What exactly does switching to H4 do?

Consider from a different point of view then;
Imagine that you have one wheel in the air on a jackstand, and the other is on the ground. You have a jack under the side on the ground. You start the engine, put it in first gear, and engage the clutch. So now the wheel in the air starts spinning, but the one on the ground is stopped.

So start jacking up the one on the ground. Soon as it is off the ground, what happens? It starts spinning. If it wasn't getting any power, then it WOULD NOT start spinning.

But it IS getting power. It is getting VERY LITTLE power -- enough to make a wheel spin if it is in the air, but not enough to move the vehicle.

 

The right tire is spinning because that's where the least amount of resistance is so all the power is getting directed there from the open differential. as you jack up the left tire that resistance is no longer there, therefore both tires begin spinning equally again.

Again power always goes to the wheel with the least amount of resistance. Same when you are turning. As your turning right, more of that power from the drive shaft gets consumed by the left tire because that tire is spinning more than the right. So there is less resistance there.

 

Yes.

NO. Power is going to BOTH wheels.

Come on, you are SOOOOOO close.
"that resistance is no longer there" ----- right... but the point is this; so what? If there is no power there, then WHAT IS IT RESISTING?

 

Well I'm glad I already understood how this stuff works because if I had to rely on what's been posted on this thread so far I'd walk away from the whole confused as hell. Lighten up, ladies.

 

This is also wrong. Just jack up one rear wheel and put the truck in gear and let off the brake. That raised wheel will spin freely and the wheel with traction will remain stationary. Because the spider gear allows the wheels to spin at any speed, just so the combination of the two speeds matches the speed of the pinion gear. If you have a 1:1 rear end (doesn't exist most likely) and you spin the pinion gear at 60 rpm, both wheels will nauturally spin at 60 RPM. Or if you lock one down, the other will spin twice as fast thanks to the spider gears transferring ALL rotational speed to just one axle.

An LSD uses springs and clutches to make it difficult to spin one side by itself, because the clutches connect BOTH rear axles together. They still have a spider gear, and one can spin faster than the other, but it is harder because of the clutch friction in the LSD. It is that clutch that tries to force BOTH wheels to drive, and when they spin at the same speed, the clutch is not slipping at all.

So your "either both or neither" is wrong. If you spin the pinion gear, one or both axles will ALWAYS be getting power. But if one is spinning freely, that power does nothing to move the truck when that wheel has zero traction.

 

The power coming from the drive shaft into the differential is ALWAYS going to take the path of least resistance, in your scenario that would be the right tire

the resistance comes from the contact of the tire on ground. As long as the right wheel is the path of least resistance, the left wheel will never have enough power to overcome that resistance. That's when TRAC comes into play by adding resistance to the right wheel causing the differential to disperse more power to the left. leveling the playing field so to speak.

 

After reading this thread I need a drink

 

We aren't talking about a zero resistance electrical circuit here. The MOTION will follow the path of least resistance, but the power goes everywhere. Well torque, technically. But this discussion is really doing a bad job of distinguishing torque from power, from ALL involved, so lets leave that be for now.

That isn't what I asked you. I asked you WHAT it is resisting, not where the resistance is coming from.

Like I said before, you are VERY close. The key WORD in that phrase -- in YOUR phrase -- is "ENOUGH".

I'm not trying to say that it is enough power to overcome the resistance, I'm saying that there is SOME power. Just like there is SOME power on the wheel that is spinning. In BOTH cases, VERY LITTLE power. It does not take much power to spin a wheel. Lift a car off the ground and put it in neutral, and you can spin the wheel BY HAND. Put it on the ground, and unless you are HUGE, you probably won't be able to spin it by hand because you will be moving the entire car.


Look, lets make up some numbers to illustrate, focusing on 2wd open differential.
Our first number: it takes 0.001 hp to spin the wheel in the air at 50 rpm "sustaining" power, not accelerating.
Second number: it takes 10 hp to move the car forward.
When you have a wheel on the ground and the other in the air, the 10 hp would have to be delivered exclusively through the wheel on the ground. That means that the engine needs to produce 20 hp in order to deliver 10 to the ground through the one wheel with traction.

Ok, so what does that mean? Well, 20/0.001 = 20,000. You need to make 20 THOUSAND times more power to move the car forward, as it takes to spin that wheel in the air.

Now the wheel spinning in the air is spinning at 50 rpm. So the engine will be spinning at approximately 800 rpm given 4:1 transmission and 4:1 differential. Right? We are IDLING the engine right now.

So what does it take in order to actually make 20,000 times more power? Remember that the wheel is in the air -- there is NO LOAD on it. The answer is that in SUSTAINING power, you would essentially have to spin the engine at 16 million RPM, which is obviously not going to happen.

Of course, you don't need to limit yourself to sustaining power, you can also accelerate it. The wheel is pretty heavy as it is, so you can conceivably ACCELERATE that wheel with more than 10 horsepower, in order to get a little bit of power to move the vehicle (go back and read the experiment I suggested with the piano board and jack stand).


It is TERRIBLE to view the spinning wheel as where the engine is "dumping all its power", because the reality is that NOT MUCH power is being dumped there.

 

Hey @Dansnare, welcome to TacomaWorld!!!

 

This thread is blowing my mind. And I love every second of it. I can't stop!

 

@Roll Tide @DCSBFTMFW @CedarPark grab your popcorn, this one could be fun

 

OK, you just confused the hell out of me with all those numbers but I think I see what you were saying. I think we are on the same page but earlier when you were saying each wheel gets equal power all the time no matter if one was on the ground or in the air is what confused everyone.

 

BRAPPPPPPPPPPPPPPPPPPPPPPP

 

Cool !

 

He's just gonna pretend that he didn't say that and insist he is right and everyone else is wrong. Or maybe since nobody reads every post, no one will ever see that he was wrong if enough posts are made.

 

What? You mean now that you are the only one on your side of the fence?

 

When I put mine in 4hi, my butthole puckers a little bit. 4lo....watch OUT!