Looking on the bright side!

rick_chasey

Wheelspinner said:

TheBigBean said:

Wheelspinner said:

rjsterry said:

Wheelspinner said:

Pross said:

Stevo_666 said:

briantrumpet said:

Stevo_666 said:

rick_chasey said:

I suspect if they want them to work as a deterrent to any speeding, doing it in a spot where more people will get caught by it make s total sense.

It is amazing how much quieter life is without cars running around though. Really noticeable. Lovely stuff.

Maybe, but they keep telling us that it is done for safety reasons - and that the cameras are deployed at accident black spots, which clearly isnt the case based on my observations.

Call me a cynic...

You're a cycnic!

I've got no problem with catching people speeding or using mobile phones, even if it isn't in an accident blackspot. I've got a very good friend who's also a petrolhead, who rails against them as being a tax on motoring. They're not, they're just a tax on people who won't abide by the rules, however unfair the person thinks the law is. People should campaign to get the law changed, if they think it's unfair.

There's an absolutely foolproof way of avoiding the 'tax'/fines: don't speed, and don't use the mobile while driving. It's even more simple than the laws on drink driving, and people don't complain about them.

And if I got caught (I've managed 39 years up till now without point on my licence), I'd know I'd been a dïck, with only myself to blame (unless signage was at fault).

Being stupid involves getting caught

I have raised my objections to the less practical speed limits in my area. Good example is a road not far from me that goes between Bromley and Lewisham. 30 mph limit for the whole stretch until recently. Then Lewishem council in their wisdom changed their end to a 20 limit. So the week before doing what was perfectly legal and sensible speed suddenly made motorists a danger to society - when they cross an invisible line part way along the road.

And they wonder why so many motorists ignore 20mph limits. Usual rule of thumb is if a law is unreasonable, people will ignore it...

20mph actually makes a lot more sense than 30mph when you look at the survival rates of a pedestrian being hit by a car but I agree it is very difficult to adapt to it. I drove up for a weekend in the Twickenham / Richmond areas and virtually all the residential streets were 20mph, it was the first time I'd seen cameras in 20 zones too. You really need to change the character of a street in order to make the 20mph self-enforcing.

In the same way that people insist if you don’t want to get a speeding ticket, then don’t speed, if pedestrians don’t want to die they should stay off the f^^*ing road.

The other part of the “reduce speed limits” to save pedestrian lives bollox that irritates me is that it comes from similar groups who whinge about climate change and pollution etc etc.

If you drive 1 mile at 30 mph it takes 2 minutes. To do the same mile at 20 takes 3 minutes. So your car engine is ticking over for 50% more time, but I can absolutely guarantee it won’t use 50% less petrol (or other energy source of your choice). So you have just deliberately increased the emissions of that vehicle and every other one on the same stretch by 30-50% because the muppet pedestrians are too thick to stay off the road or look first.

Why is that a sensible plan?

Sure, let's ignore basic physics 😄 and why won't everyone in the entire universe get out of my way?!

Explain please? What physics? Feel free to use examples 😀

I would guess

Work done = power x time.

True.

Try this experiment:

- fill car fuel tank to brim.
- Drive 100 miles at exactly (say) 40 mph with the transmission locked into second gear.
- Refill and calculate fuel consumption.
- Repeat drive of same 100 miles and let the car decide what gear is appropriate for the load required throughout, uphill and down.
- Refill and re-calculate fuel consumption.

Report back on your results.

Your physics equation is correct that the theoretical power required to move a vehicle mass over a fixed distance at a constant speed is the same. In that case the result of the above experiment should be identical fuel consumption figures, no? Same car, same mass, same duration, same road profile.

Want to bet your house on that being the case? 😀

You’re talking about the mechanical efficiency of engines.

I can assure you it takes materially less energy and therefore petrol to drive the same journey at an even 20mph vs 30mph.

rjsterry

Wheelspinner said:

rjsterry said:

Wheelspinner said:

Pross said:

Stevo_666 said:

briantrumpet said:

Stevo_666 said:

rick_chasey said:

I suspect if they want them to work as a deterrent to any speeding, doing it in a spot where more people will get caught by it make s total sense.

It is amazing how much quieter life is without cars running around though. Really noticeable. Lovely stuff.

Maybe, but they keep telling us that it is done for safety reasons - and that the cameras are deployed at accident black spots, which clearly isnt the case based on my observations.

Call me a cynic...

You're a cycnic!

I've got no problem with catching people speeding or using mobile phones, even if it isn't in an accident blackspot. I've got a very good friend who's also a petrolhead, who rails against them as being a tax on motoring. They're not, they're just a tax on people who won't abide by the rules, however unfair the person thinks the law is. People should campaign to get the law changed, if they think it's unfair.

There's an absolutely foolproof way of avoiding the 'tax'/fines: don't speed, and don't use the mobile while driving. It's even more simple than the laws on drink driving, and people don't complain about them.

And if I got caught (I've managed 39 years up till now without point on my licence), I'd know I'd been a dïck, with only myself to blame (unless signage was at fault).

Being stupid involves getting caught

I have raised my objections to the less practical speed limits in my area. Good example is a road not far from me that goes between Bromley and Lewisham. 30 mph limit for the whole stretch until recently. Then Lewishem council in their wisdom changed their end to a 20 limit. So the week before doing what was perfectly legal and sensible speed suddenly made motorists a danger to society - when they cross an invisible line part way along the road.

And they wonder why so many motorists ignore 20mph limits. Usual rule of thumb is if a law is unreasonable, people will ignore it...

20mph actually makes a lot more sense than 30mph when you look at the survival rates of a pedestrian being hit by a car but I agree it is very difficult to adapt to it. I drove up for a weekend in the Twickenham / Richmond areas and virtually all the residential streets were 20mph, it was the first time I'd seen cameras in 20 zones too. You really need to change the character of a street in order to make the 20mph self-enforcing.

In the same way that people insist if you don’t want to get a speeding ticket, then don’t speed, if pedestrians don’t want to die they should stay off the f^^*ing road.

The other part of the “reduce speed limits” to save pedestrian lives bollox that irritates me is that it comes from similar groups who whinge about climate change and pollution etc etc.

If you drive 1 mile at 30 mph it takes 2 minutes. To do the same mile at 20 takes 3 minutes. So your car engine is ticking over for 50% more time, but I can absolutely guarantee it won’t use 50% less petrol (or other energy source of your choice). So you have just deliberately increased the emissions of that vehicle and every other one on the same stretch by 30-50% because the muppet pedestrians are too thick to stay off the road or look first.

Why is that a sensible plan?

Sure, let's ignore basic physics 😄 and why won't everyone in the entire universe get out of my way?!

Explain please? What physics? Feel free to use examples 😀

Think about the relationship between speed and energy.

Pross

Seems an odd theory considering that there are an increasing number of roads where speed limits are being reduced in an attempt to improve air quality. If the theory were sound it would suggest that limits should be removed altogether in those areas.

Stevo_666

Pross said:

Stevo_666 said:

Pross said:

Stevo_666 said:

briantrumpet said:

Stevo_666 said:

rick_chasey said:

I suspect if they want them to work as a deterrent to any speeding, doing it in a spot where more people will get caught by it make s total sense.

It is amazing how much quieter life is without cars running around though. Really noticeable. Lovely stuff.

Maybe, but they keep telling us that it is done for safety reasons - and that the cameras are deployed at accident black spots, which clearly isnt the case based on my observations.

Call me a cynic...

You're a cycnic!

I've got no problem with catching people speeding or using mobile phones, even if it isn't in an accident blackspot. I've got a very good friend who's also a petrolhead, who rails against them as being a tax on motoring. They're not, they're just a tax on people who won't abide by the rules, however unfair the person thinks the law is. People should campaign to get the law changed, if they think it's unfair.

There's an absolutely foolproof way of avoiding the 'tax'/fines: don't speed, and don't use the mobile while driving. It's even more simple than the laws on drink driving, and people don't complain about them.

And if I got caught (I've managed 39 years up till now without point on my licence), I'd know I'd been a dïck, with only myself to blame (unless signage was at fault).

Being stupid involves getting caught

I have raised my objections to the less practical speed limits in my area. Good example is a road not far from me that goes between Bromley and Lewisham. 30 mph limit for the whole stretch until recently. Then Lewishem council in their wisdom changed their end to a 20 limit. So the week before doing what was perfectly legal and sensible speed suddenly made motorists a danger to society - when they cross an invisible line part way along the road.

And they wonder why so many motorists ignore 20mph limits. Usual rule of thumb is if a law is unreasonable, people will ignore it...

20mph actually makes a lot more sense than 30mph when you look at the survival rates of a pedestrian being hit by a car but I agree it is very difficult to adapt to it. I drove up for a weekend in the Twickenham / Richmond areas and virtually all the residential streets were 20mph, it was the first time I'd seen cameras in 20 zones too. You really need to change the character of a street in order to make the 20mph self-enforcing.

If you saw the road I was referring to you would see how ridiculous a 20 limit is in that case. And Bromley council clearly agree with me as they haven't changed the limit on their part.

The better way to avoid injuring pedestrians is to watch the road ahead rather than gawping at your speedo making sure you're not exceeding the limit by 1 mph. There's much more to safe driving than speed, but it's a lot harder to fine people for the other things. Call me a cynic...

Surprised you haven't got a heads up display on your posh car!

I do have one It's pretty cool and I can pretend that I'm a Messerschmitt pilot....

Stevo_666

Looks a bit like this and has the applicable limit on it to keep me out of trouble

rick_chasey

40kph in 5th gear? Alrite grandad.

Stevo_666

rick_chasey said:

40kph in 5th gear? Alrite grandad.

Stock photo from the web, Rick - might be a bit irresponsible of me to snap my head up display while driving...

Remind us again what thrilling supercar you drive

rick_chasey

You mean my 0.9 litre 2015 vw polo?

rick_chasey

Guess what my VED tax is on that.

Stevo_666

rick_chasey said:

Guess what my VED tax is on that.

£20. My daughter has exactly the same model and year of car which I taxed in January. Don't tell me yours is that garish baby blue colour as well...

rick_chasey

No I wish. It is the reddest car I have ever seen.

Not happy with the colour tbh, but at least I can spot it a mile away in a carpark.

Correct on the old VED

TheBigBean

Wheelspinner said:

TheBigBean said:

Wheelspinner said:

rjsterry said:

Wheelspinner said:

Pross said:

Stevo_666 said:

briantrumpet said:

Stevo_666 said:

rick_chasey said:

I suspect if they want them to work as a deterrent to any speeding, doing it in a spot where more people will get caught by it make s total sense.

It is amazing how much quieter life is without cars running around though. Really noticeable. Lovely stuff.

Maybe, but they keep telling us that it is done for safety reasons - and that the cameras are deployed at accident black spots, which clearly isnt the case based on my observations.

Call me a cynic...

You're a cycnic!

I've got no problem with catching people speeding or using mobile phones, even if it isn't in an accident blackspot. I've got a very good friend who's also a petrolhead, who rails against them as being a tax on motoring. They're not, they're just a tax on people who won't abide by the rules, however unfair the person thinks the law is. People should campaign to get the law changed, if they think it's unfair.

There's an absolutely foolproof way of avoiding the 'tax'/fines: don't speed, and don't use the mobile while driving. It's even more simple than the laws on drink driving, and people don't complain about them.

And if I got caught (I've managed 39 years up till now without point on my licence), I'd know I'd been a dïck, with only myself to blame (unless signage was at fault).

Being stupid involves getting caught

I have raised my objections to the less practical speed limits in my area. Good example is a road not far from me that goes between Bromley and Lewisham. 30 mph limit for the whole stretch until recently. Then Lewishem council in their wisdom changed their end to a 20 limit. So the week before doing what was perfectly legal and sensible speed suddenly made motorists a danger to society - when they cross an invisible line part way along the road.

And they wonder why so many motorists ignore 20mph limits. Usual rule of thumb is if a law is unreasonable, people will ignore it...

20mph actually makes a lot more sense than 30mph when you look at the survival rates of a pedestrian being hit by a car but I agree it is very difficult to adapt to it. I drove up for a weekend in the Twickenham / Richmond areas and virtually all the residential streets were 20mph, it was the first time I'd seen cameras in 20 zones too. You really need to change the character of a street in order to make the 20mph self-enforcing.

In the same way that people insist if you don’t want to get a speeding ticket, then don’t speed, if pedestrians don’t want to die they should stay off the f^^*ing road.

The other part of the “reduce speed limits” to save pedestrian lives bollox that irritates me is that it comes from similar groups who whinge about climate change and pollution etc etc.

If you drive 1 mile at 30 mph it takes 2 minutes. To do the same mile at 20 takes 3 minutes. So your car engine is ticking over for 50% more time, but I can absolutely guarantee it won’t use 50% less petrol (or other energy source of your choice). So you have just deliberately increased the emissions of that vehicle and every other one on the same stretch by 30-50% because the muppet pedestrians are too thick to stay off the road or look first.

Why is that a sensible plan?

Sure, let's ignore basic physics 😄 and why won't everyone in the entire universe get out of my way?!

Explain please? What physics? Feel free to use examples 😀

I would guess

Work done = power x time.

True.

Try this experiment:

- fill car fuel tank to brim.
- Drive 100 miles at exactly (say) 40 mph with the transmission locked into second gear.
- Refill and calculate fuel consumption.
- Repeat drive of same 100 miles and let the car decide what gear is appropriate for the load required throughout, uphill and down.
- Refill and re-calculate fuel consumption.

Report back on your results.

Your physics equation is correct that the theoretical power required to move a vehicle mass over a fixed distance at a constant speed is the same. In that case the result of the above experiment should be identical fuel consumption figures, no? Same car, same mass, same duration, same road profile.

Want to bet your house on that being the case? 😀

Smeone has done this before. The issue with urban driving is the accelerating and braking, , so you need another formula.

KE = 1/2 mv^2

20 mph uses half the energy, in total, to 30 mph


http://www.20splenty.org/do_emission_increase

Wheelspinner

rick_chasey said:

Wheelspinner said:

TheBigBean said:

Wheelspinner said:

rjsterry said:

Wheelspinner said:

Pross said:

Stevo_666 said:

briantrumpet said:

Stevo_666 said:

rick_chasey said:

I suspect if they want them to work as a deterrent to any speeding, doing it in a spot where more people will get caught by it make s total sense.

It is amazing how much quieter life is without cars running around though. Really noticeable. Lovely stuff.

Maybe, but they keep telling us that it is done for safety reasons - and that the cameras are deployed at accident black spots, which clearly isnt the case based on my observations.

Call me a cynic...

You're a cycnic!

I've got no problem with catching people speeding or using mobile phones, even if it isn't in an accident blackspot. I've got a very good friend who's also a petrolhead, who rails against them as being a tax on motoring. They're not, they're just a tax on people who won't abide by the rules, however unfair the person thinks the law is. People should campaign to get the law changed, if they think it's unfair.

There's an absolutely foolproof way of avoiding the 'tax'/fines: don't speed, and don't use the mobile while driving. It's even more simple than the laws on drink driving, and people don't complain about them.

And if I got caught (I've managed 39 years up till now without point on my licence), I'd know I'd been a dïck, with only myself to blame (unless signage was at fault).

Being stupid involves getting caught

I have raised my objections to the less practical speed limits in my area. Good example is a road not far from me that goes between Bromley and Lewisham. 30 mph limit for the whole stretch until recently. Then Lewishem council in their wisdom changed their end to a 20 limit. So the week before doing what was perfectly legal and sensible speed suddenly made motorists a danger to society - when they cross an invisible line part way along the road.

And they wonder why so many motorists ignore 20mph limits. Usual rule of thumb is if a law is unreasonable, people will ignore it...

20mph actually makes a lot more sense than 30mph when you look at the survival rates of a pedestrian being hit by a car but I agree it is very difficult to adapt to it. I drove up for a weekend in the Twickenham / Richmond areas and virtually all the residential streets were 20mph, it was the first time I'd seen cameras in 20 zones too. You really need to change the character of a street in order to make the 20mph self-enforcing.

In the same way that people insist if you don’t want to get a speeding ticket, then don’t speed, if pedestrians don’t want to die they should stay off the f^^*ing road.

The other part of the “reduce speed limits” to save pedestrian lives bollox that irritates me is that it comes from similar groups who whinge about climate change and pollution etc etc.

If you drive 1 mile at 30 mph it takes 2 minutes. To do the same mile at 20 takes 3 minutes. So your car engine is ticking over for 50% more time, but I can absolutely guarantee it won’t use 50% less petrol (or other energy source of your choice). So you have just deliberately increased the emissions of that vehicle and every other one on the same stretch by 30-50% because the muppet pedestrians are too thick to stay off the road or look first.

Why is that a sensible plan?

Sure, let's ignore basic physics 😄 and why won't everyone in the entire universe get out of my way?!

Explain please? What physics? Feel free to use examples 😀

I would guess

Work done = power x time.

True.

Try this experiment:

- fill car fuel tank to brim.
- Drive 100 miles at exactly (say) 40 mph with the transmission locked into second gear.
- Refill and calculate fuel consumption.
- Repeat drive of same 100 miles and let the car decide what gear is appropriate for the load required throughout, uphill and down.
- Refill and re-calculate fuel consumption.

Report back on your results.

Your physics equation is correct that the theoretical power required to move a vehicle mass over a fixed distance at a constant speed is the same. In that case the result of the above experiment should be identical fuel consumption figures, no? Same car, same mass, same duration, same road profile.

Want to bet your house on that being the case? 😀

You’re talking about the mechanical efficiency of engines.

I can assure you it takes materially less energy and therefore petrol to drive the same journey at an even 20mph vs 30mph.

Examples are what I asked for, not assurances. I suspect you are thinking that the relevant statistic is what fuel consumption does a car have per km driven (or at a given arbitrary average speed) as the benchmark. It is, for simple comparison between different vehicles because it's an easy way to do that. Car A achieves 25 MPG on the freeway cycle and Car B does 30. Therefore Car B is more efficient. So, if I drive 25 miles in both cars, I'd use less fuel in Car B. Duh.

These numbers are actually fairly meaningless in the real world. Ask VW.

Problem is that the amount of fuel burned in a car is time-based (and engine speed based) irrespective of the distance you end up travelling.

If you don't believe that statement, sit in the driveway some day, engine running and go nowhere. Run the engine at low revs (say 1200 RPM idling) for as long as it takes to empty the tank of fuel. Then refill and repeat the experiment sitting in the driveway with your foot flat on the floor, engine red-lined at 6500 RPM and see how long it takes till you run out of fuel. Think it will go as long as the idling example? In both cases your fuel "economy" is 0 MPG - you drove nowhere, so why is the result different?

My car has a 3 litre engine.

I know if I drive 100 km in 6th gear at 100 km/h it takes me precisely 1 hour. I have done exactly that innumerable times on the freeways here between Sydney and Melbourne for example where you sit with cruise control on for hours at exactly 100 on almost dead flat dull roads. The engine revolutions stay constant at (about) 2000 rpm to achieve that. That means 500 times per minute it sucks in fuel. At a fixed fuel air ratio (assume ideal stoichiometric ratios and any other ideal world factors) I "refill" the car's swept volume cylinder capacity 30,000 times in that 1 hour. That takes 8 litres of fuel in my car in 1 hour.

Therefore each engine cycle sucks through 8,000/30,000 = 0.2667 millilitres of fuel. This is an empirical calculation based on the actual consumption I know my car engine does at a *very* constant speed.

If I drop my speed to 50 km/h, the engine speed *should* drop (in your world) to 1000 rpm, and while the elapsed time goes up to 2 hours to do the same 100 km trip, in theory my engine only refills the cylinders at half the rate so it does the same 30,000 refills for combustion cycles to achieve the outcome of the 100 km trip.

Except no car (mine included) currently running works like that.

My car will NOT run turning over 1000 rpm in 6th gear. It will stall. In order for the car systems to even function, it will drop down to about 4th gear, maybe even 3rd. Assume 4th. At 50 km/h in 4th the engine turns over 1600 rpm. So, I am refilling the cylinders with fuel 400 times per minute instead of 500.

But I am now running for 2 hours, not 1. That means my total refills of the cylinder volume to complete the same 100 km trip are now 400 * 120 = 48,000 refills.

We're still in ideal fuel/air ratio land here, constant speed and load and all that, so the engine has sucked in the same volume PER REFILL.

So the theoretical fuel burned to run the engine for 2 hours at 1600 rpm constant load will be 48,000 * 0.2667 = 12.8 litres of fuel burned.

You may well believe that just driving slower will absolutely guarantee an equivalent drop in total fuel used.

You will be wrong.

Feel free to provide actual examples - not "assurances" - that driving slower will guarantee you use less fuel. You may. In many cases, you may not.

A local road near me in Sydney was about a 10 km stretch with a posted speed limit of 80 km/h. Surprisingly, most of the day that was entirely achievable as the flow was always excellent. The safety muppets decided 60 was a better number so it was changed down.

So now, the same 40,000 cars per day used that road, and they all spent considerably longer time on it then before. You can do some numbers in your head for the potential difference in fuel burnt.

Stevo_666

rick_chasey said:

No I wish. It is the reddest car I have ever seen.

Not happy with the colour tbh, but at least I can spot it a mile away in a carpark.

Correct on the old VED

VED isn't an issue for me, its insurance. Her Polo costs 3 times more to insure than my lump despite having just over 11% of the power output.

pblakeney

You bored WS?

rjsterry

Wheelspinner said:

rick_chasey said:

Wheelspinner said:

TheBigBean said:

Wheelspinner said:

rjsterry said:

Wheelspinner said:

Pross said:

Stevo_666 said:

briantrumpet said:

Stevo_666 said:

rick_chasey said:

I suspect if they want them to work as a deterrent to any speeding, doing it in a spot where more people will get caught by it make s total sense.

It is amazing how much quieter life is without cars running around though. Really noticeable. Lovely stuff.

Maybe, but they keep telling us that it is done for safety reasons - and that the cameras are deployed at accident black spots, which clearly isnt the case based on my observations.

Call me a cynic...

You're a cycnic!

I've got no problem with catching people speeding or using mobile phones, even if it isn't in an accident blackspot. I've got a very good friend who's also a petrolhead, who rails against them as being a tax on motoring. They're not, they're just a tax on people who won't abide by the rules, however unfair the person thinks the law is. People should campaign to get the law changed, if they think it's unfair.

There's an absolutely foolproof way of avoiding the 'tax'/fines: don't speed, and don't use the mobile while driving. It's even more simple than the laws on drink driving, and people don't complain about them.

And if I got caught (I've managed 39 years up till now without point on my licence), I'd know I'd been a dïck, with only myself to blame (unless signage was at fault).

Being stupid involves getting caught

I have raised my objections to the less practical speed limits in my area. Good example is a road not far from me that goes between Bromley and Lewisham. 30 mph limit for the whole stretch until recently. Then Lewishem council in their wisdom changed their end to a 20 limit. So the week before doing what was perfectly legal and sensible speed suddenly made motorists a danger to society - when they cross an invisible line part way along the road.

And they wonder why so many motorists ignore 20mph limits. Usual rule of thumb is if a law is unreasonable, people will ignore it...

20mph actually makes a lot more sense than 30mph when you look at the survival rates of a pedestrian being hit by a car but I agree it is very difficult to adapt to it. I drove up for a weekend in the Twickenham / Richmond areas and virtually all the residential streets were 20mph, it was the first time I'd seen cameras in 20 zones too. You really need to change the character of a street in order to make the 20mph self-enforcing.

In the same way that people insist if you don’t want to get a speeding ticket, then don’t speed, if pedestrians don’t want to die they should stay off the f^^*ing road.

The other part of the “reduce speed limits” to save pedestrian lives bollox that irritates me is that it comes from similar groups who whinge about climate change and pollution etc etc.

If you drive 1 mile at 30 mph it takes 2 minutes. To do the same mile at 20 takes 3 minutes. So your car engine is ticking over for 50% more time, but I can absolutely guarantee it won’t use 50% less petrol (or other energy source of your choice). So you have just deliberately increased the emissions of that vehicle and every other one on the same stretch by 30-50% because the muppet pedestrians are too thick to stay off the road or look first.

Why is that a sensible plan?

Sure, let's ignore basic physics 😄 and why won't everyone in the entire universe get out of my way?!

Explain please? What physics? Feel free to use examples 😀

I would guess

Work done = power x time.

True.

Try this experiment:

- fill car fuel tank to brim.
- Drive 100 miles at exactly (say) 40 mph with the transmission locked into second gear.
- Refill and calculate fuel consumption.
- Repeat drive of same 100 miles and let the car decide what gear is appropriate for the load required throughout, uphill and down.
- Refill and re-calculate fuel consumption.

Report back on your results.

Your physics equation is correct that the theoretical power required to move a vehicle mass over a fixed distance at a constant speed is the same. In that case the result of the above experiment should be identical fuel consumption figures, no? Same car, same mass, same duration, same road profile.

Want to bet your house on that being the case? 😀

You’re talking about the mechanical efficiency of engines.

I can assure you it takes materially less energy and therefore petrol to drive the same journey at an even 20mph vs 30mph.

Examples are what I asked for, not assurances. I suspect you are thinking that the relevant statistic is what fuel consumption does a car have per km driven (or at a given arbitrary average speed) as the benchmark. It is, for simple comparison between different vehicles because it's an easy way to do that. Car A achieves 25 MPG on the freeway cycle and Car B does 30. Therefore Car B is more efficient. So, if I drive 25 miles in both cars, I'd use less fuel in Car B. Duh.

These numbers are actually fairly meaningless in the real world. Ask VW.

Problem is that the amount of fuel burned in a car is time-based (and engine speed based) irrespective of the distance you end up travelling.

If you don't believe that statement, sit in the driveway some day, engine running and go nowhere. Run the engine at low revs (say 1200 RPM idling) for as long as it takes to empty the tank of fuel. Then refill and repeat the experiment sitting in the driveway with your foot flat on the floor, engine red-lined at 6500 RPM and see how long it takes till you run out of fuel. Think it will go as long as the idling example? In both cases your fuel "economy" is 0 MPG - you drove nowhere, so why is the result different?

My car has a 3 litre engine.

I know if I drive 100 km in 6th gear at 100 km/h it takes me precisely 1 hour. I have done exactly that innumerable times on the freeways here between Sydney and Melbourne for example where you sit with cruise control on for hours at exactly 100 on almost dead flat dull roads. The engine revolutions stay constant at (about) 2000 rpm to achieve that. That means 500 times per minute it sucks in fuel. At a fixed fuel air ratio (assume ideal stoichiometric ratios and any other ideal world factors) I "refill" the car's swept volume cylinder capacity 30,000 times in that 1 hour. That takes 8 litres of fuel in my car in 1 hour.

Therefore each engine cycle sucks through 8,000/30,000 = 0.2667 millilitres of fuel. This is an empirical calculation based on the actual consumption I know my car engine does at a *very* constant speed.

If I drop my speed to 50 km/h, the engine speed *should* drop (in your world) to 1000 rpm, and while the elapsed time goes up to 2 hours to do the same 100 km trip, in theory my engine only refills the cylinders at half the rate so it does the same 30,000 refills for combustion cycles to achieve the outcome of the 100 km trip.

Except no car (mine included) currently running works like that.

My car will NOT run turning over 1000 rpm in 6th gear. It will stall. In order for the car systems to even function, it will drop down to about 4th gear, maybe even 3rd. Assume 4th. At 50 km/h in 4th the engine turns over 1600 rpm. So, I am refilling the cylinders with fuel 400 times per minute instead of 500.

But I am now running for 2 hours, not 1. That means my total refills of the cylinder volume to complete the same 100 km trip are now 400 * 120 = 48,000 refills.

We're still in ideal fuel/air ratio land here, constant speed and load and all that, so the engine has sucked in the same volume PER REFILL.

So the theoretical fuel burned to run the engine for 2 hours at 1600 rpm constant load will be 48,000 * 0.2667 = 12.8 litres of fuel burned.

You may well believe that just driving slower will absolutely guarantee an equivalent drop in total fuel used.

You will be wrong.

Feel free to provide actual examples - not "assurances" - that driving slower will guarantee you use less fuel. You may. In many cases, you may not.

A local road near me in Sydney was about a 10 km stretch with a posted speed limit of 80 km/h. Surprisingly, most of the day that was entirely achievable as the flow was always excellent. The safety muppets decided 60 was a better number so it was changed down.

So now, the same 40,000 cars per day used that road, and they all spent considerably longer time on it then before. You can do some numbers in your head for the potential difference in fuel burnt.

Come back when you have air pollution data for the same road before and after the change. 😉

rick_chasey

Wheelspinner said:

rick_chasey said:

Wheelspinner said:

TheBigBean said:

Wheelspinner said:

rjsterry said:

Wheelspinner said:

Pross said:

Stevo_666 said:

briantrumpet said:

Stevo_666 said:

rick_chasey said:

I suspect if they want them to work as a deterrent to any speeding, doing it in a spot where more people will get caught by it make s total sense.

It is amazing how much quieter life is without cars running around though. Really noticeable. Lovely stuff.

Maybe, but they keep telling us that it is done for safety reasons - and that the cameras are deployed at accident black spots, which clearly isnt the case based on my observations.

Call me a cynic...

You're a cycnic!

I've got no problem with catching people speeding or using mobile phones, even if it isn't in an accident blackspot. I've got a very good friend who's also a petrolhead, who rails against them as being a tax on motoring. They're not, they're just a tax on people who won't abide by the rules, however unfair the person thinks the law is. People should campaign to get the law changed, if they think it's unfair.

There's an absolutely foolproof way of avoiding the 'tax'/fines: don't speed, and don't use the mobile while driving. It's even more simple than the laws on drink driving, and people don't complain about them.

And if I got caught (I've managed 39 years up till now without point on my licence), I'd know I'd been a dïck, with only myself to blame (unless signage was at fault).

Being stupid involves getting caught

I have raised my objections to the less practical speed limits in my area. Good example is a road not far from me that goes between Bromley and Lewisham. 30 mph limit for the whole stretch until recently. Then Lewishem council in their wisdom changed their end to a 20 limit. So the week before doing what was perfectly legal and sensible speed suddenly made motorists a danger to society - when they cross an invisible line part way along the road.

And they wonder why so many motorists ignore 20mph limits. Usual rule of thumb is if a law is unreasonable, people will ignore it...

20mph actually makes a lot more sense than 30mph when you look at the survival rates of a pedestrian being hit by a car but I agree it is very difficult to adapt to it. I drove up for a weekend in the Twickenham / Richmond areas and virtually all the residential streets were 20mph, it was the first time I'd seen cameras in 20 zones too. You really need to change the character of a street in order to make the 20mph self-enforcing.

In the same way that people insist if you don’t want to get a speeding ticket, then don’t speed, if pedestrians don’t want to die they should stay off the f^^*ing road.

The other part of the “reduce speed limits” to save pedestrian lives bollox that irritates me is that it comes from similar groups who whinge about climate change and pollution etc etc.

If you drive 1 mile at 30 mph it takes 2 minutes. To do the same mile at 20 takes 3 minutes. So your car engine is ticking over for 50% more time, but I can absolutely guarantee it won’t use 50% less petrol (or other energy source of your choice). So you have just deliberately increased the emissions of that vehicle and every other one on the same stretch by 30-50% because the muppet pedestrians are too thick to stay off the road or look first.

Why is that a sensible plan?

Sure, let's ignore basic physics 😄 and why won't everyone in the entire universe get out of my way?!

Explain please? What physics? Feel free to use examples 😀

I would guess

Work done = power x time.

True.

Try this experiment:

- fill car fuel tank to brim.
- Drive 100 miles at exactly (say) 40 mph with the transmission locked into second gear.
- Refill and calculate fuel consumption.
- Repeat drive of same 100 miles and let the car decide what gear is appropriate for the load required throughout, uphill and down.
- Refill and re-calculate fuel consumption.

Report back on your results.

Your physics equation is correct that the theoretical power required to move a vehicle mass over a fixed distance at a constant speed is the same. In that case the result of the above experiment should be identical fuel consumption figures, no? Same car, same mass, same duration, same road profile.

Want to bet your house on that being the case? 😀

You’re talking about the mechanical efficiency of engines.

I can assure you it takes materially less energy and therefore petrol to drive the same journey at an even 20mph vs 30mph.

Examples are what I asked for, not assurances. I suspect you are thinking that the relevant statistic is what fuel consumption does a car have per km driven (or at a given arbitrary average speed) as the benchmark. It is, for simple comparison between different vehicles because it's an easy way to do that. Car A achieves 25 MPG on the freeway cycle and Car B does 30. Therefore Car B is more efficient. So, if I drive 25 miles in both cars, I'd use less fuel in Car B. Duh.

These numbers are actually fairly meaningless in the real world. Ask VW.

Problem is that the amount of fuel burned in a car is time-based (and engine speed based) irrespective of the distance you end up travelling.

If you don't believe that statement, sit in the driveway some day, engine running and go nowhere. Run the engine at low revs (say 1200 RPM idling) for as long as it takes to empty the tank of fuel. Then refill and repeat the experiment sitting in the driveway with your foot flat on the floor, engine red-lined at 6500 RPM and see how long it takes till you run out of fuel. Think it will go as long as the idling example? In both cases your fuel "economy" is 0 MPG - you drove nowhere, so why is the result different?

My car has a 3 litre engine.

I know if I drive 100 km in 6th gear at 100 km/h it takes me precisely 1 hour. I have done exactly that innumerable times on the freeways here between Sydney and Melbourne for example where you sit with cruise control on for hours at exactly 100 on almost dead flat dull roads. The engine revolutions stay constant at (about) 2000 rpm to achieve that. That means 500 times per minute it sucks in fuel. At a fixed fuel air ratio (assume ideal stoichiometric ratios and any other ideal world factors) I "refill" the car's swept volume cylinder capacity 30,000 times in that 1 hour. That takes 8 litres of fuel in my car in 1 hour.

Therefore each engine cycle sucks through 8,000/30,000 = 0.2667 millilitres of fuel. This is an empirical calculation based on the actual consumption I know my car engine does at a *very* constant speed.

If I drop my speed to 50 km/h, the engine speed *should* drop (in your world) to 1000 rpm, and while the elapsed time goes up to 2 hours to do the same 100 km trip, in theory my engine only refills the cylinders at half the rate so it does the same 30,000 refills for combustion cycles to achieve the outcome of the 100 km trip.

Except no car (mine included) currently running works like that.

My car will NOT run turning over 1000 rpm in 6th gear. It will stall. In order for the car systems to even function, it will drop down to about 4th gear, maybe even 3rd. Assume 4th. At 50 km/h in 4th the engine turns over 1600 rpm. So, I am refilling the cylinders with fuel 400 times per minute instead of 500.

But I am now running for 2 hours, not 1. That means my total refills of the cylinder volume to complete the same 100 km trip are now 400 * 120 = 48,000 refills.

We're still in ideal fuel/air ratio land here, constant speed and load and all that, so the engine has sucked in the same volume PER REFILL.

So the theoretical fuel burned to run the engine for 2 hours at 1600 rpm constant load will be 48,000 * 0.2667 = 12.8 litres of fuel burned.

You may well believe that just driving slower will absolutely guarantee an equivalent drop in total fuel used.

You will be wrong.

Feel free to provide actual examples - not "assurances" - that driving slower will guarantee you use less fuel. You may. In many cases, you may not.

A local road near me in Sydney was about a 10 km stretch with a posted speed limit of 80 km/h. Surprisingly, most of the day that was entirely achievable as the flow was always excellent. The safety muppets decided 60 was a better number so it was changed down.

So now, the same 40,000 cars per day used that road, and they all spent considerably longer time on it then before. You can do some numbers in your head for the potential difference in fuel burnt.

Do you cycle? How much more effort is it to ride at 40kph versus 30kph?

Why do you think that is?

Stevo_666

And to add to Wheelspinners point, the immortal Jeremy Clarkson debunks the myth about so called econo-boxes being more frugal on petrol than performance cars:

https://youtu.be/F04MXepYiBs

kingstongraham

Does that factor in the fact I'm never going to drive my 1 litre Focus just for the pure enjoyment?

rjsterry

Stevo_666 said:

Wheelspinners point

What, that the laws of physics don't apply to his car? 🤔

Jeremy.89

Why not search for a graph of fuel efficiency v speed.

Both are correct on some accounts and wrong on others.

Stevo_666

rjsterry said:

Stevo_666 said:

Wheelspinners point

What, that the laws of physics don't apply to his car? 🤔

I thought that was your point, not his?

capt_slog

Anyway. Does anybody have anymore "looking on the bright side" posts?

Please?

pinno

Well, there's mass. Or put differently, there's momentum.

My old CDi Merc was most optimum at 47mph. I got 63mpg out of the thing travelling at that speed once. Sub urban stats for the same car @56mph was 57mpg.

Most car manufacturers publish sub urban economy at an average 56mph.
This by all accounts is spurious because even with motorway driving, is very hard to achieve. Maybe in Oz but not in blighty.
It's more spurious because that may not be the optimum speed for any given car. A 900cc Polo doing 60 with 3 passengers is not very efficient but a 2.0L diesel family estate doing the same will be much more efficient due to the power to drag ratio.
The extremely fuel efficient Polo may achieve the same MPG as the less efficient family estate. No pollution point scoring for either party.

In cyclists, I believe, the effort required to go faster is pretty linear up until 22.5mph (some may correct me here). After that, it's disproportionate. In a car (no matter how streamlined it is), this point is at 57mph.

I certainly know that in my oil burning Merc, I averaged approx. 22mph in town and a fuel economy of much less than 30. Yet, I could drive at 60 and achieve double the mpg.

So, Wheel spinners assertion is correct.

Engine speed though (as WS said) is critical however and engines are more economical at a given rpm depending on weight and power of the vehicle.

What he said is this: If you went at 20mph with an engine speed of 1500rpm, it would take you 180 minutes to do 60 miles.
If you went at 40mph (in the same car) at an engine speed of 1500rpm, it would take you 90 minutes to go the same distance. Therefore the engine in the former example has burnt fuel for 90 minutes longer than in the latter example, yet the mpg is identical.

Pross

We've been getting our daughter's rescue dog to get out for a walk with us. He's been terrified by cars ever since she got him, we think he may have been locked down in the past, and would refuse to walk if one passed him (getting a 20kg Staffie home when it refuses to walk if hard work!).

Once the level of traffic dropped we tried him again and though he still stops and cowers a bit until the car passes he has come to learn they aren't out to get him and will then happily go on his way again. So much nicer than him being stuck having to go out in the back garden for a limited bit of exercise.

Stevo_666

capt_slog said:

Anyway. Does anybody have anymore "looking on the bright side" posts?

Please?

I'm reinvesting the money I've saved on petrol and public transport on food and wine

morstar

Stevo_666 said:

capt_slog said:

Anyway. Does anybody have anymore "looking on the bright side" posts?

Please?

I'm reinvesting the money I've saved on petrol and public transport on food and wine

I can safely say, you are not alone in this approach.

Wheelspinner

rjsterry said:

Wheelspinner said:

rjsterry said:

Wheelspinner said:

Pross said:

Stevo_666 said:

briantrumpet said:

Stevo_666 said:

rick_chasey said:

I suspect if they want them to work as a deterrent to any speeding, doing it in a spot where more people will get caught by it make s total sense.

It is amazing how much quieter life is without cars running around though. Really noticeable. Lovely stuff.

Maybe, but they keep telling us that it is done for safety reasons - and that the cameras are deployed at accident black spots, which clearly isnt the case based on my observations.

Call me a cynic...

You're a cycnic!

I've got no problem with catching people speeding or using mobile phones, even if it isn't in an accident blackspot. I've got a very good friend who's also a petrolhead, who rails against them as being a tax on motoring. They're not, they're just a tax on people who won't abide by the rules, however unfair the person thinks the law is. People should campaign to get the law changed, if they think it's unfair.

There's an absolutely foolproof way of avoiding the 'tax'/fines: don't speed, and don't use the mobile while driving. It's even more simple than the laws on drink driving, and people don't complain about them.

And if I got caught (I've managed 39 years up till now without point on my licence), I'd know I'd been a dïck, with only myself to blame (unless signage was at fault).

Being stupid involves getting caught

I have raised my objections to the less practical speed limits in my area. Good example is a road not far from me that goes between Bromley and Lewisham. 30 mph limit for the whole stretch until recently. Then Lewishem council in their wisdom changed their end to a 20 limit. So the week before doing what was perfectly legal and sensible speed suddenly made motorists a danger to society - when they cross an invisible line part way along the road.

And they wonder why so many motorists ignore 20mph limits. Usual rule of thumb is if a law is unreasonable, people will ignore it...

20mph actually makes a lot more sense than 30mph when you look at the survival rates of a pedestrian being hit by a car but I agree it is very difficult to adapt to it. I drove up for a weekend in the Twickenham / Richmond areas and virtually all the residential streets were 20mph, it was the first time I'd seen cameras in 20 zones too. You really need to change the character of a street in order to make the 20mph self-enforcing.

In the same way that people insist if you don’t want to get a speeding ticket, then don’t speed, if pedestrians don’t want to die they should stay off the f^^*ing road.

The other part of the “reduce speed limits” to save pedestrian lives bollox that irritates me is that it comes from similar groups who whinge about climate change and pollution etc etc.

If you drive 1 mile at 30 mph it takes 2 minutes. To do the same mile at 20 takes 3 minutes. So your car engine is ticking over for 50% more time, but I can absolutely guarantee it won’t use 50% less petrol (or other energy source of your choice). So you have just deliberately increased the emissions of that vehicle and every other one on the same stretch by 30-50% because the muppet pedestrians are too thick to stay off the road or look first.

Why is that a sensible plan?

Sure, let's ignore basic physics 😄 and why won't everyone in the entire universe get out of my way?!

Explain please? What physics? Feel free to use examples 😀

Think about the relationship between speed and energy.

🙄

Do you really believe the *only* factor influencing car fuel consumption is the physics equation that calculates work required to move a fixed mass at a certain speed over a given distance? It’s one input, sure, but there’s a bit more to the real world than just this one equation.

Your air pollution comment shows just how little actual thinking you’ve done here.

Burning a fixed quantity of fuel in an engine at optimal efficiency produces a fixed amount of waste product - your air pollution contaminant.

Sitting stuck in slow traffic just means that fixed volume of pollutant is pumped into a much smaller environmental space than if you burnt the same amount of fuel to do 50 mph on the freeway.

The same quantity of pollutant comes out of your car exhaust, it just gets distributed over more space.

This is why sitting locked in the garage with your engine running very quickly becomes a bad idea, but you can safely drive that very same car out on the road without being in immediate danger of death by pollution.

This is not an experiment I recommend you try, even for the hard of thinking. 😀

Wheelspinner

rick_chasey said:

Do you cycle? How much more effort is it to ride at 40kph versus 30kph?

Why do you think that is?

Yes, I ride. Not enough, and not that quick, but still fun.

You are correct it takes more power to ride at 40 kph than it does at 30. That's overcoming aero and mechanical drag primarily on a bike. Give you are both the motor and mostly the sole resistance load causing thing on a bike, the relationship is as Pinno noted fairly linear (assuming you don't change gear!)

So what?

If you ride at those speeds for the SAME time duration, you will go further doing 40 than 30, so your work done is actually greater. Work is the energy consumption total amount, the FUEL BURNED bit... That particular calculation includes variables such as force, distance, and velocity.

It's NOT the rate at which you produce it - that's the Power bit.

If you burned the exact same amount of total energy and rode your bike at 30 instead of 40 (using the same gear ratio and riding position to minimise the comparison variables), you will go the pretty roughly the same distance in the end, it will just take you longer (time) to get there. You burn fuel (work) at a lower rate because less power is required to overcome the resistance at the lower speed.

Believe it or not, this is what bike racing is partly about, at least TT and straight speed stuff like pursuit on the track etc. Who can do the same amount of work in the least amount of time?

Put another way, if you decide to commute to work (a distance of 30 km) at a constant speed of 30 kph on your bike. You have two choices of bike to do it on:

- One is your really short geared, but lightweight fixie where you must spin at 140 rpm to keep the speed up. You are wearing chinos, trainers and an anorak, on flat pedals.
- Other is your slick carbon roadie with 24 gears, aero bars, deep rim wheels. You are wearing a teardrop helmet and a skin suit. You can pick whichever gear suits your particular physiology for most efficient pedalling.

The combined weight of rider and bike is the same for this example.

Which one will require more total energy (work, fuel burned) on your part to ride at that constant 30 kph for the 1 hour it takes?

For a clue, remember Sir Bradley Wiggins did not set the hour distance record riding a Boris bike.

The astonishing achievement he made was not really the actual distance he travelled. It was the sheer amount of work (power he maintained for the whole hour) that he could produce before failing. If he *had* ridden the Boris bike in the attempt, the odds of some other rider also riding that same Boris bike any further are pretty low, because there isn't anyone else who can produce that much power for that length of time.

Brad's team simply maximised his conversion efficiency in converting that work into distance travelled, by minimising the amount of wasted energy on aero, mechanical and bio-mechanical drag.

pblakeney

Having the ability to scroll past boring posts cheers me up.

Think I'll use some unallocated funds towards booze. Good plan.