Stopping distance question

[VegasFlyer]

14 hours ago, noteven said:

Does speed affect stopping distance?

Speed and weight do effect stopping distance.

Speed is relational to the time required to stop.  Time is relational to the distance.

Weight can be a double edged sword.  With a high amount of weight for a given tire contact area, you are overcoming the forces of kinetic energy and possibly gravity as Steve from SoCal already covered.  With a real light weight for the same tire contact area, such as a bobtail hdt with no bed, the stopping distance can be increased due to the reduced traction.

For the purest out there who love to pick technical pints, The use of the word “traction” while not technically correct, was used for simplicity.  We are not writing. A thesis here.

If anyone wants to see for the self how increased brake surface area can effect stopping distance, look on google, there were a few videos published of a study that was tied to the mandate for manufacturers to reduce the stopping distance on hdt’s.  They tested different brake media and shoe and drum sizes.

[VegasFlyer]

On the topic of ABS, keep in mind that while it is amazing technology that has saved lives, threshold braking is still the most effective form of braking.

For a standard car, if you have one vehicle driver perform a panic stop at 60 mph where they stand on the brake and let ABS work it’s magic.  The car will stop at least one to two car lengths farther than one where the driver applied the brakes up to and just prior to ABS activation.

Granted that takes training and practice and may not be a big deal for some folks, but is important to keep in mind.

[rickeieio]

6 hours ago, VegasFlyer said:

Granted that takes training and practice

And is extremely difficult under a panic scenario.  Practicing in an empty parking lot is one thing.  A panic stop on sketchy surfaces is quite another.

In the early days of ABS, I hated it.  It got me stuck, or prevented me from getting myself unstuck, with a couple of trucks.  But the modern systems are quite good. 

[VegasFlyer]

2 hours ago, rickeieio said:

And is extremely difficult under a panic scenario.  Practicing in an empty parking lot is one thing.  A panic stop on sketchy surfaces is quite another.

In the early days of ABS, I hated it.  It got me stuck, or prevented me from getting myself unstuck, with a couple of trucks.  But the modern systems are quite good. 

Rick,

The beauty of threshold braking, if you mess up and press too hard, you are in ABS.

It is true that whenever you are in a high stress situation, you will usually do exactly what you have trained to do, which for some folks, means nothing.

As far as practice, it is a transferable skill.  If you master it in a smart car, you could transfer that skill to an hdt quite easily.

A lot of LEO’s are taught it in basic and recurrent training.

[Scrap]

Boy you hit my weakness.  I could go on and on about different tracks, frozen lakes, outriggers, endless Bondurant classes, and other stuff shoved into muscle memory, but you know what my #1 crutch is?  Just a simple day of normal trucking with a lift axle.  In a WA mule train it only loads to 30-60 lbs and it is gonna skid.  You know it, the truck knows it, Les Schwab guy knows it, you see everyone elses rubber in the same spots you're leaving it, but man it just messes with my brain.  You hear a single tire slide just behind your cab and you just let up - even though the rest of the truck and trailer were just in a normal slowdown.  I don't know how many near ditchings and other screw ups I've had cuz of it but it is a hard one to let go.  I cuss myself out every time.

[Scrap]

Noteven I don't really have a reference to the numbers except it is a table somewhere in the AASHTO green book.  I get a bunch of truck design articles passed along all the time and I snip out the interesting parts into a fun facts OneNote but don't really spend the time to put a link in to get back later.  Your numbers happened to line up to one of them.  The point of the table in the green book is kind of calculating your situation backwards where they figure highway design standards per truck stopping distance so that a truck sight line (SSD) is always within stopping distance so the hope is that your blind wreck situation can't happen or, well, is greatly reduced. 

The article I was reading was kind of interesting, however, in that the CalTrans author was stating that with CARB every truck in CA five years from now will be 2010+ and therefore will all be RSD (RSD was mid- 2011 so technically he was off a year and a half, but anyways).  It was an academic exercise where they were doing the math to see how much they could change highway design in reduced SSD based on the RSD truck stopping distances.  I've seen other articles where if proposed FMVSS 150 happens for cars in 2020 (and if V2V actually does globally improve reaction time) they were doing the similar math to see what they could do with lesser stopping distances from improved reaction time.

It all brings up an interesting point I hadn't really thought about though.  If you are driving the one lone exempt CARB (thus non-RSD) truck with a 121-exempt trailer amongst a sea of trucks meeting a tighter standard then you really gotta be on your A-game!

Dolly, that log truck was a bad deal.  Hard to get a good stop when you are hunkered down far enough to run your brakes with your hand!  I can't even imagine going through that one.

[rickeieio]

8 hours ago, VegasFlyer said:

The beauty of threshold braking, if you mess up and press too hard, you are in ABS.

It is true that whenever you are in a high stress situation, you will usually do exactly what you have trained to do, which for some folks, means nothing.

Agreed.  And that's why we practice, or we should.  I ride motorsickles.  Some of them are fast. (180 hp)  Knowing your machine, and practicing for an "Oh Crap" moment has saved my bacon more than once.

That said, I'm not gonna practice threshold braking with the camper rig.  Mama doesn't like finding the contents of the medicine cabinet on the floor.  So, ABS is fine with me.

[TreyandSusan]

1 hour ago, rickeieio said:

That said, I'm not gonna practice threshold braking with the camper rig <AGAIN>.  Mama doesn't like finding the contents of the medicine cabinet on the floor.  So, ABS is fine with me.

Did it once to adjust/test new disc brakes and new brake controller and have been reminded that once is enough!

enough (as defined by the dictionary of Susan) - one too many times

[rickeieio]

1 hour ago, TreyandSusan said:

enough (as defined by the dictionary of Susan) - one too many times

Yes, those "Susans" are like that.  When we finished installing the BluDot system, I got a bit aggressive on the brakes, and that was just in the driveway.  Not only did  I re-arrange the coffee cups, I left big divots in the gravel. I got  "the look".

[Hewhoknowslittle]

2 hours ago, rickeieio said:

Yes, those "Susans" are like that.  When we finished installing the BluDot system, I got a bit aggressive on the brakes, and that was just in the driveway.  Not only did  I re-arrange the coffee cups, I left big divots in the gravel. I got  "the look".

Not the look!!

Sometimes that’s worse than the comment I get. 

Roger

[noteven]

One time at the undisclosed location Scrap sometimes is at I had a chance to drive a Yellow T660 / 2 axle trailer 80,000lbs. with disc binders in all wheel positions. How are these ABS disc brakes?  I asked my co-pilot. Give them a try says he. I exited turn 4 at 65 and took the pit road. I applied full braking capabilities. Customer’s about 20 yr old son skidded right off the sofa bed while checking his face book and landed in a pile upon the plush carpet of the Diamond spec sleeper.  The co-pilot says This is why B model sleeper floors are set below the cab floor. . Customer says While I’m down here I’ll check out the low storage area 

[GeorgiaHybrid]

Noteven, it is scary how well disks do at all 4 corners. Ours has stopped a LOT faster than I ever thought possible with a single rear axle truck and kept us from killing a few idiots on the road.

[Vegas Teacher]

On 3/6/2018 at 8:14 PM, VegasFlyer said:

It is true that whenever you are in a high stress situation, you will usually do exactly what you have trained to do, which for some folks, means nothing.

On the way back from Florida Flyer quizzed me several times on "Right now if this happens what would you do?" He made me think about everything that could go wrong.

I am not sure if I will remember anything but I have a foundation to work from. Being new to the Dark side of owning the 780 (Today is the day Flyer and I Flew to Florida) I am glad to have all of my axles and all of my brakes for the positives that were already discussed. When my Schrader Valve Blew and I lost my air, I had not trained for this or knew what to do. My wife called Flyer, never told him but I was to ashamed to call him, but she did. In his statement he said some do nothing. Honestly and I know some on the forum who read this will jump on me for this but I had no idea of what to do, I panicked, hollered a few expletives at the steering wheel and like I said my wife called Flyer. He walked me through what needed to be done next. 

Like E. F. Hutton - when Flyer talks I listen, most of us can't begin to comprehend the amount of training's he has given or gone to where physics is the ultimate explanation for what does or doesn't happen when evasive actions need to be taken. 

Later,

Cory O