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

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

#51

Post by SomeCallMeTim »

blackguardx wrote: post #5
bitL wrote: post #2

Great! Finally somebody explained this to me, I thought it was just a marketing term related to different patents of similar ideas. I was puzzled by this as I was stopped by a ranger coming out of Waipio Valley on Hawai'i, where there was a sign "4WD only" and my rental car had AWD. I thought they were the same, just different names, so I argued with the ranger that I do in fact have 4WD, which is in my case just cal…

Generally a sign saying you need 4wd in the US really means you need a lot of ground clearance. Your car probably would have high-centered, that is stuck resting on the middle of the car with the tires in the air. The annoyed ranger was probably just tired of pulling stuck tourists out.

>Generally a sign saying you need 4wd in the US really means you need a lot of ground clearance

The Subaru Outback (AWD) has 8.7" of ground clearance. The Ford Explorer ("Intelligent" 4WD) has a ground clearance of 7.8".

If "Intelligent 4WD" means some kind of differential, then it really is just a marketing term at this point, though I learned about the distinction between 4WD and AWD when I bought a Subaru.

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

#52

Post by Drdrdrq »

rconti wrote: post #34
dsr_ wrote: post #23

Earlier quoted context omitted.

And in particular, the Hawaiian rental car counters will tell you when you rent which roads your car is not allowed to go on.

I've always wondered why this matters. I've got car insurance, I've got additional rental coverage on my credit card, and there are plenty of other vendors from whom to rent cars if you want to blacklist me.

Well, they still have trouble with you if you get stuck or wreck the car, so it is easier for them to just list the "forbidden" roads. Not sure, but your insurance might be void if you crash the car where you were not supposed to drive.

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

#53

Post by petepete »

gambiting wrote: post #31
petepete wrote: post #28

Earlier quoted context omitted.

I think he means regular 'cars' rather than 4×4s (or SUVs).

Sorry, I forgot that in US "cars" and "SUVs" are two different things. Where I am from there is no such distinction, a Land Rover is still a "car".

Yes, here too. It's especially confusing now as the line between the two is increasingly blurred.

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

#54

Post by gambiting »

s917 wrote: post #32
gambiting wrote: post #24

Earlier quoted context omitted.

Any new Land Rover or Range Rover? They come with 2 locking differentials, with 3rd being an option that can be added extra. Same with Mercedes G-class - they come with 3 locks as standard. And I've no idea what you mean by "cars don't have proper ground clearance" - just buy a one that does?

>Any new Land Rover or Range Rover? They come with 2 locking differentials, with 3rd being an option that can be added extra. Source? Center locking diffs are more or less standard, rear lockers are options in LR3/4/post 2004 Disco's, Sports and Range Rovers (although standard in some, I think the Supercharged and possibly the SVRs, but I'd need to check) Front lockers are not factory options and I don't ever recall…

I had a 2005 Discovery LR3 V8(US Spec, imported to EU) and I could swear it had 3 diffs - at least the 4x4 Info screen would always show 3 diffs working independently when I was driving it offroad. Of course I might be remembering it incorrectly, but a quick search on google shows "genuine Land Rover Discovey 3 front differential" part on ebay, so I guess it must exist?

http://www.ebay.co.uk/itm/like/182246825443?lpid=122&chn=ps&...

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

#55

Post by ledriveby »

Subaru's higher end AWD system has separate output shafts from the engine for the front and the rear, with electronically-controlled clutches modifying the torque. Default is 60/40 front biased, but it can send 100% of the torque to either end of the car. Excellent performance with no manual mode switching needed, also manages good fuel economy at the same time. Best system in the business.

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

#56

Post by 4ad »

kinofcain wrote: post #30
mschuster91 wrote: post #26

I wonder why car manufacturers still use direct force transmission with hugely complex (and in case of ignoring the instructions, outright dangerous) like 4WD/AWD instead of diesel-electric or diesel-hydraulic systems like on locomotives. A computer could instantly shift torque with both of the hybrid solutions, you wouldn't need a clutch or a gearbox any more, not to mention cheap all-wheel-drive including the trail…

The diesel-electric/hydraulic systems are used in situations where the gearing ratio would have to be absurdly high, they're not used because they're efficient or because they have good torque vectoring capabilities. The electric motor can produce nearly 100% of torque at zero RPM, which helps locomotives get several million pounds of train moving. In your car, truck, or even semi, first gear plus some clutch/torque…

> a lockup torque converter or a fully engaged clutch is more efficient than the combination of an electric generator and a motor.

I doubt it, generators and motors operate at 99% efficiency. Do you have any reference?

> if you have four independent electric motors, you can only ever send 25% of available torque to one wheel, if you have front, rear, and center lockers, you can send 100% of torque to one wheel.

That assumes that engines are so small that they operate at 100% under normal conditions. This doesn't have to be the case, electric engines are so small, you can have bigger-sized engines where one single engine can use all the power. The nature of electric engine is such that the loss of efficiency by doing this is minimal. Plus you need to do this only fractions of the time, so the engine doesn't have to be designed to operate in high power mode at full duty cycle.

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

#57

Post by mikeash »

rconti wrote: post #34
dsr_ wrote: post #23

Earlier quoted context omitted.

And in particular, the Hawaiian rental car counters will tell you when you rent which roads your car is not allowed to go on.

I've always wondered why this matters. I've got car insurance, I've got additional rental coverage on my credit card, and there are plenty of other vendors from whom to rent cars if you want to blacklist me.

They probably don't want you taking a road you shouldn't, getting hurt, and then suing them because they didn't warn you about the dangers. Or they get tired of having all their cars smashed up. Insurance covers it, but it's still annoying.

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

#59

Post by auganov »

schwede wrote: post #50

The video from the 30s was fascinating. It gave a perfect progression of complexity while explaining the concept of a differential. I'd like to see more of those kind of videos (from now our from clear back then).

You might like this one https://www.youtube.com/watch?v=mBz30JhtKkg The channel also has some more.

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

#60

Post by bitL »

japhyr wrote: post #4
bitL wrote: post #2

Great! Finally somebody explained this to me, I thought it was just a marketing term related to different patents of similar ideas. I was puzzled by this as I was stopped by a ranger coming out of Waipio Valley on Hawai'i, where there was a sign "4WD only" and my rental car had AWD. I thought they were the same, just different names, so I argued with the ranger that I do in fact have 4WD, which is in my case just cal…

Did they make you turn around? Did your car do fine, or did it get a bit hairy?

He actually stopped me after climbing up back to the viewing platform. The car was some US-made SUV with high clearance (don't remember if it was Ford or GM), just there was a sign AWD in the back (I specifically asked for a 4x4 rental vehicle). The road was fine, I think the issue might have been a few streams you had to cross at the bottom of the valley, but SUV had no problem with them. Ranger wanted to fine me but after arguing about 4WD, AWD, 4x4 he dropped it, still a bit angry.
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