AWD Braking Discussion: Ideal Brake Force Distribution

[Romer]

No. ABS in the 80> chassis has 4 wheel sensors, 1 for each wheel. Be careful on how you use the term though. 3 Channel ABS usually defines the number of channels coming out of the ABS box, not the number of sensors. For instance, the audis from 1986 through 1992 used 3 channel ABS with 4 sensors.

My 94 has 3 channel ABS with 4 sensors.

ST

So is this how our system operates? If not, please reword, don't explain, just reword it.

Four-channel, four-sensor ABS - This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.

 

[firetruck41]

The major hangup I see here is that IBFD requires some sort of "ideal" condition and operator. That's just not true and *needs* correction. With CDL locked in post 1 any and all brake force (consistent or inconsistent by operator) is allocated ideally in a straight line. Change mu, it holds true. Mixed mu is outside the context of the test or post 1.

FT41, I think you attempt to present with less than ideal conditions you have less than ideal brake force distribution. Possibly. Outside of the scope of Post 1, but let's explore that further. Doesn't changing to mixed mu shift both CDL on and CDL off BOTH further from ideal brake force distribution? It's not automatic to assume at all that CDL off shifts towards IBFD under less than ideal test conditions or real world driving. Insert a huge (Up to and including ABS intevention): It Depends.

You may have difficulty understanding my simple english, but putting words into my mouth that "IBFD" changes in less than ideal conditions, is incorrect. brake force will be distributed the same, however, with CDL locked/ABS off you will not neccessarily have ideal braking.

I also don't agree that bigger brakes give better braking. That's not true. IME, rarely do they give 'better' braking, maybe (if you are lucky) more consistent braking performance. Example: I design and sell Porsche 993 and 996 brake upgrades for the quattros. Stock: 286mm rotor with 2 piston floating calipers vs 345mm rotor with 4 piston fixed caliper. Braking distance and performance doesn't change. Brake fade does. 4 channel abs doesn't give better braking than 3 channel by adding a channel, due to select low principle. A lighter vehicle doesn't give better braking, weight distribution of a given vehicle might. Better rubber? For what condition? FT, none of the changes you propose necessarily give better braking.

The sun may not come up tomorrow, but it probably will. Better rubber might not help you stop sooner, but probably will. If more consistent braking isn't "better" than what is? I have a sneaking suspicion that if I load my 80 with 2000 lbs of cement bags it will probably not brake as well as if it were empty, so I will assume that weight can actually have an effect on braking, contrary to your post.

I disagree that you have the concept right as you reworded it above, and your followup examples of 'better braking' needs defining for me to agree with you. Certainly, none of those items in and of themselves necessarily move you closer to Ideal Brake Force Distribution. Many of them move you further away.

Please either agree that I understand the concept of "IBFD" or show me where I'm wrong. (not: show me where you wish I were wrong, because I disagree with your application/recommendation of frequently driving with CDL locked for best braking during normal driving)

What did you do with the proportioning valve on your lifted truck to compensate for lift?

I adjusted the frame side of the proportioning valve ~1/4" down, IIRC, per recommendations and calculations I found on the web/forum.

Frankly I hoped for a better understanding of the content of post 1.

HTH

ST

Didn't help much, as it is obvious that I already understand IBFD, but disagree with your application, re: drive around with CDL on most of the time.

 

[SUMOTOY]

I don't agree with this. Brake work on surface friction. 100 series Pads are larger and provide more surface are which in turn increases the friction.

...Which results in what? You have increased front brake capacity (short term - long term you have increased heat), you can not yet claim any increased brake performance. You have only more friction for a given piston pressure. I see nothing that translates that to better braking performance. Be careful concluding too much from that mod.

Example: 1g of negative acceleration at 1000psi (stock pad) vs 1g of negative acceleration at 950psi (larger pad). At -1.1g the truck skids. 1100psi of brake force on the stock pad vs 1045psi on the bigger pad. What have you done to change the performance of the truck to take advantage of the extra brake capacity?

I am confused as to why you say disabling the ABS isn't warranted at all. Your test engages the CDL which disables ABS and locks the center diff. I was only suggesting disabling the ABS so that you have only one variable. If the ABS is enabled it will be a factor on the non CDL stopping test. Can't see how it would not be activated, at least thats not the way my truck works.

The test doesn't require impending lockup, you are speaking to a LOT of braking force on dry pavement to have ABS as a variable. Not necessary for the test. Do it if you want Romer, IBFD in the locked diff happens from the time you touch the pedal. I say just don't lockup the brakes. There is no doubt in my mind that ABS intervention on an 80 can't be missed. Outside the test parameter.

I'm not trying to be a hardass, just want to help bring all forum members reading this into the discussion. If you read this thread you will see some get it and some don't.

I find this the nature of all technical discussions.

ST

 

[Grench]

Organizing the bees by wing beats per second

To KISS: I just left it a *given* that CDL-on defines IBFD and CDL-off Defines "less than" IBFD in the test.

OK, I see a potential definition issue.

1. Brake force distribution - Handled by the proportioning valve and ABS to distribute the pressure that is applied through the disc brakes on an FZJ80.

2. Brake force distribution - The net vector force in reverse of the direction of travel.

Sumotoy's examples using the CDL are going to be the most expressive where the front brakes have been disconnected. By linking the axles together through a locked center differential he is forcing/allowing the unloaded rear brakes to assist the front brakes. I believe he is using definition #2.

Since many of us are shadetree wrenches, when we consider ideal brake force distribution, we consider definition #1. The proportioning valve and ABS are our truck's primary methods of distributing the hydraulic forces that control the force that our brake pads exercise in stopping our tires during normal driving.

IMHO 'Ideal' defition 2 brake force distribution would require finding the COG for the truck and mounting a retro-rocket there on the front of the truck at the height and position of the COG.

IMHO an upgrade to 100 series pads and adjusting the proportioning valve should help get a similar effect to what the CDL example is doing and still allow the vehicle to turn and brake under 'mixed mu' conditions.

IMHO the CDL braking example becomes very dangerous in real world 'mixed mu' scenarios and makes it a PITA to turn and causes tire scrubbing & black marks on the driveway.

YMMV.

 

[SUMOTOY]

OK, I see a potential definition issue.

1. Brake force distribution - Handled by the proportioning valve and ABS to distribute the pressure that is applied through the disc brakes on an FZJ80.

2. Brake force distribution - The net vector force in reverse of the direction of travel.

Sumotoy's examples using the CDL are going to be the most expressive where the front brakes have been disconnected. By linking the axles together through a locked center differential he is forcing/allowing the unloaded rear brakes to assist the front brakes. I believe he is using definition #2.

I don't believe this is correct as stated. Brake Force Distribution can follow weight distribution or Brake Force Distribution can follow proportioning valve distribution, or in the absence of a prop valve, Brake Force Distribution follows a fixed brake force distribuiton in the Master Cylinder. ABS intervention compensates for mechanical Brake Force Distribution by moving the Brake Force Distribution closer to Ideal for a given traction dynamic.

Since many of us are shadetree wrenches, when we consider ideal brake force distribution, we consider definition #1. The proportioning valve and ABS are our truck's primary methods of distributing the hydraulic forces that control the force that our brake pads exercise in stopping our tires during normal driving.

A hydraulic valve is not designed to give Ideal Brake Force Distribution, ever. ABS is designed to adjust the mechanical Brake Force Distribution by avoiding lockup.

IMHO 'Ideal' defition 2 brake force distribution would require finding the COG for the truck and mounting a retro-rocket there on the front of the truck at the height and position of the COG.

Ideal Brake Force Distribution means that the braking forces follow the available braking tire load forces caused by the braking (+turning) forces. If you increase COG height you have more front weight distribution for a given brake force. In a locked CDL in a straight line that still follows IBFD/weight transfer. Put another way, it doesn't matter what the COG is, or what the static weight distribution of the truck is. That's the best part of Post 1. Any truck with CDL on, any load, straight line, constant mu.

IMHO an upgrade to 100 series pads and adjusting the proportioning valve should help get a similar effect to what the CDL example is doing and still allow the vehicle to turn and brake under 'mixed mu' conditions.

Moving a braking system towards Ideal is really tough with 'just' hardware, especially true with just pad hardware. You can only claim increase brake capacity, and usually not affect more than capacity. If our trucks skid with maximum brake force, a bigger pad doesn't increase performance. This mod definitely increases heat, which is something the stock pads generate plenty of IME. This mod can allow skid with less applied force. A different stock pad compound and/or better - even just lighter -tires can make a bigger difference. The biggest problem with alxe mounted proportioning valves is that they are a best guess on a stock truck and are rarely linear.

IMHO the CDL braking example becomes very dangerous in real world 'mixed mu' scenarios and makes it a PITA to turn and causes tire scrubbing & black marks on the driveway.
YMMV.

Grench, the last paragraph of Romers cut/paste in #77 confirms my earlier stated positions regarding the ABS = Control falacy. ABS equipped vehicle in and of itself doesn't increase control, specifically, it hasn't shown to be 'safer' than non ABS. My bet if we broke insurance research down further, straight line rear end collisions are reduced with ABS, but *not* avoidance maneuvers with ABS. In the reality of actuary tables, this appears to support a driver training/skillset problem.

The CDL braking example in post 1 demonstrating IBFD has nothing to do with driving around with the CDL locked. Post 1 is a definition and test of Ideal Brake Force Distribution.

ST

 

[SUMOTOY]

Please either agree that I understand the concept of "IBFD" or show me where I'm wrong.
"Braking performance will improve over stock by having CDL locked and braking in ideal conditions on an ideal surface with an ideal driver under test conditions."

* Not "Braking performance will improve over stock" - Post 1 is just defining Ideal Brake Force Distribution
* Not "ideal conditions" - that's not a component of the test. Same mu x 4 (specifically dry pavement in the test, but it applies to any same mu x4 value)
* Not "ideal Driver" - that's not a requirement of the test. quite the contrary, ALL braking force up to lockup, including varying braking force (Like my 15yo in drivers ed could demonstrate this IBFD test)
* "under test conditions" - yes 3 of them - Straight line, mu value x4, CDL locked.

Ben, I'm not convinced you understand the concept, hope my corrections helped. I did try to make Post 1 simple, without commenting on 'driving around with the CDL' in this thread. Happy to continue that discussion in the thread where I did comment on it, it's just not relevent to Post 1 here.

In post 61 you upset the differential nerd in me when you miswrote:

A locked center diff works exactly like a front/rear locked diff in that it sends equal torque 2 different ways.

That is not correct. A locked diff dosen't send equal torque 2 different ways. That is what an OPEN DIFF does = always. To correct: A locked center diff works exactly like a front/rear locked diff only that in a locked diff either axle is capable of supporting 100% of applied torque to the ring gear. In turns, the locked front, locked center and locked rear all "work differently" (torque allocates differently) in relation to the turning variables.

So is this how our system operates? If not, please reword, don't explain, just reword it.

Four-channel, four-sensor ABS - This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.

That's not so easy Romer, because I need to rewrite the above, it's not correct as stated. Any awd vehicle with traction control will have Four Channel, four sensor ABS. Four Channel ABS (4 valves) is a traction control device during acceleration, it operates the same as 3 channel under braking. Some vehicles went to four channel four sensor abs prior to adapting traction control. Not sure if that includes Toyota. I really doubt it, as 4channel ABS usually deletes the rear prop valve.

Here's the easy test. Pop the hood. The ABS controller will have either 5 lines to it or 6 lines to it. If it has 6 lines to it, it has four channel, four sensor ABS. I know on my 1994 80, I have 5 lines at the ABS controller, so for my truck:

Three-Channel, four-sensor ABS - This is the same scheme as 4/4 (because select low principle means that 4/4 send equal pressure to both rear wheels during any ABS activation under braking). There is a speed sensor at each of the four wheels, and a single valve for the rear brake ciruit. With this setup the controller is monitoring each wheel individually to make sure the fronts are achieving maximum braking force and each of the rear brakes is achieving the same maximum braking force as the wheel with the least traction.

And a rewrite of the above to be more accurate to how I understand Select Low Principle to work:

Four-channel, four-sensor ABS - This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. "With this setup the controller is monitoring each wheel individually to make sure the fronts are achieving maximum braking force and each of the rear brakes is achieving the same maximum braking force as the wheel with the least traction. Normally applied with the addition of traction control, the rear valves only operate independently under acceleration, under braking they operate the same as a 3channel ABS rear circuit."

HTH

ST

 

[landtank]

I've been self absorbed in my own posts lately and missed this one. Entertaining read to say the least.

 

[firetruck41]

* Not "Braking performance will improve over stock" - Post 1 is just defining Ideal Brake Force Distribution
* Not "ideal conditions" - that's not a component of the test. Same mu x 4 (specifically dry pavement in the test, but it applies to any same mu x4 value)
* Not "ideal Driver" - that's not a requirement of the test. quite the contrary, ALL braking force up to lockup, including varying braking force (Like my 15yo in drivers ed could demonstrate this IBFD test)
* "under test conditions" - yes 3 of them - Straight line, mu value x4, CDL locked.

*"Braking performance will increase over stock"- I thought post 1 was defining IBFD, and applying IBFD by testing it? Regardless, that has no bearing on my comprehension of IBFD.
*Ideal condition- OK not "ideal conditions", just controlled conditions.
*Ideal driver- I don't know what you want to call the driver, but IBFD may not occur with any driver, as some drivers will lock up.
*"under test conditions* thanks for agreeing with me, but it also includes a driver that does not lock up

Ben, I'm not convinced you understand the concept, hope my corrections helped. I did try to make Post 1 simple, without commenting on 'driving around with the CDL' in this thread. Happy to continue that discussion in the thread where I did comment on it, it's just not relevent to Post 1 here.

In post 61 you upset the differential nerd in me when you miswrote:

That is not correct. A locked diff dosen't send equal torque 2 different ways. That is what an OPEN DIFF does = always. To correct: A locked center diff works exactly like a front/rear locked diff only that in a locked diff either axle is capable of supporting 100% of applied torque to the ring gear. In turns, the locked front, locked center and locked rear all "work differently" (torque allocates differently) in relation to the turning variables.

Sorry, I don't have the terminology down. I understand how a locked differential works. Basically, in this case one shaft goes in and two shafts come out, and both "outputs" turn at the same rate, regardless of traction or not. Maybe terminology is wrong and I'm sure you will correct it.

 

[KliersLC]

So....

nobody thinks the axle winch to keep the rear end down is a good idea?


Much simpler than this three pages of technospeak.....

 

[Jason Andrews]

So....

Much simpler than this three pages of technospeak.....

Exactly, I am not a TechHead, but I do know how to drive and test in conditions we are talking about and see the advantages and disadvantages.

I do not understand why SUMO wants us to drive CDL engaged on dry pavement as I have no control braking issues when on dry roads. However, I do see all the GREAT advantages when not in traction situations.

OK, I see a potential definition issue.

IMHO an upgrade to 100 series pads and adjusting the proportioning valve should help get a similar effect to what the CDL example is doing and still allow the vehicle to turn and brake under 'mixed mu' conditions.

IMHO the CDL braking example becomes very dangerous in real world 'mixed mu' scenarios and makes it a PITA to turn and causes tire scrubbing & black marks on the driveway.

YMMV.

Umm,...no, no and well no. If you think CDL is a PITA dont drive on pavement where all four wheels are getting traction. Does anyone acknowledge we are talking about different subjects here. I am speaking of situations where one or more wheels are loosing traction, ie snow and ice. SUMO is talking about that AND on dry pavement. Will someone at least agree that it is a 100% improvemnt with CDL on in snow and ice?

Whether ABS or not the truck has the same "braking" point to where non ABS locks up and ABS engages and still does not slow you down that much better, or give that much better control in all situations.

Oh, and Grench I will give you a break, cause I just had a friend in town that lives in Omaha. He said is has not snowed a lick there all year. Unless it has in the past week since he has been here. So, you have no idea what you are saying when you say i"t is dangerous in real world scenarios with mixed mu" It sounds correct in theory but just actually test it out if you ever have a chance. The only time I feel it is a disadvantage is pulling in and out of parking spots or making 3-point turns. Even turning onto a street at a reg 90* angle the truck handles much safer and will not slide sideways when braking or accelerating like it can if you have the CDL off and are traveling faster than you should be.

Seems like everyone is claiming that with the CDL engaged you must have ideal braking force applied to the pedal or it will potentially be dangerous. IMHO it is completely the opposite. Romer, have you tried testing out this theory?

 

[firetruck41]

Exactly, I am not a TechHead, but I do know how to drive and test in conditions we are talking about and see the advantages and disadvantages.

I do not understand why SUMO wants us to drive CDL engaged on dry pavement as I have no control braking issues when on dry roads. However, I do see all the GREAT advantages when not in traction situations.



Umm,...no, no and well no. If you think CDL is a PITA dont drive on pavement where all four wheels are getting traction. Does anyone acknowledge we are talking about different subjects here. I am speaking of situations where one or more wheels are loosing traction, ie snow and ice. SUMO is talking about that AND on dry pavement. Will someone at least agree that it is a 100% improvemnt with CDL on in snow and ice?

Whether ABS or not the truck has the same "braking" point to where non ABS locks up and ABS engages and still does not slow you down that much better, or give that much better control in all situations.

Oh, and Grench I will give you a break, cause I just had a friend in town that lives in Omaha. He said is has not snowed a lick there all year. Unless it has in the past week since he has been here. So, you have no idea what you are saying when you say i"t is dangerous in real world scenarios with mixed mu" It sounds correct in theory but just actually test it out if you ever have a chance. The only time I feel it is a disadvantage is pulling in and out of parking spots or making 3-point turns. Even turning onto a street at a reg 90* angle the truck handles much safer and will not slide sideways when braking or accelerating like it can if you have the CDL off and are traveling faster than you should be.

Seems like everyone is claiming that with the CDL engaged you must have ideal braking force applied to the pedal or it will potentially be dangerous. IMHO it is completely the opposite. Romer, have you tried testing out this theory?

A couple of points, mixed mu does not necessarily refer to snow or ice. I think some people are claiming that with CDL engaged and ABS disabled, that someone who locks up the brakes is probably at a disadvantage to someone who applies to much brake pressure but still has ABS, referring to everday driving, not necessarily deep snow.

 

[Grench]

Ahh... finally... more bees to mess with.

Umm,...no, no and well no. If you think CDL is a PITA dont drive on pavement where all four wheels are getting traction. Does anyone acknowledge we are talking about different subjects here. I am speaking of situations where one or more wheels are loosing traction, ie snow and ice. SUMO is talking about that AND on dry pavement. Will someone at least agree that it is a 100% improvemnt with CDL on in snow and ice?

Snow and ice is precisely where ABS gains a gigantic advantage. Not in braking, but in control. A stopped/sliding wheel has NO directional stability. No, you can't swerve even with ABS on a sheet of ice. What you can do is put the brake through the floor and still guide the truck instead of twisting like a top.

Whether ABS or not the truck has the same "braking" point to where non ABS locks up and ABS engages and still does not slow you down that much better, or give that much better control in all situations.

Not in all situations, but a lot more situations than a non-ABS vehicle.

Oh, and Grench I will give you a break, cause I just had a friend in town that lives in Omaha. He said is has not snowed a lick there all year. Unless it has in the past week since he has been here. So, you have no idea what you are saying when you say i"t is dangerous in real world scenarios with mixed mu" It sounds correct in theory but just actually test it out if you ever have a chance.

It snowed 5" here last weekend on top of 1.5" of ice. This was just a bit west of here:
http://www.extremeinstability.com/06-12-31-4.htm
I was out driving around in the thick of it pulling people out. I even strapped a U-haul for a mile up a sheet of ice. And yes, I tried CDL/nonCDL+ABS. Neither one had an advantage in stopping power. With the CDL example the truck would slide sideways in whatever rut or texture there was to the underlying ice. With the ABS it would brake straight as an arrow, sounding like a machine gun as the ABS rattled like mad. I've been driving Land Cruisers for nearly 6 years now including a '92 (without ABS). I have done with and without CDL braking on both a '92 and a '96 in pretty much every road condition imaginable. We do get them all here. I can tell you with 100% certainty that under snot slick conditions ABS is a godsend for control.

The only time I feel it is a disadvantage is pulling in and out of parking spots or making 3-point turns. Even turning onto a street at a reg 90* angle the truck handles much safer and will not slide sideways when braking or accelerating like it can if you have the CDL off and are traveling faster than you should be.

1. slow down.
2. If you're sliding sideways under acceleration on dry pavement in an FZJ80, I want your engine.
3. If you're sliding sideways under acceleration on snot, then by all means have the CDL on when starting off. I know I sure do. I also turn that sucker off once I get going so I can stop straight.

Seems like everyone is claiming that with the CDL engaged you must have ideal braking force applied to the pedal or it will potentially be dangerous. IMHO it is completely the opposite. Romer, have you tried testing out this theory?

You addressed this to Romer at the end, but everyone at the top so I'll respond here too. CDL or no CDL, if you have the ABS off and put more pedal in than there is traction surface, you will slide in the direction of your greatest momentum.

All you are truly doing with the CDL engaged is augmenting the front brakes using the rear brakes through the driveline. The risk is when you put your foot through the brake and slide sideways instead of coming to a controlled stop.

We mentioned that the insurance folks found that non-ABS and ABS vehicles have about the same death rates. I don't doubt it, but I think there are reasons for this beyond the safety of the vehicle. During the time period that the test was done, ABS was a new thing. People didn't know completely how to use it. I.e. the stomp, stay, steer thing wasn't happening as all of the drivers had trained on non-abs vehicles. Remember that the study was from 1996 data. What? Nothing in the last 10 years?

Now that a majority of vehicles have ABS, it is not in the insurance companies best interest to redo the study. Also, people with ABS tend to not follow the one most important rule when driving on slick roads (slow the $%^@ down.) They tend to think that the ABS will save them and over do it. Now that the majority of vehicles on the road have ABS there is still the giant issue of people driving like idiots.

IMHO... if you are cornering an FJ80 or FZJ80 hard enough on pavement to 'feel' a difference in slide between the CDL on and the CDL off, you are driving the wrong vehicle. If you would rather slide sideways in an emergency stop than to maintain control, buy a pre-1995. I -like- being able to stop in a straight line regardless of conditions. I -like- being able to maintain control with 2 wheels on ice and two on pavement when driving a 6,000lb truck.

I've had a couple of times where I needed to slam on the brakes at 80mph on the interstate. I did a 130 mile per day commute. At those speeds concrete is essentially ice. Yes, ABS helped then too. Not nearly as scary as it was in the non-ABS vehicle. Stopping straight is the key. The rest is for the track.

YMMV

 

[scottm]

Wow, interesting thread. Useful? Not really. The last two engineers we fired kept designing machines that worked on paper, but not in the real world. "Ideal Braking Force Distribution" isn't especially practical if it causes bigger problems than it solves. Any time you link axles and wheels together, you will get exactly the same braking force to each, distribution of force will be perfect. With all the diffs locked, one brake can evenly slow every wheel, because they're mechanically linked to that brake. Is that practical? If it was, we wouldn't have these heavy, expensive, complicated differentials. We'd also have one brake per axle, maybe one per vehicle, and wheel/hub/suspension design would be much simpler. Your proposal is a primitive design with obvious advantages and disadvantages. It's not practical, so why go on about it, other than to stir up an argument?

On my two '97s, the rear brakes tend to lock up before the front. I hear a quick "chirp" before the ABS evens things out. That's as close to optimum stopping effort as my truck can accomplish, and it does a good job. Without ABS, I can't apply the right braking force to each wheel to keep each tire just barely skidding. With ABS, I can do that, I just stomp and hold the pedal. If I'm in the real world, always with slightly more traction available on one side or the other, I can still do that. Hauling a trailer or with a loaded roof, I can still do that. If I have to maneuver while panic braking, I can do that. Because I have ABS. If I lock my CDL and my axles, I can't do that, because I can't possibly ever know how close to skidding I am. In the real world, I'd be well below the max braking capabilities, or skidding. "It works on paper" doesn't ease my mind when my wife or daughter or son take my 80 out on a snowy night, ABS does.

In response to the comments about upgrading brakes, if your brakes can already apply more friction than your tires can apply to the pavement (you can skid your tires), then better brakes won't allow you to stop faster. Better brakes may resist brake fade better, but that might not be a noticeable improvement in daily use or panic stops. I'm quite sure our intellectual contributors know this, not sure why they can't tell you this, instead of just telling you you're wrong.

Three of five family members are puking sick, I'm exhausted & in a foul mood. I'm venting, sorry if I've offended, but I feel better now .

 

[SUMOTOY]

Snow and ice is precisely where ABS gains a gigantic advantage. Not in braking, but in control. A stopped/sliding wheel has NO directional stability. No, you can't swerve even with ABS on a sheet of ice. What you can do is put the brake through the floor and still guide the truck instead of twisting like a top.

Not correct as stated. Snow buildup under the tires will mean the advantage goes to the non ABS vehicle in braking. As I've stated many times, ABS = Control is a falacy. For ice, you can come to Steamboat. IME, ABS on ice is almost worthless, and it makes any steering input more dramatic.

We do get them all here. I can tell you with 100% certainty that under snot slick conditions ABS is a godsend for control.

I disagree. I will be in 'snot slick' (12in of ice) next month and was there last year. I concluded many years ago, when it gets snot slick, the Blizzacks were the 'godsend for control', the ABS was worthless, so was the unlocked CDL.

... I also turn that sucker off once I get going so I can stop straight.

I think you are getting closer to driving style than equipment. On ice the best control under braking will be in a straight line.

All you are truly doing with the CDL engaged is augmenting the front brakes using the rear brakes through the driveline. The risk is when you put your foot through the brake and slide sideways instead of coming to a controlled stop.

No, mistatement. All brake capacity is equalized to weight distribution thru the driveline. That can be back to front, or front to back. You aren't 'augmenting' anything, only using the available brake capacity TO get closer to Ideal Brake Force Distribution. I don't agree with your terminology Grench. The risk of sliding sideways is not necessarily a braking problem, cause or solution.

We mentioned that the insurance folks found that non-ABS and ABS vehicles have about the same death rates. I don't doubt it, but I think there are reasons for this beyond the safety of the vehicle. During the time period that the test was done, ABS was a new thing. People didn't know completely how to use it. I.e. the stomp, stay, steer thing wasn't happening as all of the drivers had trained on non-abs vehicles. Remember that the study was from 1996 data. What? Nothing in the last 10 years?

ABS has been around for 10+ years prior to that study. I agree people aren't properly trained on how to use it effectively, that's more than 'just' in stopping distance, as the study confirms. I rephrased that to mean ABS doesn't not equal Control. What this study does is support the statement. *Steering Control* under ABS activation doesn't correlate to *Vehicle Control*. I'd bet that hasn't changed in ten years. What has is Stability Control Programming. Here's hoping *that* makes a difference. Right now there is no discount for it in the insurance actuary tables.

Now that a majority of vehicles have ABS, it is not in the insurance companies best interest to redo the study. Also, people with ABS tend to not follow the one most important rule when driving on slick roads (slow the $%^@ down.) They tend to think that the ABS will save them and over do it. Now that the majority of vehicles on the road have ABS there is still the giant issue of people driving like idiots.

My observation is that there are more SUV's in the ditch. I believe that's a problem with AWD/4wheel drive and 'over do it'. The best interest in the insurance company is to make money based on actuary tables. They do studies all the time. Moot point really, the study referenced isn't an insurance study, it's a NIHS study.

IMHO... if you are cornering an FJ80 or FZJ80 hard enough on pavement to 'feel' a difference in slide between the CDL on and the CDL off, you are driving the wrong vehicle. If you would rather slide sideways in an emergency stop than to maintain control, buy a pre-1995. I -like- being able to stop in a straight line regardless of conditions. I -like- being able to maintain control with 2 wheels on ice and two on pavement when driving a 6,000lb truck.

IMHO, if you believe ABS = Control, you accept the falacy of the marketing. Driver training and proper equipment makes a bigger difference to control. I personally like having the right tires on my truck for the conditions. Blizzacks for the winter takes the ABS argument and shelves it, period. Using the very arguments here, with Blizzacks mounted on an 80, locking the center diff gives more control on ice, snow and water than the stock tires with ABS.

I've had a couple of times where I needed to slam on the brakes at 80mph on the interstate. I did a 130 mile per day commute. At those speeds concrete is essentially ice. Yes, ABS helped then too. Not nearly as scary as it was in the non-ABS vehicle. Stopping straight is the key. The rest is for the track.
YMMV

It does. I've had several times where I needed to slam on the brakes during driving. I can say that finding the ABS threshold hasn't been very often in the 80, which I attribute to driver education/skillset issue. Maximum Braking is most efficient in a straight line.

ST

 

[SUMOTOY]

... Any time you link axles and wheels together, you will get exactly the same braking force to each, distribution of force will be perfect.

Not true as stated. With a locked center diff, braking force will follow exactly weight distribution. It's exactly *not* "the same braking force to each" (unless weight distribution is always 50/50). The unequal Front/rear braking force will exactly *follow* Weight Distribution which is considered Ideal Brake Force Distribution under the test conditions in post 1. Sorry to nitpick, but a lot of confusion on this forum from misunderstanding how diffs work under torque and reverse torque. You can say that the total braking force of all linked axles is available to any single axle, but each axle doesn't have the same braking force, that's a dependent variable. I don't want to speak to 3 diffs locked yet Scott as that changes the dynamic outcome again. Let's stick this to post 1 definition and test for now.

If I lock my CDL and my axles, I can't do that, because I can't possibly ever know how close to skidding I am. In the real world, I'd be well below the max braking capabilities, or skidding. "It works on paper" doesn't ease my mind when my wife or daughter or son take my 80 out on a snowy night, ABS does.

Read post 41 before we go too far down 'real world' scnearios. ABS is quite useful to 'help' inexperience it's not a substitute for it. It doesn't replace proper training or skillset training. I have a better confidence that with ABS on in my 'loaned" truck it will come home without scratches, but I get more confidence at home by being assured all the drivers in my house are properly trained at the limit of adhesion. Then if ABS fails, I have confidence that I have not relied on ABS to be the crutch to proper vehicle control. The available documentation on ABS vs vehicle control supports that philosophy.

In response to the comments about upgrading brakes, if your brakes can already apply more friction than your tires can apply to the pavement (you can skid your tires), then better brakes won't allow you to stop faster. Better brakes may resist brake fade better, but that might not be a noticeable improvement in daily use or panic stops. I'm quite sure our intellectual contributors know this, not sure why they can't tell you this, instead of just telling you you're wrong.

I agree with you here. I'm no intellectual, you find those exact comments in post 83 and 86 in this thread, I did the best I could.

ST

 

[FirstToy]

Wow, interesting thread. Useful? Not really. The last two engineers we fired kept designing machines that worked on paper, but not in the real world. "Ideal Braking Force Distribution" isn't especially practical if it causes bigger problems than it solves. Any time you link axles and wheels together, you will get exactly the same braking force to each, distribution of force will be perfect. With all the diffs locked, one brake can evenly slow every wheel, because they're mechanically linked to that brake. Is that practical? If it was, we wouldn't have these heavy, expensive, complicated differentials. We'd also have one brake per axle, maybe one per vehicle, and wheel/hub/suspension design would be much simpler. Your proposal is a primitive design with obvious advantages and disadvantages. It's not practical, so why go on about it, other than to stir up an argument?

On my two '97s, the rear brakes tend to lock up before the front. I hear a quick "chirp" before the ABS evens things out. That's as close to optimum stopping effort as my truck can accomplish, and it does a good job. Without ABS, I can't apply the right braking force to each wheel to keep each tire just barely skidding. With ABS, I can do that, I just stomp and hold the pedal. If I'm in the real world, always with slightly more traction available on one side or the other, I can still do that. Hauling a trailer or with a loaded roof, I can still do that. If I have to maneuver while panic braking, I can do that. Because I have ABS. If I lock my CDL and my axles, I can't do that, because I can't possibly ever know how close to skidding I am. In the real world, I'd be well below the max braking capabilities, or skidding. "It works on paper" doesn't ease my mind when my wife or daughter or son take my 80 out on a snowy night, ABS does.

In response to the comments about upgrading brakes, if your brakes can already apply more friction than your tires can apply to the pavement (you can skid your tires), then better brakes won't allow you to stop faster. Better brakes may resist brake fade better, but that might not be a noticeable improvement in daily use or panic stops. I'm quite sure our intellectual contributors know this, not sure why they can't tell you this, instead of just telling you you're wrong.

Three of five family members are puking sick, I'm exhausted & in a foul mood. I'm venting, sorry if I've offended, but I feel better now .

I think that's an awesome post.

OT- scottm- Holland, MI home of Prince had an internship there way back when. Love the B5 Q too

 

[scottm]

I think that's an awesome post.

OT- scottm- Holland, MI home of Prince had an internship there way back when. Love the B5 Q too

I'm hoping to love the B5 someday, it's not the car my old quattros & synchros were.

Not true as stated. With a locked center diff, braking force will follow exactly weight distribution. It's exactly *not* "the same braking force to each" (unless weight distribution is always 50/50). The unequal Front/rear braking force will exactly *follow* Weight Distribution which is considered Ideal Brake Force Distribution under the test conditions in post 1. Sorry to nitpick, but a lot of confusion on this forum from misunderstanding how diffs work under torque and reverse torque. You can say that the total braking force of all linked axles is available to any single axle, but each axle doesn't have the same braking force, that's a dependent variable. I don't want to speak to 3 diffs locked yet Scott as that changes the dynamic outcome again. Let's stick this to post 1 definition and test for now.

You haven't defined braking force. I take it as the torque on the wheel & axle assembly, since that's what a brake does, and stopping force would be the force between tire and pavement. A tire that is moving just barely slower than the vehicle, is providing the max stopping force possible. If all wheels are linked together, and are all moving at that speed, they're all giving the max stopping force possible regardless of surface conditions or weight on each wheel. Doesn't that qualify as ideal brake force distribution? In your case you're linking the front and rear axle, which gives perfect brake force distribution front-rear in the same way. As I said before, it's not practical to drive with a locked CDL in the real world. You can throw out all kinds of real world limitations and claim to have found a better way, but that's not real problem solving. You can develop a cheap and efficient way to land men on Mars if you ignore a few limitations like gravity, drag, and the physiological requirements of astronauts. I don't think NASA will be impressed.

Read post 41 before we go too far down 'real world' scnearios. ABS is quite useful to 'help' inexperience it's not a substitute for it. It doesn't replace proper training or skillset training. I have a better confidence that with ABS on in my 'loaned" truck it will come home without scratches, but I get more confidence at home by being assured all the drivers in my house are properly trained at the limit of adhesion. Then if ABS fails, I have confidence that I have not relied on ABS to be the crutch to proper vehicle control. The available documentation on ABS vs vehicle control supports that philosophy.

Modern ABS is excellent, and improving rapidly. Human performance is sometimes excellent, sometimes not. Our machines have caught up with us, no matter how difficult that is to admit. Pilots of advanced aircraft have been required to use automation for decades, especially in bad weather. Many pilots have resisted, and pointed to studies showing that they can be better than the automation. They sometimes are, but not consistently, and neither are you. You can't possibly apply and maintain braking on each wheel at near the limits of adhesion in the real world. Differences in the conditions of your brakes, loading, and the road surface dictate that if your are perfect at braking, you can only hold one wheel near it's limit. A properly functioning ABS will hold all four near their limit. Or at least the front two, and one rear, but that's better than just one.

 

[Jule]

How is ABS a "crutch"?

I live at 9,000 feet above sea level in the mountains above Colorado Springs. With the recent storms in CO, for the last month there has always been a solid sheet of ice or snow on ice for at least a mile of my daily commute, usually more like 10.

I am huge fan of ABS. It makes a world of difference when you are trying to stop on a road that is iced over while going downhill, that also has a steep crown also. In a vehicle without ABS, even at slow speeds, it literally tries to throw you into the gutter.

SOMOTOY - thank you for posting the suggestion for the test of braking with and without CDL. My understanding is that this will give you an idea of whether the rear proprotioning valve is doing it's job, especially on a non-stock rig.

But I don't understand why you are so critical of ABS, saying it is basically worthless to a skilled driver.

"I have confidence that I have not relied on ABS to be the crutch to proper vehicle control."

Are you saying you can brake better than the ABS system, or just that you have the common sense to drive slow in lose conditions? You seem to imply the former.

My expericence on ice has been: It is often easy to lock up the wheels on ice, even with light pedal pressure. On a non ABS vehicle, at the same speed and same surface, I can stop in a shorter distance if I pump the brakes than if keep steady pressure with locked wheels. ABS does the same thing only faster, and adjusts for each wheel.

I have a hard time understanding how you can brake better without ABS in the same vehicle with the same tires than with ABS on slippery surface, like ice. (I understand locked wheels can plow some snow to slow down faster in just snow, but I think that ice is a much more common and difficult driving situation.) If you are some how a perfect driver and can hold brake pressure to the limit of adhersion, then you would not activate the ABS and the results would be the same. If one or more wheels break traction, how do you recover and cycle faster than ABS? You have no way of releasing a single wheel, only all 4.

Can you explain why ABS is a crutch?

BTW this course at Steamboat Springs you keep talking about, does it have grades and side slopes or just a big flat ice surface?

I can and do drive without ABS on ice. My daily driver is 97 Jeep Cherokee with PT 4x4, 5 spd, and NO ABS. (My wife wife drives the 97 FZJ). I love the Jeep, the 5 spd is fun to drive and the power of the 4.0 compared to the weight of XJ really puts the FZJ to shame. It amazes me that it consistantly gets 22-24 MPG inspite of my driving and a commute up and down a mountain. There are two things I really don't like about it, first it does not have Full-time 4x4 (but that is can be fixed by transfercase swap from a ZJ) and that it does not have ABS.

I get by without ABS, but I really would like to get something new with ABS, traction control, stability control, and full time 4x4, one of the things I love most about the FZJ. (Too bad the FJ Cruiser doesn't have a solid front axle or 4 real doors or the new Wrangler doesn't have full-time 4x4 or a real engine.) I realize that vehicle control systems are much more sensitive and responsive than I could ever be. Do I want to drive faster? No, I understand that they are an extra safety measure, not a substitute for reasonable driving.

Jule

 

[SUMOTOY]

I'm hoping to love the B5 someday, it's not the car my old quattros & synchros were.

The manual lockers are still the best IMO. A discussion on Torsens (my particular pet project in Vehicle Dynamics) makes all this locked and unlocked comparo seem simple.

You haven't defined braking force.

Braking force on a locked center diff is only total reverse torque on the ring gear in the center diff. In the case of the locked center axle that would be Reng + Rfa + Rra = total reverse torque
Reng = engine compression braking
Rfa = Combined reverse torque front axle
Rra = Combined reverse torque rear axle

Total reverse torque in a locked center 80 under conditions in post 1 is distirbuted to the axles following weight distribution. Torque is only *equal* to each axle if each axle supports 50% of the total torque. In the case of Post 1, that would require that total reverse torque applied = 50/50 weight distribution

I take it as the torque on the wheel & axle assembly, since that's what a brake does, and stopping force would be the force between tire and pavement. A tire that is moving just barely slower than the vehicle, is providing the max stopping force possible. If all wheels are linked together, and are all moving at that speed, they're all giving the max stopping force possible regardless of surface conditions or weight on each wheel.

True, but reverse torque on each axle is not equal. Again, that's a dependent variable. "Any time you link axles and wheels together, you will get exactly the same braking force to each" is not a correct statement to a locked diff, that is a more common property to an unlocked diff!

Awd axles are always linked together. So you need to differentiate between open and locked diff. The only time the statement you made is true, is if the awd diffs were open, and in the above forumla Rfa = Rra (brake force front = Brake Force Rear). We know in an open diff Reng will be distributed exactly 50/50 regardless of weight distrirbution, and if Rfa = Rra, then each axle "will get exactly the same braking force to each" REGARDLESS of weight distribution on the respective axle.

Doesn't that qualify as ideal brake force distribution?

No, that qualifies as a statement to an open diff with the same brake force front and rear. Making the Weight Distribution INDEPENDENT of brake force to 2 axles. In a locked center Weight Distribution is a DEPENDENT variable to axle brake force and *exactly not* being equal regardless of each axle brake capacity.

As I said before, it's not practical to drive with a locked CDL in the real world. You can throw out all kinds of real world limitations and claim to have found a better way, but that's not real problem solving.

What I can do is look at variables to vehicle control, I do all the time. I won't debate CDL dynamics in this thread, but I can put forth a test to Ideal Brake Force Distribution in the real world. I can also put a set of Blizzacks on an 80 and make the subjective claim that in the real world, it makes more of a difference to vehicle control than CDL mode or ABS mode.

Modern ABS is excellent, and improving rapidly. Human performance is sometimes excellent, sometimes not. Our machines have caught up with us, no matter how difficult that is to admit.

They can't think Scott. In a straight line (like in a plane) they don't need to be smart, they only need to be faster than a human. In a mixed mu turn (even the same mu turn) ABS programmers bail with the Select Low Rear Brake principle. I think the reason for this, is you will never have ABS control over steering input. Or as I present many times in classroom: The nut behind the wheel is always loose in comparison to the machine it's attached to.

Pilots of advanced aircraft have been required to use automation for decades, especially in bad weather. Many pilots have resisted, and pointed to studies showing that they can be better than the automation. They sometimes are, but not consistently, and neither are you. You can't possibly apply and maintain braking on each wheel at near the limits of adhesion in the real world. Differences in the conditions of your brakes, loading, and the road surface dictate that if your are perfect at braking, you can only hold one wheel near it's limit. A properly functioning ABS will hold all four near their limit. Or at least the front two, and one rear, but that's better than just one.

Again, the falacy is that "maintaining brraking each wheel at near the limits of adhesion in the real world" correlates to something better. It *CAN*, it's not a given. Proven over and over. The latest and greatest traction control, Stability control and ABS have yaw sensors and steering input sensors to help make the programming better the matrix of dynamic scenarios. The problem is that all these systems are reactive to less than ideal driver input. Back to the loose nut behind the wheel.

I see this much more simply. Tighten the nut behind the wheel with proper training. Then with or without electronic aids, the outcome of any sudden change in vehicle dynamic has a better chance of control.
Put in Summary: Driver Training is correlated higher to Vehicle Control than ABS or any other electronic gizmo.

My .02

YMMV (your mu may vary)

ST

 

[SUMOTOY]

...

I am huge fan of ABS. It makes a world of difference when you are trying to stop on a road that is iced over while going downhill, that also has a steep crown also. In a vehicle without ABS, even at slow speeds, it literally tries to throw you into the gutter.

Locked or unlocked CDL.

SOMOTOY - thank you for posting the suggestion for the test of braking with and without CDL. My understanding is that this will give you an idea of whether the rear proprotioning valve is doing it's job, especially on a non-stock rig.

That's *A* use for it. I personally believe that everyone should understand *what* ideal brake force distribution is, and how it applies to AWD chassis dynamics. Didn't think it would create such a roil, as it's just one of many demonstrations and concepts I present in car control.

But I don't understand why you are so critical of ABS, saying it is basically worthless to a skilled driver.

I am critical of any claim that ABS = Control. I do not say it's worthless to a skilled driver, only that a skilled driver is worth more to Vehicle Control than ABS, EDL, or Stability Control. In the 80 application of ABS, it's also not very sophisticated. It just reacts to impending lockup, nothing else.

"I have confidence that I have not relied on ABS to be the crutch to proper vehicle control."

Are you saying you can brake better than the ABS system, or just that you have the common sense to drive slow in lose conditions? You seem to imply the former.

No, what I imply is that ABS and Vehicle Control have a lower correlation than Driver Training and Vehicle Control. This includes equipment and understanding basci vehicle dynamics. I don't drive slow, I drive to my confidence and skill level.

My expericence on ice has been: It is often easy to lock up the wheels on ice, even with light pedal pressure. On a non ABS vehicle, at the same speed and same surface, I can stop in a shorter distance if I pump the brakes than if keep steady pressure with locked wheels. ABS does the same thing only faster, and adjusts for each wheel.

Try it with the CDL locked (in a controlled environment please). ABS doesn't adjust for each wheel, it can only 'adjust' for the front wheels, the rears are operated in unison to the wheel with the least traction.

On the other side of that issue is tires. Instead of changing from CDL on>off, go from an all season tire to an ice tire, you begin to understand that ABS mode isn't what dictates vehicle performance on ice. IOW, the correlation to Tires = Control is higher than ABS>Control. Now, take those new Blizzacks, come up to Steamboat Center for Driving Sciences, and train yourself to drive on low mu conditions (see my even coming up at www.gruppe-q.com and/or do the first gear school at www.winterdrive.com )

Then, as a well equipped trained driver in low mu, you *choosing* to use ABS has a higher correlation to control than just having it on.

... If you are some how a perfect driver and can hold brake pressure to the limit of adhersion, then you would not activate the ABS and the results would be the same. If one or more wheels break traction, how do you recover and cycle faster than ABS? You have no way of releasing a single wheel, only all 4.

What I find on ice is that ABS really doesn't help much in terms of tractive force. I find that braking on ice has the highest correlation control by braking in a straight line. You really need to come to Steamboat. I don't use ABS there, and I tried it back to back, in every single possible low mu scenario CFDS had to offer. I love my 80 on ice with Blizzacks, I don't care for the 80 ABS algorithums. I come to that conclusion based on having the equipment and the skillset training.

BTW this course at Steamboat Springs you keep talking about, does it have grades and side slopes or just a big flat ice surface?

It's a very challenging multiplane road course on the side of a slope outside town. Offcamber turns, yumps, blind turns, tight uturns, you name it, they have it. The most impressive part I found in regards to the Blizzacks, is that when I set up the cones on the course, there are times I can't stand on the ice, but the truck can drive and be parked on it.

I get by without ABS, but I really would like to get something new with ABS, traction control, stability control, and full time 4x4, one of the things I love most about the FZJ. (Too bad the FJ Cruiser doesn't have a solid front axle or 4 real doors or the new Wrangler doesn't have full-time 4x4 or a real engine.) I realize that vehicle control systems are much more sensitive and responsive than I could ever be. Do I want to drive faster? No, I understand that they are an extra safety measure, not a substitute for reasonable driving.

Jule

I say go to the school first, get the Blizzacks second. The best thousand bucks you'll ever spend, and you just might find that the latest and greatest isn't what you need, it's a higher level of awareness that Control is correlated to the driver and baseline equipment (tires). I can tell you too, that the quattros at steamboat with the latest EDL (electronic Diff lock), ESP (electronic stability control) and ABS computers confuse easily on ice, and most folks turn it off.

HTH and my .02

ST