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Comments
I test drove a Limited FWD and it was very quiet and smooth. I own an 03 Ody w/NAV, which is an excellent minivan, but it isn't as luxurious and soft-riding as the Sienna Limited I drove.
The Sienna is definitely more "road isolated", which is the Toyota/Lexus philosophy all along.
I like it.
Personally I don't have any idea how the disparate final drive ratios front/rear "fit" into the torque distribution equation. But what I do know for sure is that my 01 AWD RX measured 95/5 F/R torque distribution on a 4 wheel dynomometer. The only possible explanation I can see for that measurement is the different F/R final drive ratios.
On the dyno, it proved to be impossible to limit the indicated road speed by braking/loading the rear wheel "traction" drum. It was only by braking/loading the front drum that we could limit "road speed" and in that way determine the disparate roadbed traction torque distribution ratio to be in the range of 75/25.
That ratio was only achieved by allowing disparate F/R rotation rates to prevail for many seconds, ~20-30, and it may have been more for a longer period but I was concerned about possible damage to the driveline or VC is we extended the test.
I think that the earlier RX-300 had a viscous center clutch assembly which may have had the torque bias that you noted. However, with the RX-330 and the Sienna the system has been re-designed to use bevel gears in the center and front differentials for a simpler assembly.
On the RX300 the VC is placed ACROSS the two center diff'l output shafts and serves to prevent the "openness" of the diff'l with extended periods of F/R disparate rotation. To allow a certain level of disparate rotation a gas bubble of a controlled size is often included within teh VC fluid. Until the VC fluids heats enough to fully compress the gas bubble no coupling occurs.
In the case of the RX330 with NO VC the F/R final drive ratios could be even more radically different, and in point of fact the RX330 does have greater F/R final drive ratio disparity than the RX300.
The overall gear ratios as they are mechanically geared bull and pinion sets have to be identical front to rear in order that the wheel speeds are identical on dry pavement. There doesn't appear to be any slippage in the system the way it is currently designed.
The torque split could vary. For example with one wheel or set of wheels on ice the spinning wheels would have a very high rotational speed due to all of the torque being transmitted to them whereas the wheels on dry pavement would not be turning due to not having any torque being sent to them (or at least not enough to rotate them). In this case there is a difference in torque being sent to each axle on opposite sides of the center differential but they still have the same mechanical gear ratio front to back. It's just that it is easier to rotate the carrier assembly (?) sending all of the torque to the spinning axle rather than rotate the axle that has an abundance of traction.
In the newer 04 design the brakes are applied to equalize the resistance at each wheel and thus force the open differential to send equal amounts of torque front and rear (thus Toyota's claim of constant 50:50 torque split front to rear). In earlier designs a viscous coupling would stiffen up due to the speed differential between the axles to force both axles to turn equally. It would seem that the viscous coupling could be tuned to allow more slippage than would a mechanically geared arrangement.
I might be wrong in the design of the earlier RX system so my VC comments may be generalities.
With an open diff'l the rotational rates of one output shaft vs the other can be infinitely variable.
Now if I take the front drive center diff'l output shaft and run it through a 3.48:1 ring and pinion reduction gearset to drive the front diff'l/wheels and the center diff'ls rear drive output shaft through a 2.92:1 ring and pinion reduction gearset to drive the rear diff'l wheels what is the effect?
As I drive forward all four wheels/tires have equal traction so the center diff'l spider gears will again come into play, spinning like mad within the carrier, as a function of the different rotational rates of the two output shafts.
Now, just for fun, let's discuss the cause and effect of "torque steering" in FWD vehicles. Torque steering is caused, mostly, by different length half-shafts to each of the front drive wheels. That will have virtually no effect at the low torque levels required for just cruising along the highway, but the instant you apply WOT, especially at low gearbox ratios (low speed) the applied torque will "twist" those halfshafts and obviously the longer one will twist slightly more than the other.
That "slightly more" causes the attached tire to lag the opposite tire by just a few compass degrees. So the vehicle is now "biased" to turn in the direction of the lagging tire.
I'm totally guessing here, but I suspect that's the same reason, basically, that the RX series exhibits torque biasing to the front. The instant you apply more throttle for acceleration that 3.48:1 front final drive ratio couples more torque to the front than is coupled to the rear by the 2.92 ratio.
When we limited ONLY the rear roller to allow a maximum vehicle speed of 40MPH it had virtually no effect on limiting engine RPM or front drive wheel speed as the throttle was depressed. When we then limited ONLY the front roller to 40MPH it was clear that the engine was "loading up" and we were successful in measuring engine HP & torque.
At one point the dyno operator even challenged me about my assertion that the vehicle was AWD. Until we forced a disparate rotational rate F/R for almost a minute to "stiffen" the VC we were never successful in using the dyno to measure HP & Torque to the rear wheels.
It is my understanding that other than a different, higher, front final drive ratio and minus the VC the RX330 and the Sienna have exactly the same drivetrain as the RX300.
1. Does park assit help at all ? Is the warning too aggressive in giving warning, when you could really park safely ?
2. Is the quality of the rear view camere good? Is the angle of coverage good enough to use realiably for back up?
3. ANy comments on dynamic cruise control ?
I do not care for navigation or dvd entertainment -but forced to for Limited with #6 (with over $3000 extra) just to get these features. I do not mind paying if it works well.
Thanks a lot!
The GPS Navigation System, although I haven't used it myself, has so far gotten us to our destination quickly without hassle. I'd say it was worth the extra $$$. Note: You'll have to get the DVD player to get the GPS. All this for around $38,000.
Of course, this is not a need, but for a long term family car, probably adds $25 a month. Also, the rearview camera which definitely is useful backing out of my garage, is bundled with the NAV on the Sienna.
I get a little chill down my spine thinking of the possibilities every time I back my not-rear-camera-equipped Yukon XL out of my garage, down the driveway, across the sidewalk and out onto the street. No matter how carefully I check before getting into the truck nor how I might watch my mirrors and look over my shoulder during the maneuver, it doesn't compare with being able to see what might have intruded into that otherwise blind zone as I'm backing. That will definitely be something I'll try to get on my next vehicle, if there is any way to afford it at all.
Add to all that the fact that the door from the house into the garage is near the front of the garage and the most likely place for the errant little ones to run out from unexpectedly, and it is probably safer to keep doing things the way I am, using my fear as an impetus to very careful maneuvering with all due diligence every single time.
Even so, a rear-view device to eliminate that blind spot down low behind the vehicle would be a welcome tool and probably would go farthest toward reducing the risk (assuming enough fear remains to use that tool each and every time!). Just MHO.
It is a must have.
It is cool.
It is fun.
It is useful and you get the R/V camera too.
And once you use it, you will absolutely love it.
I have NAV on my 03 Ody, and I use it all the time.
You have to get NAV, especially if you buy the Limited Sienna. What's a measly few grand?
I think the NAV+DVD RES is only around $3K total, right? Big deal. You are buying the best minivan on the market, basically the Lexus of Minivans, so get the best options too. Get NAV.
Back to my old fogie days. I'm assuming you would have figured out where JC Penny the old fashioned way with the yellow pages or now on the internet. Is the added convenience worth the cost? Apparently it is because all the manufacturers are adding it as an option.
With regards to finding JCPenny, I guess I wasn't being clear. The point was, I didn't have to go back home from where I was, to look at yellow page/ internet, but found the location on the fly. It wasn't planned for to begin with. The NAV saved us more than 45 minutes that day. Do I think the feature to be worth the cost?. Yes. Is it essential?. Absolutely NOT!.
The only concern I had with the LE 8 with package 7 was the sound system(only the standard not JBL)-is the sound system ok or is it worth moving up to package 10 for this.
I would also like to know how the second row seats differ. I know that they are not captains chairs because of the middle seat but are the outside second row seats smaller in the LE8 than the seats in the LE7? And if they are smaller, are they as comfortable.
I've noticed something that I've not seen much in the other fuel injected cars I've owned before - idling RPMs flactuate from 500 to 750. This can be observed when the car is warmed up and is idling (on a stop light for example). I live is So Cal and tempretures here are in the 70s (F).
Anyway, when I am sitting at the stop light and pay attention to the tach, the RPMs stay @ ~750, then drop to about 500 where the car aquires small but noticable engine vibration (roughness), and then RPMs jump back to 750. This can be observed about every 20 seconds.
I don't have to be in gear and climate control system can be turned off for this to occur.
The reason I'm asking that I've not seen this sort of thing happen to the fuel injected car under normal idling conditions. (I've owned a Jeep Cherokee, Honda Accord, Toyota 4Runner, and Nissan Pathfinder). Once these car would reach normal operating tempreture, the idling RPMs would stay on the certain number almost dead on, being in park or neutral, without AC running.
Could anyone comment on this? Does this happen for other Sienna owners or I should take the car to the doctor?
P.S> I did fill the car up with 89 oct fuel.
Be aware that most modern day climate control systems run the A/C constantly winter and summer. Additionally the A/C is "linked" to the defrost/defog/demist mode and will automatically activate with those functions, even partial/mixed defog.
Until I had the dealer unlink mine (01 RX) using the c-best option the A/C would often run without the indicator even on.
Also many new cars will not remain in the recirculate mode for more than a few minutes if the A/C is off. So I suppose some designers may have used the inverse of that logic and automatically enable the A/C when the owner switches recirculate on.
I am in Chicago suburbs.
In climate control mode once you turn it on manually it will stay on, even through restarts, until you turn it off.
Just curious?
No big deal to me.
Why would you shift gears back-and-forth on an Automatic transmission?
I've never heard of anyone doing that unless they just wanted to play around with the cool gated shifter or unless they wanted to "park" the vehicle for about 15 seconds so they can do something really quick like taking off their sweaters or jackets:-)
I've also been comparing the Drive-To-Empty miles (using my MPG). Curiously, these compare very well (usually within 5 miles; often within 2 miles); probably well within the variability in how full the tank actually gets. If I use the Sienna's average MPG (rather than mine) to calculate the DTE ((tank capacity - gallons added) x MPG), my DTE and the Sienna's DTE are way off (often 15-20 miles difference).
I wanted to find something to do that seems constructive, maybe help the gas mileage a bit, do you think i'm hurting more than helping?
i shouldn't mess with it right? i just want to do what's right, and see if anybody had tendencies to shift the van like i do.
If this is wrong to do, please let me know.
Thanks.
Provided that when you want to "go" you slip it into gear, hesitate for a second for the clutch(es) to engage, and then apply gas....
Personally I would not be at all surprised to learn that newer vehicles with e-throttles do this automatically.
thanks.
Most articles I read state that 4WD or AWD is not helpful in braking or turning, JUST for acceleration. Is it true? Why shouldn't the rear brakes help you brake better?
Asking this question, why do you FWD vehicles needs rear wheels brakes at all? If the front wheels are doing the job, what additional help do you get from the rear brakes? (I'm not into these things so maybe it's a stupid question).
Let me point out: I don't want to start again a AWD discussion (caution, wwest!), we went already over it about a million times. I just want to know about the braking difference in FWD to RWD.
Maybe I should even ask the question in AWD boards.
Thanks.
No they are not more useful.
Since the rear wheels are being used as well as the front, so if the front wheels start slipping and spinning and are unable to stop, will the rear wheels take over and stop the vehicle?
Braking is a very different process from acceleration but many of the same principals are being applied. The first is traction, the interaction between the road surface and the tire. The ABS system (or a good driver) ties hard to keep the wheel rolling under heavy braking as you have less traction with a locked tire (thus the basis of the term ABS). A tire held at incipient lockup but still rolling gives the best braking performance. Another part of traction is related to the load on the tire. Under acceleration some of the weight of the car is transferred to the rear wheels giving them more weight and more able to apply force (due to increased grip/traction). Under braking the opposite is true, the front dives to some degree and some of the weight transfers to the front giving those tires more traction. Brake systems are biased to the front wheels as the load on the rear wheels is highly variable. The reason for the bias is that a locked rear wheel will have less traction than a unlocked front wheel and can cause the car to skid actually increasing braking distance or worse yet cause the car to spin. So, in answer to your question, if the front wheels are out of traction and the rear wheels have traction the ABS system will allow for some additional rear braking up to the limit of traction and the front rear bias of pressure. Beyond that the rears cannot do much more.
Most articles I read state that 4WD or AWD is not helpful in braking or turning, JUST for acceleration. Is it true? Why shouldn't the rear brakes help you brake better?
Yes this is true for many of the reasons I outlined above. The rear brakes do help you get shorter braking distances, but due to the need for a bias to the front wheels due to variable load they cannot apply the heavy braking needed to stop much more than they do. If it could be done, it would be. Some cars use a mechanical interface to gauge rear wheel loading and adjust rear brake pressure others use pressure limiting valves that are preadjusted and rely on the ABS to adjust beyond that point.
Asking this question, why do you FWD vehicles needs rear wheels brakes at all?
Rear brakes on all cars have the same limitations, not just rear brakes. The 80/20 brake bias general rule applies to front, rear and AWD vehicles. 20% is alot of braking, imagine your braking distance being 20% greater.
If the front wheels are doing the job, what additional help do you get from the rear brakes?
They do 20% of the job (or more depending on the design of the system), that is alot of help.
http://www.stoptech.com/whitepapers/rear_brake_upgrade_is_bigger_- better120601.htm
http://www.mpbrakes.com/mpfaqvalving.htm
http://www.nhtsa.dot.gov/cars/problems/equipment/absbrakes.html
http://www.mech.uwa.edu.au/DANotes/brakes/vehicles/vehicles.html
Hope that helps.
I have heard that disc brakes are more responsive to ABS/VSC/Trac activity (lower mass, faster "pulse" rate equals more moderate control) and I wouldn't be surprised if that were true. Since the brakes are now applied/modulated to apportion engine torque that may be the main reason for disc brakes on AWD.
On the subject of AWD and braking there is a effect with regards the proper operation of the braking system.
For instance you may notice that many newer "true", part-time, 4WD vehicles do not lock the center diff'l except in (extremely) low gear range. With the center diff'l locked both the front and rear drivelines MUST turn at an EQUAL rate. This can, of course, create a very hazardous potential for loss of control during severe braking. Most modern day vehicles disengage the (rear) ABS when the center diff'l is locked.
So with an AWD vehicle whatever level of "solid" coupling exists between the front and rear during severe braking will have an adverse affect on vehicle stability during hard braking manuvers. Probably one of the reasons the VC has been dropped entire from the Toyota/Lexus AWD product line.
The Accura MDX, for instance, likely disengages the rear drive coupling clutch when the brakes are applied.
Oh, without those rear brakes you would learn recovery techniques for oversteering rather quickly. Without the rear end "bolted down" during braking it would likely come around with every hard braking manuver. That's why it's also so critical to not apply too much braking at the rear, skidding tires give the same effect as no rear braking and now here comes that rear around again.
This can be very easily demonstrated by using the hand brakes on a bicycle, the rear wheel will stay in line with no problem with no braking action on the rear.
The only way to cause such a loss of control would be to lift the rear wheels off the ground, something that won't happen on a car/van given the weight distribution and the inability to cause all that load to transfer to the front.
If I did not have to move any parts, I would not do it. I'm the "If it's not broke, don't fix it" kind of guy. Toyotas are extremely reliable, but things like shifters and stuffs can wear down if we move them around too much.
For example, I never use the mirrors on the sun visors. But my wife uses the mirrors all the time in the Avalon. Now the hinges on the mirrors are too loose or something. Just a little example of leaving things alone, expecially the gated shifter.
Besides, you got a LUXURY vehicle now, not some cheap manual car. Everything is Digital and Automatic for you now. Sit back, relax, and enjoy that new vehicle smell and the laser cruise control:-)