so what is this "rear locker" thing for?

[jss81258]

When you are in a situation where you have a wheel on each axle off the ground, and the one wheel on each axle that's on the ground has good traction, then the TM can lock the off-the-ground tire forcing torque to the wheel on the ground with traction, and then you can drive out.

If all the wheels are on the ground but traction is severely limited (wet grass, snow, ice etc) then applying a single brake on an axle just forces the opposite wheel to spin. In addition, the braked wheel may inhibit forward motion. This may or may not be enough to get you going. But, if you have an axle locked, then both wheels will receive power, may spin, but may also have enough grip to get you going.

Bear in mind that there's a lot of ifs involved. You can get yourself in a situation where no amount of locked axles or braking individual wheels is going to get you out. That's where a winch or fellow offroader comes in.

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[GTGallop]

Back in 2000, I had a Nissan Xterra. Wanted the 4wd but ended up letting my dad talk me into 2wd. Should have never listened to him... Anyway. It ended up making me a better off road driver and with a little use of the Emergency Brake as a locker, I was able to go places with just 2wd that some of the gussied up 4wds were getting stuck. That was East Texas and a lot of nice trails that had an occasional slick mudhole or a beach with a soft sand spot on them. No rock crawling.

Now in AZ, I'm rolling trails with just the 4wd Ranger and still haven't needed a locker and the only time I've had to engage the Emergency Brake as a locker has been backing into the drive way (steep slope drive way) when one tire is on the pavement and the other dips off into the gravel and breaks traction as the front wheels have the curb to contend with. And I think getting true all terrain (ATKO) tires will probably help that.

So what is the locker for?
Well for Ford, it's for selling trucks. Having that will attract a lot of buyers.
For drivers, I think the ones that really like to modify their trucks, lifts, bigger tires, bash plates, and then take them really hard core off roading, they will notice the points that it pays off. But I'll bet for about 90% of the people that buy them, it just gives them the feeling they just entered Wango-Tango Mode when they push the button.

 

[HenryMac]

gimme an example. where would a locker be mandatory where trail control couldnt pseudo-lock its way through?

Stuck in a snow drift.

 

[jss81258]

Back in 2000, I had a Nissan Xterra. Wanted the 4wd but ended up letting my dad talk me into 2wd. Should have never listened to him... Anyway. It ended up making me a better off road driver and with a little use of the Emergency Brake as a locker, I was able to go places with just 2wd that some of the gussied up 4wds were getting stuck. That was East Texas and a lot of nice trails that had an occasional slick mudhole or a beach with a soft sand spot on them. No rock crawling.

Now in AZ, I'm rolling trails with just the 4wd Ranger and still haven't needed a locker and the only time I've had to engage the Emergency Brake as a locker has been backing into the drive way (steep slope drive way) when one tire is on the pavement and the other dips off into the gravel and breaks traction as the front wheels have the curb to contend with. And I think getting true all terrain (ATKO) tires will probably help that.

So what is the locker for?
Well for Ford, it's for selling trucks. Having that will attract a lot of buyers.
For drivers, I think the ones that really like to modify their trucks, lifts, bigger tires, bash plates, and then take them really hard core off roading, they will notice the points that it pays off. But I'll bet for about 90% of the people that buy them, it just gives them the feeling they just entered Wango-Tango Mode when they push the button.

I guess I'm part of the 10%, not that I know what Wango-Tango Mode means. I purchased off the lot and the truck ticked all the boxes I required plus had a few extras. The locker was an extra. If the same truck was on the lot and didn't have a locker, I still would have bought it.

 

[NC_LFX4]

The electronics are doing a similar technique that I was taught in a off-road driving school for work. In the absence of lockers, modulate/feather the brake just enough to stop spinning the tire without traction to transfer power to the other side(the side with traction). You can achieve the same similar results as the software in our trucks in a 1990’s Jeep Cherokee(as an example) with proper foot/pedal control off-road.

 

[VAMike]

The electronics are doing a similar technique that I was taught in a off-road driving school for work. In the absence of lockers, modulate/feather the brake just enough to stop spinning the tire without traction to transfer power to the other side(the side with traction). You can achieve the same results as the software in our trucks in a 1990’s Jeep Cherokee(as an example) with proper foot/pedal control off-road.

you can do something similar, but no, you can't achieve the same results

 

[NC_LFX4]

you can do something similar, but no, you can't achieve the same results

Corrected.

 

[GTGallop]

....not that I know what Wango-Tango Mode means.....

Wild Man Mode

 

[Gizmokid2005]

As others have stated, this more/less boils down to speed/momentum.

Trail Control uses ABS/brake modulation to determine power and how to shift from one wheel to another, which when you need momentum/speed to get over an obstacle (up a hill in snow/ice, through a drift, etc), will be counteracted with these functions. A locker, however, will not modulate throttle/activate ABS to work, it'll just keep pushing out the power you're requesting. This can also be very true in deep sand (abs/modulation only works so much), when momentum and "floating" over the sand is key to getting through it where slow speeds and subsequent ABS/throttle modulation will kill your momentum and get you stuck.

It's true that TC can be helpful, but you have to relinquish power to the truck and set a "cruise" speed, which is generally low as well, in order to get the benefits.

 

[TechnicallyReal]

It sounds like the only electronic system that is relevant here is Traction Control. Trail Management just adjusts how Traction Control works and Trail Control is just low speed cruise control, but it might also tweak the Traction Control logic. The root of it all is Traction Control.

Anyway the way I see it, Traction Control can achieve similar results as a locked diff, but it does so in a more reactive manner where as locking your diff is proactive.

In order for Traction Control to kick-in and emulate a locked diff, you first need to get stuck and spin some wheels. Traction Control will then sense the spinning of the wheels and activate the brakes in them, which will prevent those particular wheels from acting as the path of least resistance any longer and for power to be redirected to the wheels that still have traction.

The problem is that its not a smooth or consistent experience like using a locker. It's a jerky and reactive experience where you have to give it enough throttle to cause the wheels to spin fast enough for Traction Control to notice that there's an issue and then try to compensate. Trail Management allows you to make Traction Control smarter by telling it that you expect wheel spin to happen and at lower speeds, which allows for it to become more sensitive and react more quickly and aggressively.

 

[JimJa]

A locker is very useful in specific conditions, but remember while cornering, or during a sharp turn, there is less traction when the rear is locked than when unlocked. This is because a slipping tire has less traction than one that is not slipping. The most traction is just prior to slippage. When the rear is locked and the vehicle is in a turn, the inner wheel is forced to turn at the same speed as the outer wheel and slippage occurs relative to the outer wheel, traction is therefore less on the inside wheel.

 

[JimJa]

Lee wrote:
"Reading through this thread I'm a little confused. I know we are talking about the rear locker, but beyond that are we discussing Traction Control, Terrain Management or Trail Control? My understanding is this. Traction Control is basically always there and can be turned off with button on the console. It uses the ABS system along with throttle control the move power to the wheel with traction."

Traction Control as Lee describes is Ford's version of "Torque Vectoring." I do not believe our trucks have that feature, at least with the normal traction control in daily driving. If I am wrong - and I hope I am - please weigh in. I also do not believe torque vectoring is present Terrain Management. I don't know about Trail Control. When in Trail Control mode and when going down a hill, the ABS kicks in frequently to maintain the set speed. That is easily felt as well as heard. There is no mentioning of Torque Vectoring in the Owner's Manual. If someone has truth about it please help. For most conditions, except hard core off-roading, torque vectoring is more useful than a rear locker. I'd like some clarity and some references. Others would as well.

 

[Rviator]

The term torque vectoring is more relevant to on pavement handling in cars. In a sense traction control is the off road version of torque vectoring, except it senses loss of forward tire traction whereas torque vectoring is also affected by side slip traction loss and possibly g force and/or steering angle when cornering.
Traction control is primarily for off road use and brakes a spinning wheel in order to transfer some of that torque to the wheel on the other side of the axle.
Terrain management just adjusts the amount to brake the spinning wheel and also adjusts throttle pedal sensitivity and gear selection as determined to be appropriate by Ford engineers for the chosen terrain condition.
Trail control is just a low speed cruise control that also incorporates automatic braking as required.

 

[jss81258]

The term torque vectoring is more relevant to on pavement handling in cars. In a sense traction control is the off road version of torque vectoring, except it senses loss of forward tire traction whereas torque vectoring is also affected by side slip traction loss and possibly g force and/or steering angle when cornering.
Traction control is primarily for off road use and brakes a spinning wheel in order to transfer some of that torque to the wheel on the other side of the axle.
Terrain management just adjusts the amount to brake the spinning wheel and also adjusts throttle pedal sensitivity and gear selection as determined to be appropriate by Ford engineers for the chosen terrain condition.
Trail control is just a low speed cruise control that also incorporates automatic braking as required.

I've always associated torque vectoring with all wheel drive cars where the center differential is torque vectoring and can change the torque split. For instance, if the front is spinning, then the differential can reduce torque to that axle, and apply more torque to the rear that isn't spinning.

Side slip, steering angle, and g-force are usually associated with stability control where a vehicle in a turn starts to either become loose or tight (oversteer or understeer). Individual brakes are applied, and power could be reduced in an effort to regain control and finish the turn as intended. GM used to call it active handling, and I can testify that it works.

Traction control can be either off road or on road, on high grip surfaces, or slick surfaces. Wheel spin is detected and the system will apply brake to that wheel and could also reduce power in an effort to maintain traction. Late model Vettes and Mustangs have traction control and I don't know anyone in their right mind that takes either for serious off roading. Well, not on purpose anyway.

Rangers have AdvanceTrac that includes Roll Control in addition to stability control and traction control. Apparently, the system monitors roll motion and will apply a wheel brake or wheel brakes to prevent roll over. It doesn't appear to care if any wheel looses grip. I haven't tested this feature.

I understand terrain management and trail control as described.

 

[P. A. Schilke]

I've always associated torque vectoring with all wheel drive cars where the center differential is torque vectoring and can change the torque split. For instance, if the front is spinning, then the differential can reduce torque to that axle, and apply more torque to the rear that isn't spinning.

Side slip, steering angle, and g-force are usually associated with stability control where a vehicle in a turn starts to either become loose or tight (oversteer or understeer). Individual brakes are applied, and power could be reduced in an effort to regain control and finish the turn as intended. GM used to call it active handling, and I can testify that it works.

Traction control can be either off road or on road, on high grip surfaces, or slick surfaces. Wheel spin is detected and the system will apply brake to that wheel and could also reduce power in an effort to maintain traction. Late model Vettes and Mustangs have traction control and I don't know anyone in their right mind that takes either for serious off roading. Well, not on purpose anyway.

Rangers have AdvanceTrac that includes Roll Control in addition to stability control and traction control. Apparently, the system monitors roll motion and will apply a wheel brake or wheel brakes to prevent roll over. It doesn't appear to care if any wheel looses grip. I haven't tested this feature.

I understand terrain management and trail control as described.

Hi James,

You jogged my memory to another back story.... I managed Ford On road racing and Off Road racing...Off road for my last 25 years before I retired. This is relative to ABS. As we at Ford piloted ABS, I went to my off road teams to inquire if it was a competitive advantage for our teams. There were many "I have no idea", but Enduro Motorsports driver Dave Ashley enlightened me. ABS has no place in off road racing. When you slam on the brakes the ABS releases the wheels to prevent lockup....however...off road..slam on the brakes and lock the wheels...the dirt builds like little plows under each wheel and you will stop significantly faster and in shorter distance than ABS. So lesson learned that there times when old school wins out.

Best,
Phil Schilke
Ranger Vehicle Engineering
Ford Motor Co. Retired

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