Last post on Mar 25, 2010 at 4:54 AM
You are in the Toyota Venza
What is this discussion about?
Toyota Venza, SUV
#14 of 33 Re: AWD MODEL,YOUR DRIVING IMPRESSIONS ON SNOW AND ICE [bobquebec]
Oct 22, 2009 (4:04 pm)
Will do, Robert.
#15 of 33 Downhill AWD perforamce
Nov 15, 2009 (4:23 pm)
I like the look of the Venza, but I'm interested to learn more about its AWD. From the brochure "Active Torque, "adjusts torque (power) to the right wheels at just the right moment".
My experience is that I prefer the predictability of permanent 4 wheel drive as in BMW X, VW 4motion and I think Subaru. I have had poor experience with some other "smart" AWD systems (especially with large low profile tire /wheel combos) changing configuration, particularly when going down hill in snow/ice conditions.
Some AWD drive vehicles allowed you to "lock" the front rear split by a switch or others when you turned off the OD - this seemed to give better driving feel.
As far as I can tell this AWD is fully automatic and I can't control the front/rear ratios for downhill icy or packed snow motorway conditions. If I'm paying for AWD I prefer to be able to control when its operational, at least in bad weather.
Can anyone tell me for sure or have experience in icy conditions?
I have no doubts about acceleration or uphill road performance its what happens going downhill when you take your foot off the the gas that concerns me.
#16 of 33 Re: Downhill AWD perforamce [britgeezer]
Nov 20, 2009 (9:46 am)
"..going downhill...concerns me..."
As well it should...!!
That is only one of the MAJOR safety short-comings of a FWD or a F/awd vehicle, downhill on a slippery slope. Get off the gas, engine braking at the front results in the rear attempting to LEAD.
Just one of the many good reasons to stay with R/awd or even RWD...SAFETY.
By the way the 2010 RX350 has this very same F/awd system but also has a manual lock control. But that doesn't change the fact that it is virtually ALWAYS front torque biased system and thus patently UNSAFE for wintertime use.
#17 of 33 Re: Downhill AWD perforamce [britgeezer]
Nov 20, 2009 (10:00 am)
"..learn more about AWD.."
Ford makes heavy use of this design for all of the F/awd product, as does Mazda. Porsche now uses the same electro-mechanical linear control clutch technique, R/awd, for the newest 911 model. It has proved to be quite problematic for Ford, early models allowed manual control but had a temperature sensor to warn the driver that the rear drive coupling was beginning to overheat.
The manual control was dropped as was the temperature sensor and then the next weakest link, the PTO began to fail due to overheating. Mazda solved the problem via cooling of the PTO using engine coolant flow. Apparently Ford chose to detune/derate the F/awd functionality in order to reduce the failure rate.
It will be interesting to see what the failure rate of the RX350's new F/awd system will be.
#18 of 33 Re: Downhill AWD perforamce [wwest]
Nov 20, 2009 (1:37 pm)
Sorry but you lost me with F/awd and R/awd .... I understand 4WD and AWD.
Not sure I agree with you on RWD (rear wheel) being safer, you only need to see the RWD limo drivers (and others) pointing the wrong way in minor ice or snow.
The worst one I experienced was my wife's FX45 - sure it was great in the dry or even rain, but show it snow or ice and it was a different story. The AWD designed to launch in AWD and revert to RWD if it sensed no traction issues. However with those big wheels and wide tires, traction was horrible. When all 4 wheels slipped on ice it could decide it liked RWD.
It had a an override for AWD but that would turn off if you went over 25mph - not the best decision.
For sure we can say a competent driver, with RWD will still do better than a fool in AWD especially if its too smart for its own good and has no manual override mode.
#19 of 33 Re: Downhill AWD perforamce [britgeezer]
Nov 20, 2009 (7:24 pm)
I use F/awd to designate that the AWD system is an "add-on" to a base FWD vehicle. Almost all of these either run in FWD only for most of the time, or are front torque biased. Only the SH-AWD system has the ability to bias engine torque primarily to the rear.
RWD and R/awd vehicles have a higher safety factor simply because even if you get to too lead-footed you will still have the front tire traction to maintain control. Get "lead-footed" with a FWD or F/awd and you better hope that TC will be QUICK to intervene, most are.
Anyone who has any high level of experience with 4WD or 4X4 vehicle driving on adverse roadbeds will tell you that once underway at a reasonable roadspeed the front drive should be disengaged.
#20 of 33 Re: Downhill AWD perforamce [wwest]
Nov 20, 2009 (7:39 pm)
OK thanks terminology now understood.
I have no experience of adverse roadbeds, just 20 odd years of driving on NJ roads in varying conditions including deep snow. I'll take full-time AWD or 4WD any day for the few weeks of the year when I need it.
Thanks for your input.
#21 of 33 Re: Downhill AWD perforamce [wwest]
Nov 21, 2009 (7:10 am)
Great explanation. Here's a question:
My 4cyl AWD Venza has an off button for Trac. Under which circumstances should I turn it off?
#22 of 33 Re: Downhill AWD perforamce [britgeezer]
Nov 21, 2009 (8:54 am)
To my (meager) knowledge there is no such thing as a "full-time" F/awd system insofar as operation on an adverse condition, low traction, roadbed is concerned. Systems wherein the rear drive capability is always enabled/armed and at the ready, yes.
Most of these systems, inclusive of the Venza, use TC, Traction Control, to automatically apportion engine torque to the rear after, ONLY after, loss of traction at the front is detected. Basically just like 4WD systems that should NEVER be engaged unless operating on a low traction system, except in the case of F/awd automatic engagement rather than manual.
#23 of 33 Re: Downhill AWD perforamce [dave139]
Nov 21, 2009 (8:57 am)
The only exception would be if stuck, cannot get moving, without (non-excessive) wheelspin and/or have the need to rock the car back and forth to get moving initially.