Safe Speed Forums

a few lowloaders have lift axles but not many general purpose trailers do.
the extra weight the "lift" mechanism adds is crucial to hauliers in this cut throat day and age. although it probably only adds a few hundred kilo's , hauliers view this as payload lost, also theres extra cost involved in eitehr converting to lift axles or specifying lift axles when new, again, haulage is very cut throat regarding rates with competition so many just run basic spec equipment to minimise costs.
The lift axle actually saves wear on tyres but in general this doesnt counteract the cost of the lifting axle over the lifespan of the vehicle.

I did some container work out of Felixstowe last year in the process getting my C+E licence.
Mass effects braking distance - empty box you stop easier and quicker, loaded box longer and slower, liquid depends on your baffles slosh slosh
And then be aware of trailer having life of its own

Tires smoking usually when empty because less mass holding trailer down they can also jump a bit.

Same in car more mass longer and harder to stop.

Trailer and cab maintenance depends on company some are good some average and some deathtraps

At least now if your air goes everything locks on used to be that you would lose your brakes.

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I walk I cycle I drive and I vote

Not entirely right, but close enough. Before you think it, I am not disagreeing with you, but with some others.
Generally speaking, trailers have their own air supply, but the actual control is done via relay valves which take the air pressure to the chambers. Spring brakes need air pressure to release them, normally about 55psi, which is what prevents trailers from moving when the red (supply) line is disconnected. Without spring brakes, the trailer would lose it's brakes once the air in the tanks is depleted.
As for crude suspension, steel springs vibrate at around 150 times per second, this means your car springs as well as trucks. Air suspension vibrates about 8 times a second. That's why it's called road friendly. It also activates the load sensor valves which regulates the amount of air going to the chambers. Load sensors can either be a valve on the axle, normally the middle of the 3, or operate on air pressure alone through a guage. I have seen this, but it is very rare in Western Europe.
That poster who said they saw a trailers wheels lock up on a bend, I bet they were the tyres on the inside of the curve, bearing less weight. Most of the ABS systems work on a per-axle system so the chambers get the same amount of air on both sides. This means that the side bearing the weight is going to have better traction. ABS is compulsory on heavy vehicles now, but it won't operate as quickly as small braking systems as there is simply too much metal to move at hundreds of pulses per second. I think truck ABS operates at 8 pulses, but don't quote me.

Disc brakes have made a huge difference. They work so much faster that they have probably saved thousands of lives. Trucks will never have the same capabilty, but on a power to weight contest and distance per tonne, your sports hatch against even my Kenworth, the truck would win.

As for what Scanny said regarding tankers, yes and no. the first golden rule with tanks is 'hard stop= handbrake on'. If you have to do an emergency stop then the handbrake should be applied as soon as the vehicle stops. The surge can be horrendous, even with a twin baffled barrel. But when the liquid surges, it transfers more weight forward and applies even more pressure to the drive and front axles. This is where the super singles come into their own on the steer axle.

I never had any trouble with SSs on the front. I found they were ideal for me. Cooler in the summer, and aquaplaning can be just about as bad on 315s.

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Once a Cornishman, always a Cornishman

I can imagine that surging liquids could be pretty dramatic under "hard stop" conditons!

Its a bit of a problem with rockets too!

Especially S1/S2 separation

To borrow somebodys "Sig" from another Forum

Rocket science? That's the easy part: Even I can do that.
It's the engineering that requires great skill and artistic genius.

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"The road to a police state is paved with public safety legislation"

Dusty being new to the forum I would like to try and answer your question without being to technical as an LGV 1 driver for over 30yrs just something to think about is that it is due to weight transference i.e. try riding a bike with only you on it then brake hard now try it with 2 people on the bike and do the same you will see that it takes longer to stop.

But to a bit more serious the reason why LGV,s take longer to stop is because of the gross weight of the vehicle (up to at present law 44 tonnes)
If you have an unladen vehicle it will stop in a shorter distance than a fully laden one due to the sheer weight of the vehicle try and roll a small ball on the floor then roll a larger one and you have the same effect of weight pushing you forwards (i.e. the more weight the longer to stop).

Another reason for rear end shunts (without blaming car drivers) is because a lot of drivers see a gap in traffic and "go for the gap" not realising that the HGV they have just passed will very likely have been using that gap as their stopping distance and suddenly (quite literally in practice it does happen I can assure you) their braking distance is halved or less hence the collision!

Should the load be a "Tanker" then it is compounded by the fact that the load is moving forwards on braking (picture a tidal wave) which adds to the braking pushing the lorry forwards.

Stormin

There was much more I could have said. Take into account the size of the braking systems involved. My old Renault discs were about 19" diameter and 1.5" thick with pads covering 1/5th of the diameter.
The drums on the drive axle had, if I remember correctly, 10" wide shoes on 22" drums. The tank I had had discs all round and you really could stop it well, but you could never stop it as quickly as a car because it is heavy. Too much braking force and the wheels lock up. A skid in a car means the control is gone and the stop takes longer. It can be disastrous. The same rule applies for trucks but the results are catastrophic by comparison.
For the record, Mercedes trucks were using the laser braking on trucks before the cars had it. A lousy idea in practice.
Take a look on google for the Canadian pre trip and air brake theory test books. You will see the amount of force generated by an air system and the actual system itself.
Be as theoretical as you wish, but the bottom line is more weight, longer to stop.

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Once a Cornishman, always a Cornishman

Pity nobody's told the muppets who write the braking distances in the Highway Code that!

What's "laser braking" anyway"?

Well if an article in this months Retro Cars is correct then the answer is pretty simple. According to the article 1 billion tyres are sold every year and 95% are for cars, so just 5% for HGVs. This despite an average truck covering 10 times the mileage of a car! So you can imagine what the truck tyres are made of! No amount of increased braking effort is any use if the tyre's ability to grip is easily overcome. So while there's been a lot of good science here it seems likely the only way to get an HGV to stop in similar distances to a car would mean very different tyres that would wear like those on an F1 car.
Barkstar

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The difference between intelligence and stupidity is that intelligence has limits.

Sorry. The laser braking is the system that measures the distance and applies the brake if you get too close. Nightmarish idea IMHO.
Regardless of the tyres, you would need radically different systems to do it. It would never happen.

Anyway, the tyre sales issue is not that good an indicator. There are more cars than trucks and more foolish car drivers than truck drivers who enjoy wearing tyres out through crazy acts.

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Once a Cornishman, always a Cornishman