Just wanted to say I'm officially in. After reading this board for over the past year, I finally found a 01' RX300 black/black with 2wd, that I had been looking for off and on.
After being a lifelong Honda owner, this is my first luxury car and very first Lexus. I love the RX, it is a really great vehicle.
I paid a little over 28K and it has about 17k miles. My wife wanted my to wait and buy a 2004 but I decided on this one. I am though waiting anxiously to see the new RX330 at the LA Auto Show in January.
Thanks for everyone's words of wisdom and advice on this board, and interesting comments from other RX owners.
If you looking at the possibility of going either way then it isn't likely you need AWD. But just in case I'm misreading then the AWD RX should be on the very bottom of your list.
On any AWD system when the brakes are severely applied the AWD system MUST be UNCOUPLED. The Lexus RX300 solves this aspect of AWD by NEVER having a high enough coupling coefficient to the rear to matter.
I traded up from a 00 AWD RX to an 01 AWD RX to get the benefit of VSC, Trac and HID. I am quite pleased with the HID and the Trac does seem to intervene at times, however lightly.
I have come to the conclusion that the Trac functionality is so moderate or possibly even completely non-functional that it is virtually useless. Like the GPS/nav.
I disagree with wwest's statement above. I have TRAC on my 99RX FWD and find it does a good job of preventing slipping of the front wheels upon acceleration on icy or wet roads. The TRAC also helps maintain stability in straight running and cornering.
Correct me if I'm wrong wwest, but you have never owned the first four of your 5 chooses given to fuhrmjo. They may seem like an idea choice for a person obsessed with the ultimate AWD system, but does it really answer fuhrmjo question concerning the RX300?
The AWD system used in the RX300 by your own admission wwest is adequate for 99%, no, make that 99.99% of the owners over the entire ownership period. This subject has been discussed to near exhaustion on your part. Suffice to say if conditions warrant an AWD system, the RX300 will do just fine.
AWD pros: Traction, stability, handling. AWD cons: read wwest's post to follow FWD pros:probable lower maintenance vs AWD, lower weight( quicker acceleration, shorter braking distances, better fuel economy). FWD cons: Not many, other than if your driving environment needs better traction than FWD can provide, then go for the AWD, it's an individual choice we all must contemplate.
I would even contend that to buy these expensive and obviously more complex AWD systems that wwest suggested is contrary to his beliefs. He would have you believe that to purchase the RX AWD is paying for a system that is "virtually meaningless", and burdens you with "useless extra weight". Since a vast majority of RX AWD owners never go off road(as well as wwest's first 4 choices), and the RX 300's system performs adequately for 99% of the conditions that occur on the road, why pay for these more complex systems...isn't that a waste of your money as well?
fuhrmjo- I'm sure you don't need me to lecture you concerning your decision to buy an RX 300 AWD vs FWD. Either decision will provide you with a terrific vehicle...I just wanted you to hear another side of the story that is IMHO shared by a majority of the people that post to this board. I will now step down from my soap box and let wwest step up. ( Here's a hint wwest- no techno babble.)
As you will obviously notice, NONE of us have any real idea what your true needs (vs WANTS) are regarding FWD vs AWD. There was an implication based on your wording that it was "optional". If that is the case, and you're not in the 00.01 category, then the FWD RX300 with VSC, Trac and HID will provide excellent service to you and yours.
My previous discussion of Trac functionality only related to the AWD implemenation. My apologies to all, I should have made that more clear.
The firmware for FWD (or RWD) Trac can be, and likely is, radically different than the AWD version. With FWD and front slippage the Trac system will likely apply both brakes and then dethrottle the engine if the condition persists, just as it does on a RWD Lexus.
On the AWD model applying both front brakes in this circumstance would defeat the need for a VC entirely, the VC would then just be extra baggage. That would result in the AWD RX300 being a REAL AWD, much more like the Sequoia.
And we wouldn't want that, would we?
Off-road: This issue keeps coming back to haunt me. My 00.01% pertains to those of us we NEED AWD for ON_ROAD wintertime conditions, say here in the GREAT & BEAUTIFUL Pacific Northwest.
When I bought my first RX300 I didn't expect to have anything even close to the 4WD capability of my two previous Jeeps. But I did expect to have something roughly equivalent to my Jeeps' AWD capability. Even with the Jeeps' 4WD capability as backup I still carried a set of snowchains, religiously, in the car in the wintertime and was forced to make use of those on many occassions.
I mistakenly assumed I could rely on the same procedure with the RX, if the AWD proved to not be adequate to the task, even more often than the Jeeps, I still had the snowchains as backup.
Then I discovered that snowchains can NEVER be used on the rear of the RX (nor the HL) due to the very tight tire/suspension clearances. Although the owners manuals, RX and HL, recommends chains be used ONLY on the front, when asked directly they readily admit that extraordinary traction on the front vs the rear can potentially be VERY HAZARDOUS.
As you will obviously notice, NONE of us have any real idea what your true needs (vs WANTS) are regarding FWD vs AWD. There was an implication based on your wording that it was "optional". If that is the case, and you're not in the 00.01 category, then the FWD RX300 with VSC, Trac and HID will provide excellent service to you and yours.
My previous discussion of Trac functionality only related to the AWD implemenation. My apologies to all, I should have made that more clear.
The firmware for FWD (or RWD) Trac can be, and likely is, radically different than the AWD version. With FWD and front slippage the Trac system will likely apply both brakes and then dethrottle the engine if the condition persists, just as it does on a RWD Lexus.
On the AWD model applying both front brakes in this circumstance would defeat the functionality of the VC entirely, the VC would then just be extra baggage. That would result in the AWD RX300 being a REAL AWD, much more like the Sequoia.
And we wouldn't want that, would we?
Off-road: This issue keeps coming back to haunt me. My 00.01% pertains to those of us we NEED AWD for ON-ROAD wintertime conditions, say here in the GREAT & BEAUTIFUL Pacific Northwest.
When I bought my first RX300 I didn't expect to have anything even close to the 4WD capability of my two previous Jeeps. But I did expect to have something roughly equivalent to my Jeeps' AWD capability. Even with the Jeeps' 4WD capability as backup I still carried a set of snowchains, religiously, in the car in the wintertime and was forced to make use of those on many occassions.
I mistakenly assumed I could rely on the same procedure with the RX, if the AWD proved to not be adequate to the task, even more often than the Jeeps, I still had the snowchains as backup.
Then I discovered that snowchains can NEVER be used on the rear of the RX (nor the HL) due to the very tight tire/suspension clearances. Although the owners manuals, RX and HL, recommends chains be used ONLY on the front, when asked directly they readily admit that extraordinary traction on the front vs the rear can potentially be VERY HAZARDOUS.
FWD pros: Much less likely to encounter a circumstance wherein the vehicle will oversteer.
FWD cons: Understeering is very common, and can become extremely unstable very quickly on low traction surfaces. Dual requirement of the use of the front tires "contact patch" to convey engine driving or lagging torque and lateral, directional, forces to the roadbed simultaneously.
If you must chose a 2WD vehicle for use on low traction surfaces, a RWD will always be much safer than ANY FWD.
wwest: "If you must chose a 2WD vehicle for use on low traction surfaces, a RWD will always be much safer than ANY FWD."
I'm surprised to read the above.
I live on a very gently-inclined road. One winter, there were 2 cars stuck there in light snow. Both were rear-wheel drive (and expensive). The econobox front-wheel drives were all going around them (happily, I imagine). Maybe this doesn't fit into wwest's definition of "safer", I dunno.
FWD cars have a definite advantage over RWD when just initially getting up and going is the issue. The front weight bias gives them addition traction over front engine RWD.
But now, push that FWD into the edge of the twilight zone, the area where you would Really, REALLY like to have the front contact patch reserved for directional control and stability, and not to ALSO convey engine driving or lagging torque, and you'll be wishing you had a CLUTCH!
If you think quickly enough you can hurriedly put the transmission in neutral, and quick but moderate application of the parking brake doesn't hurt either.
That title is so all of you doubting thomases can bail now.
For many months now I have been theorizing that the Chrysler T&C minivan's AWD system is greatly superior to that of the RX and the HL. My theory was based on the fact that the T&C AWD system had a method for uncoupling the two drivelines, front and rear, when the brakes are applied resulting in the need for disparate rotational rates front to rear.
The front brakes do about 80% of the work required to stop the vehicle and in so doing they very often turn very slowly. If that slow rate of rotation were to be coupled to the rear driveline then loss of control would oftentimes be the result.
The T&C has an over-running clutch in the rear driveline for just that purpose, allowing the rear wheels to turn at a higher rate than the front during braking.
But, up until this morning I had no T&C with which to prove out my theory. My daughters 98 is here at the moment.
So I jacked it up so all four wheels were off the ground and repeated the shade-tree mechanic's AWD test that I performed on the 01 AWD RX300.
As it happened I was not able to block the rear wheels from turning in exactly the same manner as the RX. The 98 T&C wheels do not have wide enough openings to insert the light pine 1X2' with the thin dimension to "shear". So in this case the T&C had to shear the 2" dimension if the rear wheels were to turn.
With my foot firmly on the brake and the engine at idle I shifted the transmission into gear and then started releasing the brakes. The right rear 1X2 sheared virtually instantly, at engine idle. To be sure this wasn't a fluke I blocked the right rear with an oak 1X2. The left rear 1X2 sheared virtually the instant I started releasing the brakes.
I repeated the test one more time just as assurance.
The RX300 rear wheels would not shear the thin dimension of the 1X2 even with the engine RPM raised to 2000.
I dunno Willard. I've been driving FWD since '82, and lots of that was in Anchorage. The only time I lost it like you describe was in a parking lot. It was scary and totally foreign to the "ordinary" skid control that I grew up with.
But I've yet to come anywhere close to a reoccurance, and I had to work to break it loose in the parking lot.
I like FWD a lot (and I've also been known to install chains only on the front too). Luckily I'm in a low clearance MV so when I do lose it on the road to the ski resort, I'll hang up on the shoulders instead of careening down the mountain like I would in a SUV (an interesting factoid I picked up in the I don't like SUVs, why do you? discussion <g>).
FWD, due to their very nature, are much more likely to understeer than oversteer, but if you do get one to oversteer its very likely an icy mountain road, especially downhill. Start praying immediately, do not hesitate!
...that T&C is still a Chrysler, just like it was before your tests.
Decent styling, the cheapest materials possible, move-'em-out dealers, and I-just-work-here mechanics and service writers that usually have the same basic response after dealing with hundreds if not thousands of design problems on these vans for the last 18-20 years -
"Gosh, never seen one of these vans do THAT before! Hope you got the extended warranty coverage!"
And for all you Chrysler owners that love their vans, never had repeated problems, and for all you Chrysler personnel that somehow manage to do a good job - my apologies for the above. Just my experience in owning The-Notso-Grand-Caravan (otherwise known as "The Van of Death") for way too long.
Willard, you're welcome to it. And to think you gave that POS to your own flesh and blood. Shame, shame.
Not that Willard needs any help, but in his defense, I've never read any post of his that claims that the T&C is a better vehicle, only that the AWD system is theoretically more capable than that on our RX. Granted, that conclusion is based on what seems to me to be a practical way to get some idea of what's being shunted to the rear wheels but might not actually translate to realworld experience. But, as I recall, he's also backed it up to a degree with 4 wheel dyno results. Maybe the RX330 WILL have an AW drivetrain that is more capable. (Non sequiter: the GX470 certainly does, from it's description.)
Having said all that, wifey's AWD with LSD is certainly capable enough for the weather we experience here in Arkansas, and the times that we've had snow and ice, it's been perfectly satisfactory. But Willard's road conditions are more severe by far. So what works for most of us sometimes doesn't, for him.
And as far as discussion of vehicle dynamics, I can't fault him there, either. I agree that Lexus has commited a faux pas with our RX for those who NEED chains since there is insufficient wheel clearance in the rear. In a circumstance where oversteer develops in a very low traction setting due to front wheel braking (say, going down an icy hill if a driver taps the brakes too hard or, God forbid, downshifts) as he's described, I doubt even Michael Schumacher could correct the resultant lurid slide which will occur. And then your new destination is in the hands of God and physics, but not yours!!
Yes, his posts are long (so are mine, sometimes. Like now.). Unfortunately, many questions can't be answered in 25 words or less. And Willard can answer and justify his positions more technically than most. Yes, we see them over and over. Unfortunately, newcomers obviously don't read the whole RX thread before they post questions that have been answered before. So, we ALL tend to post answers we've posted before rather than shunning them or ridiculing them for not "doing their homework". That's why this forum is so consistently helpful, imho.
Mooretorque, you keep it up and some of the doubting thomases with begin to think we're in cahoots just because we're both from Arkansas.
But, now that the Edmunds search engine actually works I will try to be more diligent about backward referrals.
And it's my understanding that the GX470 has (will have)the same underpinnings as the 03 4runner, which IMMHO is an outstanding AWD implementation. Maybe even better than the Sequoia.
I had all but forgotten this but here's a helpful hint. Maybe.
When I was living in MT I would disable the parking brake locking/latching mechanism in the wintertime so it could be used to apply moderate, "modulated" braking exclusively to the rear on ice and snow covered downhill roadbed sections.
Mooretorque's mention of downhill downshifting reminded me.
Cardinal RULE. NEVER downshift a FWD, or AWD with FWD torque bias like the RX and HL on a slippery roadbed.
I had to use my spare recently and at first I thought the spare wheel was really ugly--all black steel except for the chrome lug nuts. I used it for a few days and came to believe that it was better looking than the silver wheels that come on the RX. They have alway looked wimpy to me. Of course the spare isn't very stylish. Has anyone ever tried painting the OEM wheels gloss black? It's a lot cheaper than buying a new set of wheels, but would the paint stick? And how do you think it would look? My RX is black with gold accents.
Gee, it would be nice to actually read about the RX300 in a Lexus thread! Now, what do you all think would be a good price for a 2001 with say 24-30k miles?
I think you would need to abrade the "chrome" finish, perhaps by sand blasting; to assure proper adhesion. Next apply a very tenacious finish, like powder-coat; for satisfactory results. Not a DIY project in my opinion.
I'm not really relishing driving the T&C out to central MT and back so I ordered a set of KYB front struts to install in the rear of the RX for snowchain clearance. Here's hoping they fit.
Chrysler dexcribes the T&C's AWD system as follows:
"The heart of the system is a torque-sensing viscous coupling device that links the front and rear wheels. Under normal driving conditions, power is transmitted to the front wheels. When the front wheels begin to lose traction and slip, the viscous coupling automatically transfers torque to the rear wheels to help regain traction."
Apparently the real, or actual, difference is in the formulation of the viscous fluid within the viscous clutch coupling.
Apparently Lexus uses a fluid formulation that does not increase its "effective" viscosity at a very high rate with disparate rotational rates of the two sets of VC clutch plates. Or maybe even the initial coupling coefficient, native viscosity, is so very low that even at full "viscosity" there is still no "there" there.
My best guess as to why that do that was/is to avoid the extra hardware that would be required to uncouple the two drivelines during braking.
Cadillac put an over-running clutch in their FWD cars to alleviate the problems of loss of control due to the uniquely higher FWD braking effects from their northstar engine.
"Coasting" is only with the geartrain uncoupled. With the geartrain "coupled" you will always have some affect of the wheels "driving" the engine.
Techno babble.
With a properly formulated viscous fluid, and in some cases the addition of a gas bubble, the onset of coupling is significantly delayed from initial disparate wheelspin. But once coupling is enabled it will take a few hundred milliseconds to fully uncouple.
Sorta like the natural heating of engine oil. even with lots of surface area to radiate the heat away it takes awhile.
The best discription I have heard re front wheel drive loosing control is as follows.
If you were rowing a boat down stream and wanted to stop, you toss your anchor out. If it is tied to the back of the boat, when the anchor starts dragging, the boat will stop when it grabs and you will be facing in the direction you were heading.
Now, tie your anchor to the bow of the boat and toss it out. You are going to do one fast 180 degree turn. The anchor is acting like engine breaking when you take your foot off the gas. This is, of course, on a slippery surface.
When it comes to getting up to speed, I'll take FWD. But for stopping I'll go with RWD everytime.
And THAT's why an AWD can be so very beautiful, 70/30 for acceleration, 50/50 for cruising, 30/70 from slowing or braking, and 5/95 for turning AND slowing or braking.
New KYB front struts are to be here this PM and if I can fit them to the rear of the RX then the two sets of chains I bought last year before I discovered the clearance problem can go along for the ride. Otherwise the T&C will be going.
And yes, I should have believed the RX owners manual where it said "snowchains ONLY on the front". But even the T&C (and the MDX, and...) says that and yet rear chains can be fitted on it (them) quite readily, as is the case with most FWD or AWD vehicles.
Certainly one would not normally expect an SUV to have such a restriction.
So an "overunning clutch" is akin to the freewheeling unit in a helicopter's transmission, which allows the main rotor to continue "spinning" if the engine stops.
I agree that johngreis' example is flawed and wishnhigh is more accurate. Weight distribution has more to do with braking effort than what John said. John's example would be apt if there were NO brakes on the rear wheels at all ... which, of course, is ludicrous.
Anyway, I have a question for Willard. Williard - how in the heck do you get any work done?!?!?!? You are on this board almost, it seems, 24/7. How does someone manage to run a company and post as much as you do?
I'm not sure if this has been asked already but I wanted to confirm that my parking brake works properly. When parking on a hill, I have to set the parking brake, put it in neutral while pressing down on the brake pedal, release the brake pedal to allow the parking brake set, and then put it in park. If I put it into park right away, it rolls a little and locks up. Is this normal for the RX?
The example doesn't, wasn't intended to, relate to brakes in the literal sense, only to "drive" wheel braking due to "coasting" with the drivetrain/engine engaged.
In that circumstance in a FWD vehicle you have "brakes" ONLY on the front wheels. And now simply replace the flowing current of the river with the earth's gravity pulling you downhill on that slippery slope.
Answer for automotional.
I get to sleep with the BOSS.
The paperwork says I am retired and no longer on the payroll. So my only remaining responsibility is to drive my wife, the boss, in to work and then home at night.
She pays me VERY well for that service.
But, truly, we are a small company of about 20 people and every one of those 20 are absolutely top notch.
So all I have left to do is monitor, tweak, the trim tab on occassion.
The RX front struts bolted up to the rear without any problems. But the clearance between the tire and spring support plate was virtually the same.
So, back to the drawing board.
Good news...
When I upgraded to 17X8 wheels/tires we had to add 1.2" spacers at the rear so we added them all around.
With the original spare bolted up to the spacer there is no interference problem because the tire now sits out far enough. Now I must go off and find another spare.
As far as I know there is no such thing as a centrifugal force. It is merely an artifact of motion in an accelerated reference frame. Centripetal force, well that's another thing.
Willard was using the term correctly. They are both forces that act on a body when it is traveling in a circle. Centrifugal is the force that acts away from the center. This is the one that keeps a racecar hugging the track in the curves because the track is banked. If the track were not banked, the CENTRIFUGAL force would make the cars slide off the track. Centripetal force is the force that acts toward the center of the circle the object is traveling in. Check your Webster's.
my tuppence: Technically, the "centrifugal force" is a pseudo-force since the inertia of an object will tend to keep it moving in a straight line. The real force is the "centerseeking" centripetal force and it is the centripetal force that prevents the object from continuing its movement in a straight line.
OK, so the centripetal force caused by the radial chain links rotating and pulling the crossply chain links in towards the center of the wheel isn't enough to prevent inertia from lifting the crossply chain links away from the tire a bit...
...and the chain impinges on the strut causing a hell of a racket and maybe some damage.
...isn't enough to prevent inertia from lifting the crossply chain links away from the tire a bit..
Can someone verify this? I just did a quick calculation and came up with the equivalent of about 20 g's for the centripetal acceleration at 20 mph. If that's correct, then those tire chains should be applied very snugly to avoid "lifting" them!
Thanks! I didn't have actual tire sizes at my finger tips so I just pulled a number out of the air but adjusting for correct sizes I agree with your calculation.
I hadn't expected the acceleration to be quite that large. Keep those chains snug!
Comments
After being a lifelong Honda owner, this is my first luxury car and very first Lexus. I love the RX, it is a really great vehicle.
I paid a little over 28K and it has about 17k miles. My wife wanted my to wait and buy a 2004 but I decided on this one. I am though waiting anxiously to see the new RX330 at the LA Auto Show in January.
Thanks for everyone's words of wisdom and advice on this board, and interesting comments from other RX owners.
Jim d.
BMW X5 #1
ML320 #2
XC90 #3
03 4runner #4
T&C minivan #5
On any AWD system when the brakes are severely applied the AWD system MUST be UNCOUPLED. The Lexus RX300 solves this aspect of AWD by NEVER having a high enough coupling coefficient to the rear to matter.
I traded up from a 00 AWD RX to an 01 AWD RX to get the benefit of VSC, Trac and HID. I am quite pleased with the HID and the Trac does seem to intervene at times, however lightly.
I have come to the conclusion that the Trac functionality is so moderate or possibly even completely non-functional that it is virtually useless. Like the GPS/nav.
Pete
The AWD system used in the RX300 by your own admission wwest is adequate for 99%, no, make that 99.99% of the owners over the entire ownership period. This subject has been discussed to near exhaustion on your part. Suffice to say if conditions warrant an AWD system, the RX300 will do just fine.
AWD pros: Traction, stability, handling.
AWD cons: read wwest's post to follow
FWD pros:probable lower maintenance vs AWD, lower weight( quicker acceleration, shorter braking distances, better fuel economy).
FWD cons: Not many, other than if your driving environment needs better traction than FWD can provide, then go for the AWD, it's an individual choice we all must contemplate.
I would even contend that to buy these expensive and obviously more complex AWD systems that wwest suggested is contrary to his beliefs. He would have you believe that to purchase the RX AWD is paying for a system that is "virtually meaningless", and burdens you with "useless extra weight". Since a vast majority of RX AWD owners never go off road(as well as wwest's first 4 choices), and the RX 300's system performs adequately for 99% of the conditions that occur on the road, why pay for these more complex systems...isn't that a waste of your money as well?
fuhrmjo- I'm sure you don't need me to lecture you concerning your decision to buy an RX 300 AWD vs FWD. Either decision will provide you with a terrific vehicle...I just wanted you to hear another side of the story that is IMHO shared by a majority of the people that post to this board. I will now step down from my soap box and let wwest step up. ( Here's a hint wwest- no techno babble.)
My previous discussion of Trac functionality only related to the AWD implemenation. My apologies to all, I should have made that more clear.
The firmware for FWD (or RWD) Trac can be, and likely is, radically different than the AWD version. With FWD and front slippage the Trac system will likely apply both brakes and then dethrottle the engine if the condition persists, just as it does on a RWD Lexus.
On the AWD model applying both front brakes in this circumstance would defeat the need for a VC entirely, the VC would then just be extra baggage. That would result in the AWD RX300 being a REAL AWD, much more like the Sequoia.
And we wouldn't want that, would we?
Off-road: This issue keeps coming back to haunt me. My 00.01% pertains to those of us we NEED AWD for ON_ROAD wintertime conditions, say here in the GREAT & BEAUTIFUL Pacific Northwest.
When I bought my first RX300 I didn't expect to have anything even close to the 4WD capability of my two previous Jeeps. But I did expect to have something roughly equivalent to my Jeeps' AWD capability. Even with the Jeeps' 4WD capability as backup I still carried a set of snowchains, religiously, in the car in the wintertime and was forced to make use of those on many occassions.
I mistakenly assumed I could rely on the same procedure with the RX, if the AWD proved to not be adequate to the task, even more often than the Jeeps, I still had the snowchains as backup.
Then I discovered that snowchains can NEVER be used on the rear of the RX (nor the HL) due to the very tight tire/suspension clearances. Although the owners manuals, RX and HL, recommends chains be used ONLY on the front, when asked directly they readily admit that extraordinary traction on the front vs the rear can potentially be VERY HAZARDOUS.
As you will obviously notice, NONE of us have any real idea what your true needs (vs WANTS) are regarding FWD vs AWD. There was an implication based on your wording that it was "optional". If that is the case, and you're not in the 00.01 category, then the FWD RX300 with VSC, Trac and HID will provide excellent service to you and yours.
My previous discussion of Trac functionality only related to the AWD implemenation. My apologies to all, I should have made that more clear.
The firmware for FWD (or RWD) Trac can be, and likely is, radically different than the AWD version. With FWD and front slippage the Trac system will likely apply both brakes and then dethrottle the engine if the condition persists, just as it does on a RWD Lexus.
On the AWD model applying both front brakes in this circumstance would defeat the functionality of the VC entirely, the VC would then just be extra baggage. That would result in the AWD RX300 being a REAL AWD, much more like the Sequoia.
And we wouldn't want that, would we?
Off-road: This issue keeps coming back to haunt me. My 00.01% pertains to those of us we NEED AWD for ON-ROAD wintertime conditions, say here in the GREAT & BEAUTIFUL Pacific Northwest.
When I bought my first RX300 I didn't expect to have anything even close to the 4WD capability of my two previous Jeeps. But I did expect to have something roughly equivalent to my Jeeps' AWD capability. Even with the Jeeps' 4WD capability as backup I still carried a set of snowchains, religiously, in the car in the wintertime and was forced to make use of those on many occassions.
I mistakenly assumed I could rely on the same procedure with the RX, if the AWD proved to not be adequate to the task, even more often than the Jeeps, I still had the snowchains as backup.
Then I discovered that snowchains can NEVER be used on the rear of the RX (nor the HL) due to the very tight tire/suspension clearances. Although the owners manuals, RX and HL, recommends chains be used ONLY on the front, when asked directly they readily admit that extraordinary traction on the front vs the rear can potentially be VERY HAZARDOUS.
FWD pros: Much less likely to encounter a circumstance wherein the vehicle will oversteer.
FWD cons: Understeering is very common, and can become extremely unstable very quickly on low traction surfaces. Dual requirement of the use of the front tires "contact patch" to convey engine driving or lagging torque and lateral, directional, forces to the roadbed simultaneously.
If you must chose a 2WD vehicle for use on low traction surfaces, a RWD will always be much safer than ANY FWD.
I'm surprised to read the above.
I live on a very gently-inclined road. One winter, there were 2 cars stuck there in light snow. Both were rear-wheel drive (and expensive). The econobox front-wheel drives were all going around them (happily, I imagine).
Maybe this doesn't fit into wwest's definition of "safer", I dunno.
But now, push that FWD into the edge of the twilight zone, the area where you would Really, REALLY like to have the front contact patch reserved for directional control and stability, and not to ALSO convey engine driving or lagging torque, and you'll be wishing you had a CLUTCH!
If you think quickly enough you can hurriedly put the transmission in neutral, and quick but moderate application of the parking brake doesn't hurt either.
For many months now I have been theorizing that the Chrysler T&C minivan's AWD system is greatly superior to that of the RX and the HL. My theory was based on the fact that the T&C AWD system had a method for uncoupling the two drivelines, front and rear, when the brakes are applied resulting in the need for disparate rotational rates front to rear.
The front brakes do about 80% of the work required to stop the vehicle and in so doing they very often turn very slowly. If that slow rate of rotation were to be coupled to the rear driveline then loss of control would oftentimes be the result.
The T&C has an over-running clutch in the rear driveline for just that purpose, allowing the rear wheels to turn at a higher rate than the front during braking.
But, up until this morning I had no T&C with which to prove out my theory. My daughters 98 is here at the moment.
So I jacked it up so all four wheels were off the ground and repeated the shade-tree mechanic's AWD test that I performed on the 01 AWD RX300.
As it happened I was not able to block the rear wheels from turning in exactly the same manner as the RX. The 98 T&C wheels do not have wide enough openings to insert the light pine 1X2' with the thin dimension to "shear". So in this case the T&C had to shear the 2" dimension if the rear wheels were to turn.
With my foot firmly on the brake and the engine at idle I shifted the transmission into gear and then started releasing the brakes. The right rear 1X2 sheared virtually instantly, at engine idle. To be sure this wasn't a fluke I blocked the right rear with an oak 1X2. The left rear 1X2 sheared virtually the instant I started releasing the brakes.
I repeated the test one more time just as assurance.
The RX300 rear wheels would not shear the thin dimension of the 1X2 even with the engine RPM raised to 2000.
But I've yet to come anywhere close to a reoccurance, and I had to work to break it loose in the parking lot.
I like FWD a lot (and I've also been known to install chains only on the front too). Luckily I'm in a low clearance MV so when I do lose it on the road to the ski resort, I'll hang up on the shoulders instead of careening down the mountain like I would in a SUV (an interesting factoid I picked up in the I don't like SUVs, why do you? discussion <g>).
Steve, Host
Decent styling, the cheapest materials possible, move-'em-out dealers, and I-just-work-here mechanics and service writers that usually have the same basic response after dealing with hundreds if not thousands of design problems on these vans for the last 18-20 years -
"Gosh, never seen one of these vans do THAT before! Hope you got the extended warranty coverage!"
And for all you Chrysler owners that love their vans, never had repeated problems, and for all you Chrysler personnel that somehow manage to do a good job - my apologies for the above. Just my experience in owning The-Notso-Grand-Caravan (otherwise known as "The Van of Death") for way too long.
Willard, you're welcome to it. And to think you gave that POS to your own flesh and blood. Shame, shame.
Having said all that, wifey's AWD with LSD is certainly capable enough for the weather we experience here in Arkansas, and the times that we've had snow and ice, it's been perfectly satisfactory. But Willard's road conditions are more severe by far. So what works for most of us sometimes doesn't, for him.
And as far as discussion of vehicle dynamics, I can't fault him there, either. I agree that Lexus has commited a faux pas with our RX for those who NEED chains since there is insufficient wheel clearance in the rear. In a circumstance where oversteer develops in a very low traction setting due to front wheel braking (say, going down an icy hill if a driver taps the brakes too hard or, God forbid, downshifts) as he's described, I doubt even Michael Schumacher could correct the resultant lurid slide which will occur. And then your new destination is in the hands of God and physics, but not yours!!
Yes, his posts are long (so are mine, sometimes. Like now.). Unfortunately, many questions can't be answered in 25 words or less. And Willard can answer and justify his positions more technically than most. Yes, we see them over and over. Unfortunately, newcomers obviously don't read the whole RX thread before they post questions that have been answered before. So, we ALL tend to post answers we've posted before rather than shunning them or ridiculing them for not "doing their homework". That's why this forum is so consistently helpful, imho.
My .07; too long to be .02.
But, now that the Edmunds search engine actually works I will try to be more diligent about backward referrals.
And it's my understanding that the GX470 has (will have)the same underpinnings as the 03 4runner, which IMMHO is an outstanding AWD implementation. Maybe even better than the Sequoia.
When I was living in MT I would disable the parking brake locking/latching mechanism in the wintertime so it could be used to apply moderate, "modulated" braking exclusively to the rear on ice and snow covered downhill roadbed sections.
Mooretorque's mention of downhill downshifting reminded me.
Cardinal RULE. NEVER downshift a FWD, or AWD with FWD torque bias like the RX and HL on a slippery roadbed.
Jim d.
Pete
"The heart of the system is a torque-sensing viscous coupling device that links the front and rear wheels. Under normal driving conditions, power is transmitted to the front wheels. When the front wheels begin to lose traction and slip, the viscous coupling automatically transfers torque to the rear wheels to help regain traction."
Isn't that the same as the RX300?
Apparently Lexus uses a fluid formulation that does not increase its "effective" viscosity at a very high rate with disparate rotational rates of the two sets of VC clutch plates. Or maybe even the initial coupling coefficient, native viscosity, is so very low that even at full "viscosity" there is still no "there" there.
My best guess as to why that do that was/is to avoid the extra hardware that would be required to uncouple the two drivelines during braking.
How do you lose control in a coasting, FWD vehicle?
"Coasting" is only with the geartrain uncoupled. With the geartrain "coupled" you will always have some affect of the wheels "driving" the engine.
Techno babble.
With a properly formulated viscous fluid, and in some cases the addition of a gas bubble, the onset of coupling is significantly delayed from initial disparate wheelspin. But once coupling is enabled it will take a few hundred milliseconds to fully uncouple.
Sorta like the natural heating of engine oil. even with lots of surface area to radiate the heat away it takes awhile.
If in a manual transmission car: downshift, fail to match revs (or shift to too low a gear) and watch the world spin by.
And as Willard pointed out, even "coasting" in an auto trans car is supplying engine braking to the front wheels......
Should be just as easy to hit deer in a minivan, right?
One wonders what deer are doing in a minivan! ;-)
tidester, host
If you were rowing a boat down stream and wanted to stop, you toss your anchor out. If it is tied to the back of the boat, when the anchor starts dragging, the boat will stop when it grabs and you will be facing in the direction you were heading.
Now, tie your anchor to the bow of the boat and toss it out. You are going to do one fast 180 degree turn. The anchor is acting like engine breaking when you take your foot off the gas. This is, of course, on a slippery surface.
When it comes to getting up to speed, I'll take FWD. But for stopping I'll go with RWD everytime.
Thanks.
And THAT's why an AWD can be so very beautiful, 70/30 for acceleration, 50/50 for cruising, 30/70 from slowing or braking, and 5/95 for turning AND slowing or braking.
The 03 4runner seems to be closest to the ideal.
New KYB front struts are to be here this PM and if I can fit them to the rear of the RX then the two sets of chains I bought last year before I discovered the clearance problem can go along for the ride. Otherwise the T&C will be going.
And yes, I should have believed the RX owners manual where it said "snowchains ONLY on the front". But even the T&C (and the MDX, and...) says that and yet rear chains can be fitted on it (them) quite readily, as is the case with most FWD or AWD vehicles.
Certainly one would not normally expect an SUV to have such a restriction.
So an "overunning clutch" is akin to the freewheeling unit in a helicopter's transmission, which allows the main rotor to continue "spinning" if the engine stops.
Or if one engine failed on the learfan prototype.
I guess in the end that's what killed the program.
Anyway, I have a question for Willard. Williard - how in the heck do you get any work done?!?!?!? You are on this board almost, it seems, 24/7. How does someone manage to run a company and post as much as you do?
In that circumstance in a FWD vehicle you have "brakes" ONLY on the front wheels. And now simply replace the flowing current of the river with the earth's gravity pulling you downhill on that slippery slope.
Answer for automotional.
I get to sleep with the BOSS.
The paperwork says I am retired and no longer on the payroll. So my only remaining responsibility is to drive my wife, the boss, in to work and then home at night.
She pays me VERY well for that service.
But, truly, we are a small company of about 20 people and every one of those 20 are absolutely top notch.
So all I have left to do is monitor, tweak, the trim tab on occassion.
The RX front struts bolted up to the rear without any problems. But the clearance between the tire and spring support plate was virtually the same.
So, back to the drawing board.
Good news...
When I upgraded to 17X8 wheels/tires we had to add 1.2" spacers at the rear so we added them all around.
With the original spare bolted up to the spacer there is no interference problem because the tire now sits out far enough. Now I must go off and find another spare.
tidester, host
Your response will be great for one of my physics classes! A classic answer. Don't worry though, I will not reference you in any way.
...and the chain impinges on the strut causing a hell of a racket and maybe some damage.
So, Willard should use smaller wheels.
Can someone verify this? I just did a quick calculation and came up with the equivalent of about 20 g's for the centripetal acceleration at 20 mph. If that's correct, then those tire chains should be applied very snugly to avoid "lifting" them!
tidester, host
Steve, Host
Using the info and formula here:
http://www.sciencejoywagon.com/physicszone/lesson/03circ/centrif/centr.htm
I get about 32g's.
Gravity is about 9.8 m/sec^2.
I did the following in metric.
It's been awhile so let me know
if I forgot something...
Centripetal acceleration = velocity ^ 2 / radius
(That's velocity squared divided by radius)
Velocity = 20 mi/hr = 8.94 m/sec
If a 20" wheel (rim + tire) has 20" diameter:
Radius = 20"/2 = 10" = 0.254 m
Centripetal acceleration = 8.94^2 / 0.254 = 314.7 m/sec^2 = 32.1 g
I hadn't expected the acceleration to be quite that large. Keep those chains snug!
tidester, host