Increase Traction w/o a rear locker? How?

[SnowedIn]

No. You're getting pissed off only because you believe it works. Not because you understand how it works.

This has already been addressed. If providing resistance to the spinning wheel will allow the non-spinning wheel to rotate, then it doesn't matter if the resistance on the spinning wheel comes from braking or actually gaining traction.

All that matters is whether you can apply enough brakes to make it work while not applying so much brake that the gripping wheel fails to turn. The answer to this on many vehicles in many situations is yes; this is precisely how active braking traction control works.

 

[KLF]

I'm not mad, I am calling you out. Disprove all the reasons it might work, or stop shooting them ALL down.

It truly appears that you have not read a single thing I have written. Seriously.
Please read this entire post and save your knee jerk reactions until the end.
I am perfectly happy to “shoot down” things which make no sense. I don't know how you arrived at "ALL."

Describing why you think someone's theory isn't correct, does not disprove anything. You have to provide real world data or your argument is just a theory too. So basically, just saying NO here is why I think so, is not conducive to good discussion. That is you trying to say NO I am right and you are wrong. Yes confirmation bias is real but again you only have your theory, just as we have ours.

Now I will continue with my proposal.

You may not be aware, analysis can be conducted by taking a hypothesis and applying known physical laws to see if it results in some inconsistency. If there is, the hypothesis needs to be adjusted, if only to identify factors which may have been overlooked or omitted. I have been searching for any such unidentified factors to explain the perceived successs “left foot braking.” The “common knowledge” hypothesis tends to gloss over that a stalled wheel is receiving no more driving torque than braking torque. I.e. no net drive

I also cannot overlook that you are heavy on assumptions and light on “real world data,” as discussed further below.

The reason it works with a torque biasing diff is because it enables the exact purpose of said diff, creating thrust and binding within a set of gears so as to "lock" them together. So let's stop mentioning those as that is not what we are talking about.

I am not going to ignore anything that facilitates understanding of the whole system. Let’s at least understand WHY a torque biasing differential can be easily understood to work for the technique - even under the "common knowledge" hypothesis. Whereas (simplified version) an open differential would only provide drive torque equal to the braking torque (no net drive), the drive torque via TB differential can be, for example, 3:1 that of the braking torque. And that clearly accounts for substantial drive.

Stop with the ABS and traction control talk because that is not what we are talking about.

Again you missed that I have been trying to identify factors which would explain why people perceive success in left footed braking. Understanding how all these systems work is useful.
One aspect of traction control (or “inverse traction control” via ABS) is unequal application of braking force as resistance to cause drive torque to be increased to the stalled wheel. That works. But without some other explanation, braking the wheels on opposite ends of an axle in left footed braking fails as a hypothesis since braking torque and drive torque cancel out. I explained how ABS could achieve unequal braking which would facilitate a perception of success via left footed braking.

We are talking about a normal old open differential and stepping on the brake and gas at the same time.

Yes indeed. And we are still seeking a good explanation, not repetition of the same erroneous hypotheses.

I will also say that we aren't increasing traction, we are taking advantage of already available traction.

Absolutely.

To simplify it, increasing traction means a change of tire, a change of surface, a change of contact patch and or the weight pressing the two together. Also maybe tire tread temperature but that's not too likely here.

OK. Are we or aren’t we trying to take advantage of available traction? Now you are talking about increasing traction, not managing/utilizing that which is available.

As I've said, the brakes equalize the torque load at each wheel and help to enable momentary transmission of torque to the tire with grip.

“Saying it” is to assume facts and reach a conclusion. It is not providing any data nor even describinghow this is taking place, using physical laws. Momentary is about as weasly a word as you could use.
Sorry, Bzzzzzt!

Usually the one tire that is spinning has to stop first so in the process of stopping that tire you put some extra heat into that brake. Once BOTH tires are stopped, that brake now holds a little bit firmer than the other side.

There you go assuming again. In this case, assuming the fact that you wish to prove. That’s poor form.
The “extra heat” nonsense is addressed below.

That and the binding effect of the spider gears under load, combined or acting alone, helps to send some torque to the stationary tire. Even for just a second here and there, can help you out of a situation.

So we now have a limited slip differential? Great assumption!
But, seriously, how much binding is possible? Perhaps this should be fleshed out as it has not previously been raised. I am not intimately familiar with how the side gears normally interface with the housing. Can you fill us in on that?
But recognize that you are starting to get into the area of seeing that the “common knowledge” hypothesis for WHY left footed braking may work is probably myth, which was all I was addressing.

But in support of your theory (THIS detail - wedging side gears - not your scattered shotgun approach), it IS consistent with the anecdotal evidence suggesting there is some very slight benefit to the technique (enough to get unstuck, not enough to climb hills or over rocks). And by your theory, its effectiveness would improve with increasing application of brakes and throttle. And it would work even with operation of only the parking/emergency brake.

I think you are discounting brake temp and binding of the spider gears too much. Touching on a torsen style diff, it works by taking advantage of thrust and binding from the gears. It is built to create thrust and binding on purpose but any gear creates thrust in some direction when it is loaded and the more you load it the more thrust it creates. The more thrust it creates, the more binding you get. If one were to create a test rig with an open differential axle you could measure that binding by loading the axle like normal though the pinion. With both tires having full traction but not loaded enough to spin them, if you had a way to rotate that whole assembly so that one tire rotates forward and one rotates backwards while maintaining the load applied to the pinion and measure the force required to do that, you would see just how much the binding in the gears "locks" the two axle shafts together. This is essentially no different than a standard clutch type LSD. It is a resistance to the axle shafts spinning at different speeds.

Let’s start with brake temperature. Yes I am absolutely discounting it. Just out of curiosity, how much braking energy has to be dissipated to stopping a spinning tire? And how many hundred degrees of temperature change does that create? I think we can agree that heat will result from stopping, for example, a 6000 lb vehicle from 60 mph. How does that compare with merely topping one of its freely spinning wheels @60 lbs from, say, 20 mph (and that’s probably high for the speed of a spinning wheel). In terms of energy dissipation, it’s a factor of 900. (Energy = 1/2 mv^2)
Bottom line, we’re likely talking a VERY small difference in brake temperature and a VERY small difference in coefficient of friction from merely stopping a spinning wheel.
But, also, IF a difference in brake temperature (and friction) between sides is what enables the effect, the technique would unequivocally NOT work if the brakes are at the same temperature due to the vehicle sitting. Your hypothesis makes a spinning wheel mandatory, and probably requires that it be spun under heavy load (braking plus throttle) for a period of time to generate substantial heat. That does not fit with descriptions of applying heavy brake and throttle and slowly releasing the brake until the vehicle starts to creep.

Wedging of the differential side gears may be worthy of being added to the list of factors which may contribute to success of the technique.
I like it. It provides some consistency with physical laws, and fits with much of the anecdotal evidence. It would not provide for Hummer-like capability. It is, at best, a very, very weak LSD.

By analogy-
If ABS could indirectly provide “Poor man’s traction control,” wedging of the differential side gears could result in “Poor Man’s LSD”

 

[Haf-E]

I was doing a tire change on a regular open differential rear wheel drive car today and so I tried out the left foot braking technique with one rear tire in the air - no response other than stalling the engine when I put too much brake and not enough throttle. I've also not found it to work in my sprinter van either when I have had it get stuck. Perhaps all of the success stories are with part time 4wd and or vehicles with LSD type differentials and the owners did not know that is what they had?

 

[javajoe79]

It truly appears that you have not read a single thing I have written. Seriously.
Please read this entire post and save your knee jerk reactions until the end.
I am perfectly happy to “shoot down” things which make no sense. I don't know how you arrived at "ALL."

I've read the entire thread and all you have is theory, just like the rest of us. Pardon me if I am mistaken but it seems like you have agreed with no one and you firmly believe it is false.



You may not be aware, analysis can be conducted by taking a hypothesis and applying known physical laws to see if it results in some inconsistency. If there is, the hypothesis needs to be adjusted, if only to identify factors which may have been overlooked or omitted. I have been searching for any such unidentified factors to explain the perceived successs “left foot braking.” The “common knowledge” hypothesis tends to gloss over that a stalled wheel is receiving no more driving torque than braking torque. I.e. no net drive

I also cannot overlook that you are heavy on assumptions and light on “real world data,” as discussed further below.


That is fine. Feel free to analyze all you want but understand that beginning a statement with NO implies that the other person is wrong. There is nothing wrong with informing someone they are wrong, when they are wrong. In this case however, we are all discussing theory. You aren't wrong, we aren't wrong. No one has solid evidence for why this occurs or doesn't. I will add here that I am not glossing over anything. The stalled wheel receives more driving torque than brake torque, that is why it moves.



I am not going to ignore anything that facilitates understanding of the whole system. Let's at least understand WHY a torque biasing differential can be easily understood to work for the technique - even under the "common knowledge" hypothesis. Whereas (simplified version) an open differential would only provide drive torque equal to the braking torque (no net drive), the drive torque via TB differential can be, for example, 3:1 that of the braking torque. And that clearly accounts for substantial drive.

Again you missed that I have been trying to identify factors which would explain why people perceive success in left footed braking. Understanding how all these systems work is useful.
One aspect of traction control (or “inverse traction control” via ABS) is unequal application of braking force as resistance to cause drive torque to be increased to the stalled wheel. That works. But without some other explanation, braking the wheels on opposite ends of an axle in left footed braking fails as a hypothesis since braking torque and drive torque cancel out. I explained how ABS could achieve unequal braking which would facilitate a perception of success via left footed braking.

Again, we aren't talking about anything with either, ABS, TB diff or traction control. So if you please, leave it out of the discussion. It opens up many possibilities in this situation.



Yes indeed. And we are still seeking a good explanation, not repetition of the same erroneous hypotheses.

Let me just say here that calling a hypotheses erroneous, is just like saying NO you're wrong. When again, we are all discussing theory. Until you have actual evidence to disprove something, you can't say it's wrong or erroneous.



OK. Are we or aren't we trying to take advantage of available traction? Now you are talking about increasing traction, not managing/utilizing that which is available.

This was a further explanation of the previous sentence. I thought that was pretty obvious but I guess not


“Saying it” is to assume facts and reach a conclusion. It is not providing any data nor even describinghow this is taking place, using physical laws. Momentary is about as weasly a word as you could use.
Sorry, Bzzzzzt!

Read by itself I could see how this sentence has nothing to offer, however there is an entire post to go along with it that describes how I think it works.



There you go assuming again. In this case, assuming the fact that you wish to prove. That's poor form.
The “extra heat” nonsense is addressed below.

Assuming something that I know to be pretty common. I could see with your self professed lack of experience behind the wheel how you might not get it but this is often the case. You get stuck, tires are spinning like mad and maybe you start trying to use the brake to help you out of a jam. So you've got a spinning tire to stop and you may even be applying throttle still. It takes very little time to heat up a brake pad like that. When you're off roading, the brakes can often times never get touched for long periods of time, leaving them dead cold until now.


So we now have a limited slip differential? Great assumption!
But, seriously, how much binding is possible? Perhaps this should be fleshed out as it has not previously been raised. I am not intimately familiar with how the side gears normally interface with the housing. Can you fill us in on that?
But recognize that you are starting to get into the area of seeing that the “common knowledge” hypothesis for WHY left footed braking may work is probably myth, which was all I was addressing.

But in support of your theory (THIS detail - wedging side gears - not your scattered shotgun approach), it IS consistent with the anecdotal evidence suggesting there is some very slight benefit to the technique (enough to get unstuck, not enough to climb hills or over rocks). And by your theory, its effectiveness would improve with increasing application of brakes and throttle. And it would work even with operation of only the parking/emergency brake.

Yeah man, this kind of understanding comes along with knowing the inner working of vehicles on an intimate level. It is my profession after all. The inner workings of an open differential is automotive 101. I am not going in to that. There are plenty of youtube vids you can watch. Or spend 30 years learning about cars and working on them and building them from scratch in every form.


Let's start with brake temperature. Yes I am absolutely discounting it. Just out of curiosity, how much braking energy has to be dissipated to stopping a spinning tire? And how many hundred degrees of temperature change does that create? I think we can agree that heat will result from stopping, for example, a 6000 lb vehicle from 60 mph. How does that compare with merely topping one of its freely spinning wheels @60 lbs from, say, 20 mph (and that's probably high for the speed of a spinning wheel). In terms of energy dissipation, it's a factor of 900. (Energy = 1/2 mv^2)
Bottom line, we're likely talking a VERY small difference in brake temperature and a VERY small difference in coefficient of friction from merely stopping a spinning wheel.
But, also, IF a difference in brake temperature (and friction) between sides is what enables the effect, the technique would unequivocally NOT work if the brakes are at the same temperature due to the vehicle sitting. Your hypothesis makes a spinning wheel mandatory, and probably requires that it be spun under heavy load (braking plus throttle) for a period of time to generate substantial heat. That does not fit with descriptions of applying heavy brake and throttle and slowly releasing the brake until the vehicle starts to creep.

I will allow all of this stand as it is a fair evaluation. Except the last part, you still do that, only it comes after the spinning wheel stops.

 

[KLF]

It truly appears that you have not read a single thing I have written. Seriously.
Please read this entire post and save your knee jerk reactions until the end.
I am perfectly happy to “shoot down” things which make no sense. I don't know how you arrived at "ALL."

I've read the entire thread and all you have is theory, just like the rest of us. Pardon me if I am mistaken but it seems like you have agreed with no one and you firmly believe it is false.

Never mind. You are indeed mistaken. Sorry I bothered you.

 

[e60ral]

I'm disappointed in high school physics teachers, way too many posters in this thread conflating power and torque

 

[Stumpalump]

I'm disappointed in high school physics teachers, way too many posters in this thread conflating power and torque

For those that sat in the back of the class...Breaking to gain traction mearly slows out of control spinning and engine RPM. With that under control and your foot on the gas you have plenty of smooth power ready for a tires that happen to get some traction. Pump both pedals and away you go! Besides excessive spinning and RPM breaks stuff.

 

[javajoe79]

I'm disappointed in high school physics teachers, way too many posters in this thread conflating power and torque

Who did that?

 

[KLF]

This has already been addressed. If providing resistance to the spinning wheel will allow the non-spinning wheel to rotate, then it doesn't matter if the resistance on the spinning wheel comes from braking or actually gaining traction.

No dispute there. As you have pointed out, this is "precisely how active braking traction control works." When braking only a single wheel. But standing alone, that is of little help in an inquiry toward understanding of a system where both wheels are braked.

All that matters is whether you can apply enough brakes to make it work while not applying so much brake that the gripping wheel fails to turn.

Indeed. But the word "whether" in that sentence indicates a HUGE "if."
(What you are implying here is essentially "if the system works, then the system works." Hardly a surprise, and of little help in analyzing a system)

Please walk us through the math that would accomplish what you have described.

The nice thing about physics is that it IS mathematical and one absolutely can analyze an assumption using ONLY math, based upon known physical laws and or know physical behavior. In this case, simple newtonian physics and the known details of the operation of an open differential.

And if you walk through the math of an entire system where you are braking BOTH wheels on the opposite ends of an open-diff axle, you will find that the "whether" part of your assumption fails. I have done the math before, I'll do it again. Try doing it yourself. Hint: Don't make up numbers that assume what you are trying to prove. Use equations and physical laws to see "whether you can apply enough brakes to make it work while not applying so much brake that the gripping wheel fails to turn."
Bottom line, using your assumption, aka the "common knowledge" version, it does not work.

[AND HERES THE PART THAT MANY SEEM TO BE UNABLE TO UNDERSTAND]
That only means that the underlying assumption fails as an explanation. It does not eliminate other possible explanations within the physical realm.
It appears there are others who think that because something works, that it must work because of whatever faith-based (or oft-repeated) reason they have chosen. Physics is more objective than that. And for all practical purposes, physics is "fact" not theory.

The answer to this on many vehicles in many situations is yes; this is precisely how active braking traction control works.

Sorry. You seem to be waving your hands frantically and trying to cover up your erroneous conclusion with this over-generalized statement.
Traction control works when ONE wheel can be braked independently. As a quick rhetorical question, you might want to ask yourself why traction control systems do not brake both wheels. ("Rhetorical" in this case means PLEASE don't waste my time with the obvious answer)

Now, completely aside from everything above, I have noted that the discussion in this thread has brought to light a factual/physical detail that I believe does provide an explanation that stands up to mathematical/physical scrutiny and can be readily reconciled with the varying anecdotal descriptions that can be found. I acknowledged that in response to the post where it was first mentioned.

So I am satisfied I have the answer I sought when I reopened this ancient thread. http://forum.expeditionportal.com/t...n-w-o-a-rear-locker-How?p=2266550#post2266550
And I am comfortable concluding two things:
(1) "Left footed braking" (or use of the e-brake) can be a viable way of getting more drive to a "stalled" wheel when the wheel on the other end of an open differential has no traction, and
(2) The most commonly cited reason for left footed braking being effective is NOT an accurate physical explanation of why it works.

I don't think anyone here really cares anyhow.

 

[PJorgen]

For those that sat in the back of the class...Breaking to gain traction mearly slows out of control spinning and engine RPM. With that under control and your foot on the gas you have plenty of smooth power ready for a tires that happen to get some traction. Pump both pedals and away you go! Besides excessive spinning and RPM breaks stuff.

Wait, breaking to gain traction? What are we breaking? Maybe it was already broken. I know I didn't break it, someone else must have.

 

[KLF]

Wait, breaking to gain traction? What are we breaking? Maybe it was already broken. I know I didn't break it, someone else must have.

He was only speaking to those who sat in the back of the class with him.

 

[Buliwyf]

You have to have a Torsen style worm gear diff to be able to use the brake pedal to get extra traction. That's what the H1's have, that's why the brake pedal is effective when a tire's in the air.

The Detroit Truetrac is another good example of that. Torsen diffs use weird worm gears. Worm gears are terrible under load and have tons of friction and will bind up. That's why they work so well as an LSD. Under load they stiffen up. Remove all load and they loosen up like an open diff (tire in the air or ice). Stomp on the brake pedal and you reapply load to the diff, it stiffens up and works great.

Factory LSD's and Eaton LSD's won't effectively do that IME. The extra grip they give is about the same as the resistance of the brakes. To a certain extent, pumping the ABS, that some SUV's can do to increase traction works, but it's really really weak and pathetic. It's never saved anyone in the real world.