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SUVs 4WD & AWD systems explained
1376 messages, Last post on Nov 23, 2009 at 9:11 AM
You are in the SUVs Forum. Your Hosts are steve_ & tidester
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Guess the word "just" threw me off. As in the 4Runner would be better if you did more than just that. My wife's aunt has a Limited model and is happy with it. The only catch is the step in height is very high. -juice |
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Yes, the 4Runner's step-in height is a higher than say, the M-class or the Highlander. I suppose it's partly because of its fairly significant ground clearance. Drew Host Vans, SUVs, and Aftermarket and Accessories message boards |
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Hi Drew, I'm cross-shopping the Highlander and the Outback VDC. My primary uses for the vehicle will be: 1. to drive on beach sand and occasionally through medium-deep snow 2. enjoy a decent ride before I get to the beach so Part Time AWD is out. In the Outback I assume the VDC wouldn't be an issue after reading about Patti of SOA's test-drive in the sand with no problems. If I choose the Highlander my best choice would be the V6 with Limited Slip and WITHOUT VSC because of post #477 of 744 Snow and SC by cliffy1 Jan 24, 2001 (10:44 am)in the Highlander Forum, that describes the Highlander stuck in the snow, right? Tom |
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Drew: can you shed any light on the differences/benefits of the 4wd auto system in 2001 Yukons/Suburbans vs. the AWD in the 2001 Denalis? What are the power biases front and rear in the two systems? Can GM's 4wd auto mode be run all the time even in dry conditions? Do both systems have locking rear differentials or limited slip differentials (or are these different terms for the same thing?) Other than the lack of a 4wd low mode in the AWD is there any other reason why one system might be considered better than the other? In a towing application would one system be considered preferable to the other? |
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| OK, now I'm confused. I'll admit I am pretty ignorant about these things (not a manly thing to admit, I know!). tshaldle provided a reference to a comment by cliffy1 in the HL section in which he believes VSC is not good in the HL 4WD. I have a chance at a HL with FWD with VSC or at a HL with AWD. Which would be better in wet rainy roads in FL? | |
| There is a big difference between GM's AWD system and the auto4wd plus true 4WD(hi) and 4WD(lo). Specifically when trying to get unstuck. The Yukon Denali isn't meant to be an off-road vehicle in the true sense of the word, nor is it intended to handle the same towing capacity as its brother vehicles. In reality, the Denali's AWD system might help if you are driving on snowy pavement, but if you get stuck with anywheels either off the ground, or stuck in mud or snow you aren't going anywhere, you'll see the wonderful AWD system spin your wheels, where on a 4WD system when you put your vehicle in 4WD(high or low) all the wheels turn at the same time no matter what. So you'll be able to get unstuck, by rocking the vehicle or just powering out of it. As for better wear on your tires using auto-4WD, sorry this isn't true. Auto-4wd won't engage unless there is a considerable loss of traction while driving, so on turns and during acceleration it won't help. As for gas milage, again the previous statments are wrong. I lose at least 1 mpg when in Auto-4wd vs. 2hi. on my 2001 Yukon. I know because I have very carefully been tracking MPGs. And currently normal driving in 2hi I get 14.2 mpg and in auto-4WD in snowy conditions I get around 12.5-13.2mpg Hope this is helpful. As far a towing, if you notice the 2WD versions of the Tahoe, Yukon, Suburban, and YukonXL all have greater towing capacities than the 4WD counterparts. | |
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Drew: This may be a stupid question, but could you explain what low range gearing is? In your excellent post of Feb. 5th you say this is the difference between AWD and 4WD systems. Does it mean that AWD vehicles become 2WD in low gear? Thanks, Jim |
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You are correct in your above post about the AWD on the Denali and Escalade. I wonder why GMC didn't use a beefed up version of the TOD system that is used in the Isuzu Trooper. With this we get the advantages of a true T-case, 4wd Lo, yet we get an initial split of torque of 15%f/85%r which varies up to 50/50 based on weight distribution, wheel spin etc. And we can throw it in 4wd Lo for a locked 50/50 split with a standard LSD in the rear. We also have the fuel saving 2wd mode as well. -mike |
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Jim: a simplified example may be best. Let's say you have a AWD vehicle with a 4 speed auto tranny. You have 4 forward gears, with both axles receiving power all the time. There is no low range gearing (not to be confused with 1st or 2nd gear, which every transmission has). Compare to a traditional 4WD vehicle with a 4 speed auto. It normally operates with 4 forward gears and only one axle getting power. Put it in 4-Hi, and both axles get power. Put it in 4-Lo, and both axles get power, but you use a different set of gears, all much shorter than normal. So there are actually 8 forward gears, if you will, even though you only use 4 at a time (either the Hi or Lo set of gears). Why, then? Because the much shorter gears give the engine more leverage, if you will. I took my AWD Forester on the sand last fall, and though it got through just fine (contrary to what many predicted), I could have used lower gearing. The soft sand really eats up whatever torque you have, so a low range would have helped me pull out of deep, soft sand. -juice |
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| sidsamson: The Denali AWD is rated to tow more (8500lbs) than any 2wd or 4wd version of a 1500 Yukon. The suspensions are the same. Is it merely due to the extra hp? | |
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