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AUTO LSD (or Not) for added traction in 2WD?

Discussion in '2nd Gen. Tacomas' started by David K, Oct 19, 2010.

  1. Oct 22, 2010 at 8:40 AM
    #41
    619Tacoma

    619Tacoma Baja bound

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    I have been going to Baja for off road races ever since I bought my prerunner. I have witnessed what a 2wd Tacoma with LSD and a few hundred pounds of weight in the bed is capable of. I have only been stuck ONCE! and that was my first time driving the truck off road (First time driving off road, PERIOD). I've been in deep sandy washes and have not gotten stuck. I always have 4 people and camping gear (2 ice chests full of beer and ice, tents, chairs, etc [sometimes take the quad instead of the coolers]) in the bed and am amazed at where I can go without getting stuck in 2wd.

    The last race I went to was in laguna salada. There was a somewhat steep decline we came down and would eventually have to go back up. Later, We saw a group of jeeps and 1 ford ranger go up the incline. A couple of the jeeps made it up in what seemed 2wd, a few stopped midway and must have engaged 4wd, and poor old Ford Ranger has his rear tires spinning like crazy, so engaged 4x4. This made me nervous as we were by ourselves with no locker or 4wd. All I have to say is that I crawled up the incline without the slightest feel of wheel spin... Mechanical LSD and weight in the back of a TOYOTA FTMFW!
     
  2. Oct 22, 2010 at 8:41 AM
    #42
    whippersnapper02

    whippersnapper02 Well-Known Member

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    ^^^If you look closely you are still really doing a one tire fire and the other wheel kinda spins.
     
  3. Oct 22, 2010 at 8:47 AM
    #43
    Crom

    Crom Time is precious; use it wisely

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    I deleted my post. I misread his post so my response was not really applicable.
     
  4. Oct 22, 2010 at 8:51 AM
    #44
    619Tacoma

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    Possibly... But I still made it out:D. My post probably doesn't belong in the AUTO LSD thread but just wanted to share my experiences.
     
  5. Oct 22, 2010 at 8:53 AM
    #45
    whippersnapper02

    whippersnapper02 Well-Known Member

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    Nah I was talking about the video.
     
  6. Oct 22, 2010 at 9:02 AM
    #46
    619Tacoma

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    oh...:rolleyes:

    Yeah, I saw the video too and honestly wasn't too impressed. Those don't look like donuts to me. It looks like he's driving in circles. If those are donuts in the video posted, I can do donuts in my mom's mini-van.:cool:
     
  7. Oct 22, 2010 at 9:05 AM
    #47
    JKD

    JKD Well-Known Member

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    Mechanically, if you have one wheel in the air, a rear locker will transfer 100% of the available torque to the wheel with traction. The rear locker forces both wheels to spin at the same speed.

    If you completely stop the free-air wheel, then the differential acts like a 2:1 overdrive. With the fully braked free-air wheel not moving, the driven wheel will have half the torque but twice the rotational speed as it would with a locker.

    Auto-LSD seems to pulse the brake on the free-air wheel, right? I am inclined to think that perhaps this falls somewhere in-between the locker and fully-braked examples above. I would like to see a torque graph for each rear wheel when A-LSD is in operation...I suspect that you would see the torque on the driven wheel pulsing from less-than-half to more-than-half of the available torque. There's a lot of factors that would have to be taken into account to model the torque in a simulation...
     
  8. Oct 22, 2010 at 9:51 AM
    #48
    fishshooter

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    I'd bet you wouldn't. I'm betting that at any instance in time you would find the same amount of torque at both wheels. It is still an open differential, so both wheels receive the same rotational force, regardless of their respective angular velocities.
     
  9. Oct 22, 2010 at 10:37 AM
    #49
    JKD

    JKD Well-Known Member

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    When one wheel is braked, the differential is a 2:1 gear set. Half torque, double speed.

    The reason I think it will spike above the "half torque" level is that when you unbrake the low-traction wheel, the drivetrain speeds up. When you brake the low-traction wheel, the rotational inertia of the drivetrain (other than the braked wheel and axle) would be dumped into the wheel with traction.
     
  10. Oct 22, 2010 at 12:28 PM
    #50
    Isthatahemi

    Isthatahemi Well-Known Member

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    That's if you happen to have no traction at both sides. ALSD is not about magically creating traction, it's about using what is available. ALSD makes a huge difference in daily driving, especially in the land of 5 months of snow...... BTW I don't carry sandbags either, BFG's AT's and ALSD will get you just about anywhere there is a road, (in the winter).
     
  11. Oct 22, 2010 at 2:30 PM
    #51
    fishshooter

    fishshooter Well-Known Member

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    Angular momentum is not torque. The torque that has been converted into rotational momentum, in say the driveshaft, will be reduced by any opposite torque, like the sudden braking of the wheel. If you look at the changing angular momentum over a fixed amount of time as a vector, it would be opposite of the torque produced by the wheel being braked. Angular momentum is conserved only until outside torque is introduced.
    Besides that, any additional resistance experienced by the spinning wheel is going to instantly increase the total available torque in the system, and it is going to be split equally by the differential.
     
  12. Oct 22, 2010 at 8:09 PM
    #52
    NAYo2002

    NAYo2002 Well-Known Member

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    Well yes... that's exactly what I was saying.

    Dude I've lived in Montana for 3 years, I think I know a thing or two about snow. The fact is I highly doubt a 5 lugger has A/Ts on them. The post said, he saw no difference and I'm inclined to agree based on my experience.

    Where I live, once it snows, the roads don't get plowed and you will not get anywhere without weights in the bed. ALSD or Lockers don't help at all since most of the time you are on packed snow or snow covered ice.

    You are probably lucky enough to live in a place where they actually plow roads after heavy snow storms or not get storms that last for days. "Just about anywhere" is not everywhere. I was responding to a comment about situations/locations where ALSD makes no difference. (i.e. "when stuck in snow")

    I'm not saying ALSD doesn't work, just saying 4x4 is the way to be on packed snow/ice if you have an empty bed.
     
  13. Oct 22, 2010 at 10:42 PM
    #53
    JKD

    JKD Well-Known Member

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    Angular momentum produces torque when opposed, which is what happens when the spinning wheel is braked. The force that slows the driveshaft and engine comes from the ring gear and carrier. If one side gear is held in place by a brake, then all of the torque applied to the carrier will be split, resulting in torque on the driven wheel. The total torque available to that wheel will be half of the engine output torque plus half of the torque required to reduce the angular momentum of the drivetrain from its previous level.

    This is why I think you would see a pulse of torque to the driven wheel higher than simply half of engine output torque.
     
  14. Oct 23, 2010 at 10:36 AM
    #54
    fishshooter

    fishshooter Well-Known Member

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    Yeah, I see what your saying. There would be a difference in the net torque at each wheel due to the one being braked deducting what it sees from the rotating mass of the ring gear and carrier. I think if you were operating at a fixed torque level it would happen. But the applied torque is going up the instance it sees an increased opposition. I think this would cover up any spike because that spike could only equal the applied torque and the relatively small amount of torque from opposing the rotating mass of the carrier and ring gear. IDK and could be totally wrong. I don't know if you could measure it either. Good discussion either way.
     
  15. Oct 23, 2010 at 6:10 PM
    #55
    David K

    David K [OP] Well-Known Member

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    It is great when techies begin to discuss the science and mechanics involved!
    I may be slow to learn, but once I 'get it', I think I am good for life!

    IF all the torque coming to the back differential is diverted to one wheel (because the other is braked)... would that one wheel have 100% torque if the other wheel is 100% braked? If not, is torque frozen by a braked wheel simply 'lost'?

    Another question... Are there any more of you 2WD Tacomans who became stuck or stalled, but got free by turning on the AUTO LSD? This question could be answered by 4WD Tacomans who stayed in 2WD.

    Thanks for all the replies!
     
  16. Oct 23, 2010 at 8:09 PM
    #56
    JKD

    JKD Well-Known Member

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    And what I'd like to do more than anything else on the topic is to team up with you and go Mythbusters on it. :D
     
  17. Oct 23, 2010 at 8:15 PM
    #57
    JKD

    JKD Well-Known Member

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    With one wheel totally braked, the differential is like a 2:1 overdrive for the remaining wheel. It cuts the applied torque in half, but doubles the rotational speed.
     
  18. Nov 1, 2010 at 2:22 PM
    #58
    David K

    David K [OP] Well-Known Member

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    Thank you!
     
  19. Nov 2, 2010 at 2:19 AM
    #59
    island808

    island808 Me l've got brains.

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    seems to follow, trac is just what you're trying to do with auto LSD. Its just helping regulate your foot. If you're trying for brute spinning force, you can either hit the auto lsd button or just keep your foot in it.
    The end result would be very similar and downright untestable in the real world.

    and yea.. don't try to destroy energy.
     
  20. Nov 2, 2010 at 5:10 AM
    #60
    inouk

    inouk Well-Known Member

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    This is what I was doing on my ATV and I can confirm that it works.

    Didn't try on Tacoma, but I don't see why it wouldn't work.
     
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