So that is it then....we all have to drive at 80 kph instead on 90 kph

[Chancer]

They are needed for a peaky high revving engine with a narrow power band (excludes diesels except poids lourds) but only for competition use, a good example was the modification to the Ford T9 5 speed box to the six speeds needed for the tuned 1.4 litre Rover engine in the 80's Caterham 7, without it it fell of the cam each upshift, since then its become de rigeur for road, ' properly spaced ratios with a direct 1:1 4th gear plus and overdrive 5th coupled with the correct final drive ratio is all that is needed for most vehicles, the Smart car may be an exception with a small capacity buzzy engine and come to think of it many of the modern 3 cylinder petrol engines as well.

 

A properly geared DSG vehicle transmission can make maximum use of its 6 gears if the software parameters are properly written, for most drivers leaving it to do its thing with the 6 ratios will bring better economy than if they operate the flappy paddles themselves.

[YCCMB]

Oddly, ALBF, I don't give a @£!? How fast your car goes, nor I if it goes faster than mine. In fact, I don't give a monkey's about cars in general, despite working in, or for the motor industry for quite a while.

If it has 4 wheels, an engine, a current MOT and no immediate chance of falling apart, I really don't care if it has a top speed of 40mph and is mocked and overtaken by every other car on the road. You see, for me a car is just a means of getting from one place to another without having to walk or use public transport. It's not a status symbol nor a means of indicating that my HP agreement is bigger than yours.

Most of all, I don't mind if the speed limit is 80, 90 or 500 Kph as long as the motorists on the road exercise a modicum of common sense, courtesy to other road users and safety.

[alittlebitfrench]

A GT Avalanche is a mountain bike. Drrrrrrr

How silly do you feel ???

[BritinBretagne]

[quote user="Chancer"]

[quote user="BritinBretagne"]My turbo petrol Golf is more economical at 90-100kmh on the open road than it is at 70-80. It’s fuel consumption is very sensitive to throttle opening. Driving in high gears at its maximum torque is the most fuel efficient.[/quote]

 

It may feel that way and you might want to believe it but all you need to do is travel the same stretch of road (same direction) twice repeatedly at the two speeds with your dash display set to instantaneous MPG or L/100kms to see the difference, I think we probably have the same engine and powertrain.

 

For over 10 years being potless forced me to drive everywhere at 80km/h max autoroutes included, as a former boy racer I hated it, I no longer need to do so and drive at 90 sometimes more on route departementales and between 110 and 130kp/h on the autoroutes, I did 160000 kms at the restricted speed and have done maybe 20K at the normal speed and my fuel consumption whilst still very good has increased significantly.

 

I dont wish to drive at 80km/h again except where I choose to do so according to conditions, it wound up far too many people but there is no denying that it is more economical, wind resistance increases at the square of road speed and whilst an engine is more efficient at peak torque that efficiency is power developed divided by fuel consumed, the actual fuel consumption is always higher at higher revs even if the vehicles rolling and wind resistance could ignore the laws of physics.

 

I used to get up to 74mpg on a long slow journey where time was no object, wanting to know the maximum I experimented, my vehicle will run at 48km/h on the flat on a closed throttle, cant call it cruising as it leans out, runs with the injectors shut down to 40km/h then lurches on a WOT to 48km/h but that is eaxctly the technique in a economy record attempt, the fuel consumption doing that goes over the 2 digits 99 mpg that can be displayed but tickling the throttle to maintain +/- 50km/h gives 99mpg, I have even done it late at night up the steep hill to the aéroport and back and the average was 99mpg, fun going uphill at 48km/h in 5th gear without any throttle input and not kind to the engine but I was bored!

 

So BnB I do agree with you regarding the maximum efficiency at peak torque, in terms of what it costs compared to how quickly you arrive somewhere (if that is of value to you) its the best value for money.

 

If driverless cars become mandatory in our lifetime we wont have any choice about what speed we travel at, others will have decided for us.

[/quote]

What arrogance. It’s not how it feels to me it’s what I’ve worked out during the 13 years I’ve owned and driven the. I can also tell you the effect of changing the aerodynamics of the car be it through having an empty ladder rack, roof box or even a cycle on a cycle rack. You are not the only person who takes notice of how things affect the performance of your car. I doubt that our cars share the same engine or transmission.

[alittlebitfrench]

What version Brit is your Golf GTi ?

Just out of interest....being a golf GTI fan.

[BritinBretagne]

[quote user="Chancer"]

Do any of your 6 speed planet destroyers, sorry eco vehicules, turn at less than 2500 rpm (petrol) or 2000 rpm (diesel) at 80km/h?

 

As someone that would once have known every fact and figure about pretty much every new vehicle I have become someone with no additional knowledge since I saw the light some 20+ years ago, I know the gearing is becoming and taller and I suspect that most 6 speeds are no more than a 5 sensible ratios and a stupid low one for the mandatory emissions and urban cycle fuel economy tests, they are done at what 35mph? so it stands to reason that all the 6 speeds apart from a Bugatti Veyron could be driven at that speed in the tallest ratio so would have no problem at all at 80km/h.

 

Like "listen to your body", use a holistic approach, listen to your engine and your sensory inputs and you should have no need for silly indicators to tell you what gear you should be in, they are intended for people driving whilst using all the in built connectivity which seems to be the mainstay of all modern car advertising[:'(]

[/quote]

My car is turning at just over 1500 rpm at 80kmh. It will pull from that speed up to its maximum speed in sixth gear and is significantly faster in sixth than fifth, it is the normal top gear not an overdrive.

[BritinBretagne]

A MarkV.

[richard51]

Can you explain as you say how going at max torque (ie pulling like mad) is going to be more fuel economic?

[richard51]

ALBF was trying to be funny by saying how small Smart cars are.

However, as another example Skoda owners also got lots of stick once, but the last laugh was really on Volkswagen owners as Skodas had lots of VW parts but were at lots less price!

[BritinBretagne]

[quote user="richard51"]Can you explain as you say how going at max torque (ie pulling like mad) is going to be more fuel economic?[/quote]

It’s where the engine is most efficient, with my car at about 1800 rpm. Above that engine speed although the power increases the torque falls away.

[alittlebitfrench]

[quote user="BritinBretagne"]A MarkV.[/quote]

Once upon a time there was this guy that gave me loads of grief. Not that it bothered me.

This person lived and worked in Germany. Ring any bells ?

He knew the Vosges region of France and had been to Natzweiler-Struthof. Any more bells ?

He dove a Golf GTI Mk V. It can't be coincidence ....can it ?

This person lived in the Limousin but not Brittany. But I remember someone saying they wanted to move from Brittany to the Limousin. This is all very confusing.

Anyway, he did not like PVC windows on old buildings. Do you like PVC windows on old buildings Brit ?

There is a weird place where I joined once where ugly people post pictures of themselves talking about how bad France is.

Chancer is now scratching his head trying to work out what the hell is going on ?

[richard51]

See this as well as description of torque previously quoted.

https://www.physicsforums.com/threads/gasoline-engine-max-torque-and-efficency.750298/

With your spec I suspect that your car is not "easy on the gas".

Bottom line is that there is a big difference between efficiency and economy.

look at response of jnnx (last one). Common sense really.

[richard51]

ALBF - you talk in riddles and are diverting from a serious topic. The previous diversion to fuel economy is important as really that goes with the safety issue - (environment etc!)

That is in IMHO. (definitely humble!)

NB I do appreciate that you started the thread but hey do keep to the subject (ish)

[BritinBretagne]

Me? I love modern double glazed windows. With the crap weather we’ve had recently they’re about all that’s keeping me sane. Them, the central heating and the TV.

[BritinBretagne]

Efficiency and economy go together. In normal use my car spends a lot of time in higher gears relying on the torque of the engine rather than its power.

I don’t understand what you mean by easy on the gas.

[richard51]

No they don't in this case- please read the reference I gave to understand the definitions.

"easy on the gas" is an americanism for not using too much fuel. Perhaps I should have been more forthright in my comment.

I have no doubt you have more technical knowledge than I about engines but you are trying to defend the indefensible.

[richard51]

""Max thermal efficiency (power output / potential power input based on fuel consumption rate) is usually highest at rpm of max torque. The issue is that most engines are producing more power at peak torque rpm than what a car needs for crusing speeds, and at higher speeds, since the drag increases with speed^2, then power loss increases with speed^3 (power loss = drag x speed). For a typical car, best fuel milage occurs around 60 kph to 80 kph. I'm not sure, but in a situation such as going uphill at some fixed speed, shifting to a lower gear and running at higher rpms may be more efficient (distance covered versus fuel consumed) than running in a higher gear at lower rpm and having to use a lot more throttle input.""

Reference https://www.physicsforums.com/threads/gasoline-engine-max-torque-and-efficency.750298/

Surely you cant disagree with this extract.

The other bits are equally logical.

[YCCMB]

ALBF...I'll be honest, I had no idea. However, possibly the only thing that sends me to sleep faster than car bores is bicycle bores. And I'm married to one and spawned another, so I'm well placed to know just how boring they are.?

So, far from feeling silly, I'm feeling accomplished. It means I haven't somehow osmotically absorbed any of the crap I have to listen to about bikes OR cars.

[BritinBretagne]

[quote user="richard51"]""Max thermal efficiency (power output / potential power input based on fuel consumption rate) is usually highest at rpm of max torque. The issue is that most engines are producing more power at peak torque rpm than what a car needs for crusing speeds, and at higher speeds, since the drag increases with speed^2, then power loss increases with speed^3 (power loss = drag x speed). For a typical car, best fuel milage occurs around 60 kph to 80 kph. I'm not sure, but in a situation such as going uphill at some fixed speed, shifting to a lower gear and running at higher rpms may be more efficient (distance covered versus fuel consumed) than running in a higher gear at lower rpm and having to use a lot more throttle input.""

Reference https://www.physicsforums.com/threads/gasoline-engine-max-torque-and-efficency.750298/

Surely you cant disagree with this extract.

The other bits are equally logical.[/quote]

I can and do disagree. You are missing one important word from my first post, turbo. It is not a normally aspirated engine. The turbo produces a lot of torque low down where it is useful. Sorry. It is not easy on the gas, quite the opposite if driven hard, it is a high performance engine not an economy model.

[Gardian]

All this ‘thermal efficiency’, ‘torque’ etc is all (not) very interesting, but it digresses from the original point of the thread.

Typical Parisian law & mindset. We’ll reduce the speed limit = fewer deaths. All those country folk will reduce their speed, so everything will be fine.

Bonkers ! In my (dare I say it, informed opinion) it won’t make a jot of difference to some of the locals driving behaviour on the little local roads, where there won’t be any speed cameras and they’ll continue to cut blind corners etc. That’s where so many fatal accidents sadly occur.

[BritinBretagne]

[quote user="Gardian"]All this ‘thermal efficiency’, ‘torque’ etc is all (not) very interesting, but it digresses from the original point of the thread.

Typical Parisian law & mindset. We’ll reduce the speed limit = fewer deaths. All those country folk will reduce their speed, so everything will be fine.

Bonkers ! In my (dare I say it, informed opinion) it won’t make a jot of difference to some of the locals driving behaviour on the little local roads, where there won’t be any speed cameras and they’ll continue to cut blind corners etc. That’s where so many fatal accidents sadly occur.[/quote]

It does not digress from the topic. It is important when considering the effect of the speed limit change on real life driving.

[idun]

As soon as I moved to France, my feeling was that the only place the french felt completely 'free' was in their cars, where they did anything they wanted, including having horrific death figures. And in spite of the odd campaign, ie drapeau blanc etc, little changed.

Then the authorities started getting more severe and people do in general drive slower and stick to speed limits far more than I ever expected them to. The change in comportment though has had a side effect, at least where I used to live and that is that they are more aggressive with regards to their space, ie will not let buses out etc which they always did.

Cars, love driving, but cars per se do not interest me at all, as long as they work when I want and have a modicum of comfort, I say modicum, as I have friends with very expensive cars and some with cheap ones and none are really comfortable.

Re this speed limit, well, it is such a boring speed to drive at that I think it is nonsense. I know that driving slower is more economic, as one winter we drove from St Malo as far as just south of Dijon at about 50kph sometimes less on the autoroute,  in horrible snowy conditions and our fuel consumption was very low. That we had arrived home a day earlier though would have been lovely!

[richard51]

A turbo forces more air and proportionately more fuel into the chamber. Ok efficiency might also marginally increase but arguments previously presented still remain valid.

Isn't the issue about reducing speed also to do with the decreased probability (and I don't want to get involved in the maths or stats) of serious injuries if a person is hit at a lower speed . Doesn't this outweigh the drivers/passengers "comforts" or a few minutes extra on a journey. For longer journeys on motorways the speed limit is still high and there is less likelihood of pedestrians to be hit.

[BritinBretagne]

[quote user="richard51"]A turbo forces more air and proportionately more fuel into the chamber. Ok efficiency might also marginally increase but arguments previously presented still remain valid.

Isn't the issue about reducing speed also to do with the decreased probability (and I don't want to get involved in the maths or stats) of serious injuries if a person is hit at a lower speed . Doesn't this outweigh the drivers/passengers "comforts" or a few minutes extra on a journey. For longer journeys on motorways the speed limit is still high and there is less likelihood of pedestrians to be hit.[/quote]

The turbo completely changes the characteristics of the engine, as I pointed out before this results in a lot of low down torque which allows the relatively small car to be fuel efficient at 90 to 100kmh when it is producing maximum torque and able to drive comfortably in its highest gear.

[andyh4]

Like Gardian, I see little or no opportunity for any improvements round here. Unless I have been doing a significant amount of motorway driving (which these days tends to be 4 or 5 times per year) my average speed on journeys is likely to be around 40-45kph. The roads simply do not allow faster driving. If I drive the 40+km down to the Rhone valley, there are 4 stretches (about a total of 3 - 3.5km) where I can get speed up to 90kph. The rest is slow going bend after bend or through a couple of villages with 50 or 70kph speed limits.

The idiots with their sixth sense radar that allows them to see round corners will still drive like maniacs.