CLin9383

hey guys, this is probably a simple question for you guys, but what is the difference between 4wd and awd?? thanks for any input..

HBoss

First, a clarification:

Part-time 4WD: Can only be used on slippery or "not ideal traction" surfaces

Full-time 4WD, also known as AWD (these terms are interchangeable): Can be used all the time on any driving surface

Reason:

Part-time 4WD: front and rear diff, no center diff, transfer case locks front and rear driveshafts, front and rear turns at same speed which doesn't allow for proper wheel speeds in turns on high traction surfaces causing strain on transmission and tires when trying it

Full-time 4WD or AWD: front and rear diff, usually a center diff or housing for something such as viscous coupling, front wheels turn at different speeds than the rear because of the center diff or viscous coupling allowing for front and rear wheel speed variations when making turns

You can get into much more detail than this and the ways full-time 4WD/AWD are accomplished, but basically those are the differences and full-time 4WD is basically AWD.

Hope this helps clarify,

Al

CLin9383

yea, it makes a little more sense now...thanks AL!!!

HBoss

Hey man,

Just FYI, but I posted an article on my web page with just a little more detail regarding 4WD/AWD, etc. if you're interested.

It's the article of the week. I'll archive it next Sunday night and put a new article in.

Al

BTOWN4RUNNER

Ok, a question of my own. When I bought the 4Runner I took it to the mechanic and he said that when it is 2wd, the back 2 wheels are the powered ones. But when I put it in 4wd, which wheels are the powered ones? He said that one front and one rear, is that correct or do all 4 have power to them? Just a dumb question, but I always wondered! Thanks! :fireman:

HBoss

Ok, this one is not a simple explanation and is based on the use of differentials. It also depends on what kind of 4WD system your Toy uses, so this explanation may not neccessarily apply to all.

It is correct to say that the torque produced by your engine and transmission will be displaced evenly to your front and rear driveshafts and differentials. It is not correct to say that the power goes to one front and one rear tire.

Clarification:

The torque from your engine gets to your wheels eventually, but has to go through the transmission (including clutch plates for manual and torque converter for automatic), the driveshafts, the differentials and the axles to get there.

Torque produced by the engine makes it way down the driveshaft and ends up at the differential. It is the differential's job to apply the torque to the drive wheels. Now in the case of an open differential (usually on 4Runners, not sure about 1999 and up ones), it splits up torque evenly to both tires and allows them to turn at different speeds.

The maximum amount of torque that actually gets applied to the drive wheels, is the highest amount possible while traction is maintained. I know this sentence sounds kind of weird, but continue reading.

Let's say you have imaginary tires that have absolute traction, i.e. they will never slip no matter how much torque is applied. The maximum amount of torque that will be applied to them is the maximum the engine and transmission can produce at any given RPM.

Now in real life your tires will slip, especially on snow or ice. Let's say you have one tire on black ice and the other one on good pavement. You only need a very tiny amount of torque applied to the wheel on black ice before it begins to slip. In the case of the open differential that splits torque evenly, only the same amount of torque to the wheel on black ice, will be applied to the wheel on good pavement.

That's why you get the illusion that when you're stuck, only one wheel is spinning and the other one seems to be doing nothing. The torque is split evenly and each tire only gets a small amount, usually not enough for the tire on good pavement to get your 4000lb vehicle out of being stuck.

Does this help or did I screw up the explanation?

Al

BTOWN4RUNNER

Yes, I kinda understand what you are saying. Let's say I understad now more than I did before! Thank you and I will have to "study" alittle more and see what is going on! Thank you! :fireman:

Ron(Fla)

That's why you get the illusion that when you're stuck, only one wheel is spinning and the other one seems to be doing nothing

Yea, I had that illusion once when I was dating and parked in some sand by a lake in my 2wd car. It looked like only one tire was spinning and the other was just sitting there. I'm glad to know that it was only an illusion.

Just kidding you a little, the made me do it...

HBoss

Haha...thx a lot! You know what I meant...

The illusion that the power normally only goes to one tire, instead of both...is what I meant.