Increase Traction w/o a rear locker? How?

[roostercruiser]

I have to agree with this. I only have a few years 4x4 experience, but I haven't seen a situation yet where I needed a locking diff, and in fact in most cases where I've seen them used they were detrimental, as in slippery mud or snow conditions where the rig slides sideways.

Around here the most difficult trails are rocky, and I've always been able to keep enough tires on the ground. Having rock sliders and good armor gives me the confidence to take those better lines.

I've seen the limits of what I want my rig to do, and beyond that I'll just pull off the trail and hike the rest of it.

l ve gone15 years w/o lockers .i think it makes u a better driver . and if i cant make it i just use my winch and cheat.

 

[Mike S]

I never had lockers until I got my 80. I used "Foot Lockers" - put some brake pressure on to convince the open diff to drive the grounded wheel. Works!

 

[dust devil]

Running a spool on the street is really no big deal, and in some applications, I'd prefer a (rear) spool over something like a Detroit locker. The tires will chirp and bind a little bit when you have to negotiate tight, low-speed places, like parking lots, but it's not really much worse than turning your front tires while the vehicle isn't moving. They just scrub a bit.

I'd put my time/money into improving the suspension before buying lockers for most vehicles. Traction is best when wheels/tires are on the ground...

From your perspective it may be no big deal running a spool, or by extension a welded diff. The differences between a spool and a Detroit or other automatic locker are night and day in terms of driving and the effects on the vehicle overall, and on the life of your tires.

With a Detroit or automatic locker, as long as you are not driving under positive throttle around corners, the locker will coast. You will hear this as a clicking or knocking noise, but it is harmless and it is the way they work. At least the rear tires will differentiate while turning and save some rubber.

With a spool, both rear tires will be forever locked together and can not under any circumstances do anything other than turn at the same rate. Since the ONLY time a vehicles' tires turn at the same rate is while going dead straight, your spooled axle will be scrubbing tires any time you are not going perfectly straight down the road. This is assuming your tires are aired the same on both sides. Unequal air will cause tire scrubbing even when driving straight.

Constant tire scrubbing while driving on hard surfaces will cause accelerated tire wear, excessive tire heat, and wear and tear on drive line and steering components. It tends to wind up your axle shafts, and constant loading and unloading of the shafts is not a good thing for shafts or for splines.

It also causes a degrading in fuel economy, takes more power to simply drive down the street, stresses the transmission by increasing the load required to drive forward, increases turning circle, often dramatically, and after a very short period of time, gets to be a pain in the butt.

If the choices were to drive open, or weld or spool the rear because no locker is available, I would drive open. Welding and spools are for drag racers and trailer queens.

 

[modelbuilder]

I never had lockers until I got my 80. I used "Foot Lockers" - put some brake pressure on to convince the open diff to drive the grounded wheel. Works!

Are you saying that if you feel the wheels slip to press the brake pedal a bit?

 

[jesusgatos]

From your perspective it may be no big deal running a spool, or by extension a welded diff. The differences between a spool and a Detroit or other automatic locker are night and day in terms of driving and the effects on the vehicle overall, and on the life of your tires.

With a Detroit or automatic locker, as long as you are not driving under positive throttle around corners, the locker will coast. You will hear this as a clicking or knocking noise, but it is harmless and it is the way they work. At least the rear tires will differentiate while turning and save some rubber.

With a spool, both rear tires will be forever locked together and can not under any circumstances do anything other than turn at the same rate. Since the ONLY time a vehicles' tires turn at the same rate is while going dead straight, your spooled axle will be scrubbing tires any time you are not going perfectly straight down the road. This is assuming your tires are aired the same on both sides. Unequal air will cause tire scrubbing even when driving straight.

Constant tire scrubbing while driving on hard surfaces will cause accelerated tire wear, excessive tire heat, and wear and tear on drive line and steering components. It tends to wind up your axle shafts, and constant loading and unloading of the shafts is not a good thing for shafts or for splines.

It also causes a degrading in fuel economy, takes more power to simply drive down the street, stresses the transmission by increasing the load required to drive forward, increases turning circle, often dramatically, and after a very short period of time, gets to be a pain in the butt.

If the choices were to drive open, or weld or spool the rear because no locker is available, I would drive open. Welding and spools are for drag racers and trailer queens.

Everything you're saying is true, but to what extent? I would say, not more than a minor degree in a lightweight, short-wheelbase vehicle like a Jeep or Toyota truck. I've driven vehicles with rear spools on-road (extensively) and not noticed much of a practical downside. On the other hand, the loading and unloading of a mechanical locker (like a Detroit) can have some negative affects in certain on-road conditions (rain, snow, etc.). The spool is going to be more consistent in all cases, and while it may want to 'push' the vehicle, it's a characteristic that I haven't found very hard to adapt to. All this said, I rock an ARB in my Tacoma. I was only trying to point out that spools aren't anything to be scared of.

 

[adi]

Are you saying that if you feel the wheels slip to press the brake pedal a bit?

Its the "poor man's LSD". Brakes hold the wheel without traction, removing the power that goes there from the path of least resistance and balances it to the wheel with traction. This is how some of the modern traction control system works, but they have the ability for the brakes to be applied to the single wheel.

Its not perfect, but people have used it to good effect.

 

[Co-opski]

Everything you're saying is true, but to what extent? I would say, not more than a minor degree in a lightweight, short-wheelbase vehicle like a Jeep or Toyota truck. I've driven vehicles with rear spools on-road (extensively) and not noticed much of a practical downside. On the other hand, the loading and unloading of a mechanical locker (like a Detroit) can have some negative affects in certain on-road conditions (rain, snow, etc.). The spool is going to be more consistent in all cases, and while it may want to 'push' the vehicle, it's a characteristic that I haven't found very hard to adapt to. All this said, I rock an ARB in my Tacoma. I was only trying to point out that spools aren't anything to be scared of.

Wouldn't the spooled or welded rearend cause the vehicle to spin out more on icy or snowy roads, more than an open diff? Could be fun if that is what you were expecting scary if you are not.

 

[jesusgatos]

Compared to an open differential, sure. But I was comparing a spool to a mechanical locker, like a Detroit, where the loading and unloading can be even downright dangerous in those kind of conditions.

 

[roostercruiser]

i cant find any lockers or spools for my 04 Dakota, and I dont want to weld it. I dony really have choice but to be open.

 

[michaelgroves]

Its the "poor man's LSD". Brakes hold the wheel without traction, removing the power that goes there from the path of least resistance and balances it to the wheel with traction. This is how some of the modern traction control system works, but they have the ability for the brakes to be applied to the single wheel.

Its not perfect, but people have used it to good effect.

I noted some problems with this explanation further back in this thread. Brakes hold all the wheels, so where does the additional traction come from? So far, I've yet to hear a convincing hypothesis about how brake-throttle modulation could work. Also, no explanation of why a controlled experiment of BTM fails.

My own hypothesis - pending a better one - is that traction is often better when a wheel turns slowly, and using the brakes makes the wheels turn more slowly. So does less throttle...

 

[modelbuilder]

My BTCS applies brakes to the wheels that are slipping.

 

[michaelgroves]

My BTCS applies brakes to the wheels that are slipping.

No, absolutely, I understand how an ABS-based traction control system can increase traction by "artificially" raising the torque on any wheel that is spinning, and not applying braking to the other wheel(s).

I also understand how using the footbrake or handbrake (Brake Throttle Modulation) on a torque-biasing LSD works too. The LSD mechanism is designed specifically so that when one side is under low torque (spinning), the other side will generate, say, 4 times that torque (the multiple varies). So in this case, equal braking produces a nett gain of torque.

But equal braking across an open diff? What's the theory behind it? And why doesn't it work under controlled conditions?

 

[dust devil]

Everything you're saying is true, but to what extent? I would say, not more than a minor degree in a lightweight, short-wheelbase vehicle like a Jeep or Toyota truck. I've driven vehicles with rear spools on-road (extensively) and not noticed much of a practical downside. On the other hand, the loading and unloading of a mechanical locker (like a Detroit) can have some negative affects in certain on-road conditions (rain, snow, etc.). The spool is going to be more consistent in all cases, and while it may want to 'push' the vehicle, it's a characteristic that I haven't found very hard to adapt to. All this said, I rock an ARB in my Tacoma. I was only trying to point out that spools aren't anything to be scared of.

I'll give you one objective item. Tire temperatures. After 30 minutes driving on asphalt roads in 80 degree heat, the tires running on an open diff on the front axle of a light Jeep (2,500 pounds) were 95 degrees measured at the tread centers. The rears, running through an automatic locker, were 110, and that was allowing for coasting through most corners. So, even with an automatic locker, which is not spooled, tire temperatures were significantly higher due to scuffing. Lockers will be even worse.

If you really need empirical data for a spooled axle, I can get out the beast, lock the rear ARB and drive around. It won't be fun, though, because I have driven it on pavement with the rear locked and I can say without doubt that it doubles the turn radius, makes steering effort rise significantly, chirps the tires without mercy, and is so uncomfortable to drive that you simply can not drive with the ARB locked without knowing it.

The degree of difference between open and spooled axles is not slight. Even on my old Suzuki ATV 4X4, which is about as light an off road vehicle as you can find, was a real bugger to drive around even on dirt with the front locked. The rear was spooled and you simply could not drive the vehicle over loose terrain without leaving dig marks as you drove because one or the other tire was constantly tearing at the soil. On pavement, it left rubber behind just turning slow corners. Locking the front axle (it had a cable locker) made it nearly impossible to drive on pavement, and made steering in dirt a genuine workout. That's how spooled axles work.

 

[dust devil]

No, absolutely, I understand how an ABS-based traction control system can increase traction by "artificially" raising the torque on any wheel that is spinning, and not applying braking to the other wheel(s).

I also understand how using the footbrake or handbrake (Brake Throttle Modulation) on a torque-biasing LSD works too. The LSD mechanism is designed specifically so that when one side is under low torque (spinning), the other side will generate, say, 4 times that torque (the multiple varies). So in this case, equal braking produces a nett gain of torque.

But equal braking across an open diff? What's the theory behind it? And why doesn't it work under controlled conditions?

I know we have had this discussion before, but I disagree that brake modulation has any more or less effect on an LSD than an open diff. Braking an LSD axle doesn't raise usable torque. It may raise perceived torque or place a torque load on the drive line, but won't change traction. Any additional resistance to the drive train that might result in usable torque is dissipated by friction. Traction, as opposed to torque, will still be limited to that available as between tire and terrain, regardless of whether the brakes or on or not. An LSD provides driving force to the wheel with the most available traction. Once available traction is exceeded, even an LSD will spin tires and applying brakes won't change that. You might slow down the spin with brakes, but you can do the same by backing off the gas.

 

[michaelgroves]

I know we have had this discussion before, but I disagree that brake modulation has any more or less effect on an LSD than an open diff. Braking an LSD axle doesn't raise usable torque. It may raise perceived torque or place a torque load on the drive line, but won't change traction. Any additional resistance to the drive train that might result in usable torque is dissipated by friction. Traction, as opposed to torque, will still be limited to that available as between tire and terrain, regardless of whether the brakes or on or not. An LSD provides driving force to the wheel with the most available traction. Once available traction is exceeded, even an LSD will spin tires and applying brakes won't change that. You might slow down the spin with brakes, but you can do the same by backing off the gas.

Yes, I've had this discussion several times, and it's never uncovered any explanation!

However, I must disagree with you about BTM when applied to LSDs (of the torque-biasing type). That mechanism is well understood. Where an open diff keeps the same torque on each output shaft, a torque biasing LSD allows one shaft to have, say, 5 times the torque of the other.

If one wheel lifts into the air, it will have ~zero torque, so the other wheel (the one with good traction) will have 5x0, which is still zero. Apply the parking brake, which acts equally on both wheels, and the throttle at the same time. This will create a torque on spinning shaft. Not a useful torque, because the resistance is caused by braking, not traction. But the LSD allows 5 times that torque to be generated on the other shaft. If we applied, say, 1000Nm of braking torque on each of the two wheels, then the spinning wheel would have 1000Nm of torque (of which zero is "traction-torque"), and the other wheel would have up to 5000Nm of torque (of which 4000Nm could come from traction).

(An open diff would react differently, of course, as only 1000Nm of torque would be generated each side, and all of that would be generated and absorbed by the brakes, with no extra "traction-torque" created).