OT: modern semi-trucks brakes

[A.K. Boomer]

ABS increases stopping distance but allows control of the vehicle during a panic stop where most bad drivers would just lock up the brakes.

It just depends - I get what your saying IF a standard vehicle is perfectly tuned - and by that I mean your still reliant on other systems to be "spot on" and even just changing tires to a different compound can throw things off for you due to it effecting things like proportioning valving and such, (the more gummy the tires the more proportioning is needed to go to front braking as the weight of the vehicle shifts from the rear)

in fact many standard vehicles overkill the front brake system and use very little to the rear, it's a pre-determined safety factor and not under your control - the last thing an auto manufacturer wants is for the rear's to lock up first because this is a high risk factor that the vehicle will then go into a skid and try to swap ends - and a 100% guarantee if someone gets into them heavy during a turn,,,

So - Box stock non-ABS is at a severe disadvantage right from the start,,, it has one advantage from an experienced driver and that 's the fact that you can keep them on the ragged edge of locking up --- but keep in mind your basically just taking about your front wheels - your rear are not even close, yet with an ABS systems the rears can take full advantage of pulse engagement... this is a huge factor...

When I first bought my Del-slow I could not believe how piss poor it stopped, it was horrible and would take so long to stop in a straight line it was very unsafe, also skid the fronts around turns so you would be into a "plow mode" but plow modes to the general public are far safer then swapping ends - let off the brake and you immediately recover,,,

within the first week of owning the car I took apart the "non-tamper proof" proportioning valve and built my own shims and got things dialed - it felt like stopping distance was cut in half - not only that - I can jam on them around a turn and the fronts are still the ones that engage first... Now I can say that I think I would give an abs system a run for it's money.... but no way before - before it would have made my car look horrible...

[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.

[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

[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...

[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.

[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

[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.

[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)

[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.

[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.

[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.

[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

[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]

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

[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.