When did coasting become legal?.

[Yung Man]

I was always under the impression that to select neutral when going down hill constituted coasting, I have been given a 57 reg Mercedes 2444 tractor unit, It's very nice.
When driving along at what ever speed if you come to a down hill section and you lift off the throttle 4 or 5 seconds later it puts itself into neutral and stays like that until the speed hits about 92k then it goes back into top gear, It's an automatic BTW, the revs come down from 1400rpm at 89kph to 500rpm in neutral so it definately isn't in gear.

Is this legal, I tend to think it must be or they wouldn't make it like that but when did they change the law?.

[Towie]

What happens if you knock the exhauster in?

[davidra]

couldn't it be "in gear" but with the torque converter not converting? that would be similar to a delutched situation...

[Yung Man]

If you touch the brakes it goes back into gear, if you hit the exhaust brake it does the same, It is working out ok but if the hill is too steep the best way is to start at the top at a slower speed, say 82k then the slope will let your speed increase nice and slow, this way with a bit of luck it won't go back in gear until you get to the bottom and you apply the throttle, If the hill is too steep it goes back in gear then hold about 90k but at 1400 revs, what I do then is slow it down on the brakes to 82k ish then hit the gas for one second then lift off and it goes to neutral again 4 seconds later.
It takes a bit of getting used to but surely it can't be legal.

[R_U_LOCAL]

I don't think it's ever actually been illegal to coast. Ill-advised perhaps, but not illegal. Quite a few cars in the 50's and 60's had a freewheel mechanism to supposedly save fuel, and I imagine that's the thinking behind your new truck, bearing in mind how much fuel they go through.

[japhilip]

davidra said:

couldn't it be "in gear" but with the torque converter not converting? that would be similar to a delutched situation...

Unlikely, most if not all new auto trucks are automated manual gearboxes, not auto in the conventional sense of a torque convertor and planetary gearsets.

I've come across a number of Truck autos that have a facility to 'coast'. The Volvo equivalent only does it in certain modes IIRC (and I may not!).

I believe 'coasting' by having the vehicle in neutral isn't illegal, as all the systems remain powered (brakes, steering etc), but switching the engine off is. Coasting was discouraged as poor practice when I got my licence, but with the advent of all round disk brakes and ABS on tractors and trailers, engine braking is no longer considered essential (apparently), and in fact manufacturers claim improved fuel economy by setting the gearboxes up to coast as mentioned by the OP.

[Yung Man]

R_U_LOCAL said:

bearing in mind how much fuel they go through.

Last night I managed 398 kilometers in 5 hours 12 mins averaging 77.6kph and did 26.1 Ltrs per 100k which I thought was quite good, the day man is doing 35Ltrs per 100k.

It's all motorway.

[R_U_LOCAL]

Yung Man said:

R_U_LOCAL said:

bearing in mind how much fuel they go through.

Last night I managed 398 kilometers in 5 hours 12 mins averaging 77.6kph and did 26.1 Ltrs per 100k which I thought was quite good, the day man is doing 35Ltrs per 100k.

It's all motorway.

About 9mpg then?

Not too bad for an artic, really.

[wasted years]

Coasting is legal. The deffinition of driving is having control over the propulsion and steering.

HTH

[Hooli]

I was under the impression one reason for not coasting in HGVs/coaches was due to running out of air? i know its a problem on older coaches if the revs stay low for ages, i guess they finally make new trucks with good enough air pumps?

[delboy735]

Coasting uses more fuel downhill than engine brakeing.My old car, when going downhill with foot on brake, but in gear would do 999MPG, but knock it into neutral, and the fuel economy would be 60MPG because the engine requires fuel to be forced into the engine to make it work, but when using engine brakeing, requires virtually no fuel.

[Vipers]

Strangely enough, in the 2004 Highway Code, it states under coasting:-

This term describes a vehicle travelling in neutral or with the clutch pressed down. Do not coast, whatever the driving conditions. It reduces driver control because. etc etc.

Whereas the 2007 version states:-

This term describes a vehicle travelling in neutral or with the clutch pressed down. It can reduce driving control because. etc etc.

The 2007 version does not mention "Do not coast whatever the driving conditions"

Whislt the 5 bullet points after each are the same, I wonder why they removed that clause.

[japhilip]

delboy735 said:

Coasting uses more fuel downhill than engine brakeing.My old car, when going downhill with foot on brake, but in gear would do 999MPG, but knock it into neutral, and the fuel economy would be 60MPG because the engine requires fuel to be forced into the engine to make it work, but when using engine brakeing, requires virtually no fuel.

I wouldn't disagree with that, but truck manufacturers reckon differently, and have done many tests to back up their claims. However, trucks are a little different to cars, although in practice the amount of fuel a vehicle (truck) uses while idling is negligible compared to being under power anyway, and I'd guess that the engine braking effect (and thus speed reduction, thus requiring more fuel to maintain speed) would cancel out the saving compared to no engine braking while coasting.

[s2art]

delboy735 said:

Coasting uses more fuel downhill than engine brakeing.My old car, when going downhill with foot on brake, but in gear would do 999MPG, but knock it into neutral, and the fuel economy would be 60MPG because the engine requires fuel to be forced into the engine to make it work, but when using engine brakeing, requires virtually no fuel.

This is a function of modern fuel injection/engine management systems on cars. It doesnt need to be that way, certainly with carb fed engines the opposite applies.

[Parrot of Doom]

I would have thought coasting in an automatic was a very bad idea tbh.

[Peter Ward]

s2art said:

delboy735 said:

Coasting uses more fuel downhill than engine brakeing.My old car, when going downhill with foot on brake, but in gear would do 999MPG, but knock it into neutral, and the fuel economy would be 60MPG because the engine requires fuel to be forced into the engine to make it work, but when using engine brakeing, requires virtually no fuel.

This is a function of modern fuel injection/engine management systems on cars. It doesnt need to be that way, certainly with carb fed engines the opposite applies.

Yes, I found out recently that in-gear-foot-off-accelerator uses no fuel, while of course idling uses a little. Carbs are different, <sigh, thinks back to twin 45s on old Westfield>.

[Cooperman]

All SAAB's used to have a 'freewheel' mode where if you lifted off the throttle, the car would 'coast' until you re-applied the power and the revs matched the speed. It was quite good as you could do 'clutchless' gear changes, but it did cause a lot of wear on the diff due to 'snatch' when re-engaging. I believe Rover's also had this up to the late 50's.

[Yung Man]

Yung Man said:

R_U_LOCAL said:

bearing in mind how much fuel they go through.

Last night I managed 398 kilometers in 5 hours 12 mins averaging 77.6kph and did 26.1 Ltrs per 100k which I thought was quite good, the day man is doing 35Ltrs per 100k.

It's all motorway.

I drove an identical truck last night that had averaged 33.3 Litres per 100 kilometres for the 6000k it has done so far, I managed 385.5K in 4hrs 55mins at 78.5 kph which equalled 27.8 L/100k, this was 1,7 L/100k worse than yesterday but I saved 5.2 L/100k on my journey.(based on the 33.3 average) That is 20 Litres saved for my shift which just goes to show if all truckers where able to drive economically they could save collectively 20%.

I wonder if it will work with my car.

[Ean218]

As the OP is talking litres and kilometres instead of gallons and miles, would it not be pertinent to ask of which country he wishes to know the law?

I presume the UK highway code is irrelevant.

[Joshw]

Yung Man said:

I was always under the impression that to select neutral when going down hill constituted coasting, I have been given a 57 reg Mercedes 2444 tractor unit, It's very nice.
When driving along at what ever speed if you come to a down hill section and you lift off the throttle 4 or 5 seconds later it puts itself into neutral and stays like that until the speed hits about 92k then it goes back into top gear, It's an automatic BTW, the revs come down from 1400rpm at 89kph to 500rpm in neutral so it definately isn't in gear.

Is this legal, I tend to think it must be or they wouldn't make it like that but when did they change the law?.

What model is your truck? the Axor or the Actros? And what gearchange does it have? I'll assume its the powershift? Armrest mounted gear selector with the clutch? I recently did a one day training course on this system, Any questions feel free to pm me!

The box is designed to re-engage a gear and engine brake if the speed goes above a percentage of the origional speed, It's just another fuel saving measure really.. If you can and your company will fund it, look into taking part in the driver training at wentworth mercedes in barnsley, I sat in on one of the courses recently, apparently can help make massive savings on fleet fuel bills..