seater cars weighing
(say) 500kg? There aren’t any." What about Clubmans (Lotus 7 replicas)? I'm sure
you were meaning mass produced cars though. Truth is there would be a lot more
of these cars sold/built if the government wasn't so ridiculous regarding their
emissions requirements for these cars (which is making them expensive to build)
and recognized that when building these cars we are "recycling" parts from older
cars to build our sports cars rather than place a higher burden on the
environment by buying a newly manufactured sports car.
Bring on a carbon trading scheme I
say!!
Julian Kenny
Australia
Weight and per Person Fuel Consumption
3
Comments: Weight and per person fuel consumption. I thought this
article was very interesting. The only point i tend to disagree with was the
last paragraph or two where you lament the lack of small, lightweight vehicles.
These sort of cars are available in other markets. They seem fine
and dandy until you crash in one. The G-Wiz is one such car
that recently became infamous after it was tested in the
UK.www.topgear.com By
all means lets have lightweight cars, but i think making them safe in the
current market will be extremely difficult.
Richard Fay
Australia
Future Technologies
Today I read an article in BBC's "Top Gear"
print magazine – the current issue: June 2007. For a change, Top Gear
decided to review the "environmentally friendly" automotive
technologies.
In the particular article of interest, Elon Musk, the
founder of Tesla motors is interviewed. When queried about the relative
merits of electric cars with respect to other emerging technologies,
particularly Fuel cells, Musk states "There really aren't a lot of
alternatives to batteries. The use of fuel cells is flat-out stupid and
anyone with a fair knowledge of physics should understand that." And
further he says "There are some basic energy equations that show that
[using fuel cells]
is quite stupid".
Has Autospeed ever considered
looking at the relative merits of emerging technologies? I would be
very interested to see a series of articles dedicated to evaluating the use of
batteries, fuel cells, bio fuels, and even Hydrogen technology from an
engineering point of view.
Is something like this in the
works?
Adam Seedsman
Germany
We tend to cover car technologies when they’re
in production and being sold in reasonable numbers to the public.
More on RWD
Comments: RWD Vs FWD Safety and Speed
I
believe that one of the issues in this ongoing debate is due to the
fact that most of our RWD cars over here are either: Heavy and poorly set up
(eg, Commodores, Falcons) Better set up, Heavy and Powerful (eg, SS, XR6 Turbo,
XR8 R33 GTST)Lighter and powerful (Silvias, MR2s, etc) Old and Tired (Cortinas,
Geminis, Sigmas)
We do not have a large selection of late model cars in
RWD with moderate to low power, and low to medium weight. It makes
it hard to compare apples with apples.
I am someone who has no
preference towards which wheels the car drives through as long as it is
set up well for all conditions, and is quick point to point.
A good
example of a medium weight medium power RWD is the R34 Skyline Sedan in manual
form, from the factory they are set up brilliantly with Hicas in the rear
and brilliant brakes front and back the car is never one to make a driver
feel unsafe, like a falcon on a wet road.
Perhaps the reason most
aussies have a preference for RWD cars is that the Japs just don't bring
anything exciting to our shores, it is hard to get passionate about a VRX Magna
or a Sportivo Camry whenthey just don't seem to have any passion about
them.
Stephen Mason
Australia
MUCH More on RWD
Rear wheel drive, front wheel drive and all wheel
drive all have their good and bad points. Like you I have owned and / or driven
many cars – HK Holden 186 s Monaro, HK Holden V* Monaro, Morris 1100, Austin
1800, Cortina SW, Aston Martin DB5, MGB, Toyota Corona SW, XD Falcon, EA Falcon,
VS Berlina, VS Calais, VS Statesman, 2002 Statesman, Ford Focus, .....
For a baby boomer like me, originally front wheel
drive wasn’t an option in “normal” cars because it was expensive and high
maintenance. The Mini changed that for small cars, and progressively front wheel
drive has moved to large cars.
So basically we started with rear wheel drive
because that was the only option and a fair number learnt to drive them very
well in all sorts of situations including towing trailers (I towed a 2 tonne
tandem trailer, and separately a 36 foot caravan, at speeds of 130 km/h with a
108 kW 186S Monaro). And we started with narrow high tyres (6.40 13 were
standard), rigid axles and leaf springs at the rear, and engine power for the
base family sedan around 75 kW – 85kW.
Over time suspensions went to independent rear,
engine power with these vehicles went to 175 kW – 200 kW, and vehicle weight
went from 1.25 tonnes to 1.65 tonnes.
Interestingly in 1960’s you could only pull a
heavy trailer with a manual transmission and now you can only do so with an
automatic (and I understand the reasons – see later).
Enough preamble.
Comments on your vehicle and situation
above
Falcon suspensions have tended to be at the lower
end of performance in respect of the engine power and torque. Losing traction at
the rear has been a feature that was reduced with the introduction of the EA in
1988. However the original EF had a reputation for excessive roll steer that
could generate surprises, and this was related to chassis dynamics. Perhaps you
are perceiving excessive roll steering as power oversteering? The effect is much
the same.
Five speed manual could be part of the problem –
reason modern Falcons and Commodores have to be automatics to tow the heaviest
loads is that with the engine power and torque available torque peaks from the
car plus trailer have the potential to damage the drive train and push the
chassis dynamics. Don’t know what the all up weight of your 300 kg workbench and
heavy trailer was but it might have approached the limit for a manual
transmission (which is 1200 kg for a Falcon).
Re fuel consumption, by and large it is
proportional to weight (1.5 tonne sedan plus 0.75 tonne trailer and load = 50%
increase in fuel consumption). And in a hilly environment you use lots of energy
getting up the slopes and then “give it away” as heat in the brakes travelling
on down slopes.
Re spinning rear wheels in first and second gear –
my calculations show this would be easy and occur at 20 km/h (and 30% of full
torque) and 35 km/h (and 50% of full torque), given the coefficient of friction
between the tyres and the bitumen could be 0.6 or lower (if the intersection was
either wet for the first time after a long dry spell, or it had become polished
due to accelerating vehicles), and the 360 Nm of torque available from the
engine.
Re trailer set up the recommended set up is to
have about 10% of the weight of the trailer as a vertical force through the tow
ball. In this case the vertical load should be 75 kg. This would impose an
additional 100 – 105 kg on the rear axle and take around 25 – 30 kg off the
steer tyres. The weight distribution front top back would then be around 50% -
50% which is ideal in a situation where you are neither braking or
accelerating.
So all you’re required to do is brake or
accelerate appropriately.
Is front wheel drive inherently better than rear
wheel drive for towing? Well no, but the problems are different:
-
The tow ball load takes weight off the front
drive wheels,
-
going up a hill the forces trying to pull the
car and trailer back down the slope take weight off the front drive wheels, and
-
the engine torque reaction takes weight off the
front drive wheels.
So going up a marginal friction factor slope like
green grass, the front wheel drive can just come to a halt in situations where
the rear wheel drive will keep going. And that leaves the driver of the front
wheel drive in the difficult and risky position of having to back down the slope
in marginal traction conditions where an over-ride brake on the trailer does
nothing.
Simple question – why are heavy trucks and prime
movers rear wheel drive? Because that’s where there is most weight on the axles
and so that’s where there is most traction.
Another simple question: why are drag vehicles,
formula 1 vehicles and all very high power to weight ratio vehicles rear wheel
drive? Because where you want to get maximum acceleration with a high power to
weight ratio a lot of weight is transferred to the rear wheels with the weight
transfer being greatest for the best traction conditions. With rear wheel drive
as traction conditions get better there is more weight transferred to the drive
so even better acceleration is possible. With front wheel drive the opposite
occurs – as traction conditions improve more weight is potentially transferred
off the drive wheels thereby limiting maximum acceleration.
In summary rear wheel, front wheel and all wheel
drive all have their good and bad points and all have to be driven in a way that
is appropriate to the vehicle design, whether operated alone of with a trailer.
And I suggest the real issue is that vehicles now
have too much power and torque. If I could safely tow a 36 foot caravan at 130
kph with a 108 kW 249 Nm engine in a car with rudimentary tyres and suspensions,
why do we need 165 – 200 kW 330 – 360 Nm engines when we can’t legally drive at
greater than 110 km/h plus the enforcement tolerance in any state or territory
except NT (and there the legal limit is now 130 km/h).
ABS
In spite of all the hype ABS reduces road safety
for the majority of good Australian drivers (you can stop faster without it).
Why can you stop faster? The ABS has to act when the wheel starts to slow (slip
is increasing but traction has not yet been lost) and then ABS has to back off
the braking torque far enough for the wheel to accelerate up to speed again. As
a result its average deceleration is well below the peak. And drivers are told
that with ABS you just push hard down on the pedal – so all wheels cycle with
the ABS and all wheels are braking at well below the peak possible.
And ABS is a disaster on heavy trucks with air
brakes because it takes too long to exhaust air from the brake canisters. As a
result maximum ABS cycle speeds are low. ABS designers hence have to initiate
ABS very early or wheels will lock, and this early initiation means the brakes
are backed off well before maximum brake torque is reached.
Traction control
Traction Control – systems obviously vary but
those commonly fitted on Australian vehicles are an absolute joke! In poor
traction where you want to deliver torque to the ground (especially where the
surface is not flat) the traction control reduces engine power and torque
(theory being to reduce wheel slip). End result is your car slows to a stop
whereas without traction control you can drive through! Give me LSD anytime.
ESC
And ESC – what competent driver wants control of
his vehicle to be taken away from him right at the time control is critical? I
have two friends, both who are better than average drivers, both who have cars
with ESC, and both who have already had experience of ESC coming on when in fact
there was absolutely no need – and neither could get it to disengage! – just had
to ride it out with feelings of having no control of their vehicle. Remember ESC
can have no knowledge of the road surface or geometry ahead – it acts based on
the situation at the wheels at the present or past. So it is quite possible that
a good driver wants to slide or spin the vehicle in a certain way but ESC takes
over – conceivably ESC could “drive” a vehicle over the road edge or into a
fixed object in a way that could kill a good driver who without ESC would not
die.
You might reference the USA research – the
research quoted on the TAC site – “ESC reduces the risk of single car crashes by
up to 40%”. (and as run off road single vehicle crashes = 50% of fatalities in
Victoria that infers a 20% reduction in deaths in Victoria with 100% ESC). The
USA research of course includes snow and ice conditions. And it also showed
those who bought ESC were more concerned about safety – had higher seat belt
wearing rates (not compulsory in USA) so that the results were distorted by the
fact the drivers were safer drivers, I’d always prefer to look at all the
research (and keep in mind that road safety research by and large over-estimates
fatal and injury reduction – it is usually biased). Swedish research with no
correction for safety attitude of drivers – with dry roads ESC has no effect;
wet roads at least 7.8% reduction and with ice and snow at least 12.1%. In
Victoria 75% of crashes are on dry roads so potential reduction is trauma
crashes is 2%. Hey, that’s only a tenth of the TAC estimate!!! Interestingly a good researcher in UK calculated ESC (including wet
conditions and ice and snow conditions as they experience them) could reduce
trauma crashes by 3% (adjust to Victoria conditions and hey figure might be 2%).
Ice and snow are virtual non-events in Australia,
but gravel roads, gravel shoulders, corrugated roads and large trees close to
the running lane are big issues.
I can’t find any research re ESC and gravel roads
– but as ABS is a disaster on gravel and especially corrugated gravel roads, and
as ESC requires ABS I’d predict ESC is also a disaster. Note that in the USA
vehicle standard proposal for ESC it states:
“E. ESC Off Switch, Telltale and Symbol
The proposal would permit (but not require)
vehicle manufacturers to install a driver-selectable switch to temporarily
disable or limit the ESC functions. This would allow drivers to disengage ESC or
limit the ESC intervention capability in certain circumstances when the full ESC
intervention might not be appropriate. Examples include circumstances such as
when a vehicle is stuck in sand/gravel or when the vehicle is being operated
within the controlled confines of a racetrack for maximum performance.”
Note that you switch off ESC for maximum
performance – inference is that with ESC off a good driver will be better able
to protect themselves.
John Lambert
Australia
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