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4WD vs. AWD. What's the Difference?

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Re: 4WD vs. AWD. What's the Difference?

#201

Post by dghughes »

garyrichardson wrote: post #157
tombrossman wrote: post #48

Earlier quoted context omitted.

That's right. A poorly-engineered 4WD system means you are stuck on a hill because one wheel is on slippery wet leaves. AWD should mean you can get up that hill with three wheels on slippery wet leaves, and one with grip. That's the simplest explanation. I had an old Toyota Tercel 4WD station wagon and it was very difficult to steer sharply at low speed with 4WD engaged because of the lack of a differential. It would…

That's the nature of 4wd -- take a modern jeep, but it in 4wd on dry pavement and feel it lurch and moan because it can't slip. Put it in 4lo and on dry pavement and it'll lurch so hard your face will go through the windshield. 4wd without lockers means you can still get stuck (been there) because front and rear each have their own diffs. One wheel in each diff will be spinning and then you need to get a tug from a f…

It will even lurch and moan on slippery surfaces too if you turn a corner too tight.

I have a Dodge 2500 4x4 diesel and even with all that torque (about ~600 ft-lbs) it still bucks if I turn too tight even on ice.

I'm guessing it's due to the transfer case my truck doesn't have a center differential.

Here I am in snow no buck I guess no tight turns https://www.youtube.com/watch?v=zdK75UmoRMY

Re: 4WD vs. AWD. What's the Difference?

#202

Post by bitL »

rconti wrote: post #36
ghaff wrote: post #13

Earlier quoted context omitted.

The Waipio Valley road, as I understand it, is mostly paved but extremely steep and narrow/twisty. So the 4x4 requirement is probably more about being able to control speed without burning up brakes and dealing with often wet conditions. However, in the general case throughout most of the US West, "4WD roads" do indeed tend to be as much about having high clearance as about having 4WD per se. It's also just a way of…

In Death Valley they often specify 4x4 high clearance. Of course, you don't REALLY need 4wd or even 2wd; you can tackle it on a motorcycle :)

In Death Valley you rather need more spare tires (if you go e.g. to Racetrack; seen a car that got 2 punctures at different locations). Otherwise high clearance is needed only if you go off-the-beaten track; even Titus Canyon is fine on a normal road vehicle.

Re: 4WD vs. AWD. What's the Difference?

#203

Post by epx »

fnj wrote: post #187
esaym wrote: post #164

Earlier quoted context omitted.

I've never heard that jet engines are less efficient. From what I remember piston engines are 33% thermally efficient, diesels 36% and turbine engines are upwards of 60%+. Of course there are many types of jet engines and ways to get power off of them.

You heard wrong. Diesels under optimum conditions can easily exceed 45%, and state of the art is right around 50%. Gasoline engines can reach 40% or better (again, under optimum conditions). Turboshafts are generally around 35-40% efficiency at best-economy conditions, and dismal under low-load conditions. The very largest turboshafts can reach 40-45%, but come nowhere near to diesel efficiency at low load. In all ca…

And they burn cheaper fuel

Re: 4WD vs. AWD. What's the Difference?

#204

Post by sliverstorm »

mtreis86 wrote: post #193

This article is good but goes overboard in explanation. AWD and 4wd by all accounts are just buzz words for having front and rear differentials. In actual use, a 4x4 (a term I mean to refer to both 4x4s and awds as its just a buzz word) has three differentials. A center diff splits power from the transmission out to the other diffs, which split power to the wheels. There are three general types of diffs, whether cent…

There is a non-buzzword practical difference; one system cannot be driven on dry pavement (part-time 4x4). One system can be driven on dry pavement (full-time AWD).

Re: 4WD vs. AWD. What's the Difference?

#206

Post by pkaeding »

justinph wrote: post #100

In real life, in most situations, ground clearance, good tires, traction control and ABS make more difference than driving all four wheels, most of the time. Personally, I'm more concerned with stopping than starting, and that's where ABS and good tires matter and what kind of transmission you have doesn't. This is a sales pitch video, but it is interesting to illustrate the differences in AWD approaches, with differ…

Learning to drive in New England, I was taught "four wheel drive is not four wheel stop", so I definitely agree.

Re: 4WD vs. AWD. What's the Difference?

#207

Post by phpnode »

spacerace wrote: post #82
spacerace wrote: post #64

Earlier quoted context omitted.

That's rich. The lack of understanding of the fundamental mechanics is exactly what makes this article shit and your comment along with it. But do go ahead a school me on this PLEASE.

To user: phpnode that replied to me. I can't reply directly to you but that's a fair enough point. I was avoiding doing so before because I didn't (and still don't) think this article is even deserving of being picked apart. I would be happy to do so for the sole benefit of users here though. Just give me a little time to get back from doing some errands and I promise I'll clarify my grievances with the information i…

Still waiting for you to make good on this promise :)

Re: 4WD vs. AWD. What's the Difference?

#208

Post by joushou »

dghughes wrote: post #201
garyrichardson wrote: post #157

Earlier quoted context omitted.

That's the nature of 4wd -- take a modern jeep, but it in 4wd on dry pavement and feel it lurch and moan because it can't slip. Put it in 4lo and on dry pavement and it'll lurch so hard your face will go through the windshield. 4wd without lockers means you can still get stuck (been there) because front and rear each have their own diffs. One wheel in each diff will be spinning and then you need to get a tug from a f…

It will even lurch and moan on slippery surfaces too if you turn a corner too tight. I have a Dodge 2500 4x4 diesel and even with all that torque (about ~600 ft-lbs) it still bucks if I turn too tight even on ice. I'm guessing it's due to the transfer case my truck doesn't have a center differential. Here I am in snow no buck I guess no tight turns https://www.youtube.com/watch?v=zdK75UmoRMY

Yeah, it probably has full-time 4WD with a viscous clutch at center - when you turn, your axles lock, and 3 out of 4 wheels will have to slip to let you get anywhere. This will cause jumping and tire noise. Engine torque won't change much.

LSD's front and rear makes this worse, but center is the most important when it comes to on-road maneuverability.

Re: 4WD vs. AWD. What's the Difference?

#209

Post by linsomniac »

userbinator wrote: post #169

No mention of the "Detroit Locker", IMHO one of the more clever automatic-locking differential designs --- it uses a pair of dog clutches which are normally engaged, one for each side, and the wheel that spins faster is allowed to. It's self-contained and requires no additional controls, just like a regular differential. I think the only reasons why they didn't become more popular are due to their cost and the noise…

Detroit locker is effective, but I wouldn't really call it clever. For that I think of Torsen, the Torque Sensing differential that uses planetary gears. The problem with the Detroit is primarily noise, as you mention. The problem with Torsen is that it doesn't work in the presence of near 0 traction on one of the outputs, so people will drag the hand brake in that case.
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