Most trucks/coaches I have driven have had the gearing set to have the rpm around 1300 when in top gear at top limited speed. 56 Plate renos 1400 rpm and the old 420 around 1500. Call me sad but sometimes when overtaking other wagons I glance inside the cab and have noticed loads of scannies slogging away at something that looks like 1100-1200rpm. More often than not it’s Stobart.
Just how much torque does a scanny 420 have? Surely when running at 44t even the slightest uphill will see the motor die and have to change gear? How is that saving fuel if you’re having to drop gears at the slightest hill? When I’m running heavy I can get the motor to slog all the way down to 950rpm and return 4mpg on the display whereas if I change gear and rev it higher like what these scannies must have to do then the mpg drops to 3… Yes yes I know different motors but I don’t see the point. The reason behind 1300 in my truck is (I’m guessing) because 1300 is just where the max torque drops off so when I hit a hill I have full pulling power avalible without the need to change gear
The Scania gearbox has on overdrive top gear , it’s crap to say the least . The newer ones on our fleet have a sticker in them telling you not to use top when loaded ! What is the point in that ? May as well have just put an 11 speed box in !
I think most if not all trucks these days have a green band on the rev counter,this is supposed to be the area where maximum torque is available and our Axors will slog all day at the lower end of the green band.This is supposed to be the most economical driving range,that is why most trucks speed limiters set at 56mph are in the middle of the green band.Keep it in the green!.
spanky spangler:
The Scania gearbox has on overdrive top gear , it’s crap to say the least . The newer ones on our fleet have a sticker in them telling you not to use top when loaded ! What is the point in that ? May as well have just put an 11 speed box in !
Whoever’s idea was that? Manufacturers spend millions on R&D, testing and tweaking and someone without a clue visits Prontaprint and defeats the point of all that research.
In a haulage yard of old the various marques salesman would call in, look at the operation, meet the drivers and the boss, between them all they would look at all the choices, gearbox type, horsepower, wheelbase, engine make and more importantly gear and axle ratios.
It is foolish to spec an 8 wheel tipper working around the high peak with a high ratio diff or to spec a 38 tonne supermarket delivery truck with a low geared differential. It is a compromise but rather than the operator spending 5k on chrome, he would do better to spend a couple of hours studying the specifications offered by each manufacturer.
There are mmtm myths of operators specifying coach diffs in their trucks, the truth is, although possible to do, the truck wouldn’t pull your ■■■■■■■■ back
It seems now that if someone wants a new truck, the choice is between white and red.
I guess it’s all about matching the power output to the load.
Why waste fuel to produce e.g. 100 bhp if 90 bhp is enough to keep rolling.
(Anyone got a pic of the torque curve for these engines?)
Q. How often do you run at full 44 tonnes? I guess the high top gear is also to take into account empty/light running where minimal power is required. They still hold 12th fully loaded on the flat.
It depends on the points where max power and max torque are produced in the rev range.But usually it’s best to be using a low enough gear to run the engine at max power not max torque before a hill.Then the motor should gradually fall back to the max torque revs while it climbs and you’ll get over the hill faster.But the problem is today is that most trucks are geared too high for the low speeds that we run at .Most of the time people are running at the hills with the engine already running at max torque and then it falls back off of the torque peak instead of falling back onto it.
Carryfast:
It depends on the points where max power and max torque are produced in the rev range.But usually it’s best to be using a low enough gear to run the engine at max power not max torque before a hill.Then the motor should gradually fall back to the max torque revs while it climbs and you’ll get over the hill faster.But the problem is today is that most trucks are geared too high for the low speeds that we run at .Most of the time people are running at the hills with the engine already running at max torque and then it falls back off of the torque peak instead of falling back onto it.
Not so sure about the speeds as most countries in Europe run at a lower speed than the UK, 10 km lower in Germany and Holland with less chance to overtake too
Carryfast:
It depends on the points where max power and max torque are produced in the rev range.But usually it’s best to be using a low enough gear to run the engine at max power not max torque before a hill.Then the motor should gradually fall back to the max torque revs while it climbs and you’ll get over the hill faster.But the problem is today is that most trucks are geared too high for the low speeds that we run at .Most of the time people are running at the hills with the engine already running at max torque and then it falls back off of the torque peak instead of falling back onto it.
Not so sure about the speeds as most countries in Europe run at a lower speed than the UK, 10 km lower in Germany and Holland with less chance to overtake too
You’re right about those lower speed limits over there wheelnut and those even lower speeds together with high gearing and drivers who run at hills at peak torque just makes the problem even worse shown by the lines of lumbering trucks out there on any big motorway hill all bunched up getting nowhere fast?.
most trucks have an optimum rpm of 1400 at 56mph. this is the most ecconomical according to the manufacturers.
so why the [zb] do people think 50mph is more ecconomical?
well i’ll tell you. they do 50mph but show 55mph. therefore the office bods think a truck has travelled 55 miles on ■■ litres of fuel. when it hasn’t, it’s done 50 miles. [zb]in morons.
Id say all lorries and cars are set differently… Lot has to do with tyre sizes etc as well… Just recently I went by a Renault Premium, not exceedingly fast, but noticed his dial read “56MPH”, yet my unit and TOMTOM both read 55mph. My RPM is 1450 I think. Some say TOMTOMs overead by 2mph, but I think thats a myth as I was through a wee town the otehr day on the A617 which reads your speed when you drive by and when I drove by it flashed 28mph, exactly the same as what my satnav read…
Ive also stuck bigger wheels onto my car and I reckon its up to about 3-4mph out if I compare my speedo to a local speed camera also…
Almost 1300rpm on mine-around 2000nm/torque-around 400hp,the truck is a 460hp.
Oh, no, be careful, you will have people screaming "OVERSPEED! Cowboy, and Dangerous Juggernaut at you and your relatives
But Bestbooties mentioned keeping it in the green, I am sure he will remind me the coloured rev counter isn’t new, his F89 would have had it along with a turbo boost gauge iirc, although I don’t remember the Transcon like that.
In 1986 I bought a DAF 3300 which had a ZF Ecosplit gearbox linked to the dashboard lights, these arrowed lights blinked and flashed for all to see until you learned how to drive the truck properly. After a few weeks these lights were hardly lit at all.
I later took part in a truck manufacturers open day in Hull, the route was good, it took us from the Humber bridge car park to KG Dock over Myton Bridge and we could return using the old Boothferry hill which used to level an F86 to about 25mph at 32ton. I remember driving a 38ton Foden with a CAT, an F16 and a 113 which all romped up this hill at almost 40mph near the crest by letting the engine lug down to use the engines torque.
The salesman were impressed too and I remember them talking about it in the pub later, the best bit of the day of course
Yes yes I know different motors but I don’t see the point. The reason behind 1300 in my truck is (I’m guessing) because 1300 is just where the max torque drops off so when I hit a hill I have full pulling power avalible without the need to change gear
