Fast Economical Car

Squall19

So they are talking about speed limits going up in the UK and maybe even some parts being unrestricted like the autobahn in Germany.

I'm all for higher speed limits, but why do petrols cars in particular have such short gear ratios.

I regularly hit over 100mph on a stretch of empty motorway and in my modern car it feels completely safe.

So why don't car manufacturers make an overdrive or a tall upper ratios on gearboxes, so that the car can be idling at 100mph, hence returning about great mpg at high speed.

My Mazda 3 bounces off 155mph easily, but it's gear ratio's are so short that in 6th it's screaming and taking an incredible amount of fuel.

I have slowed down especially on motorways because I have seen the vast difference it has made to fuel economy.

But it's not just my Mazda, I had 1.6 TDCI Focus as a rental car in Poland and it drank fuel as well at high speeds.

Would love to see an engine that can dish out enough power to idle and cut through the air at 120mph and return good mpg.

All the eco cars still drink the fuel at high speeds.

Anyone out there care to do the sums?

Just how much power do you need to propel the average family car at this speed and therefore working on the typical engine efficency just how much fuel is required etc.

stimpson

Drag (wind resistance) increases proportionally to the square of the speed so you will consume exponentially more fuel at higher speeds. Gear ratios aren't the problem.

x in the city

Squall19 wrote: »

So they are talking about speed limits going up in the UK and maybe even some parts being unrestricted like the autobahn in Germany.

I'm all for higher speed limits, but why do petrols cars in particular have such short gear ratios.

I regularly hit over 100mph on a stretch of empty motorway and in my modern car it feels completely safe.

So why don't car manufacturers make an overdrive or a tall upper ratios on gearboxes, so that the car can be idling at 100mph, hence returning about great mpg at high speed.

My Mazda 3 bounces off 155mph easily, but it's gear ratio's are so short that in 6th it's screaming and taking an incredible amount of fuel.

I have slowed down especially on motorways because I have seen the vast difference it has made to fuel economy.

But it's not just my Mazda, I had 1.6 TDCI Focus as a rental car in Poland and it drank fuel as well at high speeds.

Would love to see an engine that can dish out enough power to idle and cut through the air at 120mph and return good mpg.

All the eco cars still drink the fuel at high speeds.

Anyone out there care to do the sums?

Just how much power do you need to propel the average family car at this speed and therefore working on the typical engine efficency just how much fuel is required etc.

155mph...:rolleyes:

good economy at 120mph

am i missing out here...?

Squall19

Its kinda of future question alright for ous here in Ireland x in the city

German's have it now though:)

Good point on the wind stimpson.

I would love to see a car that has the power to be barely ticking over in idle and cutting through the air at 120mph and return good mpg.

Can any car do that?

Can a modern BMW/Audi etc V10 8 speed turbo diesel do it.

Alanstrainor

Friction's a bitch. No engine is ever going to change that!

x in the city

Squall19 wrote: »

Its kinda of future question alright for ous here in Ireland x in the city

German's have it now though:)

Good point on the wind stimpson.

I would love to see a car that has the power to be barely ticking over in idle and cutting through the air at 120mph and return good mpg.

Can any car do that?

Can a modern BMW/Audi etc V10 8 speed turbo diesel do it.

BMW 330d can do it (155mph)

and give you almost 50mpg

makes me want to say bye bye to petrol and make a brave move to a diesel..

x in the city

Squall19 wrote: »

Its kinda of future question alright for ous here in Ireland x in the city

German's have it now though:)

Good point on the wind stimpson.

I would love to see a car that has the power to be barely ticking over in idle and cutting through the air at 120mph and return good mpg.

Can any car do that?

Can a modern BMW/Audi etc V10 8 speed turbo diesel do it.

http://www.autotrader.co.uk/classified/advert/201118386485399/sort/priceasc/usedcars/maximum-age/up_to_4_years_old/body-type/coupe/transmission/manual/engine-size-cars/3l_to_3-9l/fuel-type/diesel/model/3_series/make/bmw/radius/1501/postcode/kw147dh/page/1?logcode=p

unkel

x in the city wrote: »

BMW 330d can do it (155mph)

and give you almost 50mpg

Not at 155mph, lad

You wouldn't even see 10MPG...

@OP - you need a car with a very good drag coefficient, which has an overdrive. The new 911 (dunno if the drag is that good) has a 7 speed manual box, with the top gear specifically added for low rpm / low fuel consumption at speed. An ueber over drive

MugMugs

You need a Flux Capictor and one of these. You can run it off your domestic waste with the upgrade and even nip back to see your own birth (which could be a bit weird)

tossy

50mpg at 155 mph?? if i pressed the H and A buttons on my keyboard the amount of times necessary to express my amusement at that statement i would surely break it

Waterford26

mondeo st 2,2 tdci

TestTransmission

Waterford26 wrote: »

mondeo st 2,2 tdci

What about it?

Chriscl1

Squall19 wrote: »

I would love to see a car that has the power to be barely ticking over in idle and cutting through the air at 120mph and return good mpg.

Can any car do .

Monaro vxr 500 has very long gears, can do 70 mph in 1st so I imagine in 6th it wouldn't take too many rpm to top the ton.

TestTransmission

Chriscl1 wrote: »

Monaro vxr 500 has very long gears, can do 70 mph in 1st so I imagine in 6th it wouldn't take too many rpm to top the ton.

and the good mpg part?

mullingar

As the second poster stated, its DRAG/wind resistance.

When you double your speed, the drag quadruples and the fuel demand is also proportional by quadrupling.

strife

x in the city wrote: »

BMW 330d can do it (155mph)

and give you almost 50mpg

makes me want to say bye bye to petrol and make a brave move to a diesel..

http://auto.howstuffworks.com/fuel-efficiency/fuel-economy/aerodynamics.htm

Impossible to get 50MPG while doing 155MPH :rolleyes:

Gophur

Isaac Newton would have trouble getting a Mazda 3 to 155mph, and that's pushing it over a cliff!

tossy

Gophur wrote: »

Isaac Newton would have trouble getting a Mazda 3 to 155mph, and that's pushing it over a cliff!

That was the other funny statement

Drag is a bitch,i remember reading somewhere that a Veyron uses 300/400BHP to get to 200mph and the rest to carrier it to its top speed*

*not exact figures.

EPM

Gophur wrote: »

Isaac Newton would have trouble getting a Mazda 3 to 155mph, and that's pushing it over a cliff!

An MPS has a top speed of 250km/h which is 155mp/h in old money.

Atomic Pineapple

Gophur wrote: »

Isaac Newton would have trouble getting a Mazda 3 to 155mph, and that's pushing it over a cliff!

http://www.carfolio.com/specifications/models/car/?car=195756

Top speed 250 km/h (155 mph)

Waterford26

TestTransmission wrote: »

What about it?

fast enought, comfortable, and economical too

heate

I recently went looking for a replacement for my car - I've a 745d that I have seen 11.5l/100km on the flat at 180km/h.
I test drove a 535d with the 8 speed auto , at 180km/h the car slotted in 8th and the revs sat under 3k. The car was doing 7.8l/100km at between 170-200km/h (the traffic on the autobahn was heavy in spots)
Big diesels with lots of torque and hp will pull along nicely at serious speeds because they are not under much stress.
As for replacing my car - well I can't really decide I don't need a diesel as its not a requirement for reimbursement for business mileage anymore.

Mycroft H

Fast or economical.

Choose one.

Victor Meldrew

heate wrote: »

The car was doing 7.8l/100km at between 170-200km/h
Big diesels with lots of torque and hp will pull along nicely at serious speeds because they are not under much stress.

Pictures or GTFO....:rolleyes:

at 200km/h there is no way that you are getting that. It may show that intermittently as you lift off or as the cruise control cycles, but not over a distance. Simply too much wind resistance..

pajo1981

stimpson wrote: »

Drag (wind resistance) increases proportionaly to the cube of the speed so you will consume exponentially more fuel at higher speeds. Gear ratios aren't the problem.

Don't mean to be an asshole, but drag is actually proportional to speed squared. Power is proportional to speed cubed.

ed: Also, exponential is not the same as cubic.

x in the city

unkel wrote: »

Not at 155mph, lad

You wouldn't even see 10MPG...

@OP - you need a car with a very good drag coefficient, which has an overdrive. The new 911 (dunno if the drag is that good) has a 7 speed manual box, with the top gear specifically added for low rpm / low fuel consumption at speed. An ueber over drive

i never said it would do 50mpg @ 155mph.

not sure what average speed was used for 50mpg...

x in the city

strife wrote: »

http://auto.howstuffworks.com/fuel-efficiency/fuel-economy/aerodynamics.htm

Impossible to get 50MPG while doing 155MPH :rolleyes:

i was just referring to the BMW claimed max speed and average mpg

of course it wont do 50mpg @ that speed...jeebus

x in the city

EPM wrote: »

An MPS has a top speed of 250km/h which is 155mp/h in old money.

dont fancy being inside a mazda 3 @ 155mph

mps or not.

Mr Benevolent

In general most cars will be as max fuel efficient speed between 35-50mph and it'll drop off from there. At 100mph most cars will get 20mpg and 155mph you're going to see 10mpg or less.

heate

Victor Meldrew wrote: »

heate wrote: »

The car was doing 7.8l/100km at between 170-200km/h
Big diesels with lots of torque and hp will pull along nicely at serious speeds because they are not under much stress.

Pictures or GTFO....:rolleyes:

at 200km/h there is no way that you are getting that. It may show that intermittently as you lift off or as the cruise control cycles, but not over a distance. Simply too much wind resistance..

I don't know about you but taking pictures at between 170-200km/h with the salesman in the passenger seat isnt exactly wise.
The average consumption at reset showed at 7.8l/100km - you're not going to get that everyday at those speeds and the computer isn't accurate.
What I was getting at is that anything below 11l 100/km is quite 'economical'. The focus isn't on economy as such it's about being able to drive large distances without having to slow down pull of into services to refuel.

txpjl

BX 19 wrote: »

Fast or economical.

Choose one.

In this country, we need both. Least I do

Anan1

heate wrote: »

I don't know about you but taking pictures at between 170-200km/h with the salesman in the passenger seat isnt exactly wise.
The average consumption at reset showed at 7.8l/100km - you're not going to get that everyday at those speeds and the computer isn't accurate.
What I was getting at is that anything below 11l 100/km is quite 'economical'. The focus isn't on economy as such it's about being able to drive large distances without having to slow down pull of into services to refuel.

Can we take this as an admission that you weren't in fact getting 7.8l/100km at 170-200km/h?;)

heate

An admission? I reset the trip as i was entering the A5, hit the accelerator and set the cruise at 200km/h - there were other cars in front of me the dynamic cruise took account for this and was slowing me and again speeding me back up - we were out for the best part of an hour.
The trip said 7.8 when i went to pull off and turn around I would say it was using a little more than that (the computers are not intrinsically accurate ASFAIK).
I found that the 8 speed gearbox has a huge effect on high speed economy

stimpson

pajo1981 wrote: »

Don't mean to be an asshole, but drag is actually proportional to speed squared. Power is proportional to speed cubed.

ed: Also, exponential is not the same as cubic.

You're not an asshole - just a square

OK - drag is proportional to speed squared - power (and therefore fuel consumption) is cubed. I didn't bother to look it up.

But cubic is exponential. It's to the power of 3, 3 being the exponent.

http://en.wikipedia.org/wiki/Exponential_growth

BrianD3

7.8 l/km at 180 km/h in an 8 speed 535d doesn't sound too outlandish to me. That's 36 mpg. The car's official extra urban figure is 58.9 mpg.

Autocar got 55 mpg from a diesel S class on a 200 mile Autobahn run.
http://www.autocar.co.uk/CarReviews/FirstDrives/Mercedes-Benz-S-Class-S250-CDI/257143/

Doesn't say what speed they did but it is fairly likely they weren't dawdling along at 80 km/h.

PS I have always found fuel computers in cars to be pretty accurate.

unkel

Very impressive figures, heate. Even if the speedo is overreading and the OBC can not be trusted. That said, there is a massive difference in doing 170km/h or 250km/h. As in using 2 - 3 times as much fuel at a guess.

heate

unkel wrote: »

Very impressive figures, heate. Even if the speedo is overreading and the OBC can not be trusted. That said, there is a massive difference in doing 170km/h or 250km/h. As in using 2 - 3 times as much fuel at a guess.

Though speedo's tend to over read I think I may be right in saying that systems like ACC and having a fully digital dash combat this issue - or is it still in place for legal purposes.

unkel

It's still in place for legal reasons. 180km/h on the speedo is legally anything between 160km/h and 180km/h in real speed

pajo1981

stimpson wrote: »

You're not an asshole - just a square

OK - drag is proportional to speed squared - power (and therefore fuel consumption) is cubed. I didn't bother to look it up.

But cubic is exponential. It's to the power of 3, 3 being the exponent.

http://en.wikipedia.org/wiki/Exponential_growth

I didn't look it up either - I just knew it

On exponentials:

Cubic: y=x^3
Exponential: y=e^x

Two completely different relationships.

ed: check out your own link!

stimpson

pajo1981 wrote: »

I didn't look it up either - I just knew it

On exponentials:

Cubic: y=x^3
Exponential: y=e^x

Two completely different relationships.

ed: check out your own link!

Meh. You can use facts to prove anything that's even remotely true.

Tea 1000

x in the city wrote: »

dont fancy being inside a mazda 3 @ 155mph

mps or not.

That's because you're thinking like a narrow-minded person.
Why wouldn't a Mazda be as stable at 155 as anything else from another manufacturer? If you have decent suspension on a car with good wheels and aerodynamics that don't make it unstable, then it doesn't matter what badge is on the nose!

superfish

ive the yaris t sport 1.5 vvti 0 to 60 in 8.7 seconds and does 40 mpg easily ive also a celica ss3 2.0 beams 220bhp 0 to 60 in 7.2 mpg around 33mpg, yaris cost 50 euro for a full tank and celica cost 75 the yaris is nippy in the lower gears where as the celica is better in higher gears.

heate

Tea 1000 wrote: »

x in the city wrote: »

dont fancy being inside a mazda 3 @ 155mph

mps or not.

That's because you're thinking like a narrow-minded person.
Why wouldn't a Mazda be as stable at 155 as anything else from another manufacturer? If you have decent suspension on a car with good wheels and aerodynamics that don't make it unstable, then it doesn't matter what badge is on the nose!

Well other than the 155mph gentlemans agreement made by the auto industry; manufacturers rarely limit the top speed of their cars.
I've been in cars whose v/max stands at 140odd - and you hit 120ish and your head just goes holy crap this isn't safe - other cars designed for high speed are quite relaxing leaving the driver to concentrate on the road an not if the is going to implode - as for the mps I've no clue how it would be at speed like that.

Matt Simis

Tea 1000 wrote: »

That's because you're thinking like a narrow-minded person.
Why wouldn't a Mazda be as stable at 155 as anything else from another manufacturer? If you have decent suspension on a car with good wheels and aerodynamics that don't make it unstable, then it doesn't matter what badge is on the nose!

I have no idea on the 3/MPS, but obviously some cars are better than others at this speed. Generally cars from a country where such speeds are legal and the norm are, logically, going to excel at this.

Again, Im sure the Mazda is reasonable, but to say that all cars kinda perform similar at 250kph is obviously not true. For example the Alfa we have not only wouldnt reach this speed, I wouldnt feel it safe to do so. Thats with premium tyres, uprated Koni suspension, good wheels and a well running car. Given its lightweight and unfavourable gearing it would feel floaty and dangerous.

The recent Mazda I have been in felt totally stable at 160kph by comparison, but I dont think that would carry through to 250.