i only do 3.2 miles per day on the motorway on my present run,so not worried about doing 52 or 56 mph at the moment.my Daf CF auto is showing an average 10.5 mpg,no idea if that’s good or bad.
For me definately less fuel at less MPH, driving where the engine produces max torque gets me the best results, thats 1100 rpm which equates to 50 mph on my truck in top gear with the auto locked down in M.
Weather conditions also have a big effect and need to be taken into consideration, such as wind direction and air temperature, powering into a strong headwind in single figure temperatures is hard work for a truck, but good MPG figures for any truck are only available with the right driver.
Not necessarily hence more trucks coming with auto boxes nowadays. Just yesterday I did around 620km during my shift, at least 90% of that was on the motorway so flat out doing 56, I weighed 39t to, 37t from & my indicated consumption was 9.8mpg, I’m not the greatest of drivers out there so how did I manage that eh…■■?
Pimpdaddy:
Not necessarily hence more trucks coming with auto boxes nowadays.
Auto’s don’t make up for tearass drivers
Pimpdaddy:
& my indicated consumption was 9.8mpg
trip computers are not to be trusted, full tank to full tank the only sure way to work out MPG then compare with what the trip puter says. The only way to compare MPG for different cruise speeds is maybe try the same trip at lower speeds on a day with similar weather 
Pimpdaddy:
I’m not the greatest of drivers out there so how did I manage that eh…■■?
Don’t undersell yourself 
I noticed on Morrison Fm’s the side wind deflectors on the cabs now have what looks like defussiors (like at the back of F1 and performance cars) small “Y” shaped obtrusions rather than the usual flat deflector .
We tried it (brim to brim) with man tgs/tga a few years ago when they started dropping them & the tgs limited to 51 used more juice because of the random gear changes, hence me saying ‘indicated’. They say only a ‘good’ driver can get better mpg on a manual, auto averages everyone out…
Those things on Morrison units are some sort of vortex generators probably fitted to create a turbulent airflow directed away from the big gap they have between the coupling that’s causing a lot of profile/induced drag. If they had sleeper cabs & a closer coupling then they might not have this problem…
Good fuel consumption starts in the planning department ! A drivers contribution amounts to nothing if the route and load planning is crap to start with.
Trev_H:
Good fuel consumption starts in the planning department ! A drivers contribution amounts to nothing if the route and load planning is crap to start with.
+1
We run 6w Daf CF 75 curtainsiders. All are 310bhp and are 8spd manuals. These wont do 56 and remain in the green band. They all vary between 52-55 for optimum mpg figures. I’ve driven a hired Axor that would do 57 and stay well inside the green band, and the hired Volvo FM will (flatout at 55) also be well in the green. The Axor was an 8spd manual (the hideous slap across type) and the FM had I-Shift.
Trev_H:
Good fuel consumption starts in the planning department ! A drivers contribution amounts to nothing if the route and load planning is crap to start with.
+2.
There must be something in this 85kph lark, so many companies wouldnt be doing it otherwise. Regardless though, i am pretty sure that most fuel saving efforts made by companies and drivers are totally wiped out by ropey route planning.
rivits:
vehicles will fail their annual test if they are 1 mph over 56mph so why not the same rule for being under it.give me some feedback please Guys
1mph over?
Can’t wait for my truck to fail then… cough58cough
Fallmonk:
I noticed on Morrison Fm’s the side wind deflectors on the cabs now have what looks like defussiors (like at the back of F1 and performance cars) small “Y” shaped obtrusions rather than the usual flat deflector .
yes - these are “Airtabs”. I believe these have demonstrated savings of over 2.5% and yet only cost around £250 for the average truck. they can also be used on the trailing edges of trailers, box bodies etc (although there are reports of width issues).
They simply create a vortex with the air and fire it off away from the truck instead of it rushing in to fill the void left behind the truck which in turn causes drag. My understanding is the back of the vehicle also stays cleaner - especially handy on boxes and trailers.
All this reduction of speed business does invariably work. As speed increases the air resistance and drag increases exponentially. The saving from the drop in speed is little to do with max torque or engine revs or even gear ratios - it is the simple fact that drag/resistance is reduced tremendously at lower speeds. Trucks are not particularly aero dynamically good meaning the higher the speed to more aero dynamics come into it. Combine this drop in speed with correctly adjusted air kits etc and it is good news for savings.
In an effort to show just how much effect aerodynamics have - take an 8 wheel tipper and run it at 56mph with the back open (not sheeted). Now put the sheet across and run at 56mph. Huddersfield University found a saving of over 9% yet at 37 mph the saving with the sheet was only around 1.6%. Drag and air resistance was the issue
There are issues with some trucks not wanting top gear at a reduced speed but not many and easily overcome.
As for journey times … depends on the journey but generally not a great difference. yes there are some runs just can’t be done at 85kph but better planning is needed. yes it can occasionally force a night out but … the savings are worth it for the odd ocassion.
I was involved in a trial of this with a large number of vehicles. We fitted advanced telematics that tapped into the vehicles canbus system giving live fuel usage. Vehicles were monitored and logged over a period of months followed by being slowed down. The savings on fuel were pretty much obvious and in some cases substantial. The odd vehicle didn’t seem to benefit and one or two got worse, which turned out to be the auto box issue and easily overcome by manual usage.
Ultimately some drivers were ■■■■■■ off yet others reported a less stressfull journey and maybe 20 minutes difference over a days shift. We left a few at 90kph for certain runs.
It did cause planning issues at times and we had to be more cautious with running times. it would have been nice to think the drivers would back off on the speed on those occasions where time was on their side and then speed up when it wasn’t but we generally found most ended up at speed limiter speed simply because it would. therefore the limiters were wound down.
In particular we saw a really good improvement on a couple of Iveco Stralis. Even Iveco told us it wouldn’t work yet the figures proved it. They claimed it would take the engine out of it’s optimum range - and maybe it did - but the fuel saving was there. We monitored at 90kph, then reduced it, then put it back up. The figures said it all and we achieved over 1mpg improvement.
Of course this all only has an effect on certain legs of a journey and has no effect on others.
As for wear and tear on engines and gearboxes etc … I don’t have any figures or facts but I personally don’t think it is an issue. The drop on rpm for 4mph is minimal.
My belief is the drop in speed does save money and the more diesel prices rise the more money it will save. The percentage saving remains the same but the monetary value rises with diesel prices. yes labour etc may go up but it is my firm belief there is still a saving to be had and I base that on experience.
limeyphil:
From the research i did several years ago, It appeared the the production of adblu was creating eight times more Co2 than the emissions saving when it was used in trucks.
It’s just another con.
Production of AdBlue does not create Carbon Dioxide, in fact it’s made from Carbon Dioxide (and Ammonia)
It’s purpose is to turn Nitrogen Dioxide, which is highly poisonous, into Nitrogen and water, both of which are benign. It certainly isn’t some type of con.
Harry Monk:
limeyphil:
From the research i did several years ago, It appeared the the production of adblu was creating eight times more Co2 than the emissions saving when it was used in trucks.
It’s just another con.Production of AdBlue does not create Carbon Dioxide, in fact it’s made from Carbon Dioxide (and Ammonia)
It’s purpose is to turn Nitrogen Dioxide, which is highly poisonous, into Nitrogen and water, both of which are benign. It certainly isn’t some type of con.
I was refering to the amount of fuel used to produce it, ship it, and distribute it.
Pimpdaddy:
They say only a ‘good’ driver can get better mpg on a manual, auto averages everyone out…
Give an auto to a lazy or bad driver and they’ll get even worse MPG as they believe the hype that the autobox does it all correctly for them, been there with one guy and there was no telling him despite the figures proving him wrong.
thelorryist:
rivits:
vehicles will fail their annual test if they are 1 mph over 56mph so why not the same rule for being under it.give me some feedback please Guys
1mph over?
Can’t wait for my truck to fail then… cough58cough
Aint you a lucky boy, 58mph!!! I dont know if I could handle such breakneck speeds anymore!!!
Harry Monk:
limeyphil:
From the research i did several years ago, It appeared the the production of adblu was creating eight times more Co2 than the emissions saving when it was used in trucks.
It’s just another con.It’s purpose is to turn Nitrogen Dioxide, which is highly poisonous, into Nitrogen and water, both of which are benign. It certainly isn’t some type of con.
If NO2 emissions from vehicles is as poisonous as they say then how do they explain the fact that some of us have grown up from an early age into middle/old age to date living amongst traffic which was subject to no emissions controls and in addition sometimes worked around vehicles which involved breathing in large quantities of exhaust emissions and also in some cases spent a lot of our spare time around private vehicles such as racing environments etc etc with no health effects whatsoever .
No doubt the believers will probably use some bs argument concerning some people having more tolerance to it than others when the fact is human physiology is all equal and the same.It’s either a ‘highly poisonous’ emission to humans or it’s not.If it’s the former then it would have shown up in massive numbers of casualties by now.Myself being one of them.
jase:
My truck has been turned down to 83kph and it doesn’t bother me in the slightest.
Driving it in manual and letting the engine lug down to 800rpm on hills before changing down certainly saves fuel too.
I find it less stressful too as I don’t get involved with the driving up each others arse in the middle lane overtaking game,u just there.
As for the op saying trucks are designed for 90 kph,if that’s the case then how come the speed limits for trucks in Europe are lower in some countries than us?,Isbt Germany for example still 80kph?
My fuel figures have gotten a lot higher since being turned down and if I can help the companies bottom line by doing my little bit then at least i’ll stay in a job.
My boss got me an auto truck.
If he’d wanted me to drive a manual, he’d have got me a manual, so I leave it in auto.
When the need arises, I’ll knock it down a gear or two manually, but the rest of the time it stays in auto.
Stressful at 90 kmh?
I don’t get stressed at 90, I don’t play at stress games in the middle lane either.
If I’m very gradually catching another wagon, I’ll get to a safe distance and slow down a few km to trundle along behind. If the wagon in front starts to slow down further in comparison to me, I’ll speed up again and pass if it’s safe to, then reset my CC back to 90 and gradually pull away.
If I’m catching them fairly quickly (you, at 83?) I simply wait for a suitable opportunity, indicate, pull out, pass, pull in and carry on at 90.
As simple and stress free as it gets.
I don’t see why anyone gets stressed in normal driving.
Screwdrivers as they say, If anything I get stressed doing anything less than 90…
dont know why we cant run on red diesel like busses and farmers can as i always thought we run an essential service like they do i.e without trucks the country gets nowt! 