Cutting speed limits for cleaner air?
Discussion
Evanivitch said:
Pan Pan Pan said:
Are you serious?. Most modern cars have very low drag coefficients, and every vehicle has an optimum speed at which it can travel, covering the most distance at its optimum speed.
50 mph is not, let me repeat that, not an optimum speed for most of the vehicles on UK roads, especially for those who must cover long distances, Artificially limiting speed to 50mph is not going to change emissions from UK vehicles very much from a vehicle doing 70 mph.
For a given journey artificially limiting a vehicles speed below its optimum speed means it will have to run for another half hour to cover the same distance If you were talking about speed well above a vehicles optimum speed, you might have a point, but that is not what is being discussed.
This suggested 50 mph limit is just another snide attempt by some, to make the whole point of car use less desirable or useful to the majority of road users, and would do virtually nothing if anything to change emissions from cars, Only a drastic reduction in the number of cars on UK roads would do that, but perhaps that is what you want to happen, are you anti car?
At what point does the aerodynamic resistance and friction on a car decrease at a greater speed?50 mph is not, let me repeat that, not an optimum speed for most of the vehicles on UK roads, especially for those who must cover long distances, Artificially limiting speed to 50mph is not going to change emissions from UK vehicles very much from a vehicle doing 70 mph.
For a given journey artificially limiting a vehicles speed below its optimum speed means it will have to run for another half hour to cover the same distance If you were talking about speed well above a vehicles optimum speed, you might have a point, but that is not what is being discussed.
This suggested 50 mph limit is just another snide attempt by some, to make the whole point of car use less desirable or useful to the majority of road users, and would do virtually nothing if anything to change emissions from cars, Only a drastic reduction in the number of cars on UK roads would do that, but perhaps that is what you want to happen, are you anti car?
So say 50mph was the optimum speed for a car. Over 100 miles, would it use more or less fuel than travelling at 25mph? Broad terms, no need to reach into BSFC.
Where do you want to stop? when we have got back to the man walking in front of every car with a red flag?
Pan Pan Pan said:
Evanivitch said:
Pan Pan Pan said:
Are you serious?. Most modern cars have very low drag coefficients, and every vehicle has an optimum speed at which it can travel, covering the most distance at its optimum speed.
50 mph is not, let me repeat that, not an optimum speed for most of the vehicles on UK roads, especially for those who must cover long distances, Artificially limiting speed to 50mph is not going to change emissions from UK vehicles very much from a vehicle doing 70 mph.
For a given journey artificially limiting a vehicles speed below its optimum speed means it will have to run for another half hour to cover the same distance If you were talking about speed well above a vehicles optimum speed, you might have a point, but that is not what is being discussed.
This suggested 50 mph limit is just another snide attempt by some, to make the whole point of car use less desirable or useful to the majority of road users, and would do virtually nothing if anything to change emissions from cars, Only a drastic reduction in the number of cars on UK roads would do that, but perhaps that is what you want to happen, are you anti car?
At what point does the aerodynamic resistance and friction on a car decrease at a greater speed?50 mph is not, let me repeat that, not an optimum speed for most of the vehicles on UK roads, especially for those who must cover long distances, Artificially limiting speed to 50mph is not going to change emissions from UK vehicles very much from a vehicle doing 70 mph.
For a given journey artificially limiting a vehicles speed below its optimum speed means it will have to run for another half hour to cover the same distance If you were talking about speed well above a vehicles optimum speed, you might have a point, but that is not what is being discussed.
This suggested 50 mph limit is just another snide attempt by some, to make the whole point of car use less desirable or useful to the majority of road users, and would do virtually nothing if anything to change emissions from cars, Only a drastic reduction in the number of cars on UK roads would do that, but perhaps that is what you want to happen, are you anti car?
So say 50mph was the optimum speed for a car. Over 100 miles, would it use more or less fuel than travelling at 25mph? Broad terms, no need to reach into BSFC.
Where do you want to stop? when we have got back to the man walking in front of every car with a red flag?
What car is it?
TheDrBrian said:
Why would any manufacture design a car with a peak efficiency is illegal to use in every country ?
What car is it?
My E60 530d achieved an absolute maximum of 39mpg in the uk driving at 70-75mph. Now I’m in Germany same car is averaging 41mpg. Same tyres, same everything, only difference is average speed has increased 30mph. (Average in uk is 55 and in Germany 85),What car is it?
I think the root causes of this are that it is tuned to be efficient at 2krpm for the German market (which is 85 mph or 140km/h) and that in Germany there is much more consistency to the velocity.
In the UK it is almost impossible to get a 70mph cruise as lorries are continuously overtaking. Whereas in Germany on busy roads or peak times they’re simply banned from overtaking. To the point where lorries are crawling up hill in lane 1 and lanes 2 and 3 are flowing clear at 130km/h.
Apart from having to drive at 50mph the bit of all this that I find most frustrating is the analysis, evidence and justification is not put in the public domain.
As a result of this it cannot be scrutinised and generally understood so people see why. All we get is a headline and mostly a lot of frustrated people because it looks like a dictatorial order which annoys people no end.
As a result of this it cannot be scrutinised and generally understood so people see why. All we get is a headline and mostly a lot of frustrated people because it looks like a dictatorial order which annoys people no end.
I've just driven parallel to the extended M4 Port Talbot 50 mph limit and the most incredible thing occurred to me...
The A48 dual carriageway in Baglan that runs parallel to the M4 is still 70, as is the A48/M4 on-slip east bound!
So say 50mph was the optimum speed for a car. Over 100 miles, would it use more or less fuel than travelling at 25mph? Broad terms, no need to reach into BSFC.The optimum speed for my car is 75mph. Optimum speed means that which allows it to cover the greatest distance for the lest amount of fuel. but let`s keep it legal and say the optimum speed is 70mph. At this speed I can technically cover a distance of 100 miles in 1 hour twenty minutes. If I did the same journey at 50 mph it would take another 25 minutes to cover the same distance. That means the engine is burning fuel for another 25 minutes, after the car which did 70mph has been switched off, If I drive faster than the optimum speed for my car, I burn more fuel, If I drive well below the optimum speed at 50mph, I burn more fuel, not least because at 50mph I would have to be continually changing from 4th to top and back again to keep the engine revs in a comfortable range, not forgetting that as above I would have to keep the engine running for another 25 minutes to reach the same destination. So any overall effects on fuel burned and emissions between a car doing 70mph and one doing 50, are going to be small, but will make the journeys for those who do long distances tedious and inefficient, with the attendant negative effect on peoples time, businesses deliveries etc.
Where do you want to stop? when we have got back to the man walking in front of every car with a red flag?Oh wow.
You actually genuinely believe that travelling to a destination faster is more efficient?
If I did 50 MPG at 50 mph, and just say I did 45 MPG (being kind) at 75mph. Say I travelled 50 miles, who would use more fuel?
The A48 dual carriageway in Baglan that runs parallel to the M4 is still 70, as is the A48/M4 on-slip east bound!
Pan Pan Pan said:
Evanivitch said:
Pan Pan Pan said:
Are you serious?. Most modern cars have very low drag coefficients, and every vehicle has an optimum speed at which it can travel, covering the most distance at its optimum speed.
50 mph is not, let me repeat that, not an optimum speed for most of the vehicles on UK roads, especially for those who must cover long distances, Artificially limiting speed to 50mph is not going to change emissions from UK vehicles very much from a vehicle doing 70 mph.
For a given journey artificially limiting a vehicles speed below its optimum speed means it will have to run for another half hour to cover the same distance If you were talking about speed well above a vehicles optimum speed, you might have a point, but that is not what is being discussed.
This suggested 50 mph limit is just another snide attempt by some, to make the whole point of car use less desirable or useful to the majority of road users, and would do virtually nothing if anything to change emissions from cars, Only a drastic reduction in the number of cars on UK roads would do that, but perhaps that is what you want to happen, are you anti car?
At what point does the aerodynamic resistance and friction on a car decrease at a greater speed?50 mph is not, let me repeat that, not an optimum speed for most of the vehicles on UK roads, especially for those who must cover long distances, Artificially limiting speed to 50mph is not going to change emissions from UK vehicles very much from a vehicle doing 70 mph.
For a given journey artificially limiting a vehicles speed below its optimum speed means it will have to run for another half hour to cover the same distance If you were talking about speed well above a vehicles optimum speed, you might have a point, but that is not what is being discussed.
This suggested 50 mph limit is just another snide attempt by some, to make the whole point of car use less desirable or useful to the majority of road users, and would do virtually nothing if anything to change emissions from cars, Only a drastic reduction in the number of cars on UK roads would do that, but perhaps that is what you want to happen, are you anti car?
So say 50mph was the optimum speed for a car. Over 100 miles, would it use more or less fuel than travelling at 25mph? Broad terms, no need to reach into BSFC.
Where do you want to stop? when we have got back to the man walking in front of every car with a red flag?
You actually genuinely believe that travelling to a destination faster is more efficient?
If I did 50 MPG at 50 mph, and just say I did 45 MPG (being kind) at 75mph. Say I travelled 50 miles, who would use more fuel?
I've tried different diff's on the same car in the past, on my old E30, and the difference in fuel economy depending on revs was not noticeable in my case. I had a diesel style diff doing 1500rpm at 70 and shorter diffs doing 2500-3000 and it made sod all difference to mpg. Obviously if you were doing 70mph in 2nd bouncing off the limiter you'd notice but talking about little differences in gearing making a bigger difference than a massive increase in drag is rediculous in my oppinion.
Evanivitch said:
Willy Nilly said:
Effeciency and economy aren't the same thing though.
Semantics. Both the ratio of fuel used to useful work.That may be power, it may be distance travelled.
Willy Nilly said:
I was under the impression that engines convert fuel to useful work best at peak torque. Look at the damage pottering about is doing to diesel engines
Which is why we have gearboxes, to keep engines at their optimum rev position for what we desire.My 100hp bike does about 52mpg, my 100hp car does about 48, so which is the most efficient?
Efficiency is grams of fuel used per kilowatt hour and AFAIK the Rolls Royce Trent 900 turbo fans do about 190g/kw/hr, which is good and I believe the Warsila R96 Flex ship engines are about as good.
Here is the test data for my company vehicle https://tractortestlab.unl.edu/documents/Massey%20... where is the one for my car? There isn't one. Note how the company vehicle is more efficient at full load, it's using a lot of fuel, but doing a lot of work.
Evanivitch said:
I've just driven parallel to the extended M4 Port Talbot 50 mph limit and the most incredible thing occurred to me...
The A48 dual carriageway in Baglan that runs parallel to the M4 is still 70, as is the A48/M4 on-slip east bound!
So say 50mph was the optimum speed for a car. Over 100 miles, would it use more or less fuel than travelling at 25mph? Broad terms, no need to reach into BSFC.The optimum speed for my car is 75mph. Optimum speed means that which allows it to cover the greatest distance for the lest amount of fuel. but let`s keep it legal and say the optimum speed is 70mph. At this speed I can technically cover a distance of 100 miles in 1 hour twenty minutes. If I did the same journey at 50 mph it would take another 25 minutes to cover the same distance. That means the engine is burning fuel for another 25 minutes, after the car which did 70mph has been switched off, If I drive faster than the optimum speed for my car, I burn more fuel, If I drive well below the optimum speed at 50mph, I burn more fuel, not least because at 50mph I would have to be continually changing from 4th to top and back again to keep the engine revs in a comfortable range, not forgetting that as above I would have to keep the engine running for another 25 minutes to reach the same destination. So any overall effects on fuel burned and emissions between a car doing 70mph and one doing 50, are going to be small, but will make the journeys for those who do long distances tedious and inefficient, with the attendant negative effect on peoples time, businesses deliveries etc.
Where do you want to stop? when we have got back to the man walking in front of every car with a red flag?Oh wow.
You actually genuinely believe that travelling to a destination faster is more efficient?
If I did 50 MPG at 50 mph, and just say I did 45 MPG (being kind) at 75mph. Say I travelled 50 miles, who would use more fuel?
The one who would have to run their engine for almost another half an hour to get to the same destination, and at a speed that does not allow the engine to run in its most fuel efficient rev range. The A48 dual carriageway in Baglan that runs parallel to the M4 is still 70, as is the A48/M4 on-slip east bound!
Pan Pan Pan said:
Evanivitch said:
Pan Pan Pan said:
Are you serious?. Most modern cars have very low drag coefficients, and every vehicle has an optimum speed at which it can travel, covering the most distance at its optimum speed.
50 mph is not, let me repeat that, not an optimum speed for most of the vehicles on UK roads, especially for those who must cover long distances, Artificially limiting speed to 50mph is not going to change emissions from UK vehicles very much from a vehicle doing 70 mph.
For a given journey artificially limiting a vehicles speed below its optimum speed means it will have to run for another half hour to cover the same distance If you were talking about speed well above a vehicles optimum speed, you might have a point, but that is not what is being discussed.
This suggested 50 mph limit is just another snide attempt by some, to make the whole point of car use less desirable or useful to the majority of road users, and would do virtually nothing if anything to change emissions from cars, Only a drastic reduction in the number of cars on UK roads would do that, but perhaps that is what you want to happen, are you anti car?
At what point does the aerodynamic resistance and friction on a car decrease at a greater speed?50 mph is not, let me repeat that, not an optimum speed for most of the vehicles on UK roads, especially for those who must cover long distances, Artificially limiting speed to 50mph is not going to change emissions from UK vehicles very much from a vehicle doing 70 mph.
For a given journey artificially limiting a vehicles speed below its optimum speed means it will have to run for another half hour to cover the same distance If you were talking about speed well above a vehicles optimum speed, you might have a point, but that is not what is being discussed.
This suggested 50 mph limit is just another snide attempt by some, to make the whole point of car use less desirable or useful to the majority of road users, and would do virtually nothing if anything to change emissions from cars, Only a drastic reduction in the number of cars on UK roads would do that, but perhaps that is what you want to happen, are you anti car?
So say 50mph was the optimum speed for a car. Over 100 miles, would it use more or less fuel than travelling at 25mph? Broad terms, no need to reach into BSFC.
Where do you want to stop? when we have got back to the man walking in front of every car with a red flag?
You actually genuinely believe that travelling to a destination faster is more efficient?
If I did 50 MPG at 50 mph, and just say I did 45 MPG (being kind) at 75mph. Say I travelled 50 miles, who would use more fuel?
Welshbeef said:
My car will not go into its top 8th gear at 50mph
55mph yes 50mph it switches into 7th.
As such for my vehicle that not the best option
Your vehicle will be finding the most efficient gear for the speed your are doing, while cruising. To be precise any car with 8 gears actually has a cvt with infinite options, so will put it in one of the pre determined gears that is closest to optimum while still giving the driver a reassuring change in revs while it varies the ratio.55mph yes 50mph it switches into 7th.
As such for my vehicle that not the best option
For years the standard fuel economy test has included a run at 90km/h (56mph). For this reason manufacturers have tuned their cars to run as efficiently as possible at this speed. Possibly also why lorries have been restricted to this speed. So for that reason you will improve fuel economy by reducing to 50 or 60 mph. The USA in the 70s reduced the national limit to 55 due to oil prices going up. Not really sure what difference it made to journey times, but people still got around and commuted for hours each way like they do now.
Rostfritt said:
Welshbeef said:
My car will not go into its top 8th gear at 50mph
55mph yes 50mph it switches into 7th.
As such for my vehicle that not the best option
Your vehicle will be finding the most efficient gear for the speed your are doing, while cruising. To be precise any car with 8 gears actually has a cvt with infinite options, so will put it in one of the pre determined gears that is closest to optimum while still giving the driver a reassuring change in revs while it varies the ratio.55mph yes 50mph it switches into 7th.
As such for my vehicle that not the best option
For years the standard fuel economy test has included a run at 90km/h (56mph). For this reason manufacturers have tuned their cars to run as efficiently as possible at this speed. Possibly also why lorries have been restricted to this speed. So for that reason you will improve fuel economy by reducing to 50 or 60 mph. The USA in the 70s reduced the national limit to 55 due to oil prices going up. Not really sure what difference it made to journey times, but people still got around and commuted for hours each way like they do now.
Driving at 50 will however have a significant impact on businesses, and people lives, where vans/trucks. salesmen, businessmen, individuals, where a reduced number of deliveries, meetings, appointments in a day, will reduce the efficiencies of those activities. As for the US, driving at 55 mph to destinations many hundreds of miles away is not generally viable, and increases time and costs (for hotels/overnight accommodation), which is why in the US aviation both public and private is much more prevalent.
Usually lower limits are supported by those who don't, or dont have to do high mileages in support of their jobs/family lives etc. Those who putter around to the local shops etc, but who get out of their depth when required to drive long distances on motorways etc. Others for whom time means money/ successfully carrying out their jobs etc would prefer to see motorway speed limits increased, e.g to the 80 mph dry road limits used on French motorways.
Evanivitch said:
Pan Pan Pan said:
The one who would have to run their engine for almost another half an hour to get to the same destination, and at a speed that does not allow the engine to run in its most fuel efficient rev range.
Oh dear.I suggest you retake GCSE maths.
Pan Pan Pan said:
Evanivitch said:
Pan Pan Pan said:
The one who would have to run their engine for almost another half an hour to get to the same destination, and at a speed that does not allow the engine to run in its most fuel efficient rev range.
Oh dear.I suggest you retake GCSE maths.
If both cars travel 50 miles, and one does 50 MPG, and one does 45 MPG, how many gallons will each car use?
Pan Pan Pan said:
The optimum speed for my car is 75mph. Optimum speed means that which allows it to cover the greatest distance for the lest amount of fuel. but let`s keep it legal and say the optimum speed is 70mph. At this speed I can technically cover a distance of 100 miles in 1 hour twenty minutes. If I did the same journey at 50 mph it would take another 25 minutes to cover the same distance. That means the engine is burning fuel for another 25 minutes, after the car which did 70mph has been switched off,
MPG, MPG, MPG, miles per gallon. The time taken to cover those miles is irrelevant in total fuel consumption terms. If your figures were gallons per hour then your argument would be valid, but they're not. If you do 50 miles at 50 mpg you will use a gallon of fuel, whether that's at 30 mph or 50 mph makes no difference.Evanivitch said:
Pan Pan Pan said:
Evanivitch said:
Pan Pan Pan said:
The one who would have to run their engine for almost another half an hour to get to the same destination, and at a speed that does not allow the engine to run in its most fuel efficient rev range.
Oh dear.I suggest you retake GCSE maths.
If both cars travel 50 miles, and one does 50 MPG, and one does 45 MPG, how many gallons will each car use?
Doing 50 rather than 70 does almost nothing to reduce the OVERALL fuel use, and emissions, because the extra time the 50 mph car has to run to reach its destination will virtually wipe out the difference in fuel use between a car doing 50 and a car doing 70.
speedking31 said:
PG, MPG, MPG, miles per gallon. The time taken to cover those miles is irrelevant in total fuel consumption terms. If your figures were gallons per hour then your argument would be valid, but they're not. If you do 50 miles at 50 mpg you will use a gallon of fuel, whether that's at 30 mph or 50 mph makes no difference.
MPG is measured with the Air conditioning off. Aircon (like all subsystems) are effectively measured in gallons per hour as such reducing their usage is the only way to improve efficiency. Ergo total time taken to destination is relevant in these discussions.Gassing Station | News, Politics & Economics | Top of Page | What's New | My Stuff