Well, well, you learn something new every day. No wonder they call it the “spy in the cab.”
Harry Monk:
I monitor my own card and I get harsh braking warnings sometimes, and I’m baffled by them because I can’t recall having braked heavily on any of the occasions I get them.
Knock off the cruise control before you brake Harry. If you are travelling downhill you don’t need to.
If there is the slightest amount of acceleration whilst the cruise control is set, and you touch the footbrake, it will record a harsh brake. I was told this by one of our driver trainers, I didn’t believe it at first until I tested it out.
But surely all the tachograph really detects when you’re moving along (apart from who is apparently driving) is apparent speed at any point in time. Things like distance travelled, how long events have been happening and acceleration might be deduced, but it surely wouldn’t know that cruise control was engaged. I’ve never seen any harsh braking recorded - mind you we are not monitored at our place like some places obviously are - that’s just a job for the monitors.
Snudger:
But surely all the tachograph really detects when you’re moving along (apart from who is apparently driving) is apparent speed at any point in time. Things like distance travelled, how long events have been happening and acceleration might be deduced, but it surely wouldn’t know that cruise control was engaged. I’ve never seen any harsh braking recorded - mind you we are not monitored at our place like some places obviously are - that’s just a job for the monitors.
Quite correct, Snudger, the tacho cannot detect that the cruise control is engaged, but it does detect that you are braking against forward force which it records as a harsh brake. Sounds ridiculous I know, but that’s how it appears to be.
Ah, I see. Presumably the same would apply in the odd situation of somehow accelerating whilst braking then?!
Snudger:
Ah, I see. Presumably the same would apply in the odd situation of somehow accelerating whilst braking then?!
I believe so mate, it was explained to me in a rather technical way, but I’m unable to relay it as some of it went over my head. I did test the theory out and it seems to be correct.
I daresay someone will prove me wrong before the day is out. 
DieselDemon:
Snudger:
But surely all the tachograph really detects when you’re moving along (apart from who is apparently driving) is apparent speed at any point in time. Things like distance travelled, how long events have been happening and acceleration might be deduced, but it surely wouldn’t know that cruise control was engaged. I’ve never seen any harsh braking recorded - mind you we are not monitored at our place like some places obviously are - that’s just a job for the monitors.Quite correct, Snudger, the tacho cannot detect that the cruise control is engaged, but it does detect that you are braking against forward force which it records as a harsh brake. Sounds ridiculous I know, but that’s how it appears to be.
According to Newton’s First Law of Motion, if an object experiences no net force, unless the lorry is stationary (zero velocity) an object (the truck), will move in a straight line at a constant velocity (nonzero velocity) unless you accelerate or decelerate (apply a change in velocity). Therefore, there is always a forward force operating while the object (the truck) is in motion.
Which means that based on the above theory you would always record harsh braking unless you brake when you are already stationary, as, if the vehicle is in motion there is (according to Newton’s Law), a forward force being applied.
PS my memory of Physics is not what it was. I believe the above is about right!
Truckulent:
According to Newton’s First Law of Motion, if an object experiences no net force, unless the lorry is stationary (zero velocity) an object (the truck), will move in a straight line at a constant velocity (nonzero velocity) unless you accelerate or decelerate (apply a change in velocity). Therefore, there is always a forward force operating while the object (the truck) is in motion.Which means that based on the above theory you would always record harsh braking unless you brake when you are already stationary, as, if the vehicle is in motion there is (according to Newton’s Law), a forward force being applied.
PS my memory of Physics is not what it was. I believe the above is about right!
Yes but Isaac Newton knew more about apples than trucks 
Aha! What about if you are going uphill and braking? Surely the force of gravity, which obviously tends to slow a vehicle up, in such a scenario has a rearward effect and yet I bet harsh braking can still be obtained.
Also, you should know, can you record harsh braking tachograph?
Snudger:
Also, you should know, can you record harsh braking tachograph?
tachograph records many things you may not be aware of but due to bad programming not always accurately 
Snudger:
Aha! What about if you are going uphill and braking? Surely the force of gravity, which obviously tends to slow a vehicle up, in such a scenario has a rearward effect and yet I bet harsh braking can still be obtained.Also, you should know, can you record harsh braking tachograph?
Until the vehicle actually stops - it still has forward inertia, but of course this will gradually reduce as the force of the hill and gravity take their toll on the truck. Until it stops though it still has forward momentum. Yes, i’d say harsh braking could still be obtained as unless the vehicle is stopped or an opposite force is applied it still has forward inertia.
The force is known as Impulse, in the case of a lorry the engine accelerating the vehicle. You apply more power on hills to overcome the force of gravity and the slope. The force and time applied are instrumental in applying a change of momentum and the effect is dependant on weight, length of time force applied, friction etc.
So: Impulse = Force x Time…
I doubt whether a tacho can record harsh braking completely accurately. It can probably hint at it with the info it has, speed and time, but there are other variables involved. I doubt it would provide evidence that is cast iron.
But, I’m not a physicist!!!
green456:
but you are a owner driver who monitors his card to see how your driving, [zb] unbeliavble, ratshit indeed
I don’t monitor my driving as such, I do my own tachograph analysis (this will be one of the things VOSA will want to see when they come calling round sometime in the next month or so), and “harsh braking” is something which automatically shows up on tachograph analysis, although that won’t be something VOSA will be interested in.