Stopping distance question

[noteven]

Downgrade emergency stopping distance: In a truck driving course I was taught on a 6% downgrade/ 80000lbs 5 axles with cool brakes stopping distance at 45mph is around 400ft and at 65mph it is around 780ft. 

I wonder if the ratio is similar with a HDT and weedy brakes rv trailer? 

 

 

 

 

 

 

[Yarome]

43 minutes ago, noteven said:

Brakes are cool. What is your stopping distance

Not to worry.... in that case braking distance is relative and never past the scene of the crash. 

[Steve from SoCal]

1 hour ago, noteven said:

Downgrade emergency stopping distance: In a truck driving course I was taught on a 6% downgrade/ 80000lbs 5 axles with cool brakes stopping distance at 45mph is around 400ft and at 65mph it is around 780ft. 

I wonder if the ratio is similar with a HDT and weedy brakes rv trailer? 

 

 

 

 

 

 

I'm not so sure, a 5 axle truck at 80K has about twice the mass of a typical truck/camper set up.      The truck itself has enough brake for at least 32K on the front and single rear axle, trailer brakes?      The real question with the truck and camper is, are the back tires loaded enough to use all the stopping power they can exert? 

[Alie&Jim's Carrilite]

I know the truck can out brake our RV, even with 6 disc brakes on the trailer.  I don't think its so much the distance involved as it is keeping the trailer from coming around and passing the truck.  

[Mastercraft]

Greetings - For me in that situation with our setup, 50,000#, hitch 6' behind the rear axle, I would be conservative with hammering the brake on a curve so tight that I couldn't see the issue with plenty of time to react.   It seems like I would be going slower than 45 mph if there was a curve coming up that I couldn't see if it was one of those decreasing radius deals as well.  

The 65 mph scenario is undefined for me. Two reasons, usually I go 63ish max, when I can see for a mile ahead. On a 6% downgrade, even at low altitude, the truck would probably be in 10th, so that speed would be too high for that gear.

I know if I were singled in that situation, I would be wishing I still had my other rear axle...... for the next 10 seconds anyway.

[VegasFlyer]

13 hours ago, noteven said:

Downgrade emergency stopping distance: In a truck driving course I was taught on a 6% downgrade/ 80000lbs 5 axles with cool brakes stopping distance at 45mph is around 400ft and at 65mph it is around 780ft. 

I wonder if the ratio is similar with a HDT and weedy brakes rv trailer? 

 

 

 

 

 

 

Based on manufacturing standards for vehicles, I would say that the rv setup would be the same to better, due to the truck having a surplus of brake surface area for the weight.

The prudent rule in operating said rv would be to double or triple those distances with a bit more added in for reaction and denial time.

[VegasFlyer]

1 hour ago, Mastercraft said:

Greetings - For me in that situation with our setup, 50,000#, hitch 6' behind the rear axle, I would be conservative with hammering the brake on a curve so tight that I couldn't see the issue with plenty of time to react.   It seems like I would be going slower than 45 mph if there was a curve coming up that I couldn't see if it was one of those decreasing radius deals as well.  

The 65 mph scenario is undefined for me. Two reasons, usually I go 63ish max, when I can see for a mile ahead. On a 6% downgrade, even at low altitude, the truck would probably be in 10th, so that speed would be too high for that gear.

I know if I were singled in that situation, I would be wishing I still had my other rear axle...... for the next 10 seconds anyway.

Very well said!

There are so many that don’t believe that taking that extra axle worth of brake surface area away, is a big deal.  

With our magnificent country and it’s amazing Constitution, that is thier God given right to have and express thier opinion.  And it is my right to say that they are nuts.....lol

[Pete Kildow]

Used to drive a Tri Axle Dump truck. So tandem axle truck, with a lift axle. 16ft bed sitting on back. Grossing 74,000 lbs and could stop faster then I would have though it would. Never had to try it on a 6% grade. But had to use short braking a few times per day. Something about Paving and cars. There trying to get a dump truck to hit them all the time.

Now if your tractor was a road Tractor. And not set up for bob tailing. Some will take longer to stop empty. Then loaded, as around 1994. Our new trucks had ABS brakes. And would not stop without a trailer. Would take 120ft more bob tailing  to stop.

 

[GlennWest]

My truck is singled and with my 3 axle disc brake system on my Teton, it stops faster than I care to. Had to stop fairly fast on last trip. Had some items to pick up in Teton.

[jkoenig24]

Put head between legs and..........

[Exile]

There are a few factors that change the result for this situation.

 

Is the limiting factor braking power or tire grip?

The answer should depend on weight vs braking power

high braking power and low grip (unloaded truck) the limiting factor is tire grip, and that is why cdl manual says a loaded truck will stop faster than an empty one. There are sufficient brakes, and the grip is high  

If the limiting factor is braking power, then another axle and more braking surface helps.  If lightly loaded and skid starts, or abs kicks in,  too much braking power already, so single might stop faster with better grip. 

I havent stayed in a Holiday Inn Express recently..

[noteven]

In the 2 scenarios (45 mph & 65 mph) with the same vehicle combination, wouldn’t the speed be the determining factor for the stopping distance? 

[rickeieio]

I'm surprised DT doesn't have a spread sheet for this, using the weight transfer from the trailer to the tow vehicle.  With many 5ers being so tall, pin weight might increase  a good bit, putting weight on the rear of the truck, which is itself throwing weight from the drivers to the steer axle. 

I think I'll just use common sense and not over drive my sight distance.

[Scrap]

Your DSRC "hears" of a stoppage within your range.  It pauses your cruise, puts your brakes in take-up, shifts you out of OD, puts your lidar in "bird dog".  It finds the hole, ACB slows you into it, and your lane keeping steers you in it.  You cross the fog line, half hit the gravel, your Hiwghway Departure Warning slows you yet again to where you need to be, deals with the RH side in the gravel, trailer stability jerks you straight, and your lane keeping stops you from trying to steer more than physics allow.  Traction control keeps your RH side moving and you get a ding and a vibration in the azz of your seat with the truck saying it is your turn now, get us out.

You look up, say "whoooa where did that come from!", grab another jerky stick and a sip from the Bubba Keg and ride off into the sunset thinkin to yourself, "man, sucks to be that guy, EH?"   Whole thing wasn't even enough of a deal to burn a smoke over.

Someday it'll come to be!

Anyways, to answer the difference between scenarios, I get 70-ish ft due to take-up, 270-ish ft due to speed, and 80-ish ft due to grade.

[Dollytrolley]

4 hours ago, Scrap said:

Your DSRC "hears" of a stoppage within your range.  It pauses your cruise, puts your brakes in take-up, shifts you out of OD, puts your lidar in "bird dog".  It finds the hole, ACB slows you into it, and your lane keeping steers you in it.  You cross the fog line, half hit the gravel, your Hiwghway Departure Warning slows you yet again to where you need to be, deals with the RH side in the gravel, trailer stability jerks you straight, and your lane keeping stops you from trying to steer more than physics allow.  Traction control keeps your RH side moving and you get a ding and a vibration in the azz of your seat with the truck saying it is your turn now, get us out.

You look up, say "whoooa where did that come from!", grab another jerky stick and a sip from the Bubba Keg and ride off into the sunset thinkin to yourself, "man, sucks to be that guy, EH?"   Whole thing wasn't even enough of a deal to burn a smoke over.

Someday it'll come to be!

Anyways, to answer the difference between scenarios, I get 70-ish ft due to take-up, 270-ish ft due to speed, and 80-ish ft due to grade.

Scrap......your gig sounds like too many electrons and too much work so........just get a few hundred RED printed stickers and paste them on the "operators-Beverage-Mug".........sorta like below......

 

Once I was short of money so I took a gig to test a very bad airplane that had a drag-chute to slow the wreckage before you applied the way way too tiny brakes that would catch fire if you did NOT deploy the chute to get down to brake speed.....so.........

So......... the placard instructions next the the chute leaver printed in RED letters said.......

1. .DO NOT DEPLOY THE DRAG CHUTE UNLESS  THE LANDING GEAR WHEELS ARE IN CONTACT WITH THE GROUND AND THE LANDING IS ASSURED, AS A REJECTED LANDING WILL RESULT IN THE FAILURE TO ATTAIN ROTATION AND A FAILED TAKE OFF ATTEMPT IF CHUTE IS NOT JETTISONED PRIOR TO TAKE OFF!!

2.   IF THE DRAG CHUTE HAS BEEN JETTISONED AND A LANDING IS TO BE ATTEMPTED, LANDING ROLL-OUT IN EXCESS OF 10,000            FT   MAY BE NEEDED TO ATTAIN BRAKE APPLICATION MAX SPEED

3.   LANDING ROLL-OUTS IN EXCESS OF 8,000 FT MAY EXCEED THE TIRE TEMP LIMITS.

4.  GOOD LUCK (sucker) 

 

Did I mention that this turkey was so bad that it never made it to production.........

 

Drive on..........(sometimes stopping is a .........pain.....)

[Dollytrolley]

9 hours ago, rickeieio said:

I'm surprised DT doesn't have a spread sheet for this, using the weight transfer from the trailer to the tow vehicle.  With many 5ers being so tall, pin weight might increase  a good bit, putting weight on the rear of the truck, which is itself throwing weight from the drivers to the steer axle. 

I think I'll just use common sense and not over drive my sight distance.

Rikei-I-Owe..........

Of course I have a spreadsheet that I charge BIG $$$$ to slimy-TrucK-Tort-Wreck-Lawyers when they win huge bucks from jury's and then the insurance  geeks raise YOUR premiums........

Grumps had .........GRUMPS RULE # 1a: ...............NEVER, EVER, E V E R, drive a truck down ANY hill faster than you can get out on the running board and jump off onto the road and land soft enough to NOT jiggle the ash hanging off the end of your roll-your-own-cig...........

 

Drive on............(Drive by the...........RULES......)

[Dollytrolley]

8 hours ago, Scrap said:

Your DSRC "hears" of a stoppage within your range.  It pauses your cruise, puts your brakes in take-up, shifts you out of OD, puts your lidar in "bird dog".  It finds the hole, ACB slows you into it, and your lane keeping steers you in it.  You cross the fog line, half hit the gravel, your Hiwghway Departure Warning slows you yet again to where you need to be, deals with the RH side in the gravel, trailer stability jerks you straight, and your lane keeping stops you from trying to steer more than physics allow.  Traction control keeps your RH side moving and you get a ding and a vibration in the azz of your seat with the truck saying it is your turn now, get us out.

You look up, say "whoooa where did that come from!", grab another jerky stick and a sip from the Bubba Keg and ride off into the sunset thinkin to yourself, "man, sucks to be that guy, EH?"   Whole thing wasn't even enough of a deal to burn a smoke over.

Someday it'll come to be!

Anyways, to answer the difference between scenarios, I get 70-ish ft due to take-up, 270-ish ft due to speed, and 80-ish ft due to grade.

Scrap.........so take a gander at the link below and maybe give a estimate on how much $$$ it might take to replace the Windshield AND the back cab window AFTER they pull the load of logs that pushed all the way through the CAB on I-5 in Tacoma the other day............Bad Juju.......

http://www.kiro7.com/news/south-sound-news/crash-involving-logging-trucks-send-logs-through-trucks-cab/709207438

I can tell you first hand that IF you need to ride in a truck with Logs pushing through the cab its best to have the logs come in to the cab through the back window and then push you out the passenger half of the 54 KW but when you slide to a stop at the front of the hood that nickle plated radiator cap the size of a coffee cup saucer is pretty darn hot.........Thank god no one knew about seat belts and for sure a shoulder strap would have been Bad News.........

Not sure about the new K Woopers but a 54 model flopping on its side in the ditch stops pretty darn fast.........

 

Drive on.............(Get out of the way when the logs come through the cab.........)

[Jemstone]

“There are so many that don’t believe that taking that extra axle worth of brake surface area away, is a big deal.  With our magnificent country and it’s amazing Constitution, that is thier God given right to have and express thier opinion.  And it is my right to say that they are nuts.....lol”

As a “Nut” I feel I need to respond.  I singled my Volvo VNL 730 long, using the vacated axle area for large storage boxes under the deck.  I have no doubt I could stop faster with the other axle still attached, but my stopping distance is good and it’s predictable.  I know how long it will take me to stop and I have NEVER had an exerience in which my brakes were not more than adequate.  My response to your being happy to be in a tandem wheel truck going down hill is that you must have been going faster than I would have been comfortable with.  I rarely use my brakes going down mountains.  The brakes are there as backups for the engine brake.  In emergency situations they have served well.  After all, my entire rig weighs half of what the truck brakes were designed to handle.  

I came to my HDT from a Ford 350.  I suspect most of us coming from pickups will see the singled HDT as a huge upgrade from the pickup, not as a degraded HDT.  Driving the Volvo I have never been pushed into the middle of an intersection by the 5th wheel.  Being pushed into an intersection during a quick stop is what brought me to a HDT.  

[VegasFlyer]

1 hour ago, Jemstone said:

“There are so many that don’t believe that taking that extra axle worth of brake surface area away, is a big deal.  With our magnificent country and it’s amazing Constitution, that is thier God given right to have and express thier opinion.  And it is my right to say that they are nuts.....lol”

As a “Nut” I feel I need to respond.  I singled my Volvo VNL 730 long, using the vacated axle area for large storage boxes under the deck.  I have no doubt I could stop faster with the other axle still attached, but my stopping distance is good and it’s predictable.  I know how long it will take me to stop and I have NEVER had an exerience in which my brakes were not more than adequate.  My response to your being happy to be in a tandem wheel truck going down hill is that you must have been going faster than I would have been comfortable with.  I rarely use my brakes going down mountains.  The brakes are there as backups for the engine brake.  In emergency situations they have served well.  After all, my entire rig weighs half of what the truck brakes were designed to handle.  

I came to my HDT from a Ford 350.  I suspect most of us coming from pickups will see the singled HDT as a huge upgrade from the pickup, not as a degraded HDT.  Driving the Volvo I have never been pushed into the middle of an intersection by the 5th wheel.  Being pushed into an intersection during a quick stop is what brought me to a HDT.  

Well John, that is a valid viewpoint, though your response is flawed with assumption.

While it is great that you are aware of your stopping distances and you have been blessed with never having an experience where your brakes have not been more than adequate.  There are many situations where even the most cautious driver could find themself in a situation where they would be wishing for ten more axles worth of brakes.  One example would be a truck in an oncoming lane, overturning across all the lanes in the direction you are traveling, or another vehicle blowing through a stop sign.

Unfortunately I have personally experienced a couple such issues that were way too close for comfort.   In my professional life, I have investigated a few crashes that had nothing to do with excessive speed, the crash resulted from the inability to stop in time.  Some would not have made a difference with greater brake surface area and some would.

The last federal mandate for truck manufacturers to increase the size of brakes on trucks had a lot to do with those type of crashes.  Not so that truckers could just drive faster.

[beemergary]

Been pulling trailers over 40 yrs. First time out with my dual axle HDT I got cut off and no were to go but run over someone. Well just to say I was" Impressed ". ABS brakes are for morons who can't drive. I am old school.

 

[Alie&Jim's Carrilite]

8 hours ago, VegasFlyer said:

Well John, that is a valid viewpoint, though your response is flawed with assumption.

While it is great that you are aware of your stopping distances and you have been blessed with never having an experience where your brakes have not been more than adequate.  There are many situations where even the most cautious driver could find themself in a situation where they would be wishing for ten more axles worth of brakes.  One example would be a truck in an oncoming lane, overturning across all the lanes in the direction you are traveling, or another vehicle blowing through a stop sign.

Unfortunately I have personally experienced a couple such issues that were way too close for comfort.   In my professional life, I have investigated a few crashes that had nothing to do with excessive speed, the crash resulted from the inability to stop in time.  Some would not have made a difference with greater brake surface area and some would.

The last federal mandate for truck manufacturers to increase the size of brakes on trucks had a lot to do with those type of crashes.  Not so that truckers could just drive faster.

We have been the victim of a brake failure on the RV when we had a pick-up.  Moving to the HDT, even though single, is a huge upgrade in braking ability, and the ability to control an RV.

This is a discussion that needs to involve real scientific data that we as a group do not have.  We need to understand the braking capability of a tandem truck weighing 80,000lb.  A single axle truck weighing 60,000lbs, and the physics that occurs during braking with weight transfer to the front axle, downforce applied by the RV style swing arm hitch (Pick a Brand- ET, Comfort Ride, Trailer Saver, etc) to the rear axle(s) and the trailer braking capability. 

Trailer braking I believe is a mystery science where the manufacturer declares that we will fit the brakes by weight of the RV, but with exceptions.  I have seen older RV's that have 3- 6k axles that have brakes on all axles.  Theoretically one would think that that RV should have better ability than a 2 axle RV weighing the same.  But if the 3 axle RV brakes locks and skids, is it displaying better braking than a 2 axle that the tires never skid, but maintain traction and slow the RV?  

On our HDT's, is singling the truck affecting the amount of downward pressure applied to the contact patch of the tires?  

Does this increase the traction of the rear tractor tires, given the lighter pin weight of our RV's?

Why do some companies run single rears for city deliveries or routes?  Take UPS for instance.  UPS pulls doubles with a single rear day cab tractor on city to city routes?  I would believe that if rear axle traction per pin weight of the pup trailer was an issue it would have been addressed years ago.

Now all that said,  we do need to take into consideration our use of the vehicle.  If I was out west boondocking, I would want tandems, with interaxle lock, and axle lockers.  If I'm carrying a Jeep, and 5000lbs + of pin weight, staying tandem is best because you will overload the rear axle weight wise.  

We're single, and short at 182".  In a hard braking situation with the RV disconnected, the rear of OUR truck squats.  Been there, tried it INTENTIONALLY from 60mph to see what would happen.  (On a straight road, with no traffic in sight for miles).  

[noteven]

Does stopping distance change with speed?

[peety3]

On 3/1/2018 at 10:08 PM, Steve from SoCal said:

I'm not so sure, a 5 axle truck at 80K has about twice the mass of a typical truck/camper set up.      The truck itself has enough brake for at least 32K on the front and single rear axle, trailer brakes?      The real question with the truck and camper is, are the back tires loaded enough to use all the stopping power they can exert? 

Weight does not matter. Coefficient of friction does. Angle of incline does (some of the gravitational force is not applied in a direction that benefits traction). The only difference in stopping distance between a bicycle, car, pickup, HDT, etc., assuming they all have the same tires, is that the vehicle(s) with air brakes have a delay for the air to get to the brakes. That delay is decreased through the use of relay valves, but nonetheless it's non-zero.

Now, if you have any axles without brakes, that's a problem. Any axles without anti-lock brakes is a problem. Etc.

[Steve from SoCal]

Weight doesn't matter?     Kinetic energy is what it all boils down to and weight or potential energy is a part of that.    Coefficient of friction is also relying on the weight on the wheel to attain that level of friction.    ABS will stop the wheel from skidding but, it will apply less braking energy to a wheel that doesn't have a good grip.    A tandem axle with 40" of tire contact loaded with 18K will apply more KE to slow the vehicle than the same axle with 8K.  

 

Steve 

[noteven]

Does speed affect stopping distance?