All Wheel Drive Class 101

[Jason Andrews]

There seem to be two camps here.

I fall in with the second. Drivelines build tension when locked. When that tension releases there is a push & skid resulting in less traction momentarily. 99% of the time driving on the highway you won't notice.

If a truck slams on the brakes and jack knifes covering the 3 lanes in front of you causing you to pile on the brakes and swerve at speed while CDL locked... with the driveline tension built up one of the tires will have to break free. That unloaded back tire on the inside of your emergency maneuver will likely be it. You are now doing a pirouette down an interstate headed for the side of a semi.

I think this is why Toyota left the CDL switch off a lot of the 80s. US drivers weren't smart enough to turn them off.

I agree dlines build tension and do not endorse the Sumo driving on pavement with CDL style, But I am doing 40-60 when everyone else is doing 25 so the traction is not good. The CDL keeps you from getting yanked to the side by hitting a drift or deep slush.

It is not hard to brake fast while not locking up the front or rear brakes with the CDL engaged making it easier to keep the truck strait if you start fish-tailing....at any speed!!!!

Push and skid? Its not a Bobcat.... UNLESS maybe your doing a 3-point turn on ice

 

[SUMOTOY]

For snow and gravel with the mound buildup in front of the locked tires, yes.

On ice, professional drivers with LOTS of practice can outbrake the ABS.

On ice, the average person who doesn't drive on ice daily can't come within 10% of the ABS braking distance.

Not true. ABS algorithyms don't do well with 4 wheels having impending lockup. I urge folks to try it. With an ice tire (raise the cf) it's possible to reduce braking distance with abs. In less than a day anyone can understand and educate themselves on vehicle dynamics. I rent the same track and require this school- see www.winterdrive.com - or 1 800 WHY SKID (yup that's really the number, and yup they really do have some awd toyota trucks in the corporate fleet) - First gear 1/2 day school required to attend my event www.gruppe-q.com - Sixth gear - 2x2day back to back track rentals

Stoping on Ice to beat the ABS is all about modulating the brakes in a manner finner than the ABS computer is capable of. You may be able to do this since you spend a lot of time racing on ice. The other 99% of the population will not be able to beat the ABS on the FIRST run. Give them 10 runs and they MIGHT beat it by 2%.

To be clear, I've ice raced maybe 6 times in my life, though I come from a prorally background. I go to the Steamboat Center for Driving Sciences to practice and teach awd vehicle dynamics on ice. I look at some of the oversimplifications here of awd chassis dynamics based on my understanding, experience and knowlege of how awd chassis handle. In the case of the 80, put a set of blizzacks on the truck, my 15 yo daughter and no ABS could out brake the best driver without an ice tire but with ABS. Hence my claim that it's possible to oversimplify a drivers education problem.

Then you get into the whole control issue. Professional ice racers used to sliding about aren't as likely to panic. You're taking advice and techniques used by a VERY small set of elite drivers and making broad statements to a general population that frankly doesn' thave the time to practice or the skillset or interest to do it.

Not true. I speak to everyday drivers that return to my Steamboat Event every year because it teaches more in 4 days than they will learn in a lifetime. Including my own nother, who never had been to an ice driving school before. Not having the interest to do it is a change I work on and practice what I preach daily. In addition to this yearly event, I am also actively involved in establishing teen car control schools. First comes education and skillset, then add ABS, traction control, friction circle etc. Saving a life in your own family doesn't require elite driving skills.... Step from the podium sumotoy.....

Now, this discussion was not about the ABS/no ABS debate. It was about driving with a truck locked/unlocked at highway speeds on normal varying condition pavement. On ice you have no windup. On clean, dry pavement that high tire may or may not break free depending on how much windup is in the driveline at the time of the maneuver. This makes it unpredictable and dangerous.

I see this discussion as about awd vehicle dynamics, you brought in the braking aspect. I have a basic problem with the concept of 'windup' frankly. You have no effective windup in straight line. In a turn you have forced tire slip caused by 2 axles that must rotate at the same speed. I believe understeer in a locked truck on pavement to be more predictable than in an open diff truck. The documentation of predictable understeer with a locked diff is extensive from a chassis dynamics standpoint, from street to race to offroad. 80's aren't special cases, lock the CDL, understeer is very predictable. In fact, in a couple hours I found the 80 more predictable than the quattros I locked for the 15years previous...

A statement of "unpredictable and dangerous" clearly discards the documentation available and demonstrates a misunderstanding of awd chassis dynamics. IME/O. I am most comfortable discussing this misconception in any context of awd chassis dynamics, in theory or practice. Including the 80, I got a lot of 80 seat time at this facility last year. The 80 handles and I drive it just like the quattros I have driven in years past. I'd be more pleased to invite any 80 owner to educate themselves the second week in Feb. I highly suggest the CDL 7pin mod, even with a set of blizzacks, btdt.

ST

 

[XXXR]

I'm always blown away by the wealth of knowledge that is found here on this forum. It's funny to think that many that make up this forum have become or are, true professionals on the subject, outwitting most local mechanics here in the NorCal.

I've learned more on this forum about engineering than the past 20 years of my life wrenching on British bikes and old American Fords! Cheers to you all.

 

[SUMOTOY]

I agree dlines build tension and do not endorse the Sumo driving on pavement with CDL style, But I am doing 40-60 when everyone else is doing 25 so the traction is not good. The CDL keeps you from getting yanked to the side by hitting a drift or deep slush.

... or water. Ther is no documentation that supports the claim that drivelines 'build tension'. Drivelines by definition are constantly under torque. A front and rear axle will force wheels to turn at the same speed with a locked center difff. There is no sudden relief of any built up tension. Axle windup has exactly two variables turning radius and applied torque, and wheel slip is exactly proportional to the matrix of these two variables. "Building tension" implies a time aspect of windup caused just by locking diffs. There is no 'time' property/variable associated with axle windup of a locked center diff.

It is not hard to brake fast while not locking up the front or rear brakes with the CDL engaged making it easier to keep the truck strait if you start fish-tailing....at any speed!!!!

Exactly. The reason being that a locked center diff brake force follows weight distribution in a strait line, hence 'ideal brake force distribution'. What ABS does is tries to emulate ideal brake force distribution when the front and rear axles aren't locked. ABS *can* have an advantage in a turning scenario vs a locked center diff. A lot of specific factors dictate that advantage vs a locked center diff vehicle. FWD or RWD? The advantage will go to ABS almost every time.

Braking thru the front and rear driveshafts is how a locked center chassis dynamics differ from the hype associated with ABS 'advantage'.

ST

 

[Nay]

I agree dlines build tension and do not endorse the Sumo driving on pavement with CDL style, But I am doing 40-60 when everyone else is doing 25 so the traction is not good. The CDL keeps you from getting yanked to the side by hitting a drift or deep slush.

It is not hard to brake fast while not locking up the front or rear brakes with the CDL engaged making it easier to keep the truck strait if you start fish-tailing....at any speed!!!!

Push and skid? Its not a Bobcat.... UNLESS maybe your doing a 3-point turn on ice

Interesting experience on how a locked center diff can keep you from getting yanked by deeper snow on one side. I don't think the VC reacts quickly enough to make any difference to the tires slowing on one side and/or one end, but YMMV. I've been driving out of my 200 ft. driveway after last week's 30" snowstorm and the more locked I am, the more it wants to grab the snowbank sides. Low range AWD has been the best mode once I got it packed - fully locked was essential when I was drift busting out through 40 inches+ of snow.

CDL is the exact same thing as "part time 4wd" that used to come on most 4x4's, but it is there in the form of a switch - if you leave it on in bad weather, which is about the only place AWD is functional on a truck, then you really don't need AWD at all. There is a reason that "AWD" of "full time 4wd" has penetrated most of the so called "truck" markets. Your average driver is not going to know when the best time is to be engaged or not engaged, and it is better to have a computer and or mechanical functions doing the work (isn't VSC going to become mandatory? How bad does that suck if you can't turn it off?)

I still don't ever drive at speed in part time 4wd (CDL engaged). If I was willing to essentially ditch AWD in bad weather it would open up all kinds of t-case options such as the Atlas and the huge low gearing advantages that would come with it. An Atlas would be the same functional case as the 80 with CDL engaged, but you'd have a choice of some seriously low gearing. I can see zero reason to retain the stock case if you don't use it for AWD in snow and ice and you are interested in lower gearing. A Mark's crawler box is $3K plus gas tank mods. Ditch AWD functionality and a whole host of options may open up to you at better pricing - where it is a more complex issue is when you really want to retain AWD and have the lower gearing offroad.

In any case, CDL plus 7-pin mod creates an incredibly versatile system. Do both and figure out how to use them. If you see a lot of snow, go and get yourself stuck a bunch of times and figure out what works for each condition for your driving style.

Here are my general snow usage guidelines:

Any type of variable condition where some pavement is dry: AWD high, CDL off
Packed and icy snow at traffic speeds: AWD high, CDL off
Packed and icy snow where slow speed and additional gearing is advantageous: AWD low, CDL off
Moderate depth snow (6"-10" or so) at slower speeds where AWD may be slipping: Low range, CDL on
Moderately deep snow (10"-18") at slow speed: Low range, CDL on, rear locked
Completely unplowed snow (18"+) with drifts and no other vehicles on the road because they can't get out: Low range, CDL on, front and rear locked.

Also remember that you cannot disconnect the function of these systems from the tires you choose. Nokian, for example, is now designing their snow tires for use with TC and VSC systems. Aggressive offroad tires that excel in snow such as trxus MT's will work very differently to all terrains and dedicated snow tires in varying conditions. It is an area where you really do need to try different options in different conditions to find out what really works for you.

I have a neighbor with a '94 that is stock without lockers and Revos. His rig was useless in the last storm and would be useless in the 18" or so that is now on the ground in the current storm and the 12"+ that is coming over the next couple of days. I'd be loving a lot lower gearing with this kind of snow. It is all a system, not independent variables.

Nay

 

[Grench]

Smacking the beehive yet again.

... or water. Ther is no documentation that supports the claim that drivelines 'build tension'.

Lock it, turn the steering wheel all the way and do 1 circle in a parking lot. Hear/feel the scrub? Documentation done.

The reason being that a locked center diff brake force follows weight distribution in a strait line

An inability to steer isn't a hazard to you? I don't always drive my truck in a straight line.

, hence 'ideal brake force distribution'. What ABS does is tries to emulate ideal brake force distribution when the front and rear axles aren't locked. ABS *can* have an advantage in a turning scenario vs a locked center diff. A lot of specific factors dictate that advantage vs a locked center diff vehicle. FWD or RWD? The advantage will go to ABS almost every time.

Skip the ABS. Ignore the ABS. Leave the ice. We aren't takling about Ice or low traction situations. We are talking about every day pavement driving in a vehicle with a center differential locked or unlocked. The real everyday driving that we all do.

Locked Vs. Unlocked truck at highway speeds in an emergency maneuver on pavement. This means turning/swerving under brake load. Turning in a locked truck means windup/binding. See your own posts mentioning scrub and understeer at LOW speeds. The front wheels are on a smaller loop than the rear wheels.

Under braking on PAVEMENT, the rear wheels are unloaded as the weight shifts forward. During steering while braking, that windup WILL go someplace. It will go to the wheel with the least resistance. The back high side wheel may momentarily go slower than the track that it is on resulting in an oversteer situation. Remember, we're talking pavement, not ice. This oversteer/loose rear end will result in a sudden lack of lateral stability on that one wheel as a wheel in a skid has no directional control. The truck has just lost a small portion of the lateral stability on the rear end. Enough to force the back end to swing around? Maybe. It is a much lesser version of turning and grabbing a fistfull of parking brake.

The ABS will not have a choice in the matter, i.e. releasing the brakes momentarily will do no good as the driveline is forcing the issue not the brakes.

Now that our hypothetical center locked truck involved in a highway emergency brake/turn maneuver is going sideways, lets consider the center of gravity issue. On ice, sliding sideways is a blast. On pavement at highway speeds, sliding sideways is a quick way to a rollover. Rollovers at highway speeds kill people.

 

[SUMOTOY]

Interesting experience on how a locked center diff can keep you from getting yanked by deeper snow on one side. I don't think the VC reacts quickly enough to make any difference to the tires slowing on one side and/or one end, but YMMV. I've been driving out of my 200 ft. driveway after last week's 30" snowstorm and the more locked I am, the more it wants to grab the snowbank sides. Low range AWD has been the best mode once I got it packed - fully locked was essential when I was drift busting out through 40 inches+ of snow.

In awd vehicle dynamics the reason you have less 'pull' at speed is that there can be no speed differential of the driveshafts, so in a straight line, tires speeds are always equal. I beleive Jason refers to less pull as you hydroplane or find mixed mu, because a driveshaft can't spin up in relation to the other. His claim doesn't really apply at lower speeds. Since you have an understeer propensity, fast steering action at low speeds becomes difficult. Worse in low range because higher torque is applied to the ring gear.

CDL is the exact same thing as "part time 4wd" that used to come on most 4x4's, but it is there in the form of a switch - if you leave it on in bad weather, which is about the only place AWD is functional on a truck, then you really don't need AWD at all. There is a reason that "AWD" of "full time 4wd" has penetrated most of the so called "truck" markets. Your average driver is not going to know when the best time is to be engaged or not engaged, and it is better to have a computer and or mechanical functions doing the work (isn't VSC going to become mandatory? How bad does that suck if you can't turn it off?)

I don't agree. The reason AWD is disabled, automatic or restart reset is that Automakers legal boys want ABS to be the default position. I believe my wife drives the last of the Audis that bucked that idea: There is a factory installed ABS defeat switch beside the steering wheel, and instructions on when to disable it. (I will say it will reset on car restart). The same can be said for locking diffs. The early quattros had manual knobs for center and rear (ABS disabled on either/both activation). Audi took a step back IMO with the Torsen center diff, but it's main advantage and audi's expressed goal was awd with full time ABS. They gave traction and dynmaic handling to attain this goal, to this day.

The 80 followed a similar path with the addition of the HF2AV center diff. Take away the locking center during hi awd mode driving, but add a LSD to the center diff. A *major* and expensive (and I consider it the ultimate system) commitment to ABS. That said, the VC doesn't perform as well as a locker in terms of traction, it just is better than an open diff and retains ABS. Adding CDL switch is just the cats meow, you have good, better and best. All wins.

In any case, CDL plus 7-pin mod creates an incredibly versatile system. Do both and figure out how to use them. If you see a lot of snow, go and get yourself stuck a bunch of times and figure out what works for each condition for your driving style.

Agree

Here are my general snow usage guidelines:

Any type of variable condition where some pavement is dry: AWD high, CDL off
Packed and icy snow at traffic speeds: AWD high, CDL off
Packed and icy snow where slow speed and additional gearing is advantageous: AWD low, CDL off
Moderate depth snow (6"-10" or so) at slower speeds where AWD may be slipping: Low range, CDL on
Moderately deep snow (10"-18") at slow speed: Low range, CDL on, rear locked
Completely unplowed snow (18"+) with drifts and no other vehicles on the road because they can't get out: Low range, CDL on, front and rear locked.

The only time I use AWD lo without CDL is tight maneuvers with the trailer. Variable conditions or split mu conditions I favor AWD hi, CDL on. Packed and icy snow at traffic speeds I favor AWD hi CDL on.

Also remember that you cannot disconnect the function of these systems from the tires you choose. Nokian, for example, is now designing their snow tires for use with TC and VSC systems. Aggressive offroad tires that excel in snow such as trxus MT's will work very differently to all terrains and dedicated snow tires in varying conditions. It is an area where you really do need to try different options in different conditions to find out what really works for you.

I don't think the TC and VSC dictates a tire design or performance, I see that as strictly a marketing thing, the algorithyms for these systems already need to have a spinning wheel (TC) or a outside parameter input (VSC) to enact = reactive devices. A locker or better yet a torsen in addition to TC will make a bigger difference than tire design. The advantage torsen has is that the TBR transfer is complete before the wheel spins, about as close to active as you are going to get. Reactive traction systems have distinct disadvantages to them. Well augmented with the addition of a Torsen, btdt.

IME, for on road driving in ice, slush, hardpack and water, the Blizzack is tough to beat on the 80. Up to high center, it is very good in snow, but a dedicated snow vs ice has a slight advantage.

It is all a system, not independent variables.
Nay

Not just the equipment, but the education and skillset of the guy behind the wheel.

I find VSC gets confused in snow and ice quite easily. Audi oxymoronically calls it ESP, and it so isn't. Computers and algorithyms can't substitute for good judgement and proper education. When I see VSC tied to the brakes AND the accelerator, then confused, my immediate thought is to find that switch or that fuse.

ST

 

[FirstToy]

This is an informative topic but can I get the cliffs notes version?

On the 80 series w/ abs- (assuming you did the 7 pin mod, a normal driver doing normal things- like driving to the mtns, playing on the trails)

Is this correct? It's nice to have bullet points. for me, easy to remember while driving.

-Packed and icy snow at traffic speeds: AWD high, CDL off

-Packed and icy snow where slow speed and additional gearing is advantageous: AWD low, CDL off

-Moderate depth snow (6"-10" or so) at slower speeds where AWD may be slipping: Low range, CDL on

-AWD hi w/ cdl is dangerous for onroad driving in snow/wet conditions (?)

 

[Grench]

-AWD hi w/ cdl is dangerous for onroad driving in snow/wet conditions (?)

IMHO not a lot more than it is without the CDL. Since you're going to be sliding about anyway, there isn't the weight shift to unload a high side tire.

My objection is to the idea that we should all be driving around with the CDL locked regardless of conditions. I feel that doing so on clean dry pavement at speed is a ticket to disaster as it conflicts with proper control over the vehicle.

 

[FJnAK]

I'm new to FZJ80's and will be picking mine up next week. How is running theAWD with CDL any different from running my Dodge Ram 3500 in 4 hi which I do all the time up here in Alaska? From what I'm reading it makes it the same as any 4x4 truck when you put the CDL on.

 

[FirstToy]

Gench,
I always thought that CDL was a no-no on the road so I agree w/ you.

Actually, my real concern is on-road in these incliment conditions. On the trail, you can always play around but I just want to be as safe as possible on road.

 

[Grench]

Need more bees. Thwack.

For wet/slush/ice and soggy conditions by normal drivers and normal roads, my preference is to leave the CDL off, the ABS on and drive like a granny.

In general, for normal non superhuman people, four wheel drive or all wheel drive does not allow you to stop or steer any better than a two wheel drive car. It CAN allow you to out accelerate a two wheel drive car and to move when the two wheel drive car can't. Remember that they are all four wheel stop. This means you can get into trouble faster.

If you're a racer, you'll throw the truck sideways and nail the gas to purposely throw the truck into a counter steering drift turn around the track. It is to your advantage in this scenario to be able to force the back end free. Do this on an ice covered interstate and even if you make it you'll scare the $@$% out of the guys behind you.

So, the safest bet IMHO is to slow down. If you have problems getting rolling from a stop, throw on the CDL. It can be disengaged after you get going again by a push of a button. That is why it is so handy. On the earlier trucks without a VC in the TC, this was a critical thing to do in snow/ice. With the VC, you aren't getting stuck unless there is a stupid amount of snow or you're on a hill with two tires on ice.

Again, IMHO, don't use it on clean dry pavement. Use it when you need it to get going. If the roads suck, slow the down.

YMMV.

 

[Jason Andrews]

You all have some good points and to each their own. With0ut CDL at the speed I travel I would lock up my truck everytime I braked on slippery roads. And with the 24" of snow that fell a week ago. and more now I test the traction conditions and how the rig reacts with and without numerous.

I am not saying to cdl it when more than one tire is getting pavement traction.


OK, YES if your truck goes sideways having the CDL on at any speed it will make it harder to regain control, especially if your not using the gas, BUT the CDL makes the breaking point of the tires with a snow packed road at any speed much higher. Going downhill and braking fast THE CDL SAVES MY ASS!!! So dont engage it when pulling out of a parking spot. There is a disadvantage. I get that part. I do not have ABS but still think if you have half and brain as to how your truck reacts on slippery road conditions it will never get to a sideways sliding situation.

 

[Jason Andrews]

Gench,
I always thought that CDL was a no-no on the road so I agree w/ you.

That depends what the road condition is. If the road looks like a trail with 6" of snow or ice it improves braking distribution.

True, "on road" on a road with traction you would not need it unless you are worried about sliding.

 

[Grench]

That depends what the road condition is. If the road looks like a trail with 6" of snow or ice it improves braking distribution.

True, "on road" on a road with traction you would not need it unless you are worried about sliding.

If you are worried about sliding, slow down.

 

[Romer]

This is a good discussion with differences of opinion. I always appreciate when people can disagree, but respect the others opinion without resorting to name calling.

I would never run the lockers engaged on dry pavement, that will cause extra stress on the axles, especially the front.

The CDL is less clear, but my personal preference would not be to run on pavement with the CDL engaged.

 

[SUMOTOY]

In general, for normal non superhuman people, four wheel drive or all wheel drive does not allow you to stop or steer any better than a two wheel drive car. It CAN allow you to out accelerate a two wheel drive car and to move when the two wheel drive car can't. Remember that they are all four wheel stop. This means you can get into trouble faster.

A basic misunderstanding of locked center differentials and awd chassis dynamics. It's accepted theory and physics that a locked center differential gives ideal brake force distribution in a straight line up to lockup (read: front and rear brake force is balanced exactly to weight distribution thru the locked driveshafts). Which means exacty that it will brake and steer better than a car with or without ABS. Remember, ABS needs to be ACTIVATED before an ABS equipped vehicle has close to ideal brake force distribution. Prior to activation, an ABS vehicle will have mechanical proportioning only, which is far from ideal brake force distribution.

What ideal brake force distribution does BEFORE you steer is reduce the front end loading of braking force, which allows more ability for the front wheels to steer. For maximum traction on dry pavement, there are several awd race cars that have welded center diffs, and have been known to win championships. This means that awd and locking differentials is not a lo mu surface advantage only.

So, the safest bet IMHO is to slow down. If you have problems getting rolling from a stop, throw on the CDL. It can be disengaged after you get going again by a push of a button. That is why it is so handy. On the earlier trucks without a VC in the TC, this was a critical thing to do in snow/ice. With the VC, you aren't getting stuck unless there is a stupid amount of snow or you're on a hill with two tires on ice.

Again, IMHO, don't use it on clean dry pavement. Use it when you need it to get going. If the roads suck, slow the down.

YMMV.

I say the arguments presented are marketing, not physics or acceopted practice. Change your brake fluid as PM, make sure your rotors and pads are in good shape, Front and rear. Ck your tire pressures regularly, and general tire condition. Pack your vehicle thinking about heavy things at the bottom and forward in the rear space. Train yourself and other drivers in your house with educational drivers schools that include lane change maneuvers and limit of adhesion exercises. Place your hands at 9 and 3 o'oclock position on the wheel as habit, any other position won't allow you an avoidance maneuver. These are the things that make more of a difference in an avoidance maneuver than if your center diff is locked or not.

Saying that a locked center diff is anymore unsafe on dry pavement than unlocked with ABS is disengaging the driver from proper skillset. In AWD, the misconception is that the vehicle dynamics under braking are the same as in RWD or FWD. That can't be further from the truth. Chassis dynamics is a complex issue, but hardly rocket science or above basic skillset learning.

Grench et. al. happy to point you to some SAE articles on the subject of traction, braking and awd dynamics.

ST

 

[SUMOTOY]

IMHO not a lot more than it is without the CDL. Since you're going to be sliding about anyway, there isn't the weight shift to unload a high side tire.

My objection is to the idea that we should all be driving around with the CDL locked regardless of conditions. I feel that doing so on clean dry pavement at speed is a ticket to disaster as it conflicts with proper control over the vehicle.

That is just plain incorrect Grench. First, I say you can, there's nothing wrong with it. I also say any claims that it REDUCES proper control over the vehicle is buying the ABS hype on awd. In my 15 years of teaching car control in awd and other vehicles, I see and focus on many more basic and demonstrated safety steps to vehicle control. The very first is hand position on the wheel. When I see a 12 o'clock, not sure I care if the ABS was just tested.

Loose tie rods, a basic safety ck, improperly loaded vehicles (SUV's tend to be the worst), and my list could go on forever. Concentrate on being a pilot of your vehicle, not just a way to get here to there. Skillset is practice, limit of adhesion exercises, and mindset. The best driver in an avoidance maneuver is one that has the brain, skillset and control over both. ABS vs locked center diff? As a rule, I really don't care what a driver uses on track or off. It's how he can perform with it that makes the difference.

I only get involved in this type of thread when I see more buying into the marketing of car control than understanding chassis dynamics. 2 80 drivers, one with ABS and CDL off and 1 with CDL on, isn't enough information to claim a damn thing in terms of who has more control. I'll ride with the one that does all the 'other' things right first.

Which means car control has little to do with CDL operation.

ST

 

[dealmaker]

It conflicts with control and also will lead to driveline damage. There is a reason Toyota puts warning lablels in their CDL-equipped SUV's about not engaging the lock on dry pavement. And I believe my non-CDL equipped 4WD's also had warnings about not driving in 4WD on dry pavement. My guess is the Toyota engineer's probably have at least a small idea of knowledge.

...
I feel that doing so on clean dry pavement at speed is a ticket to disaster as it conflicts with proper control over the vehicle.

 

[Jason Andrews]

The CDL is less clear, but my personal preference would not be to run on pavement with the CDL engaged.

Again, I am not endorsing the SUMO drive on pavement with CDL engaged.

It conflicts with control and also will lead to driveline damage. There is a reason Toyota puts warning lablels in their CDL-equipped SUV's about not engaging the lock on dry pavement. And I believe my non-CDL equipped 4WD's also had warnings about not driving in 4WD on dry pavement. My guess is the Toyota engineer's probably have at least a small idea of knowledge.

Hello again, I am not talking about dry pavement here guys, I am speaking of snow packed roadways at close to highway speeds.

A better question to answer on this thread would be what is the safest top speed to run with the CDL engaged? I run up and down snow packed I-70 to and fro the ski slopes at 50-60 with CDl on. Did someone say Toyota suggests not exceeding 60? Thought I remember something about that.

If you dont believe me about the CDL slap on a set of 35" BFG M/T's and see how the truck drives on ice and snow.

The only time I feel unsafe with CDL on is in tight turning/braking situations and sometimes switch it off.