Does A 4WD Truck Need Limited Slip

[Dean2]

Exactly. Excluding offroading, the amount of situations one can get into in a modern 4x4 truck that absolutely requires a LS to get out of, has to be close to zero. Might take a tiny bit more effort without, but really, "need"? No. Nice to have? Yes.

If you guys lived where i do, LSD as as required option would be no question. Here you have to turn off traction control often. If you don't you aren't going anywhere. Depowering a slipping wheel means you aren't going up the road because you can't develop enough speed to get up the hill or through the soft spot. I have seen the traction control so f'ed up that it shuts off completely and says service TCS. Always goes away after you get out and get restarted but while you are trying to get out, TCS is a major impediment.

They actually make harnesses to completely defeat TCS in high 4x4 for the conditions we operate in.

 

[Travelin Ram]

I refer back to my example of using 2 hub dyno's to measure torque output at the wheels.The only dyno that's going to give you a torque reading is the 1 hooked to the spinning tire,the locked stationary dyno isn't going to give you a torque output reading.Dyno's read torque then compute that number to a horsepower reading

I’m not sure I understand your point?

Both tires are spinning, when doing a 1 tire burnout as you described in your example. If you’re doing 50, then the gripping tire is spinning at 50 mph, the slipping tire is doing some higher rpm / mph. There is no stationary tire.

I agree a wheel dyno is incapable of measuring stationary torque. That’s a limitation of its design; it’s nothing more than a generator measuring current and RPM. In a zero RPM situation an instrument for measuring stationary torque would be required. Such as a torque wrench.

 

[Travelin Ram]

If you guys lived where i do, LSD as as required option would be no question. Here you have to turn off traction control often. If you don't you aren't going anywhere. Depowering a slipping wheel means you aren't going up the road because you can't develop enough speed to get up the hill or through the soft spot. I have seen the traction control so f'ed up that it shuts off completely and says service TCS. Always goes away after you get out and get restarted but while you are trying to get out, TCS is a major impediment.

They actually make harnesses to completely defeat TCS in high 4x4 for the conditions we operate in.

The specific situation described prior was the one side of the vehicle off pavement and “stuck”. That’s where TC is helpful. For higher speeds where wheel spin is desired, there’s an off button.

These arguments in some ways are circular. Pretty much any vehicle feature has both advantages and disadvantages, depending on the precise circumstances.

I’ll take all the features I can get, preferably driver controlled. Nannies without an off switch are what I despise. ABS, for example: for almost all situations, it’s better than humans. But it dam near killed me on a gravel road once. We’d have been off a cliff except I hit the parking brake in the Jeep.

 

[Wild one]

I’m not sure I understand your point?

Both tires are spinning, when doing a 1 tire burnout as you described in your example. If you’re doing 50, then the gripping tire is spinning at 50 mph, the slipping tire is doing some higher rpm / mph. There is no stationary tire.

I agree a wheel dyno is incapable of measuring stationary torque. That’s a limitation of its design; it’s nothing more than a generator measuring current and RPM. In a zero RPM situation an instrument for measuring stationary torque would be required. Such as a torque wrench.

Then lets change it over to a water brake dyno,where water temperature is the differance,the stationary tire still isn't going to generate a torque reading,while the spinning tire is generating a torque reading. I get what you're saying,but in the real world torque between tires is not equal at all times,as it's torque that spins a tire,not horsepower. In an open diff a stationary tire is not applying the same torque to the ground as the spinning tire is.One example that comes to mind,is way back when i was a kid,i got the old mans truck stuck on dry pavement,by digging a hole doing one hell'va 1 wheel brake stand,then as 16 year old kids we got out to look at the hole i'd dug in the pavement with the 1 tire,when i went to drive away the truck was stuck,it wouldn't budge,because the tire that had dug a hole wouldn't turn,the pavement had cooled off around the tire,and locked the tire into the surface of the road,and then the truck spun the other tire,and wouldn't budge the truck out of the hole the other tire was stuck in.If both tires were recieving equal amounts of applied and usable torque,the truck should have moved.In the real world applied and usable torque are not the same,and in this situation we're talking usable torque,as applied torque isn't doing much of anything

 

[Bike_Pilot]

If you guys lived where i do, LSD as as required option would be no question. Here you have to turn off traction control often. If you don't you aren't going anywhere. Depowering a slipping wheel means you aren't going up the road because you can't develop enough speed to get up the hill or through the soft spot. I have seen the traction control so f'ed up that it shuts off completely and says service TCS. Always goes away after you get out and get restarted but while you are trying to get out, TCS is a major impediment.

They actually make harnesses to completely defeat TCS in high 4x4 for the conditions we operate in.

Yep the nanny kill switch is a necessity on these trucks imo. Factory programming is awful and you can't actually turn the nannies off without some shenanigans. I run the Able switch. Easy to install and works great!

 

[cdn cj]

The TCS would be fine if it only applied brake pressure.
Unfortunately when it shuts off your throttle as you’re trying to power through a snow plow windrow or snow drift it is super annoying.
That’s where the TSC off and LSD come in …..

 

[ramffml]

If you guys lived where i do, LSD as as required option would be no question. Here you have to turn off traction control often. If you don't you aren't going anywhere. Depowering a slipping wheel means you aren't going up the road because you can't develop enough speed to get up the hill or through the soft spot. I have seen the traction control so f'ed up that it shuts off completely and says service TCS. Always goes away after you get out and get restarted but while you are trying to get out, TCS is a major impediment.

They actually make harnesses to completely defeat TCS in high 4x4 for the conditions we operate in.

I'm not going to get in an argument about who has worse driving conditions. We get nasty winters where I live as well, and yet little civics still go on their merry way where I live, and I guarantee where you live as well.

I have turned off T/C more than once every winter, sometimes for fun in a parking lot. And when the L/S hooks up you can find yourself pointing in the wrong direction very quickly.

Again, pros and cons. It's NOT a requirement, nor should you treat it as something you need to go about your day.

 

[TestPilot57]

...it's torque that spins a tire, not horsepower. In an open diff a stationary tire is not applying the same torque to the ground as the spinning tire is.

Yes, it is.

The one spinning is only putting a fraction of the potential power to the ground, because a spinning/sliding/slipping tire only has a fraction of the potential traction as an immobile tire. Yeah, that's why drag racers spin their tires to warm them up, but NOT to get their times...

Even if a vehicle is completely stationary and one tire is spinning at X MPH and the other dead stopped, they both have the same torque applied. As you stated, it's torque, which is a FORCE, not a measure of WORK (which is force over time/distance) that a differential applies.

An LSD or locked differential get/keeps you going because it allows one wheel to get MORE torque than the other, instead of equal. Read again, the full article https://www.rrtransmissions.com/technical/open-locked-differentials

Locked differentials on the other hand work by forcing both wheels to spin at the same rate, but they do allow for an uneven distribution of torque. 100% of the torque can be transferred to either wheel, which allows for the maximum amount of torque to be put down at any one time. However it has severe effects on handling.

Granted, they are talking about full lockers, but an LSD has similar benefits.

 

[Wild one]

Yes, it is.

The one spinning is only putting a fraction of the potential power to the ground, because a spinning/sliding/slipping tire only has a fraction of the potential traction as an immobile tire. Yeah, that's why drag racers spin their tires to warm them up, but NOT to get their times...

Torque gives you your ET /elapsed time ,horsepower is what gives you your MPH through the lights.The idea behind heating a drag radial or slick,is to soften it up,so it has more grip to the concrete launch pad or pavement.With soft rubber compounds with tread wear factors a 100 or lower,they get stickier when heated,and give you more traction. The post is about usable torque not applied torque,all the applied torque in the world isn't going to do you any good when you're stuck,it's usable torque to the wheel with traction that the thread is about Pound your chest all you want,but when you're stuck your theory really means squat about applied torque to each wheel with an open diff,you're still stuck and the wheel with the least amount of traction is the 1 spinning.The OP was asking about whether a limited slip was a benefit with a 4X4 or not,and in most circumstances yes a limited slip is still a benefit,as all the applied torque in the world isn't getting you out of the ditch or up that snow covered hill is it,in that case you actually want usable torque,not applied torque. Did you happen to catch this comment in the article you're referring to,seems to contradict what your implying.

"For example, if the axle speed is 700 RPM and there is 100 FtLb of torque at the axle, there will be 50 FtLb at each wheel. When turning, the outside wheel is at 800 RPM and the inside wheel is at 600 RPM. This means that the power split is 57% outside and 43% inside.
As mentioned earlier, open differentials are only able to transfer twice the amount of torque which the wheel with the least amount of grip is capable of transferring. Locked differentials can transfer all the torque from both the left and right wheels combined. In certain conditions this can be a significant increase in torque transferred to the ground, and will make the difference between moving or not when in low traction conditions."

 

[Dean2]

I'm not going to get in an argument about who has worse driving conditions. We get nasty winters where I live as well, and yet little civics still go on their merry way where I live, and I guarantee where you live as well.

I have turned off T/C more than once every winter, sometimes for fun in a parking lot. And when the L/S hooks up you can find yourself pointing in the wrong direction very quickly.

Again, pros and cons. It's NOT a requirement, nor should you treat it as something you need to go about your day.

You are entitled to your opinion. The places i am talking about needing to turn TCS off is not a parking lot, there are zero Honda anythings there. You need clearnace and horsepower as well as 4x4 or you are going nowhere.

If your driving pavement and good gravel, sure LSD is optional. It is inexpensive when ordered new, but you can get away without it 99% of the time. Mud or snow up to your running boards, no longer optional because TCS both applies brakes and cuts power, neither of which works well when navigating 30 miles of wet, snowy or muddy, deeply rutted road. On those roads an open diff is a big handicap.

 

[ramffml]

You are entitled to your opinion. The places i am talking about needing to turn TCS off is not a parking lot, there are zero Honda anythings there. You need clearnace and horsepower as well as 4x4 or you are going nowhere.

If your driving pavement and good gravel, sure LSD is optional. It is inexpensive when ordered new, but you can get away without it 99% of the time. Mud or snow up to your running boards, no longer optional because TCS both applies brakes and cuts power, neither of which works well when navigating 30 miles of wet, snowy or muddy, deeply rutted road. On those roads an open diff is a big handicap.

I've already said many posts ago that offroad is a somewhat different story (and in the examples you gave I'd actually want a real locker, not the LS). If you are burying your running boards or regularly driving in spots that ordinary traffic can't go, then that would qualify as "offroad", don't you think?

Why not argue for 38 inch mud terrains? How about winches, are those a requirement in your mind? Front lockers? 4 inch lift? Why not push him in the direction of a powerwagon? One can always make up more and more demanding situations to justify better equipment. If that's how you want to argue then go for it but if you read the OP's original question its quite clear that LS is absolutely not a requirement.

 

[Dean2]

Get limited slip. It is a real cheap option new and a REALLY expensive option to add later. No upside to open differential in the rear. Whether you need a locker up front (limited slip on the front is a BAD idea) depends on how much off roading you do. Mostly pavement, not needed and not usually a factory option on most pickups anyhow.

Same hold true of getting the right gears. 4:10 are a $100 option, swapping them later is a couple of thousand. Order the truck exactly how you want it, moding them later is very expensive. Guys that complain about the cost of options packages have never paid to do the add-ons later.

I was the second guy to answer the OPs original question. Answer above. The discussion moved a LONG ways from where it started. Most threads evolve, this one did too. I think a lot of great info got shared in here.

At this point, I don't think there is much more to be added or said on the topic of LSD so I am moving on to other topics.

 

[Fatbob Frank]

This thread...

 

[kdoublep]

Wouldn't have been the same if he wasn't wearing the jacket

 

[Mike Wenrich]

Well it looks like it will be LS for me. I found a new 2023 2500 Laramie about 200 miles from me. This dealer seems to order all the trucks for the lot the same. L/S ,410, protection group, Level 1 option, tow hooks, towing technology, performance tuned shocks (whatever those are) and spray in bedliner. A person of course can order other options if you want something different but they have/had a variety of these in different colors and interior. As mentioned above this topic got a bit technical but I got the info I needed for my climate zone. Thanks again for the education.

 

[Dean2]

Well it looks like it will be LS for me. I found a new 2023 2500 Laramie about 200 miles from me. This dealer seems to order all the trucks for the lot the same. L/S ,410, protection group, Level 1 option, tow hooks, towing technology, performance tuned shocks (whatever those are) and spray in bedliner. A person of course can order other options if you want something different but they have/had a variety of these in different colors and interior. As mentioned above this topic got a bit technical but I got the info I needed for my climate zone. Thanks again for the education.

Looks like a dealer that knows how to order a pickup properly for performance rather than for show. Glad you found what you are looking for.

 

[Mike Wenrich]

I agree. He is located in farm country west of Sacramento. Probably has a lot of business from them and then pulls people from the burbs as well because he doesn't have a glitsy showroom. The salesmen are in a portable trailer but the lot is huge and full of 1500, 2500 and 3500 trucks. There is also a shop there. Same family has been in business for over 80 years. Can't say I got a killer deal but I did get 5K off MSRP. That's good in this state (of confusion).

 

[TestPilot57]

Can't say I got a killer deal but I did get 5K off MSRP. That's good in this state (of confusion).

I haven't tried to buy a truck since the pandemic, but we recently bought my wife a new Telluride. We looked at them 1.5 years ago and dealers were asking $10k OVER list. This summer they were asking $3k but we settled on $1500. So I would say that you got a Good deal, if not a killer one.

 

[kdoublep]

I haven't tried to buy a truck since the pandemic, but we recently bought my wife a new Telluride. We looked at them 1.5 years ago and dealers were asking $10k OVER list. This summer they were asking $3k but we settled on $1500. So I would say that you got a Good deal, if not a killer one.

We got my wife a 2022 Telluride new for $45K. Great vehicle.

 

[TestPilot57]

...it's torque that spins a tire, not horsepower.

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.