BBC article on ludicrous cars

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mark a.
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Re: BBC article on ludicrous cars

Postby mark a. » 3 Mar 2012, 10:29am

ALL of my points were based on the assumption that at no point does any driver break the speed limit. So if you want to overtake a car doing 30mph in a 60mph zone, then the RS6 can accelerate from 30-60mph quicker and so overtaking is safer.

Hence a quicker car is safer for a given overtaking situation.

Ultimately it comes down to driving skill. A teenage boy in a slow Corsa will be more likely to crash than a racing driver in a Ferrari.

By the way, electric cars currently have slower top speeds but have great torque (hence good acceleration). So these will be ideal overtaking machines. Currently we have G-Wiz on the slow and rubbish end, and the Tesla on the performance end, but we are getting a better range of cars now, such as the Nissan Leaf.

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meic
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Re: BBC article on ludicrous cars

Postby meic » 3 Mar 2012, 10:34am

mark a. wrote:ALL of my points were based on the assumption that at no point does any driver break the speed limit. So if you want to overtake a car doing 30mph in a 60mph zone, then the RS6 can accelerate from 30-60mph quicker and so overtaking is safer.

Hence a quicker car is safer for a given overtaking situation.

Ultimately it comes down to driving skill. A teenage boy in a slow Corsa will be more likely to crash than a racing driver in a Ferrari.

By the way, electric cars currently have slower top speeds but have great torque (hence good acceleration). So these will be ideal overtaking machines. Currently we have G-Wiz on the slow and rubbish end, and the Tesla on the performance end, but we are getting a better range of cars now, such as the Nissan Leaf.


Quite a few racers thought that too. We know their names, I can start with Mike Hailwood.
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Mick F
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Re: BBC article on ludicrous cars

Postby Mick F » 3 Mar 2012, 10:42am

mark a. wrote:......... if you want to overtake a car doing 30mph in a 60mph zone, then the RS6 can accelerate from 30-60mph quicker and so overtaking is safer.
In principle and in theory, I agree with you.

It's just in the practical world on the roads in a 60mph limit, the traffic coming the other way has to be taken into account. Normally, in that scenario, there will be a gap, and any car could overtake safely. With a performance car, you'd have to be very quick off the mark at a given opportunity, but you'd scare the oncoming drivers to death!

I would suggest that a performance car isn't worth it. I built and drove a "performance" Mini for a few years. 110bhp and went like a rocket! 0 to 60 in perhaps 8secs or less, but it took a great deal of concentration to use the power and acceleration to good effect in traffic. It was great fun and a great talking point, but actually pointless.
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philg
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Re: BBC article on ludicrous cars

Postby philg » 3 Mar 2012, 10:47am

Mick F wrote:
philg wrote:
Cunobelin wrote:As a concept these may have a significant potential, but are saddled with the reputation of being slow, poorly designed and impractical for daily use

And not in the least bit green whilst electricity generation remains non-renewable (although the transfer of pollution from cities has some benefit)
The CO2 output of electric cars is minute compared to petrol/diesel cars even though the electricity to power them has to be generated.

Exactly! the 2nd law of thermodynamics applies equally to power stations as to infernal combustion engines

Fossil fuel power stations are about 33% efficient for coal, rising to around 50% for gas; from which you can subtract electrical losses from transmission through to the charger and battery/cable/motor losses.

A modern car diesel is around 35% so the is in fact little if any difference.

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Re: BBC article on ludicrous cars

Postby PW » 3 Mar 2012, 10:49am

Performance cars? Been there, done that and grew up. :roll:
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Re: BBC article on ludicrous cars

Postby hubgearfreak » 3 Mar 2012, 12:43pm

kwackers wrote:I'd simply make black boxes compulsory.


spot on. which makes people's choice of cars an irrelavence - if the taxation system ensures that the polluter pays. i fail to see the need or desire to limit the choice of power:weight through legislative limits

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Re: BBC article on ludicrous cars

Postby hubgearfreak » 3 Mar 2012, 12:47pm

Cunobelin wrote:However this is about selling the electric car
As a concept these may have a significant potential


when electricity can be produced without pollution or danger, then maybe. until that utopian dream comes along, i don't see their potential

Mick F wrote:The CO2 output of electric cars is minute compared to petrol/diesel cars


would you care to back up that outrageous claim with an independant and respectable reference? because it sounds unlikely to my understanding of basic physics

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Re: BBC article on ludicrous cars

Postby pete75 » 3 Mar 2012, 1:33pm

A question to the OP and others making similar claims . Have you any evidence that Alex Wotke injures and kills people on the roads or drives dangerously? If you haven't I'd shut up - the man is obviously wealthy enough to afford an action for libel.

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Re: BBC article on ludicrous cars

Postby kwackers » 3 Mar 2012, 2:40pm

philg wrote:Fossil fuel power stations are about 33% efficient for coal, rising to around 50% for gas; from which you can subtract electrical losses from transmission through to the charger and battery/cable/motor losses.

A modern car diesel is around 35% so the is in fact little if any difference.

For *any* form of fuel a power station is much more efficient than a car engine. Which suggests we should be burning that fuel in a power station - not squandering it in cars!

In the interests of fairness, whilst you're dealing with losses in the electrical system don't forget to do the same for the diesel car. Those tyres don't get warm for no reason... Diesel cars are also pretty heavy and have no mechanism for recovering energy lost due to braking.

The real problem with electric cars is the demands they put on the grid. They'll simply push the price of electricity up and it'll end up being a cost born mainly by the poor in society. That's not to say there's no place for lightweight, low powered electrical vehicles, just that as a replacement for the modern car I think they're a bad idea.
A much better idea is to create a decent public transport system and wean people off the idea of private cars.

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Re: BBC article on ludicrous cars

Postby kwackers » 3 Mar 2012, 2:43pm

mark a. wrote:ALL of my points were based on the assumption that at no point does any driver break the speed limit. So if you want to overtake a car doing 30mph in a 60mph zone, then the RS6 can accelerate from 30-60mph quicker and so overtaking is safer.

30 - 60 in a Fiesta is no biggie. Plus if you're doing it properly you'll have left space between you and the car in front and used that to accelerate in before indicating and moving out. If by then something is coming you can still drop back in.
It's all just a timing thing.

Of course if people didn't brake the speed limit then my points would be moot. But we both live in the real world... ;-)

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philg
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Re: BBC article on ludicrous cars

Postby philg » 3 Mar 2012, 3:27pm

kwackers wrote:
philg wrote:Fossil fuel power stations are about 33% efficient for coal, rising to around 50% for gas; from which you can subtract electrical losses from transmission through to the charger and battery/cable/motor losses.

A modern car diesel is around 35% so the is in fact little if any difference.

For *any* form of fuel a power station is much more efficient than a car engine. Which suggests we should be burning that fuel in a power station - not squandering it in cars!


This disagrees with you
Typical thermal efficiency for electrical generators in the industry is around 33% for coal and oil-fired plants, and up to 50% for combined-cycle gas-fired plants. Plants designed to achieve peak efficiency while operating at capacity will be less efficient when operating off-design (i.e. temperatures too low.)

kwackers wrote:In the interests of fairness, whilst you're dealing with losses in the electrical system don't forget to do the same for the diesel car. Those tyres don't get warm for no reason... Diesel cars are also pretty heavy and have no mechanism for recovering energy lost due to braking

Yes, there are mechanical losses from engine to wheels - but not huge.

Li-ion battery packs are pretty heavy too - and if you want the 500 mile range of a 5 seater ICE car then currently prohibitively so (and expensive)

Regenerative braking systems are available to hybrid cars - I have no axe to grind on these, I was merely hoping to debunk the myth that (currently) EVs are green.

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Re: BBC article on ludicrous cars

Postby mark a. » 3 Mar 2012, 3:48pm

kwackers wrote:Plus if you're doing it properly you'll have left space between you and the car in front and used that to accelerate in before indicating and moving out.


Just to point that this isn't the proper way of doing it. The police / IAM say you should only accelerate only once you've pulled out.

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Re: BBC article on ludicrous cars

Postby kwackers » 3 Mar 2012, 4:09pm

philg wrote:
kwackers wrote:For *any* form of fuel a power station is much more efficient than a car engine. Which suggests we should be burning that fuel in a power station - not squandering it in cars!


This disagrees with you

Typical thermal efficiency for electrical generators in the industry is around 33% for coal and oil-fired plants, and up to 50% for combined-cycle gas-fired plants. Plants designed to achieve peak efficiency while operating at capacity will be less efficient when operating off-design (i.e. temperatures too low.)

In what way does it disagree?
Car engines by their mobile nature are not very efficient (incidentally the figure you quote for diesels is way above any I could find - all of which put the figure in the low to mid twenties).

My point is that a stationary diesel engine running at a constant RPM and with all the niceties that come from being static is far more efficient than a lightweight variable RPM engine as fitted to a car. This goes for any mechanism of fuel burning you can think of - it will always be more efficient to use it in a static system than a mobile one.

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philg
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Re: BBC article on ludicrous cars

Postby philg » 3 Mar 2012, 4:46pm

kwackers wrote:In what way does it disagree?
Car engines by their mobile nature are not very efficient (incidentally the figure you quote for diesels is way above any I could find - all of which put the figure in the low to mid twenties).


With this?

Even though diesel engines have a theoretical fuel efficiency of 75 percent, in practice it is lower. Engines in large diesel trucks, buses, and newer diesel cars can achieve peak efficiencies around 45 percent,[47] and could reach 55 percent efficiency in the near future.[48] However, average efficiency over a driving cycle is lower than peak efficiency. For example, it might be 37 percent for an engine with a peak efficiency of 44 percent.[49]


kwackers wrote:My point is that a stationary diesel engine running at a constant RPM and with all the niceties that come from being static is far more efficient than a lightweight variable RPM engine as fitted to a car. This goes for any mechanism of fuel burning you can think of - it will always be more efficient to use it in a static system than a mobile one.

That sounds like a good theory :)
But we were talking about electric generators, so you need to add the gearbox, alternator & HV gear losses before you even get out of the power station.
Last edited by philg on 3 Mar 2012, 4:50pm, edited 1 time in total.

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meic
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Re: BBC article on ludicrous cars

Postby meic » 3 Mar 2012, 4:47pm

mark a. wrote:
kwackers wrote:Plus if you're doing it properly you'll have left space between you and the car in front and used that to accelerate in before indicating and moving out.


Just to point that this isn't the proper way of doing it. The police / IAM say you should only accelerate only once you've pulled out.



We know what sorts of car they drive and what mpg figures they get. So they can do that sort of thing.
I suspect that they actually meant you should only accelerate when you are far enough out to have adequate visibility. Or you should only commit yourself to the overtake when you are pulled out.

If you could not accelerate before pulling out then we would end up with a lot of very long traffic lines as the safe clear space needed for an overtake would be much larger.
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