Does A 4WD Truck Need Limited Slip

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

ppine

Forester
Joined
Jun 24, 2022
Posts
337
Reaction score
279
Location
Nevada
Ram Year
2022
Engine
6.7 liter diesel
Yes. Otherwise you have 2wd on different axles.
 

Wild one

Senior Member
Joined
Jan 17, 2016
Posts
13,882
Reaction score
23,780
Ram Year
14 Sport
Engine
5.7
This is where you are going off the rails.

Torque is only a force. HP is force x distance/time.

Put 100# on the end of a 1 foot long bar that is perpendicular to the ground and anchored so that the fixed end cannot move. Like on a lug nut that you've already set to 100 #/ft. The torque is there for eternity, even though the tire is not moving.

Now, if that lug nut is attached to a wheel/tire that is in contact with the ground, and there is little enough resistance that the wheel will start to turn, you then have HP. If you maintain force perpendicular to the bar, HP is the result and will vary based on how fast the wheel turns and how much force is applied.

An open diff (apart from extremely small, generally unmeasurable differences due to manufacturing tolerances) will ALWAYS apply equal torque to both wheels. It's physics 101. Ok, maybe 102.
In laymans terms when it comes to ICE engines, HP is torque X rpm divided by 5252,lets employ the "Kiss principle" here,hopefully you know what that means.Some guys might be baffled with BS,but i'm well past that,lol.
In real life with an open diff,the wheel with the least amount of traction,will always receive the majority of usable torque,other wise the wheel on dry pavement would push the vehicle out of the ditch even if the other wheel is off the ground,little tidbit for you,it won't.If you're stuck with an open diff according to your theory of applied torque to the tires,you should have the same amount of usable torque at both tires,and drive right out of the ditch/snowbank/mudpit etc., i'd love to see that happen.And that sir is physics 101.Did you even read the links you were trying to shove down my throat,they don't really agree with your idea you don't need a limited slip diff,in a snowbank :Big Laugh: When you're stuck "applied" torque means squat,what you need is"usable" torque,as all the applied torque in the world,still isn't going to make the wheel with the most amount of traction spin,if the other wheel is on ice or in the air.You can compensate some by applying a restriction to the wheel with the least amount of traction (BLD) but realistically in real life,a limited slip diff will do more towards keeping you moving then a BLD system will
I know you'll try to put another spin on this,as that seems to be the way you work:waytogo:
BTW the OP was asking about whether a limited slip diff was needed with a 4X4,how you managed to spin this off to a theory that only works on paper is beyond me.When your stuck with an open diff,nobody really gives 2 sh!!ts about your applied torque theory,they're more concerned about the usable torque that's available,just saying:Big Laugh:
Keep a shovel handy for the next time your applied theory works in a snowbank,you might need it :waytogo:
 

TestPilot57

Senior Member
Joined
Dec 13, 2015
Posts
1,487
Reaction score
893
Location
Vermont
Ram Year
2020
Engine
Hemi
...according to your theory of applied torque to the tires,you should have the same amount of usable torque at both tires,and drive right out of the ditch/snowbank/mudpit etc.
You do have the same amount of torque applied. Unfortunately, the tire with the least traction limits the amount of torque that can be applied.
...your idea you don't need a limited slip diff,in a snowbank :Big Laugh:
No one "needs" an LSD. For decades 99+% of vehicles driven were 2WD cars with open diffs. FWIW I have an LSD in my truck and would never buy one without it unless it were not possible.

My response was to the claim that without LSD you only have a 2WD truck when you paid for a 4WD one.
 

DILLIGAF

Senior Member
Military
Joined
May 28, 2016
Posts
4,245
Reaction score
7,625
Location
Canada
Ram Year
2012
Engine
5.7
My response was to the claim that without LSD you only have a 2WD truck when you paid for a 4WD one.

Well go in the snow / mud in 4wd without a locker and send me the video of all your 4 wheel spinning. Ill wait.

I have a 3WD truck in the snow / mud. since they dont make a locker for the Gen 3 front diff.

So yes everyone that buys 4WD truck without lockers dont have actually 4WD... lol..

I just came back from Limestone Mountain, I had to use the Bypasses on 2 different trails because my JK dosent have lockers. I slid sideways on a 5000 ft cliff. That made my ass pucker. because under load it became 2wd even on loose rocks.


nc_ohc=KHrGsS1yPmIAX9V3Zeg&_nc_ht=scontent.fyxd1-1.jpg
 
Last edited:

Dean2

Senior Member
Joined
Jun 17, 2021
Posts
2,744
Reaction score
4,007
Location
Near Edmonton
Ram Year
2021 2500
Engine
6.4
You can lead a horse to water but you can't make it drink.

Peace, out.
You can be as dismissive as you like but the problem is, you are talking to guys who actually use our 4x4s in really rugged locations. Deep mud, snow, loose rock, steep grades etc. However you cut it and whatever the theory, lsd in the rear and a locker in the front will take you WAY WAY more places than open diffs in really tough country. Brake limiting and traction control are actually handi caps in most really bad terrain. I know this doesn't apply to 70% of 4x4 users but for some of us, LSD and/or lockers are not nice to have, they are need to have.
 

Wild one

Senior Member
Joined
Jan 17, 2016
Posts
13,882
Reaction score
23,780
Ram Year
14 Sport
Engine
5.7
You do have the same amount of torque applied. Unfortunately, the tire with the least traction limits the amount of torque that can be applied.

No one "needs" an LSD. For decades 99+% of vehicles driven were 2WD cars with open diffs. FWIW I have an LSD in my truck and would never buy one without it unless it were not possible.

My response was to the claim that without LSD you only have a 2WD truck when you paid for a 4WD one.
Here's a test for you to do with a pegleg truck,lol. Find a dyno shop with an in ground dyno,ask them if you can back the drivers side tire onto the roller,and keep the pass side of the truck off the dyno,then jack the pass side rear tire off the ground,and chain the hell out of the truck to the ground so it won't fall off the jack,then fire the truck up and put it in gear and give us the dyno reading off the drivers side tire.Remember dyno's only read torque,so using your theory we should get a dyno number off the drivers side wheel showing applied torque. I'll wait for your hypothesis :Big Laugh: :waytogo:
 

Docwagon1776

Senior Member
Military
Joined
Mar 16, 2012
Posts
2,199
Reaction score
3,629
Location
Midwest
Ram Year
2012, 2021
Engine
5.7, 6.4
Like on a lug nut that you've already set to 100 #/ft. The torque is there for eternity, even though the tire is not moving.

The rotational energy of applied torque was used to stretch the bolt, creating tension, which is now the clamping force holding the lug nut in place.

So now tension is present, but not torque. There's no rotational energy remaining just sitting there as some potential energy in the lug nut.
 

TestPilot57

Senior Member
Joined
Dec 13, 2015
Posts
1,487
Reaction score
893
Location
Vermont
Ram Year
2020
Engine
Hemi
Here's a test for you to do with a pegleg truck,lol. Find a dyno shop with an in ground dyno,ask them if you can back the drivers side tire onto the roller,and keep the pass side of the truck off the dyno,then jack the pass side rear tire off the ground,and chain the hell out of the truck to the ground so it won't fall off the jack,then fire the truck up and put it in gear and give us the dyno reading off the drivers side tire.Remember dyno's only read torque,so using your theory we should get a dyno number off the drivers side wheel showing applied torque. I'll wait for your hypothesis :Big Laugh: :waytogo:
(By the way, not trolling)

Yes, the tire on the dyno is showing the applied torque. If you could measure the torque on the tire not on the dyno it would be the same.

I don't know how many times I've said this but apparently it's not sinking in. Guess I'm better at comprehending than teaching.

I know "it's the internet" and you can"t "believe anything on the internet" but I have yet to find and article from a seemingly reliable source that says anything other than "an open differential splits torque evenly between both wheels".


As I've also said (perhaps in different words), that does NOT mean that it applies the most torque available. And again I say that does not mean I recommend against getting an LSD - I would not order a truck without one (yeah, said that too). Yes, an LSD or Locker will get you out ot places an open differential will not. ALL I'M SAYING IS THAT AN OPEN DIFFERENTIAL APPLIES TORQUE EVENLY TO BOTH WHEELS, which a torque-load of peeps on here seem to have no idea what that means.

Seriously - when I said before that it's physics 101 I meant it. Maybe the forum should require an entrance exam before posting is allowed in technical forums.
 

Wild one

Senior Member
Joined
Jan 17, 2016
Posts
13,882
Reaction score
23,780
Ram Year
14 Sport
Engine
5.7
(By the way, not trolling)

Yes, the tire on the dyno is showing the applied torque. If you could measure the torque on the tire not on the dyno it would be the same.

I don't know how many times I've said this but apparently it's not sinking in. Guess I'm better at comprehending than teaching.

I know "it's the internet" and you can"t "believe anything on the internet" but I have yet to find and article from a seemingly reliable source that says anything other than "an open differential splits torque evenly between both wheels".


As I've also said (perhaps in different words), that does NOT mean that it applies the most torque available. And again I say that does not mean I recommend against getting an LSD - I would not order a truck without one (yeah, said that too). Yes, an LSD or Locker will get you out ot places an open differential will not. ALL I'M SAYING IS THAT AN OPEN DIFFERENTIAL APPLIES TORQUE EVENLY TO BOTH WHEELS, which a torque-load of peeps on here seem to have no idea what that means.

Seriously - when I said before that it's physics 101 I meant it. Maybe the forum should require an entrance exam before posting is allowed in technical forums.
Give it up Dude,as all the theories in the world aren't getting you unstuck. Nobody really cares about "applied" torque when they're stuck,they care about usable torque,and when one wheel is spinning on ice,and the other axle or spider gear isn't applying any usable torque to the wheel with traction,you're still stuck.
You should actually read some of the links you've posted,even they admit the torque split changes when you turn a corner etc..This latest one you linked to says in a "straight line" there's equal torque applied to both wheels,which actually does apply if both tires are on dry pavement,but on a corner the torque is split between the wheels,that means the outside wheel can have say 60% of available torque,while the inside wheel will have 40% of the available torque.
BTW please explain how you thought your theory actually has any bearing on this thread,the OP wanted to know about the benefits of a limited slip with a 4X4,not some engineering theory that has no bearing in the real world,especially when you're stuck.
The more you keep beating this thread to death with theories that actually have no real bearing in the real world,the more i think you're not all there when it comes to common sense. :cheers:

" In a straight line this means both wheels have even amounts of power applied to them."

This is from your other link you posted a few pages back.

"At this point the outside wheel remains at 800 RPM, axle speed has increased to 1100 RPM and the inside wheel is at 1400 RPM. The power split between the wheels is at 36% outside and 64% inside. "
 
Last edited:

ramffml

Senior Member
Joined
Jul 12, 2019
Posts
2,808
Reaction score
5,128
Location
ramforum
Ram Year
2019
Engine
hemi 5.7
I always loved this ancient video from GM describing how open diffs work, maybe it helps:

 

Wild one

Senior Member
Joined
Jan 17, 2016
Posts
13,882
Reaction score
23,780
Ram Year
14 Sport
Engine
5.7
I always loved this ancient video from GM describing how open diffs work, maybe it helps:

It explains how the spider gears works pretty decently though. I remember that video from my shop class in high school way back in the 70's,lol
 

Docwagon1776

Senior Member
Military
Joined
Mar 16, 2012
Posts
2,199
Reaction score
3,629
Location
Midwest
Ram Year
2012, 2021
Engine
5.7, 6.4
(By the way, not trolling)

Yes, the tire on the dyno is showing the applied torque. If you could measure the torque on the tire not on the dyno it would be the same.

I don't know how many times I've said this but apparently it's not sinking in. Guess I'm better at comprehending than teaching.

Probably because you are trying to teach without using the correct terms and your understanding is Physics 101, which is spherical cows level at best. I mean, wtf is applied torque? Is there unapplied torque? Some sort of potential energy? If you want to talk down to people, pass your own exam first.

How about this: Torque distribution from the diff is equal, however that information is useless to say what work is then done because it lacks variables of time and distance. Energy or force is not work, it's the potential to do work. When one tire is spinning, so that the surface of the tire is covering a much greater distance than the tire rocking an inch or so in the same time frame, work is not being accomplished equally and the vehicle is not moving as desired. Nobody outside the engineering lab gives AF what the torque distribution is, they want the work done by each tire to be equal enough that both tire surfaces cover the same distance over the same time, or near enough that the vehicle moves like they want it to.
 

TestPilot57

Senior Member
Joined
Dec 13, 2015
Posts
1,487
Reaction score
893
Location
Vermont
Ram Year
2020
Engine
Hemi
Apparently I'm a bad teacher. I really think we are all saying the same thing, but there is one little point that is being missed.

What I'm saying is that an open diff applies equal torque to each wheel - that DOES NOT mean that it's the best way to get unstuck (or keep from getting stuck in the first place). In fact, it's the worst.

If I have one tire on slick ice and one on dry pavement I want the tire on the pavement to have 10-100-1000 times more torque applied to it. This is not possible with an open diff.

That is all I have said from day 1.

:popcorn:
 

Wild one

Senior Member
Joined
Jan 17, 2016
Posts
13,882
Reaction score
23,780
Ram Year
14 Sport
Engine
5.7
Apparently I'm a bad teacher. I really think we are all saying the same thing, but there is one little point that is being missed.

What I'm saying is that an open diff applies equal torque to each wheel - that DOES NOT mean that it's the best way to get unstuck (or keep from getting stuck in the first place). In fact, it's the worst.

If I have one tire on slick ice and one on dry pavement I want the tire on the pavement to have 10-100-1000 times more torque applied to it. This is not possible with an open diff.

That is all I have said from day 1.

:popcorn:
Just what possessed you to think an engineering theory that has no real benefits in the real world,would apply to the OP's question.About all i can come up with,you were thinking you were smarter then anybody else on this thread.
All you've accomplished is a few of us really question your common sense
 

TestPilot57

Senior Member
Joined
Dec 13, 2015
Posts
1,487
Reaction score
893
Location
Vermont
Ram Year
2020
Engine
Hemi
Just what possessed you to think an engineering theory that has no real benefits in the real world,would apply to the OP's question.About all i can come up with,you were thinking you were smarter then anybody else on this thread.
All you've accomplished is a few of us really question your common sense
It's not a theory, it's a fact.

A fact that may cause some to stick with the stock open differential, others to go with the LSD and still others with the locker.

As for how "smart" I am, I try to always surround myself with and hire people smarter than me, with the goal of me being the dumbest person in the room. Unfortunately, I do not have the same option in an online forum.
 

Wild one

Senior Member
Joined
Jan 17, 2016
Posts
13,882
Reaction score
23,780
Ram Year
14 Sport
Engine
5.7
It's not a theory, it's a fact.

A fact that may cause some to stick with the stock open differential, others to go with the LSD and still others with the locker.

As for how "smart" I am, I try to always surround myself with and hire people smarter than me, with the goal of me being the dumbest person in the room. Unfortunately, I do not have the same option in an online forum.
I guess you can think that,if it makes you sleep better at night :waytogo:
I highly doubt an engineering theory that's been around since the dawn of the automobile is going to make anybody decide whether they need a pegleg or a LSD:Big Laugh:
BTW it's an engineering theory that can't be proven in real life,and has no real application to this thread,or pretty well any other real world application.It's nothing more then a paper theory
Personally on this one,i definitely think you just might qualify as the dumb one,and i'd hate to disagree with you,:Big Laugh:
I'm guessing you recently stumbled on this theory,and thought you'd expound on it,to make yourself look smarter then the majority.Little tidbit for you,this theory has been around for forever,but nobody ever tries to promote it,as having any real world application.If you had any common sense you'd realize that ;)
 
Last edited:

Forum statistics

Threads
195,338
Posts
2,868,956
Members
155,973
Latest member
Bobby023
Top