|
I see - thanks for this and other explanations. Presumably the speed indicator on a sat-nav would be more accurate too, though I'm happy to be put right on that. I'll try it out some time.
|
|
I had a non-EU truck pass me on the M1 going North. I was doing a satnav indicated 70. It was smoking abit but didnt look unstable or anything. Looked like quite an elderly Mercedes judging by the shape, sure wasnt anything remotely modern, possibly late 80's early 90's.
|
Trucks pre 1988 don't need limiters - for any sensible UK haulier, that's an age ago, and the only use for a truck so old would be for yard duties as a shunter to move the trailers around.
|
It appears that 3.5 tonne to 7.5 tonne vehicles are now limited to 56 mph now too - is that the case?
|
It appears that 3.5 tonne to 7.5 tonne vehicles are now limited to 56 mph now too - is that the case? Apart from certain age considerations, like the full-blown HGV's, yes. They are being retro-fitted with limiters, our 05 plate Daf had one fitted about 18 months ago.
Those fitted with limiters are also disqualified from using the third lane of a motorway; prior to this 7.5 tonners could do this although I personally think this is a positive step.
|
|
|
|
the only use for a truck so old would be for yard duties as a shunter to move the trailers around.
... or as a sporting, press-on truck for scandalising people like stunorthants on the motorway...
:o}
|
|
|
|
|
Yes a SatNav should be more accurate (some may even show the average as you go through a restricted area).
I really don't understand why motorists allow a truck/coach to tailgate them - there's almost always a way to let them pass; but to some people that just doesn't seem to be an option.
|
|
Plenty of pre-88 7.5 tonners in use as private horse-boxes. My B reg Cargo was happy at 65 in the M-way.
|
It appears that 3.5 tonne to 7.5 tonne vehicles are now limited to 56 mph now too - is that the case?
Yes, anything over 3.5t GVW (ie anything requiring a tachograph to be fitted) first used on or after 1st January 2002 now has to be speed restricted in line with the regulations already in place for post-1988 larger vehicles. This law was brought into force in January 2007 with a 12-month "bedding-in" period, therefore retro-fitting was required during 2007 for late 51-plate 7.5t lorries onwards.
This speed restriction is most often carried out by way of a main dealer with a laptop using their diagnostic software to adjust the vehicle's electronic parameters, hence there is no way to "bypass" the "limiter" as it is not an added device with its own fused circuit, rather a function of the EMS in much the same was as most high-end cars are now restricted to 155mph. This also means that one or two less scrupulous operators may take a somewhat flexible attitude to its enforcement, as they may also do to the regulation of drivers' hours, working time, income tax etc.
Most of the vehicles in this category will be 7.5t GVW, ie Iveco Cargo, Mercedes Actros etc lorries although there are heavier versions of 3.5t vans built, mostly for the utility companies and for some parcel delivery firms. These have the outward appearance of a Transit or Sprinter but can actually carry much more weight, hence are bound by tacho and speed limiter laws. Occasionally they can be seen with "Limited to 56mph" or similar emblazoned on the back doors.
All vehicles limited to 56mph are banned from using the outside lane of motorways and dual carriageways with 3 or more lanes.
The biggest problem I have found when driving a (restricted) 7.5t lorry on a 2-lane dual carriageway such as the A14 from Catthorpe to Cambridge, the A43 past Brackley or the A34 from the M40 down (all v-e-r-y long roads) is that vehicles larger than mine are ostensibly subject to a 50mph speed limit on these roads whereas I am subject to a 60mph speed limit. 99.999% of large lorries travel on these roads at a steady 56mph plus or minus 2% which can make overtaking them a very drawn-out and unpopular process.
I was once told that the guidelines issued to dealers for setting speed limiters were that the range of limited speeds should be between 80-90km/h, ie 50-56mph, with a median speed of 85km/h (53mph). Dealers were supposed to ensure that different vehicles they sent out onto the road had different limiter settings within this range, thus ensuring a range of vehicle cruising speeds and less likelihood across the entire vehicle parc of "bunching" or 10-mile overtaking manoeuvres. Of course all the dealers set limiters at the upper end of the permissible range, with a wink to the driver when he collects his vehicle. This could explain why some fleets' trailers bear stickers claiming a restriction of 52 or 53mph.
Blimey, I never realised I'd absorbed so much info on the subject.
Dave TD
Edited by Dave_TD {P} on 04/08/2009 at 01:21
|
>>>> most high-end cars are now restricted to 155mph. This also means that one or two
very informative thanks but why 155mph? which is over twice the legal maximum. Why not limit all vehicles to 70? or do they want ot collect more fines.
|
very informative thanks but why 155mph?
Presumably it's 250kph - 200 too low for the autobahns?
|
|
|
|
I really don't understand why motorists allow a truck/coach to tailgate them - there's almost always a way to let them pass; but to some people that just doesn't seem to be an option.
I will inevitably get some flak for saying this, but I find some of the biggest pains on a motorway to be the growing numbers of car drivers who seem to think that a cruising speed of about 52 is fine; then when you pull out in an HGV to overtake them, speed up to about 55.
|
Tell me about it Harleyman.
Just imagine what these people are like on two-lane A-road blacktop.
Heart attacks ain't in it.
|
|
|
biggest pains on a motorway
I had a quite old, white-haired chap driving a '52 plate silver Mondeo estate seemingly do this deliberately to me, all the way up the M42/A42 from the M6 to the M1, a couple of months back, but it still sticks in the mind.
He was doing 54mph as I caught him up, then accelerated to 58mph and pulled out just as I was about to box him in behind another lorry, then slowed down to 54mph immediately afterwards, the net effect being that I had to stay in the outside lane for far longer than would otherwise have been necessary. (Well I didn't have to stay there, but it was that or knock the cruise control off.) This happened 10 or more times over 30 miles.
I started getting a little paranoid about him after he ended up getting boxed in behind an artic which joined the motorway in front of him, because he then sped up to around 80-odd and swerved in and out between us to take up his position just ahead of me at 56mph again.
This carried on until the position of vehicles was such that a scaffolders' 7.5t truck took over my "position", when Mondeo man wilfully obstructed him for the final 5 miles or so before we joined the M1 with its manifold lanes and the Ford zoomed off ahead never to be seen again.
There is no way the Mondeo driver was just pootling along, oblivious to all around him. He was clearly playing cat-and-mouse, but for what reason I have no idea. I wonder if he does it a lot?
|
|
|
I totally agree harleyman and is the reason I always suggest that other road users should look at what the lorry is overtaking before complaining about it.
Locally our Scania sealer sets the limiter at 53MPH, Mercedes at 52 MPH and Volvo at 54MPH, and it shows!
Pat
|
|
Although the limit is set at 56 it seems to me some trucks have more grunt than others which can lead to the 10 mile overtake - if two trucks are nose to tail and they get to an incline sometimes the rear truck has the grunt to overtake the lead truck but he must do it before the brow of hill as first truck then gathers speed and truck two is stuck blocking lane - This is where I can't understand truck driver mentality - surely truck one could back off slightly for a second or two - My worst stuck behind truck race was from Junc 3 to Junc 2 on M54. Reading the replies it seems all trucks now have cruise control so now when I leave a reasonable stopping distance from truck ahead and truck behind is tailgating it's not driver but the cruise.
|
Let me try and explain dxp!
The vehicle overtaking gains momentum when running downhill considerably because he weighs 44 tonnes gross. His speed increases well above the limiter and he can see another steep hill ahead so he lets it roll and gains on the empty vehicle in front that weighs only 15 tonnes gross.
Halfway up the hill the overtaking vehicle starts to have to work down the gearbox to maintain 56 mph, and the empty vehicle can maintain it easily. The same happens once over the brow of the hill again.
Of course, what should happen, according to the Highway Code, is that the vehicle being overtaken eases off and lets the other one pass.
Fine in theory but no quite so good in practice, as what happens is that these two vehicles then end up overtaking each other on every slope and in some parts of the rolling countryside that can happen forever.
Points to consider here.
The loaded vehicle needs to use his momentum to save fuel and emissions.
Both vehicles are expected to complete journeys at maximum legal speed as well.
Both will have timed deliveries that don't take into account traffic hold ups and in some cases incur financial penalties for the haulage contractor.
easing off for just a few minutes is fine, but in theory you may have to do it many times over a 10 hour driving day and it does make a considerable difference at the end of a day.
Hope this helps!
Pat
|
|
Some interesting perspectives. I must admit to becoming extremely frustrated at lorry drivers who seem to hog the middle of three or outside of two lanes (the M54 and A42 are two examples that stick in the mind). This is because of the behaviour of the driver of a lorry who was blatantly holding up the traffic on the latter road some years ago, and doing so using frankly dangerous driving, but having read these posts, I realise that there's usually more to it than that.
|
|
|
>>easing off for just a few minutes is fine,
It doesn't take minutes if one dirver eases off - seconds more like
>>but in theory you may have to do it many times over a 10 hour driving day and it does make a considerable difference at the end of a day.
That's a bit of a myth Pat. Think about it and do the sums - the spread of limiter settings you mentioned higher up the thread has a much bigger effect.
|
HGVs have as much right to overtake as any other vehicle, and I don't expect one to whizz past another in a couple of seconds.
But I do think the speed differential should be at least walking pace.
If it's not, either one lorry or the other should ease off.
Allowing an overtake to go on for miles is nothing other than bad driving.
|
|
|
|
>The vehicle overtaking gains momentum when running downhill considerably because he >weighs 44 tonnes gross. His speed increases well above the limiter and he can see >another steep hill ahead so he lets it roll and gains on the empty vehicle in front that >weighs only 15 tonnes gross.
>Halfway up the hill the overtaking vehicle starts to have to work down the gearbox to >maintain 56 mph, and the empty vehicle can maintain it easily. The same happens once >over the brow of the hill again.
You seem to be suggesting that the heavier truck will accelerate faster down hill than a lighter one. They will both be subject to the exact same acceleration. In fact I wonder if the heavier truck will be subject to more friction between the tyres and the road so may actually accelerate slower!
|
>>They will both be subject to the exact same acceleration.
Quite so.
|
>>They will both be subject to the exact same acceleration. Quite so.
A feather and a ball bearing are both subject to the same force per unit mass due to gravity, but the ball bearing accelerates faster (unless in a vacuum). So won't a heavier truck accelerate faster than a lighter one, or is this insignificant, or is it cancelled out by non-air-resistance related drag (as mentioned by previous poster)? Or am I talking rubbish? :-)
|
|
But what about the drag on each lorry - it'll vary, so acceleration down hill will vary.
|
>>Or am I talking rubbish? :-)
If you have 2 identical trucks at the top of the hill - one laden, one unladen - and you let the brakes off and allow them to roll down the hill...
Apart from the higher rolling resistance of the tyres on the laden truck which suffer more deformation, the trucks would both accelerate at the same rate. The aerodynamic drag for both trucks (assuming an enclosed body, like a boxvan body for example) is exactly the same.
If, the drag terms are temporarily ignored, the maths of the situation look like this;
mg sin(theta) = ma
where;
m is the total (effective) mass of the truck (kg)
g is the acceleration due to gravity (approx 9.81 m/s^2)
theta is the angle of the road (radians)
a is the acceleration of the truck (m/s^2)
The vital point is that the m on each side of the equation cancels out, and is therefore irrelevant.
When driven by the engine, i.e., at speeds below where the limiter cuts in, the unladen truck will always accelerate faster than the laden one, uphill, on the level, or downhill. The engine provides another term on the left hand side of the equation above which does not contain the mass of the truck, and so, does not cancel out.
|
NC- thanks, but I'm still missing something.
If you drop an ordinary ping pong ball and one filled with water, the one filled with water will out-accelerate the empty one. They are the same shape. How is this different to the trucks?
|
>>If you drop an ordinary ping pong ball and one filled with water, the one filled with water will out-accelerate the empty one.
No, they'll both fall at the same rate.
|
>>If you drop an ordinary ping pong ball and one filled with water the one filled with water will out-accelerate the empty one. No they'll both fall at the same rate.
I beg to differ! A solid metal ping pong ball has a higher terminal velocity than a hollow plastic one, surely? Which implies its acceleration is also greater, unless they accelerate at the same rate until they reach the plastic ball's terminal velocity at which point the plastic ball suddenly stops accelerating, which seems unlikely?
|
A solid metal ping pong ball has a higher terminal velocity
Sorry - that's a bad example isn't it, because it doesn't take into account the time it takes to reach the terminal velocity. But I still maintain that the metal ball hits the ground first if dropped at the same time as a plastic ball.
|
Yes, the terminal velocity is proportional to the square root of the object's mass, and, I should have added the rider that the acceleration of both objects is the same only at speeds which are low compared with the terminal velocity of the lighter object.
On a road with a light gradient, it's quite reasonable that the terminal velocity is in the speed range that the trucks would be doing.
EDIT: What I did say was this:-
>>If, the drag terms are temporarily ignored, the maths of the situation look like this;
which amounts to the same thing
Edited by Number_Cruncher on 04/08/2009 at 13:31
|
I can't believe this:)
The fact is that most of you have had a far better education than I have to prove theories like that BUT far less experience of the force of 26 tonnes of goods pushing you downhill.
You are NOT accelerating at all
It's simple gravity pushing the lorry downhill.
To prove it I can reach 74MPH fully laden down Corley Bank on the M6 but it stays rigidly to 54 MPH empty.
Pat
|
|
Its nothing to do with gravity, the gravity is a constant. I think the cause for what you're experiencing is likely to be to do with the effect of mass on terminal velocity. If you were in a vacuum (clearly unlikely) then i don't think you'd notice a difference between laden and unladen
|
Pat,
We're talking about how gravity will accelerate the truck.
The trucks starting from rest will accelerate down the slope (in neutral) together. Until the lighter one nears its terminal velocity (your 54 mph example).
>>It's simple gravity pushing the lorry downhill.
No, it's a little more complex than that. It's the interplay between gravity and aerodynamic drag which causes the difference.
As the equation I posted a few posts back shows, without drag forces, there's no difference at all - rolling down a hill, you would not be able to tell one truck from the other.
|
ordinary ping pong ball and one filled with water,
No, they'll both fall at the same rate.
... in a vacuum. In air, the water-filled one will progressively out-accelerate the empty one and reach a higher terminal velocity (I think you'll find, NC).
|
>>(I think you'll find, NC).
That's been dealt with by earlier posts Lud (see the one at 12:29)
|
Right, forget complicated equations then and just tell me why I can reach 74MPH downhill fully laden, but only 54mph unladen?
Pat
|
This is something that obviously DOES happen enough to worry DVLA and VOSA.
They are currently both calling for HGV tests, and training, to be taken in a fully laden vehicle to stop inexperienced drivers being unaware of this effect.
Pat
|
Pat - the answer is in the post timed at 13:07
It's because the terminal velocity of a heavy object is higher than the terminal velocity for a light object - terminal velocity is where the gravity force and the drag forces on the vehicle cancel out.
|
Yes.....................I believe that's just what I said at 9.07, but in simpler terms:)
Pat
|
>>I believe that's just what I said at 9.07, but in simpler terms:)
Yes...., and no!
Yes in that we can understand that a heavier truck will reach a higher terminal velocity, BUT, our detour into Newton's laws of motion have also brought out that the effect is proportional to the square root of the truck's mass - i.e., a truck twice as heavy only achieves 40% or so extra speed if left to acheive terminal velocity.
|
Am I correct in thinking that these trucks doing 70 are freewheeling with neutral engaged? If so there's nothing new under the sun. Big trucks in the late fifties - my hitch-hiking days - were governed I believe to 38 mph. I certainly remember drivers freewheeling down hills at speeds greatly in excess of that. In particular a Tate&Lyle molasses or sugar tanker with trailer, two very heavy, compact vehicles, very smart looking too in navy blue livery, going through the middles of East Anglian villages in the dead of night at 60 or 70.
Very sporting, I thought it.
Edited by Lud on 04/08/2009 at 18:48
|
Certainly not Lud, Aberdeen Overdrive is strictly forbidden:)
Pat
|
Am I correct in thinking that these trucks doing 70 are freewheeling with neutral engaged?
Having once done that with a Fordson Major tractor with a trailer half full of logs, (when I was young and foolish)...I can quite categorically state I will never do so again. That was the first and only time I have ever felt true terror. The fact that i'm still here typing this was down to pure chance.
|
With a tractor's 'suspension', steering and brakes, and a two-wheel trailer with a lopsided load of logs, I think you were out the other side of sporting and verging on jackass territory Westpig (familiar to many of us I hasten to add)... Did you get it to balance for several heart-stopping seconds on two wheels?
:o}
Those fifties and early sixties truckers, or some of them, did some pretty skilled high-speed stuff, but with hindsight I realise it could all have ended quite badly. No doubt it did from time to time.
'What if a kid runs out?'
'It's two in the morning for heaven's sake.'
'I meant an insomniac kid.'
|
it wasn't verging on it Lud...it was definitely 'jackass' territory
the trailer was wider than the tractor and had big metal bolsters (i think they were called that) to keep goods on...i went down a hill off Dartmoor and there was a VW Caravanette coming up the hill. I pulled in tight to a granite wall to give the camper room, but misjudged it and caught the trailer on the wall...which after a terrible grinding sound bounced up in the air and half filled the opposite carriageway. I know all this as i'd set off early, but two lads i'd been working with had caught me up, one of them riding my bike (fizzy) as i was the only one daft enough to drive the thing that far. They filled me in afterwards amongst fits of laughter.
Apaprently I missed the camper van by a gnat's wotsit, then left thick tyre marks through an 'S' bend at the bottom. I can remember one of the front wheels was wobbling badly which affected the steering wheel, presumably because it didn't usually go that fast.
That is not an experience I would ever wish to repeat..and extremely stupid. Trouble is at 16 you think you know it all.
|
And what would you say to the driver if you saw that sort of thing repeated in front of you when you're working? ;>)
ps. I'm sure lots of us have been there and can laugh it off now!
|
Trouble is at 16 you think you know it all
You do, yes, but all those short sharp shocks, so miraculously seldom fatal (Alhamdulillah!), put you on a nice steep learning curve.
Provided, that is, you have the memory of a goldfish or even a cat.
|
|
|
|
|
|
|
|
|
Thanks for that tip about "tail-gating."
It partially explains something I noticed driving London to Inverness in a Mercedes 313 CDI LWB van on a "13" plate from Enterprise van hire.
When the 20/40/60/80 mph speedo was on what I judged to be 40, 50, 60 or 70, the digital display, in kph, was at variance with this. With the digital display reading 106 kph, the needle was on 60mph.
I opted to use the digital display. I inadvertently sailed past a cluster of traffic all matching their speed to a police car in their midst. The digital display was showing 124 kph (77mph). The needles was on 70mph. The police showed no interest.
Who knows what speed I was doing.
I thought of pulling the police over to ask them but rejected this idea on the basis that it might prove very time consuming.
|
|
|
|
