New Speed Limits for Lorries Slip In

RideOnTime

http://home.bt.com/lifestyle/motoring/motoring-news/new-speed-limits-for-lorry-drivers-11363973700001

Zendog1

Good

How Far is too Far

Most trucks have been doing them speeds for years already. Save cars wanting to pass them as much. Could result in less aggressive driving which is a good thing.

VTech

I don't see how this will make a difference to the vast majority as limits are set at 56mph on the dash.
Likewise, foreign trucks don't have the same restrictions as the UK but to be honest, it isn't a fair playing field for UK hauliers.
The government have failed the truckers for years in this country, its a disgrace that to the average man isn't an issue but it has crippled an industry.

bompington

Not sure what having a limiter set at 56mph has to do with speed limit being raised from 40 to 50?

This has been a bit of an issue round here with the A9. It runs for something like 140 miles from Stirling to Inverness, is single carriageway for more than half of that, and is in effect the only road to northern Scotland.
They've recently put average speed cameras along the whole length of the road, along with raising the speed limit for lorries to 50 on the single carriageway bits.
Plenty of controversy there, the big question being whether it will actually make any difference to the (pretty bad) accident rates on the road. If you come by car from the continent, the first single carriageway you see is north of Perth, that's about 550 miles from Dover: there are regular horror stories of continental drivers stopping to see the view and setting off again on the wrong side of the road. Friends of mine somehow walked away from a head on smash at 60 caused by exactly that. And then there all all the frustrated drivers stuck in long tailbacks behind slow vehicles, and there are also the comlpete idiots.
Traditionally it was regarded as a free run to go more or less as fast as you liked, so people are a bit narked at having to stick at 60: but for years now, it's usually been busy enough with lorries crawling along that the real problem comes from frustrated drivers doing silly overtaking manoeuvres. Whether the new limit will help that is questionable.

In the end, I'm not sure how many trucks were ever going at 40 anyway, so I wouldn't anticipate a lot of change.

VTech

Sorry, should of explained better.
Having a 56 limit on the dash will mean that drivers will not really change to a limit law due to the fact that the vast majority already drive at that limit anyway.
It is vastly less economical to drive at the lower speeds and as costs are such a vital component to the haulier industry, owner drivers or drivers trying to look after their job will try and be more economical with fuel usage.
Can you imagine how a UK haulier feels as he is driving at 40mph getting 3.6mpg from his volvo truck as a french driver who is paying far less for fuel (tax rebates) and who is driving at 60mph getting 5.2mpg.

The difference isn't pennies here, its many tens of thousands of pounds different.

bompington

Hmmm.

Volvo website wrote:

Lowering the speed from 90km/h to 80km/h reduces fuel consumption by 6%.

(source: volvotrucks.com)

I know you're an expert in fuel systems, but I have some knowledge of the laws of physics. A truck going at a steady 60 will require more energy than one going at 60: I don't know what the split is between air resistance and rolling resistance, but rolling resistance is going to be 50% or so greater at 60, wind resistance over 3 times greater.
So can the difference in engine efficiency really be so vast that you can use 40% less fuel to do somewhere between 50% and 330% more work? And if so, why don't Volvo know that?

VTech

Without wanting to start an argument against vehicle manufacturers, the problem is that they can hardly be trusted to give correct data considering they have control over testing, like in-vehicle testing at 17.5 degrees as apposed to real weather data and then with engine HP and torque based with the engine on an engine dyno rather than in a vehicle with all of the vehicle losses attached.

With that in mind, to answer the question. To get optimum efficiency you would ideally get to the point of peak performance at a quicker rate and once there use less fuel to stay consistently there.

Increasing torque delivery (hp not needed for this data) will speed the point at which peak power arrives, so the driver can back off and remain at a constant for a longer period.
Increasing injection pressure will vaporise the fuel more efficiently for a cleaner burn therefor converting more accelerant into energy and of course less wastage through the exhaust system.
Driving at low speeds is often very bad for fuel efficiency as your engine may not have reached peak efficiency levels and so you may drive in a lower gear, lets say 4th in a car and 12th in a truck as apposed to 6th in a car and 18th in a truck.
An engine that "labours" (when too high a gear is used for the speed driven and causes the body of the vehicle to rumble) is bad for efficiency and vehicle life, as well as prematurely wearing key components like clutch and drivetrain.

The volvo quote you used is both right and wrong, right in that the case study they did to find that out would be correct but wrong in that it is a set finding which we can base all other settings at.
The drop in fuel consumption would be based upon the software of the vehicle being the same during the test but that is smoke and mirrors because it wouldn't be the same, the manufacturer could implement very easily a method of increasing the pressure as speed goes up (they do actually do this anyway to a degree) and this would counter the speed v fuel usage.

hangeron

If your business model means you can only stay profitable if you break the law then you are morally no different than the Mafia.

VTech

hangeron wrote:

If your business model means you can only stay profitable if you break the law then you are morally no different than the Mafia.

I think there are many thousands of people who have been honest throughout life and worked as hard as they possibly could and lost everything due to legislation change who would be a tad upset with that post.

Quite a daft reply to this otherwise good thread really.