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SUVs 4WD & AWD systems explained
1377 messages, Last post on Dec 05, 2009 at 1:47 PM
You are in the SUVs Forum. Your Hosts are steve_ & tidester
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Replying to: steve_ (May 20, 2008 12:29 pm) 
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Replying to: kurtamaxxxguy (May 20, 2008 7:28 am) I think we are getting confused here between L/R and F/R movement of power. If you see a spinning wheel and then it shifts the power from that wheel, it could be shifting it L/R which is slower to react than F/R. The F/R transfer is a lot smoother and more fluid than the L/R movement of the power. A true LSD will be more fluid in transitioning power from L/R, however it still won't transfer 100% of power left and right and in addition as the LSD (either mechanical clutches or the viscous fluid in the Viscous LSDs) wear down over time the percent of power that is actually transferred L/R diminishes and the reaction time increases. Take for instance a Subaru with 100k miles on a Viscous rear LSD, the reaction time and % of Limiting of the slip will be approaching that of an open diffy. Same goes for a mechanical LSD that employs clutches in the diffy. The ABLS (Anti-lock Brake Limited Slip) found in the VDC and other "traction control" systems do not loose any of their reaction time or capabilities over time, perhaps your brake pads will wear out slightly quicker but they are a $50 item to replace. Rebuilding a the Mechnical LSD is about $300ish maybe more and a Viscous LSD requires an entire Diffy swap out. -mike
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Replying to: paisan (May 20, 2008 5:22 pm) On a few they stop intentionally to open the doors, to demonstrate chassis rigidity. I'm wondering if that pause is due to the driver. This hill climb is pretty amazing, note the angle of incline (37.5 degrees) and that there is no wheelspin whatsoever: http://www.youtube.com/watch?v=feFRI9juwV4 The hill climb occurs at 3:00, though there are two instances. If the Forester were nearly FWD, as some have alleged, the front wheels would spin and only then would the rears bite down and climb. At that angle, all the weight has shifted to the rear axle, so the front axle has very little traction and there's no way it could pull the car up. Here's a funny (and very unscientific) comparison of the Forester and Outlander. They have a tug-of-war and the Forester wins, FWIW: http://www.youtube.com/watch?v=HdXjw5hACVI&feature=related The tug-of-war happens at 6:48.
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I'd like to observe the behavior of both of these in the various modes with all 4 wheels up in the air. We could test and verify several things on the Outlander: * FWD only mode - the rear axle should not spin at all if it truly disengages * 4WD lock - both axles should spin at the same speed * Auto mode - does the front axle spin faster? Does the rear begin right away, or react only after the front axle spins? * Stability/Traction control - we could repeat all 3 tests with this On and Off For the Forester, we'd have 3 scenarios to test: * FWD mode with VDC off - again, is the rear axle totally disengaged? * AWD, VDC on - any side to side variance? * AWD, VDC off - reactive, proactive, same axle speeds, or what? The interesting part would be to observe the differences specifically. |
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Replying to: ateixeira (May 21, 2008 5:59 am) Hey, wait a second, this is just as scientific as other videos that have been posted. Maybe even moreso. Furthermore, it's manufacturer neutral. I just think the judge, let this video be entered into evidence in the case Outlander vs Forester.
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Replying to: kdshapiro (May 21, 2008 7:32 am)  Let's get 'em both up on jack stands. I'm curious to see how both rear axles behave, especially Auto mode for the Outlander. And to see if Lock is any different.
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Replying to: ateixeira (May 20, 2008 6:24 am) When you don't have to fix safety recalls for 24 years (1977 to 2004) that leaves a LOT of money left over for your racing program. I'm sure the racing Pajeros cost them MILLIONS, which they had due to neglecting their street cars and the safety of their customers. Honestly, when you post statements like that, you are inviting flaming (baiting people). Smiley faces or not. To balance out your post, you could have mentioned that Subaru was also guilty of hiding defects and was forced to recall 2 million cars in 1997. Fair play.
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Replying to: psychogun (May 21, 2008 12:05 pm) To be fair, they weren't guilty of it for 24 years.
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Replying to: ateixeira (May 21, 2008 7:50 am) The jack stand trick won't work. I'm pretty sure that the AWD system takes into account TPS, and weight shift (F/R) as well to determine where to put the power. It also learns combinations of TPS, weight shift, speed to pre-emptively move the power. -mike
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Replying to: kdshapiro (May 21, 2008 12:57 pm) I'm not here to blindly defend any manufacturer. In my humble opinion, you can be guilty of hiding defects for just a month, you're still guilty of a serious lapse in judgment and ethics. Regardless, both companies are past this. Both have new, more transparent management structures in place. I find it unproductive to rehash the past. Especially considering that this is 2 full model generations behind us.
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