Trail 4x4-HI driving?

[Jeremy556]

And for the record, nobody is likely to jack up their transfer case or differential gears by rolling for 10 feet on pavement.

A friend of mine forgot to take his 200K mile Yukon out of 4hi when leaving Colorado on his way back to Florida. He realized it was still in 4hi a couple of months later.

 

[pwrtrain]

It's just a transfer case, same as they've ever been. I don't run mine when I don't need to pavement or gravel, but there is no harm in running it on pavement. It's just extra gears turning. As mentioned you want to keep the full lock turns to a minimum but that's all low speed low load anyway.
In the situation you are talking about, patchy ice, I would absolutely run 4wd. You run more risk of damage taking it in and out at speed than just leaving it engaged.

I disagree. Using 4H on dry pavement can lead to driveline wind up, even in a straight line. Depending on a lot of factors such as road conditions and tires, this can be a significant amount of stress on your driveshaft and axle. As JB posted, when cornering or taking tight turns, it can cause hopping and scrubbing at low speeds, anyone who has tried to park a truck in 4H knows what I am talking about. Another concern is driving at speed with very small differences in tire diameter due to slight variations in tire pressure or tire wear. According to some simple calculations (feel free to correct me if I missed something or made an error) at 45MPH a simple 1/16" difference in effective rolling radius between the front and rear axle can lead to about 1" of windup at the tire per second! Even more important is that this windup is magnified by 3.727 to the driveshaft, which is usually why the transfer case or driveshaft acts as the "fuse" and fails. Even if there is not a catastrophic failure, there is extra wear on all of the components within the powertrain system, which will decrease life of the system and lead to premature failure.

In reality, one of the axles will wind up to the point where the driveline gets strained until it has enough energy to break the tires loose while driving. At this point the driveshaft will unwind and then start the whole cycle over again. While driving on wet pavement or snow/ice, the strain energy to break the tires loose is significantly lower and within the design parameters of the 4WD system. If you want to get an idea how much effort this takes, go out and try to push your truck on dry pavement while it is parked with the brake on

I am fairly confident that some engineer across the pond went through similar calculations and continued to design the bearings, bolted joints and cross sections to handle these stresses. Since the manual states not to drive it in 4H on dry, I can safely assume they did not design it to handle those additional stresses. For short distances and slower speeds it is less harmful.

To answer the question of the OP, it won't hurt your transmission, but can hurt your transfer case or driveshaft. 4WD helps some on ice, but slowing down is the right answer. Switching between 2WD and 4H on the fly does introduce some system wear, but there are synchronizers that are designed to do this at or below the recommended speed. I would suggest some good winter tires, but I doubt they are worth it in TX and I doubt you could find a shop that stocks them!? Stay safe!


Assumptions
Diameter of P265/70R17 is 31.6"
µ*N > Net Tractive effort
tires are not slipping ( i.e. as in dry pavement)
Radius Delta of 1/16" for 2 PSI Tire Pressure Difference
this value changes significantally with different tires, but is very conservative
Df = Front Tire Diameter
Dr = Rear Tire Diameter
not necessary to know left to right tire diameters due to axle differentials (except for those of you running lockers..)

When travelling in a straight line in 4WH (transfer case locked)

π* Df = Cf effective ROLLING Circumference of Front wheels
π* Dr = Cr effective ROLLING Circumference of Rear wheels
assume front tires are low (if only one tire is low, reduce radius delta by half)
IF Df = Dr - .125"
Cf = Cr - .125"
0.125 Difference per revolution

when tires are not slipping and driving in straight line @45MPH

45 MPH
convert to inches per minute
792 Inches / second
99.27 inches / rev of tire
7.98 revs per second
multiply Difference per revolution BY revs per second
0.997 difference in inches / second

 

[ar15kittykat]

Pwrtrain,
so running 4HI on dry pavement can stress n potential damage transfer case n drive shaft, so when the manual states to run at least 10miles every month in 4HI to keep unused parts lubed, I have to go off roading or find dirt, gravel to do my 4HI driving. That is a bit high maintenance for a rugged 4x4.

I never owned a truck nor 4x4, so all this 4x4 part time stuff is new to me...

 

[Jeremy556]

I have to go off roading or find dirt, gravel to do my 4HI driving. That is a bit high maintenance for a rugged 4x4.

Does it rain much there? If you are real worried about it, do it in the rain when driving straight. I would skip the rain part though and just do it on dry pavement going straight.

Every 4x4 that goes off-road around here drives on slickrock (which when dry is about 87 times grippier than asphalt) in 4LO. Your tires howl when making turns, often full-lock turns, and you can feel them scrubbing. I have to think this is putting way more stress on the drivetrain than going straight in 4hi, and we do this all of the time. I have never heard of a transfer case or driveshaft failure from it; too much skinny pedal and a tire touching back down on slickrock is usually what does it.

 

[pwrtrain]

Pwrtrain,
so running 4HI on dry pavement can stress n potential damage transfer case n drive shaft, so when the manual states to run at least 10miles every month in 4HI to keep unused parts lubed, I have to go off roading or find dirt, gravel to do my 4HI driving. That is a bit high maintenance for a rugged 4x4.

I never owned a truck nor 4x4, so all this 4x4 part time stuff is new to me...

Make sure your tires are properly inflated and avoid highway speeds in 4H. Using it in the rain is a very good suggestion as well.

 

[Orc]

The problem is when you hit a patch of ice and your in 2wd did this in my taco on roads with some snow sections and some "dry" and wound up doing a 360 on the interstate in front of a semi.

 

[jrob]

I disagree. Using 4H on dry pavement can lead to driveline wind up, even in a straight line. Depending on a lot of factors such as road conditions and tires, this can be a significant amount of stress on your driveshaft and axle. As JB posted, when cornering or taking tight turns, it can cause hopping and scrubbing at low speeds, anyone who has tried to park a truck in 4H knows what I am talking about. Another concern is driving at speed with very small differences in tire diameter due to slight variations in tire pressure or tire wear. According to some simple calculations (feel free to correct me if I missed something or made an error) at 45MPH a simple 1/16" difference in effective rolling radius between the front and rear axle can lead to about 1" of windup at the tire per second! Even more important is that this windup is magnified by 3.727 to the driveshaft, which is usually why the transfer case or driveshaft acts as the "fuse" and fails. Even if there is not a catastrophic failure, there is extra wear on all of the components within the powertrain system, which will decrease life of the system and lead to premature failure.

In reality, one of the axles will wind up to the point where the driveline gets strained until it has enough energy to break the tires loose while driving. At this point the driveshaft will unwind and then start the whole cycle over again. While driving on wet pavement or snow/ice, the strain energy to break the tires loose is significantly lower and within the design parameters of the 4WD system. If you want to get an idea how much effort this takes, go out and try to push your truck on dry pavement while it is parked with the brake on

I am fairly confident that some engineer across the pond went through similar calculations and continued to design the bearings, bolted joints and cross sections to handle these stresses. Since the manual states not to drive it in 4H on dry, I can safely assume they did not design it to handle those additional stresses. For short distances and slower speeds it is less harmful.

To answer the question of the OP, it won't hurt your transmission, but can hurt your transfer case or driveshaft. 4WD helps some on ice, but slowing down is the right answer. Switching between 2WD and 4H on the fly does introduce some system wear, but there are synchronizers that are designed to do this at or below the recommended speed. I would suggest some good winter tires, but I doubt they are worth it in TX and I doubt you could find a shop that stocks them!? Stay safe!


Assumptions
Diameter of P265/70R17 is 31.6"
µ*N > Net Tractive effort
tires are not slipping ( i.e. as in dry pavement)
Radius Delta of 1/16" for 2 PSI Tire Pressure Difference
this value changes significantally with different tires, but is very conservative
Df = Front Tire Diameter
Dr = Rear Tire Diameter
not necessary to know left to right tire diameters due to axle differentials (except for those of you running lockers..)

When travelling in a straight line in 4WH (transfer case locked)

π* Df = Cf effective ROLLING Circumference of Front wheels
π* Dr = Cr effective ROLLING Circumference of Rear wheels
assume front tires are low (if only one tire is low, reduce radius delta by half)
IF Df = Dr - .125"
Cf = Cr - .125"
0.125 Difference per revolution

when tires are not slipping and driving in straight line @45MPH

45 MPH
convert to inches per minute
792 Inches / second
99.27 inches / rev of tire
7.98 revs per second
multiply Difference per revolution BY revs per second
0.997 difference in inches / second

Wow, you sure put some math into that one.
I once drove my 87 half way across the state of Texas before realizing I forgot to take it out of 4wd when I left Durango. Miraculously my t case escaped unphased by this reckless stunt. I grew up and learned to drive in an area where 4wd was a necessity not an option and have driven thousands of miles on snow and ice.
Speaking from experience I have never, nor have I ever known anyone to have any issues arise from driving in mixed conditions with 4wd engaged.
It's what it's there for man.
Just trying to be helpful, not trying to argue.

 

[MeBe4running]

Good read, always good to be reminded. I will add that I have used my 4wd "on the fly" at low speeds during tougher surface conditions and have had NO problems yet. I see why that can be problematic though.

 

[1engineer]

Wow, you sure put some math into that one.
I once drove my 87 half way across the state of Texas before realizing I forgot to take it out of 4wd when I left Durango. Miraculously my t case escaped unphased by this reckless stunt. I grew up and learned to drive in an area where 4wd was a necessity not an option and have driven thousands of miles on snow and ice.
Speaking from experience I have never, nor have I ever known anyone to have any issues arise from driving in mixed conditions with 4wd engaged.
It's what it's there for man.
Just trying to be helpful, not trying to argue.

Good read, always good to be reminded. I will add that I have used my 4wd "on the fly" at low speeds during tougher surface conditions and have had NO problems yet. I see why that can be problematic though.

[MENTION=100538]pwrtrain[/MENTION] I commend you on the math. Your dire warnings are valid but lack a certain sense of reality.
In reality, the manual tells us to drive it several miles a month for lubrication purposes. It's pretty tough to find snow in July and I'm sure the Toyota engineers knew that too.
In reality the tire coefficient of adhesion between dry snow and hard pack dirt is not much different.
In reality there are certain situations where 4WD is needed and all tires are not in a reduced traction condition. ex: A few weeks ago I was on an old service road. At times I had two wheels on dry rock and two wheels in the mud. Had to use 4WD even though I know the drive train could wind up.
And lastly, in reality there are about 1% of 4Runner drivers that even know or care about driveline binding!

I am quite confident the Toyota engineers know about this and have developed a transfer case design that will easily handle the extra induced loads required to scrub a tire on pavement. If they had not then our 4Runners would have several thousand driveline issues every year. I know several locals who have SR5's and some of them put it in 4HI and drive for weeks before taking it out of 4WD! Weeks! On dry roads and parking lots!

Yes, theoretically you are correct. If I designed a drivetrain that could only handle the stress of a tire spinning on reduced traction surfaces it would grenade the driveline. The truth is much different. Our differentials and transfer case HAS to be designed to handle the extra induced loads a normal 4WD would see, and it has to be designed for a long life in those conditions too.

So yes, we are inducing greater loads by driving on dry pavement. How much are we reducing the life of the components by doing so? As I do not have the design specs I do not know nor do you, unless you can convince me you are a Toyota drivetrain design engineer. I will hazard a guess though that we are talking about a drivetrain designed to be used and abused for DECADES. Driving regularly on dry roads (like the ten miles a month) on surfaces such as interstates or two lane highways will only result in useable life being reduced by DAYS due to the additional resultant loads those conditions require.

Now, going out in a mall parking, putting it in 4HI and doing doughnuts for hours on end is not such a good idea though!

Again, liked your math but tell the whole story next time. Like if the design is robust enough then scrubbing tires is not a big deal after all.

 

[pwrtrain]

[MENTION=100538]pwrtrain[/MENTION] I commend you on the math. Your dire warnings are valid but lack a certain sense of reality.
In reality, the manual tells us to drive it several miles a month for lubrication purposes. It's pretty tough to find snow in July and I'm sure the Toyota engineers knew that too.
In reality the tire coefficient of adhesion between dry snow and hard pack dirt is not much different.
In reality there are certain situations where 4WD is needed and all tires are not in a reduced traction condition. ex: A few weeks ago I was on an old service road. At times I had two wheels on dry rock and two wheels in the mud. Had to use 4WD even though I know the drive train could wind up.
And lastly, in reality there are about 1% of 4Runner drivers that even know or care about driveline binding!

I am quite confident the Toyota engineers know about this and have developed a transfer case design that will easily handle the extra induced loads required to scrub a tire on pavement. If they had not then our 4Runners would have several thousand driveline issues every year. I know several locals who have SR5's and some of them put it in 4HI and drive for weeks before taking it out of 4WD! Weeks! On dry roads and parking lots!

Yes, theoretically you are correct. If I designed a drivetrain that could only handle the stress of a tire spinning on reduced traction surfaces it would grenade the driveline. The truth is much different. Our differentials and transfer case HAS to be designed to handle the extra induced loads a normal 4WD would see, and it has to be designed for a long life in those conditions too.

So yes, we are inducing greater loads by driving on dry pavement. How much are we reducing the life of the components by doing so? As I do not have the design specs I do not know nor do you, unless you can convince me you are a Toyota drivetrain design engineer. I will hazard a guess though that we are talking about a drivetrain designed to be used and abused for DECADES. Driving regularly on dry roads (like the ten miles a month) on surfaces such as interstates or two lane highways will only result in useable life being reduced by DAYS due to the additional resultant loads those conditions require.

Now, going out in a mall parking, putting it in 4HI and doing doughnuts for hours on end is not such a good idea though!

Again, liked your math but tell the whole story next time. Like if the design is robust enough then scrubbing tires is not a big deal after all.

I do agree with you on this, I didn't mean for this to be a dire warning, but for someone not familiar with 4x4 systems it's better to err on the side of caution and realize there are certain circumstances where it can be a problem.

In fact, I just looked at my manual and it states: Shifting from H2 to H4, Reduce vehicle speed to less than 50 MPH. On page 229 (right after the full time 4WD section) , there is a Notice that says "For normal driving on dry and hard surfaces, unlock the center differential." on page 225 (after the part time 4WD) it does not mention driving on dry or hard surfaces, it just says don't shift to 4HI if wheels are spinning. Maybe the SR5/Trail transfer case is fine with driving on dry and hard surfaces? Like you said, there aren't piles of broken transfer cases in the service department these days?


Regarding the design parameters and limits, I don't know what they are (I am not a Toyota engineer..), which is why I ended the calculations at simple geometry. I agree that the powertrain system is designed to handle many other loads and that minor scrubbing and driveline windup is probably within those limits, but I wanted to convey that under the right circumstances there could be windup even in straight line driving. I was curious myself how much that could be, so I quickly ran the numbers, didn't mean to nerd out, just wanted to put the numbers out there for discussion.

 

[KidVermicious]

didn't mean to nerd out,

Never go full nerd.

 

[1engineer]

I do agree with you on this, I didn't mean for this to be a dire warning, but for someone not familiar with 4x4 systems it's better to err on the side of caution and realize there are certain circumstances where it can be a problem.

In fact, I just looked at my manual and it states: Shifting from H2 to H4, Reduce vehicle speed to less than 50 MPH. On page 229 (right after the full time 4WD section) , there is a Notice that says "For normal driving on dry and hard surfaces, unlock the center differential." on page 225 (after the part time 4WD) it does not mention driving on dry or hard surfaces, it just says don't shift to 4HI if wheels are spinning. Maybe the SR5/Trail transfer case is fine with driving on dry and hard surfaces? Like you said, there aren't piles of broken transfer cases in the service department these days?


Regarding the design parameters and limits, I don't know what they are (I am not a Toyota engineer..), which is why I ended the calculations at simple geometry. I agree that the powertrain system is designed to handle many other loads and that minor scrubbing and driveline windup is probably within those limits, but I wanted to convey that under the right circumstances there could be windup even in straight line driving. I was curious myself how much that could be, so I quickly ran the numbers, didn't mean to nerd out, just wanted to put the numbers out there for discussion.

Understood. You must remember though that some of our posts will be read 100's of times by laymen. Most of us here try really hard to convey the facts and dispel any myths or rumors that seem to perpetuate 4WD forums and specifically 4Runner specific myths.

What I am trying to say is there are ways to present caution without leaving the reader scared or misinformed, or dazed and confused. Sometimes I think my posts are gone over with a fine toothed comb looking for any mistake, conceptual or otherwise lol.

Now if we want to talk about portable carnival rides....

 

[Canazes9]

Never go full nerd.

I think if we stuck to that, quite a few of us would be banned outright...

:banplease:

David

 

[1000MPH]

My personal issue with the overuse of 4H is that it tends to mask the true road conditions. For me, a little wheelspin or vsc/trac kicking in is a good indicator there's ice under that snow or the intersections are still frozen.
Seen plenty of Subarus and other 4wd cars spin out in just the last week here while I'm doing just fine in 2H.

 

[Intruder]

Seen plenty of Subarus and other 4wd cars spin out in just the last week here while I'm doing just fine in 2H.

A lot of people forget that 4WD or AWD is for go and not stop or corner. The other thing I've noticed around here is a lot of Subies and Audis having trouble because they seem to think their low profile all seasons will be fine since they have AWD. I've been popping into 4Hi at intersections to get going then back into 2Hi. Winter tires ftw.

 

[1engineer]

A lot of people forget that 4WD or AWD is for go and not stop or corner. The other thing I've noticed around here is a lot of Subies and Audis having trouble because they seem to think their low profile all seasons will be fine since they have AWD. I've been popping into 4Hi at intersections to get going then back into 2Hi. Winter tires ftw.

Exactly what I do. If it's deep though I leave it in 4HI. We have quite a few hills where I live. Sometimes though I do have to press that cute little button above me because let's face it - I am still 16 years old.

 

[Antman]

sometimes though i do have to press that cute little button above me because let's face it - i am still 16 years old.

 

[Ol'Baditude]

I've been popping into 4Hi at intersections to get going then back into 2Hi. Winter tires ftw.

Exactly! That is a great combination of equipment and technique and a great example for anyone with a part time 4x4 IMO.
Although for the last week or more, with the hills and snow and ice buildup on pretty much every street in our area of the city and routes to and from work, the Runner never left 4Hi at all save for some brief freeway travel where there was a bit of "dry" pavement showing. For the rest of the year though, it's what you said above, minus the snow tires of course since the ATZ's seem to do quite well coupled with reducing speed to conditions.

 

[LandCruiser]

Don't want to ***** again, but I think that this thing needed a center diff. What does it cost? 800 bucks? What does the Entune cost, the Homelink that doesn't recognize my garage door opener, the stupid cargo tray that rattles like a coffee can full of nuts and bolts?

I leave this thing in 4HI around town because I really don't want to lose traction before I realize I need traction... because there's snow, ice, and slush everywhere. That means that when I pull into a dry parking spot in an icy parking lot, the drivetrain binds up. It's annoying as hell, but I'm not going to sacrifice safety.

My wife's LE, which is running on 285s on 17" FJ rims has full time 4WD and this doesn't happen... because it has a center diff... And I can drive it at 80mph.

Really, Toyota.

 

[Canazes9]

A lot of people forget that 4WD or AWD is for go and not stop or corner. The other thing I've noticed around here is a lot of Subies and Audis having trouble because they seem to think their low profile all seasons will be fine since they have AWD. I've been popping into 4Hi at intersections to get going then back into 2Hi. Winter tires ftw.

Inexperienced winter driver question:

I see comments like yours frequently w/ regards to 4WD only helping you get started - no help in stopping, cornering. That seems like its not entirely true. If you are driving slowly in poor weather conditions (say sub 30mph) and you lift throttle in 4wd doesn't the engagement of the front wheels help with engine braking (which would seem to help gingerly slow the vehicle)? No that doesn't help a panic stop, but it would seem to help when driving at appropriate speeds for the conditions

Similarly, in a very low traction, low speed skid -wouldn't having the front wheels pulling help pull the vehicle the direction you wanted to go as compared to being in 2wd? I have noticed this effect in muddy trail conditions and it seems to me I have significantly more steering control/steering correction.

Again - I have limited (very) winter weather driving experience. I'm asking not telling....


David