Last post on Mar 15, 2012 at 9:02 PM
You are in the Lexus RX 300/330/350
What is this discussion about?
Lexus RX 300, Lexus RX 330, Lexus RX 350, Toyota Highlander, Car Comparisons, SUV
#29 of 58 Re: RX350 vs. Highlander [wwest]
Mar 01, 2011 (7:16 pm)
I can't comment on "the fairly common "stuck" situation wherein you're trying to start up, initially, from a stop, a slight incline that is icy or slippery" for a simple reason that MY Highlander never got stuck in this situation and started moving with ease. As a matter of fact MY Highlander didn't get stuck even once since the time I purchased it back in 2008.
I can see that you have wast theoretical knowledge about AWD but it worth zilch to me. I'm not a Toyota transmission engineer to go over AWD design implementation, it's shortcomings and advantages. Toyota doesn't engineer and manufacture vehicles that are "DANGEROUS" too drive (at list no one was able to get any credible proof too this date). You'll have very hard time finding a second Gen Highlander owner being unhappy with it's AWD performance under severe weather conditions. You on the contrary never bothered to drive the vehicle and trying to prove that it has inferior design based purely on your own theoretical conclusions. Real life experience proves you wrong! Read here:
http://townhall-talk.edmunds.com/WebX/.f21ebcd/21!make=Toyota&model=Highlander&e- - - - - - - d_makeindex=.f21ebcd
#30 of 58 Re: RX350 vs. Highlander [luckyseven]
Mar 01, 2011 (7:10 pm)
Sorry, but is well understood that FWD vehicles and F/awd vehicles are patently dangerous to life and limb on an adverse, slippery, roadbed. That's why TDC is so important and has become horribly aggressive, it needs to be in order to sunstantually lower the potential for an accident resulting from loss of directional control.
Mar 01, 2011 (8:14 pm)
Let's get back to comparing the 350 and the Highlander, and I don't mean the minutia of AWD systems that are only of interest to one or two gearheads out there.
#33 of 58 Re: enough already [steve_]
Mar 02, 2011 (6:03 am)
I feel this is enough too. Just sad to see how wwest turns every discussion on this board into baseless bashing of Toyota AWD and misleads people into thinking that it is inferior based on his own theoretical conclusions.
#34 of 58 Re: enough already [luckyseven]
Mar 02, 2011 (6:26 am)
This discussion is about purchasing a new RX350 versus a HL Limited.
Other than the up-pricing due to the upscale features, heated/memory/leather seats, HID headlamps, etc, etc, just what are the differences???
3rd row seating and the F/awd system.
You either need or want that third row, so question answered.
I do find myself puzzled that Toyota has used, adopted the new, more functional F/awd system across the product line with the sole exception of the HL. I fully expected that as of the new model year the HL would also be so equipped.
Maybe we can get someone from Toyota to chime in and tell us why the HL is being left out in the cold...?
So, nuff said, bye.
#37 of 58 Re: enough already [wwest]
Mar 06, 2011 (8:20 am)
"I do find myself puzzled that Toyota has used, adopted the new, more functional F/awd system across the product line with the sole exception of the HL. I fully expected that as of the new model year the HL would also be so equipped."
Hi again wwest - Would you expand on the improved Toyota system. Is it in the RX/ 4Runner /RAV4/Toyota trucks but not the '10/'11 HL? Interested in purchasing a Lexus RX or Toyota crossover this year. Thanks.
What's your opinion on the Honda Pilot and CR-V? Any idea if Honda/Acura is going to upgrade their somewhat dated 5 speed automatic transmission?
#38 of 58 Re: enough already [johnxyz]
Mar 06, 2011 (10:23 am)
For quite a few years now, going back to the '01 F/awd RX300 and the F/awd HL, the F/awd system has been basically a ONE-WHEEL drive system. Three simple, fully "open" differentials. Meaning if any one wheel begins slipping then it gets all the "drive", sapping the torque level down to just enough to keep that slipping wheel or wheels spinning.
Care of wording must be exerted here, as one should realize that even as above ALL four wheels are still getting EQUAL torque. It's just that for the wheel(s) remaining with traction the torque is now so low that no motion results.
The "legacy" technique, TC(TDC IMMHO) technique, that was in use, moderately (ABS "style" "pulse" moderation) brakes the slipping wheel(s) to simulate traction. But that could easily result in over-heating of the brake components so the engine was always dethrottled just as quickly.
While that proved to be satisfactory in some cases, maybe even most, there was enough public outcry about one serious shortcoming that it was addressed via adding a manual TC(TDC) disable feature.
Basically this legacy system was a REACTIVE, after-the-fact, F/awd system. Prior to a wheelspin/slip the system was, by default, a ONE-WHEEL drive system.
The new systems are "pre-emptive", "before-the-fact"...! So, has Toyota found a way to predict the future..."
Not at all.
The new system engages the rear drive capability in situations that are most likely to result in loss of traction on the primary drive wheels, the FRONT wheels.
A) During acceleration from a stop or from a relatively low speed, below 25 MPH. The higher the acceleration level, the more engine torque will be routed, coupled, to the rear.
B) When turning a F/awd vehicle then engine drive torque will oftentimes overcome the front tires' roadbed traction capabilities needed to provide enough lateral traction for maintaining or sustaining directional control. This, in effect, is what results in FWD vehicles becoming so patently UNSAFE on adverse roadbed conditions, and F/awd systems slightly less so.
With a R/awd system one might simply reduce the torque coupling level to the front, entirely so if the need should arise, a tight accelerating turn, for instance.
F/awd systems have a HARD, non-modulateable, front drive coupling. So all torque re-apportionment, F/R torque re-apportionment, must be toward the rear drive.
The obvious shortcoming of this new pre-emptive F/awd system is that unless the roadbed happens to be slippery enough to not incur driveline windup and/or tire scrubbing/hopping the driveline components might be subject to premature failures.
Your can see that in the long history of the use of this new F/awd design approach in the Ford Escape and Mariner, and more recently in the Acura MDX VTM-4 system. Both fraught with failures historically.
IMMHO the proper design approach would have been to have these new systems default to "reactive" mode but allow the driver to manually switch into "pre-emptive" mode when roadbed conditions are recognizably. In either case should the system not encounter a "slip" condition within a given time period or # of miles it would automatically switch back into reactive mode.
The Ford AeroStar R/awd system runs by default with 30/70 torque distribution. When wheelspin/slip occurs it automatically switches into 50/50 F/R torque delivery mode. It will UNCONDITIONALLY switch back in 50/50 mode in 3-4 minutes. The if wheelspin/slip repeats.....