OT: modern semi-trucks brakes

[Willy]

Yes when you stop and think about not only the sluggish response inherent to air but also the cushioning effect that air has on the system you can quickly visualize why it would be hard to pulse the system rapidly enough to impart the same reaction that hydraulic ABS does.
A quick analogy would be the effect a water hammer arrester has on it's ability to quell water pressure spikes, all it takes is a small amount of air to dampen the pressure spikes.

Truck air brake system incorporate a number of relay valves and quick release valves to speed up the response times of application and release pressure and volume. However as good as they are for their intended purpose they can never approach the speed of a fluid that is essentially non-compressible.

I do have one older 3/4 ton truck with hydraulic drums at the rear that a rear axle only ABS and it works surprisingly well. It is very nose heavy being a diesel powered truck, this combined with large drums at the back to handle it's rated payload capacity gives me ample opportunity to experience the ABS on wet roads frequently if I'm not careful.

I'm not surprised that you haven't seen too many of the telltale tire skid marks signs of large trucks that signify it being ABS equipped since the industry has been slow to accept the new technology. Lots of new technologies wanting everybody's attention coming up to the forefront monthly it seems, coupled with an audience that is apprehensive to spend serious money on it unless they can see it being a viable long term choice.
So everyone sits on the sidelines to see how deep and cold the water is before they jump in. Unlike automobiles trucks and trailers are usually ordered to a buyer's spec to a large extent, hence the slow adoption rate unless the technology has been mandated.

[J Tiers]

Willy, you may be right about the air brakes and response time. makes sense , especially if they have drum brakes, which do not release well anyway.

The type and pattern of the mark made it look rather different, and the ones I have seen are not always dark black streaks, some are more continuous but may seem to have a variation pattern in the streak, and those may be ABS. I do not see as many of them.

[A.K. Boomer]

I can't even wrap my brain around that,,, to look for a larger power source one would have to look to the sun or planetary mass traveling at such and such speed...

I guess dam storage or geothermal would give it a run for it's money lol

[MattiJ]

So what your saying is you would have to make it an unmanned drag car due to separating your aorta from your heart and also keeping your eyes out of your gray matter? lol

My stupidly high horsepower favourite is still the Rocketdyne F1 engine where fuel pump alone is 55 000 HP

[A.K. Boomer]

13 000 hp assuming 0.6G deceleration.
Even a normal passenger sedan brakes ”sees ” over 2000hp if you are doing German Autobahn.

So what your saying is you would have to make it an unmanned drag car due to separating your aorta from your heart and also keeping your eyes out of your gray matter? lol

[Willy]

Yes, but most of the combo's people complain about are 53/102's with 2 axles.

Or 5 axles with the tractor. Even then most of those guys cube out before they weigh out.

[QSIMDO]

Len looking at the weight and the number of axles it looks like the axle loading or weight per axle is the same as here at least.
I've driven 8 axle B-trains here at 140,000 lbs., pretty well the same as the 9 axle 76 ton load that was shown and that had a 2nd steering axle so that would be rated slightly lower, so yeah I'd say the same axle loads.

Yes, but most of the combo's people complain about are 53/102's with 2 axles.

[MattiJ]

Anyone who's good at math care to take a stab at the amount of HP being dumped into the brake system in that short of time frame, then maybe a quick hypothetical on what kind of quarter mile time you would come up with in an average weight drag car (if you could get hypothetical traction lol)

13 000 hp assuming 0.6G deceleration.
Even a normal passenger sedan brakes ”sees ” over 2000hp if you are doing German Autobahn.

[A.K. Boomer]

Anyone who's good at math care to take a stab at the amount of HP being dumped into the brake system in that short of time frame, then maybe a quick hypothetical on what kind of quarter mile time you would come up with in an average weight drag car (if you could get hypothetical traction lol)

[Willy]

Len looking at the weight and the number of axles it looks like the axle loading or weight per axle is the same as here at least.
I've driven 8 axle B-trains here at 140,000 lbs., pretty well the same as the 9 axle 76 ton load that was shown and that had a 2nd steering axle so that would be rated slightly lower, so yeah I'd say the same axle loads.

[MattiJ]

Take note of the number of axles those trucks are on.
Total weight with all that hardware and you couldn't haul more than the proverbial feathers.
That's where the braking capability is, on those axles.

Also note that its 76 metric ton truck, not F150 pulling a trailer

[QSIMDO]

Long time truck driver here, way before CDL's and A/B licenses.

Take note of the number of axles those trucks are on.
Total weight with all that hardware and you couldn't haul more than the proverbial feathers.
That's where the braking capability is, on those axles.

[A.K. Boomer]

Well that first vid in the OP tells me they have made leaps and bounds im just amazed at how fast their stopping those rigs,,,

would be interesting to see a "live" temperature gauge on those brake components ! although it would just be a blur of numbers so you would need a good old fashioned needle and scale...

[Willy]

interesting - could also just be the size and mass of the wheels pretty much adding to the difficulty of "pulsing" something of that nature,,, also the predictability of the rotational mass would be more apt to help to keep it on the threshold - in many ways this a superior system in comparison to the "lock up and let go" tactic,

Willy have trucks gone disc yet? if not that may be a factor too as drums have allot of mechanism to engage and disengage - also - drums are much harder to predict, disc are totally dependent on pressure applied for the needed results - Drums on the other hand are "self energizing" due to the shoes being designed to "rock" into the drum and self wedge to some degree - try pulsing a system like that with any good predictable results... not only very hard to do - think of the wear factor with the shoes fluttering about and the wheel cylinders and seals traveling back and forth so many times a second - things like shoe wear on the backing plate, all the above ------ disc brakes are nearly immune to this effect....

Another factor in favor of the "non-pulse" method of the big rigs, think of all the wheels and wheel sensors you can get involved - this can be very handy feedback to toss into the computer system and use certain wheels as a guideline and then add or subtract to other wheels to make them follow the given RPM's

im not saying that's what they do - but as a mechanical engineer am saying it's possible to do it... the more wheels a vehicle has the closer you can come to perfection... IF the system is fine tuned...

Although disc brakes have been out for a number of years they are only now starting to gain more widespread acceptance. Cost is high compared to drum brakes, about $1,200-$1,500/axle more, but that too has been dropping with wider acceptance. Regulations for decreased stopping distances helped usher in the greater acceptance rate. Much like anything else often time it's legislation that helps the acceptance and adoption of new technologies.
Just think where we'd be without clean air legislation insofar as engine management. We all hate new rules but sometimes that's what it takes, folks don't move unless prodded.

Yes lots of benefits to disc brakes, reduced stopping distance plus the they never go out of adjustment. Auto slack adjusters have helped with drum brakes but they have issues ass well.
Air brake systems including discs simply do not respond rapidly enough for quick on/off pulsations like a solid hydraulic system can. Just not enough time to increase pressure in the system, exhaust it down to zero psi and then rapidly build it up again so the system modulates pressure in order maintain directional control of the vehicle, an attribute that can be very important. Once the wheels are locked solid all you're doing is going for the ride, nice to be able to direct where that 40-70 tons ends up at!
Lots of new drivers out there every day and the demographics have changed substantially over the last decade or two, automated manual transmissions and ABS are helping them be a bit safer and productive. Although many new drivers that only have experience on with the new tech are SOL when their regular ride breaks down and the replacement has 13 or 18 speed transmission and non-ABS drum brakes with manual slacks. It all takes time. LOL

[MattiJ]

interesting - could also just be the size and mass of the wheels pretty much adding to the difficulty of "pulsing" something of that nature,,, also the predictability of the rotational mass would be more apt to help to keep it on the threshold - in many ways this a superior system in comparison to the "lock up and let go" tactic,

Willy have trucks gone disc yet? if not that may be a factor too as drums have allot of mechanism to engage and disengage - also - drums are much harder to predict, disc are totally dependent on pressure applied for the needed results - Drums on the other hand are "self energizing" due to the shoes being designed to "rock" into the drum and self wedge to some degree - try pulsing a system like that with any good predictable results... not only very hard to do - think of the wear factor with the shoes fluttering about and the wheel cylinders and seals traveling back and forth so many times a second - things like shoe wear on the backing plate, all the above ------ disc brakes are nearly immune to this effect....

Another factor in favor of the "non-pulse" method of the big rigs, think of all the wheels and wheel sensors you can get involved - this can be very handy feedback to toss into the computer system and use certain wheels as a guideline and then add or subtract to other wheels to make them follow the given RPM's

im not saying that's what they do - but as a mechanical engineer am saying it's possible to do it... the more wheels a vehicle has the closer you can come to perfection... IF the system is fine tuned...

Disk brakes are nowadays quite common here in Europe, as well as ABS. But not every semi is required to have ABS, only those over 22 meters.
Couldn't pull any % numbers as how many new trucks are still without ABS.
Trucks are also heaver in here than US or (most of the Europe). 76 ton is the new "normal" and with special permission up to 104 tons.