Question on singling a truck

[G&K]

Lol. I can usually get at least 1-wheel drive with all three of the lockers engaged. I'm surprised by some of the snowy stuff you can manage even bobtail.

[Dollytrolley]

Lol. I can usually get at least 1-wheel drive with all three of the lockers engaged. I'm surprised by some of the snowy stuff you can manage even bobtail.

Desolation......ya I hear you.....it is amazing were you can go locked-up.......

 

Part of my problem was that I needed to keep the front steers at about 40 degrees right and hard turns work against the lockers.

 

I am know the old shaker would have crawled across the driveway in a hard right turn but the driveway would have been scared pretty deep.

 

As the Brits say.........The old Shaker had "her knickers-n-a-twist".........

 

Likely I would have been better off with a single in this odd twisty little drive.........

 

Drive on......(No wheel spin.....)

[CDR]

If you've got a problem with my NUMBERS, cough up some better ones.

 

If you want to customize the tire pressures better than my 100 psi average, GO AHEAD. Newton has yet to be proven wrong. Plain and simple: an inflated tire is going to be in equilibrium: the air pressure inside is going to press equally around the tire's inner surfaces, which in turn are connected to the outer surfaces. The tire will deform such that the contact path area times the inflation pressure (times the number of tires on the axle) will equal the scale weight for that axle. A tandem truck, loaded the same as a singled truck, will have the increased weight of an additional axle but further distribution of weight across the additional axle, lowering the weight (on ground) per axle. Braking force is calculated strictly on the "normal force" (the downward component of mass under the influence of gravity, so uphill and downhill conditions do change things) times the coefficient of friction. Want better braking? Change tires to a different compound that offers a higher coefficient of friction. Change ABS systems to one that puts sensors on every axle. Otherwise, it's all going to be a wash.

Peety3;

 

No way your going to tell me a 1500lb formula 1 car cannot out brake an HDT!

Physics or not, so I think some calculations need to be recalculated.

 

Curt

[Big5er]

Curt, I'm not getting into the debate but re-read the formula. Of course a car of any kind will out stop an HDT. Use the formula. Its amazing what doing math with teach you.

[CDR]

Big5ver;

 

Ok I will take the shot, but it was a generality that was stated that took me on that tangent.

 

True tires are was seperates (as they say, "the oily bits") from touching down and how we "feel" the road.

 

Curt

[G&K]

Google "chalk method tire pressure".

 

Use either chalk or a strip of masking tape across your steers and drives.

 

If anyone has time, please report back on the difference in contact patches and what pressures you had in the tired on each measured axle.

 

The formula is great, but rubber compounds can vary greatly in how they perform under compressive loading. The smaller the contact patch, the greater the compressive and shear loading per square inch in contact with the road.

 

Given the hard compounds on HDT tires, is a smaller contact patch better or worse than a larger one? You will certainly get closer to the designed psi on your rubber with a smaller contact area.

 

Just from personal experience driving my prejudices, I prefer more rubber on the road, so I like more axles and tires inflated so the manufactures designed contact area is achieved.

 

You mileage may vary, and it's likely my way of setting up is far from the most fuel efficient.

 

Geo

[VegasFlyer]

Curt, I'm not getting into the debate but re-read the formula. Of course a car of any kind will out stop an HDT. Use the formula. Its amazing what doing math with teach you.

It is amazing what math will teach you, however, that formula is only a small portion in determining braking efficiency.

 

This link is a White Paper published by Bendix relating to the new mandate for HDT manufacturers to meet increased stopping distance. There is a lot of dry reading, though a lot of good coverage on the involved physics.

 

http://www.foundationbrakes.com/media/documents/BW7515RSDWhitePaper.pdf

[Big5er]

How this went from the stopping distance to tire inflation beats me but the issue that Peety3 said is still correct...even using the new requirements for big trucks. When all aspects are the same, proper tire inflation, same year, make and model, etc a tandem axle vehicle will not stop that much shorter than a single.

 

Proper tire inflation is crucial..period. Under inflation does not put more patch on the road. It may make your ride "feel" smoother, but it is not safe, no matter how many axles you have.

[G&K]

Nobody is talking about under inflation.

 

We are talking about how much air to put in to make the tire perform as the manufacturer intended.

 

And the correct answer is not to default to 110 psi unless you have good reason for it, like Jack being right on the edge of single axle capacity.

 

Geo

[Dollytrolley]

Wow......this thread is making this old geezer feel younger every day.......Single axle vs two-many-axles, coefficients of friction, rubber compounds, tire-patch-PSI, and then mid-too-high-math.........man oh man......how long do we have to complete the test at the end of this class?

 

OK suppose you weigh 380,000 pounds and you just are inbound from Hilo Hi to Los Angles with 287 folks sitting behind you and the 14 year California drought is finally over........it's raining.........what-ya-gonna-do......simple........tune in the squawk-box and get the latest braking action report for LAX then get out your bird-machine-operations-manual and turn the page 399 and calc the landing speed for the temp. weight , wind component, (and your horoscope).........now you know about what your touch-down speed will LIKELY be (if your not to tired, bored, hung-over, Etc) .......then.........turn to page 653 and look at graph that looks like all of the stock markets plotted for 50 years and then find where your stopping point should be.........IF.........BIG IF.......your auto-spoiler-squat-switch send some electrons to the black-box that DECIDES if it is OK to deploy the spoilers AND then the black-box decides if indeed it's OK to deploy REVERSE Thrust on a bunch of 35,000 HP turbine engines and then the black-box decides is it will allow the ABS to modulate way-more-wheel-barkes then any bird-man could ever count...........so.........IF............just some of the above thing turn out OK you'll get the old turkey stopped in under 10,000 feet and not lose too much luggage along the way......

 

The point is that ya you might have just the right "axle-count" and maybe you have the right "tire-patch-size-PSI" and you have the correct rubber-compound for the exact patch of pavement you are driving on so..........are we totally "Correct" .....yet.........

 

Too many years ago I was supposed to learn to "drive" a old Four-engine- airliner (5 engines if you count the maytag 2 cyl APU) and as I paged trough a manual as big as the NAPA parts-store-counter-book........I could not find ANY page that listed the take-off performance with FOUR engines operating ......plenty of pages were devoted to take offs with two or three engines operating but NO pages listed ALL engines operating............So the next morning I corner the crabby-old-geezer-captain and said " hey Cap......the manual is missing the pages for four engine takeoffs..........I need those pages.........he chuckled and said "no you don't need those pages"............I said "oh ya I do" .........he said " oh no you don't ........those pages don't exist.........you see.....It's-not-a-perfect-world-sonny......some days you will have four engines and your numbers will be much better than with two or three engines......those are the days you are over-paid.......the two and three engine days.... you will be under-paid......provided you make it to pay-day......."

 

Listed or computed distance is great fun.......but remember .......it's-not-a-perfect-world.........

 

Drive on...........( Be careful......../it's-not-a-perfect-world)

[peety3]

Peety3;

 

No way your going to tell me a 1500lb formula 1 car cannot out brake an HDT!

Physics or not, so I think some calculations need to be recalculated.

 

Curt

A bicycle, a formula 1 car, and a hydraulic-braked HDT can, in theory, be stopped in the same distance from the same speed (reaction time aside; we all expect the F1 driver to have better reflexes). Chances are

 

Guess what else? Putting sand in the back of a pickup (that has ABS...) won't change the stopping distance whatsoever. If it's in 4WD, it won't change the traction either.

 

(Big5er, I know I'm wasting my breath, but I'm going to keep repeating myself in the hopes that one of these will stick...)

[rickeieio]

How this went from the stopping distance to tire inflation beats me but the issue that Peety3 said is still correct...even using the new requirements for big trucks. When all aspects are the same, proper tire inflation, same year, make and model, etc a tandem axle vehicle will not stop that much shorter than a single.

 

Proper tire inflation is crucial..period. Under inflation does not put more patch on the road. It may make your ride "feel" smoother, but it is not safe, no matter how many axles you have.

Hmm. I would agree that stopping distance would not be that different, because of weight transfer to the front axle under hard braking. Sort of like when I grab a handful of brake on a sport bike and lift the rear wheel.

 

However, with additional rear weight, stability would increase under that scenario.

[VegasFlyer]

How this went from the stopping distance to tire inflation beats me but the issue that Peety3 said is still correct...even using the new requirements for big trucks. When all aspects are the same, proper tire inflation, same year, make and model, etc a tandem axle vehicle will not stop that much shorter than a single.

 

Proper tire inflation is crucial..period. Under inflation does not put more patch on the road. It may make your ride "feel" smoother, but it is not safe, no matter how many axles you have.

 

 

I would hope that everyone involved here would agree that proper inflation is very important.

 

Big5er, there is a similar diagram to the one you posted which shows the profile of an over inflated tire that is equally bad. I believe that is the point that both Geo and I were trying to make. Nobody is talking about airing down to go off-road and none of the discussion has been about driving offroad, other than a few antecdotal things a couple members added in.

 

If you truly think that increasing the braking surface on one truck will not make it stop in a shorter distance than another equally loaded truck with normal brakes, you might want to tell Bendix and all of the major truck manufacturers, because that is a major component in thier plan to make trucks stop in a shorter distance as required by the new federal mandate. The larger braking surface allows for a greater applied friction force and handling the greater heat produced in a sudden stop.

 

I, for one, am not argueing the formulas or Newtons law. I am saying that this subject is a lot more complex than that, especially when you take it out of a laboratory or test track and throw in uneven road surface, a negative road grade, load shifting, weight tranfer or factors such as centrifugal force in a turn.

 

This probably would be a better discussion around a campfire. The problem with internet debates is that written words sometime take on a different tone that was intended.

 

One other unrelated minor point that I think should be brought up for new drivers. The comparison that Peety3 used included maximum braking to the point of ABS being activated. It is important for folks to understand that Threshold Braking is far more effective in a panic type stop than utilizing ABS. Threshold Braking will take up a whole new thread, but is worth researching if you not aware of it. It is something that is taught to operators of emergency vehicles of all sizes, in most states.

[Dollytrolley]

 

 

I would hope that everyone involved here would agree that proper inflation is very important.

 

Big5er, there is a similar diagram to the one you posted which shows the profile of an over inflated tire that is equally bad. I believe that is the point that both Geo and I were trying to make. Nobody is talking about airing down to go off-road and none of the discussion has been about driving offroad, other than a few antecdotal things a couple members added in.

 

If you truly think that increasing the braking surface on one truck will not make it stop in a shorter distance than another equally loaded truck with normal brakes, you might want to tell Bendix and all of the major truck manufacturers, because that is a major component in thier plan to make trucks stop in a shorter distance as required by the new federal mandate. The larger braking surface allows for a greater applied friction force and handling the greater heat produced in a sudden stop.

 

I, for one, am not argueing the formulas or Newtons law. I am saying that this subject is a lot more complex than that, especially when you take it out of a laboratory or test track and throw in uneven road surface, a negative road grade, load shifting, weight tranfer or factors such as centrifugal force in a turn.

 

This probably would be a better discussion around a campfire. The problem with internet debates is that written words sometime take on a different tone that was intended.

 

One other unrelated minor point that I think should be brought up for new drivers. The comparison that Peety3 used included maximum braking to the point of ABS being activated. It is important for folks to understand that Threshold Braking is far more effective in a panic type stop than utilizing ABS. Threshold Braking will take up a whole new thread, but is worth researching if you not aware of it. It is something that is taught to operators of emergency vehicles of all sizes, in most states.

Yup Vegas..........like the old Capt said " It's-not-a-perfect-world"

 

Drive on........(Brake with care.......)

[G&K]

Amen. Threshold braking was taught on my original CDL course many moons ago. No ABS around at the time.

 

My more recent course taught that truck drum brake systems could absorb about 200hp per drum until heat levels raised to the point brakes faded. Drum expansion came into it at that point too.

 

Modern discs systems were supposed to be capable of absorbing up to about 500 hp per disc and maintaining that level for longer periods.

 

In context, that course was aimed at professional drivers running heavy metal in the Rockies. My 137,500lb liquid N2 tanker was at the low end of that scale. I understand some logging trucks can get up to 250k lbs off road and use water-cooled brakes.

 

So anytime someone calls a braking discussion a simple matter of applying a formula, head for the hills. It ain't nearly that simple unless you have textbook conditions. That would be ISA for the flighty ones among us, and how often do you really see that? Lol.

 

Geo

[Dollytrolley]

Amen. Threshold braking was taught on my original CDL course many moons ago. No ABS around at the time.

 

My more recent course taught that truck drum brake systems could absorb about 200hp per drum until heat levels raised to the point brakes faded. Drum expansion came into it at that point too.

 

Modern discs systems were supposed to be capable of absorbing up to about 500 hp per disc and maintaining that level for longer periods.

 

In context, that course was aimed at professional drivers running heavy metal in the Rockies. My 137,500lb liquid N2 tanker was at the low end of that scale. I understand some logging trucks can get up to 250k lbs off road and use water-cooled brakes.

 

So anytime someone calls a braking discussion a simple matter of applying a formula, head for the hills. It ain't nearly that simple unless you have textbook conditions. That would be ISA for the flighty ones among us, and how often do you really see that? Lol.

 

Geo

Geo.....right on.........

 

IF in a blue-moon you get a ISA day you can bet that the ABS warning lite will be flashing and one thrust-reverser will be inop.........It's-not-a-perfect-world..........

 

I still have some OLD log truck brake-water tanks in the bone-pile behind the shop.......about 250 gallons lasted 20 minutes in the descent down the steep twisty S. Santiam Pass with a load of logs..........with a full-dress D-8 Cat on a lowboy we stopped at Soda-fork and refilled so it took 500 gallons of water for a 20 minute trip and the brakes were still toasty.....

 

Don't forget to calc the brake temp curves class.............

 

Drive on..........(keep those brakes cool......)

[rickeieio]

A bicycle, a formula 1 car, and a hydraulic-braked HDT can, in theory, be stopped in the same distance from the same speed (reaction time aside; we all expect the F1 driver to have better reflexes). Chances are

 

Guess what else? Putting sand in the back of a pickup (that has ABS...) won't change the stopping distance whatsoever. If it's in 4WD, it won't change the traction either.

 

(Big5er, I know I'm wasting my breath, but I'm going to keep repeating myself in the hopes that one of these will stick...)

Yup. And I had a physics teacher who said the same thing.. He dodged the question about why dragsters use big tires at low pressures, much as you are doing.

 

Thy theories of physics don't always work in a real world. Been there, done that, have the cancelled checks.

[GeorgiaHybrid]

Yup. And I had a physics teacher who said the same thing.. He dodged the question about why dragsters use big tires at low pressures, much as you are doing.

 

Thy theories of physics don't always work in a real world. Been there, done that, have the cancelled checks.

 

A dragster uses the increasing tire diameter as part of it's "gear change" at faster speeds. Take a look sometime at launch and then at the 1/8 mile mark. The tire will have a dramatic increase in diameter and it effectively gives them another gear. Running a lower pressure will allow the tire to deform into a less wide but taller shape under acceleration.

[VegasFlyer]

Amen. Threshold braking was taught on my original CDL course many moons ago. No ABS around at the time.

 

My more recent course taught that truck drum brake systems could absorb about 200hp per drum until heat levels raised to the point brakes faded. Drum expansion came into it at that point too.

 

Modern discs systems were supposed to be capable of absorbing up to about 500 hp per disc and maintaining that level for longer periods.

 

In context, that course was aimed at professional drivers running heavy metal in the Rockies. My 137,500lb liquid N2 tanker was at the low end of that scale. I understand some logging trucks can get up to 250k lbs off road and use water-cooled brakes.

 

So anytime someone calls a braking discussion a simple matter of applying a formula, head for the hills. It ain't nearly that simple unless you have textbook conditions. That would be ISA for the flighty ones among us, and how often do you really see that? Lol.

 

Geo

 

 

For a flighty example, my other 18wheeler job involved a Boeing 747. With the 200 series 747 that is identical in nearly every aspect to the 100 series, except the number of brake disks. The 200 series has a major difference in shorter computed stopping distance over an identical weight 100 series, at any given airport. Both aircraft have the same number and type of tires (18).

 

The Boeing data is hauntingly accurate for both takeoff and landing data. All braking data for transport category aircraft is also computed predicated on engine reversers being inoperative. If an airline has a plane with one or two defective brakes, they can still take off but have to invoke a substantial cargo or passenger weight reduction, in case they need to abort the takeoff.

 

As you mentioned, Geo, as the temp goes above ISA, the braking efficiency decreases.

[rickeieio]

A dragster uses the increasing tire diameter as part of it's "gear change" at faster speeds. Take a look sometime at launch and then at the 1/8 mile mark. The tire will have a dramatic increase in diameter and it effectively gives them another gear. Running a lower pressure will allow the tire to deform into a less wide but taller shape under acceleration.

Ha-ha. I had that discussion with the "teacher" long before the move to those tires. AA/FD was just breaking into the low 7 sec. times.

 

I was strictly comparing tire contact patch to lb/in.sq. theory.

[Big5er]

If you truly think that increasing the braking surface on one truck will not make it stop in a shorter distance than another equally loaded truck with normal brakes, you might want to tell Bendix and all of the major truck manufacturers

Yeah, bigger BRAKES make the difference, not bigger or more tires. If you are SKIDDING to a stop, then yes more tires to skid (or drag on the road) will help stopping distance. Rolling resistance does not change much between one axle or two.

 

Performance sufficient to meet the regulation can usually be attained by using larger S-cam drum brakes with more aggressive linings, along with discs in some cases, say representatives at suppliers and original equipment manufacturers. A big majority of buyers will continue using drums because they are familiar items, cost less to buy, sometimes weigh less than discs and still do a proper job. Also, shoes and linings for drum brakes are relatively inexpensive.

But air disc brakes will be used in some vehicles.

“There will be a trend, just like in Phase One vehicles, where we increase brake size on steer axles from 15 inches by 4 inches to 16.5 inches by 5 inches, or from 16.5 inches by 5 inches to a 16.5 inches by 6 inches, or move to an air disc brake,” explains Joseph Kay, director of engineering for brake systems at Meritor. The drive axle drum brakes will also increase in width from 7 inches to 8.625 inches in many cases.

“Moving to a wider brake shoe allows for better energy distribution across the area, which reduces in stop fade,” Kay says. “The drum is larger, and with a larger mass drum, it can manage the energy better and operate at lower temperatures. The benefit of the wider brake’s heavier drums and optimized brake friction materials is increased brake life.”

Full article HERE

I didn't see anything about adding axles or tires, making tires wider, bigger around, or increasing surface contact in order to increase stopping efficiency and cut stopping distance. All they mentioned was better brake PARTS...including those made by Bendix. It would seem that Bendix understands that brake components, not the tire patch on the road equals better braking. Maybe you should have them explain it to you. It appears that Bendix agrees with Peety3 and I.

 

Hmm. I would agree that stopping distance would not be that different, because of weight transfer to the front axle under hard braking. Sort of like when I grab a handful of brake on a sport bike and lift the rear wheel.

 

However, with additional rear weight, stability would increase under that scenario.

And if you add THE SAME weight to both a single rear axle and a tandem real axle truck, it will not radically effect the braking distance between the two.

 

Yup. And I had a physics teacher who said the same thing.. He dodged the question about why dragsters use big tires at low pressures, much as you are doing.

 

Thy theories of physics don't always work in a real world. Been there, done that, have the cancelled checks.

Oh well that is an easy question to answer. I wonder why he dodsged the question, since it has nothing to do with braking..thats why they have a parachute.

A Top Fuel Dragster tire is 36 inches in diameter and uses about 7psi which means that a whole lot of rubber will be in contact with the ground. Big tires create big smoke clouds. Burnouts are done for three reasons:

• To heat the tires making them stickier which creates the necessary traction needed when a Top Fuel Dragster launches from the starting line.
• To lay two patches of rubber, one for each tire, on the race track which helps guides the Top Fuel Dragster in a straight line at the launch.
• To remove debris from the tires which ensures all of the rubber gets in contact with the racing surface.

If you think that will help you with the braking on your HDT then replace your tires with some and see how they hold up to turns and such.

[Big5er]

(Big5er, I know I'm wasting my breath, but I'm going to keep repeating myself in the hopes that one of these will stick...)

It won't..........and now you've got me doing it.

 

I'm done. This debate will go nowhere.

 

One last point. Michelin claims that their super single puts more foot print on the road which helps in "TRACTION" for better "STABILITY". They also talk about better fuel economy and less weight, but nowhere do they mention better stopping ability with this larger foot print. I wonder why?

[VegasFlyer]

Yeah, bigger BRAKES make the difference, not bigger or more tires. If you are SKIDDING to a stop, then yes more tires to skid (or drag on the road) will help stopping distance. Rolling resistance does not change much between one axle or two.

 

Performance sufficient to meet the regulation can usually be attained by using larger S-cam drum brakes with more aggressive linings, along with discs in some cases, say representatives at suppliers and original equipment manufacturers. A big majority of buyers will continue using drums because they are familiar items, cost less to buy, sometimes weigh less than discs and still do a proper job. Also, shoes and linings for drum brakes are relatively inexpensive.

But air disc brakes will be used in some vehicles.

“There will be a trend, just like in Phase One vehicles, where we increase brake size on steer axles from 15 inches by 4 inches to 16.5 inches by 5 inches, or from 16.5 inches by 5 inches to a 16.5 inches by 6 inches, or move to an air disc brake,” explains Joseph Kay, director of engineering for brake systems at Meritor. The drive axle drum brakes will also increase in width from 7 inches to 8.625 inches in many cases.

“Moving to a wider brake shoe allows for better energy distribution across the area, which reduces in stop fade,” Kay says. “The drum is larger, and with a larger mass drum, it can manage the energy better and operate at lower temperatures. The benefit of the wider brake’s heavier drums and optimized brake friction materials is increased brake life.”

Full article HERE

I didn't see anything about adding axles or tires, making tires wider, bigger around, or increasing surface contact in order to increase stopping efficiency and cut stopping distance. All they mentioned was better brake PARTS...including those made by Bendix. It would seem that Bendix understands that brake components, not the tire patch on the road equals better braking. Maybe you should have them explain it to you. It appears that Bendix agrees with Peety3 and I.

 

 

And if you add THE SAME weight to both a single rear axle and a tandem real axle truck, it will not radically effect the braking distance between the two.

 

 

Oh well that is an easy question to answer. I wonder why he dodsged the question, since it has nothing to do with braking..thats why they have a parachute.

A Top Fuel Dragster tire is 36 inches in diameter and uses about 7psi which means that a whole lot of rubber will be in contact with the ground. Big tires create big smoke clouds. Burnouts are done for three reasons:

 

• To heat the tires making them stickier which creates the necessary traction needed when a Top Fuel Dragster launches from the starting line.
• To lay two patches of rubber, one for each tire, on the race track which helps guides the Top Fuel Dragster in a straight line at the launch.
• To remove debris from the tires which ensures all of the rubber gets in contact with the racing surface.

If you think that will help you with the braking on your HDT then replace your tires with some and see how they hold up to turns and such.

You seriously can't see the correlation of manufacturers putting bigger brakes on new trucks and having two extra sets of brakes by keeping the second axle? Braking surface is braking surface whether you have ninety five little brakes or one big one.

 

As to your post on the increased traction of a super single. Michelin doesn't have to say that increased traction equals greater stopping efficiency, the formula that you and Peety3 keep saying is the simple proof to this debate, as well as Newton's Law which Peety3 quoted, proves it.

 

Just sayin......

[G&K]

It won't..........and now you've got me doing it.

 

I'm done. This debate will go nowhere.

 

One last point. Michelin claims that their super single puts more foot print on the road which helps in "TRACTION" for better "STABILITY". They also talk about better fuel economy and less weight, but nowhere do they mention better stopping ability with this larger foot print. I wonder why?

Maybe they aren't pushing braking performance because the brake systems on North American trucks have traditionally been horrible.

 

So the tire 'traction' is not necessarily the limiting factor in OTR work. But that is a flat lander, on highway only point of view.

 

The obsession with the braking formula that I really take exception to is its sensitivity. There are so many really odd factors in the real world that have a huge impact on both traction and braking. Or sometimes just your ability to keep your rig out of the ditch.

 

But my points are all more about finding out the correct inflation pressure, and the interesting point of view that adding an axle doesn't have any effect on ideal inflation pressures assuming you carrying the same load...

[PSD_Tweaker]

I think I'm starting to understand....

 

Rick