Fwd Or Awd

[4482]

I'm retired and live in northern Ohio. I've been thinking of getting a 2005 RX330.

The local Lexus dealer said he only orders AWD but could special order a FWD but it would take months to come in. Being retired I don't drive much in bad weather unless I have a very real need to do so. My question is do most people that buy the RX get the AWD ? The sales person told me the AWD is controlled by a computer and not used "full time" ? The mileage is a little better with the FWD model I know.

Any advise ?

[Husker4theSpurs]

hmmmm ... I would personally get the AWD b/c it would help when it's even a little slushy out after a storm, etc. I'd say if you have winters at all get the AWD, but can understand wanting better economy and lower price.

[wwest]

The RX330 AWD is really a FWD vehicle with the ability to route engine torque to the rear if front wheelspin is detected. Lexus uses a different, lower, final drive ratio at the front vs the rear so that the engine torque is heavily biased to the front, 95/5, in normal driving circumstances. If front wheelspin is detected then the front brakes are applied somewhat moderately to simulate roadbed traction and thereby force engine torque to the rear wheels.

If the front wheelspin persists for more than a few hundred milliseconds then the engine will be quickly dethrottled to prevent brake rotor overheating and the resulting warpage.

If you're really stuck, say in mud, after about 45 seconds of wheelspin activity the AWD system will shut down completely long enough for the fractional HP ABS pumpmotor to cool down so it doesn't overheat and fail.

But a note of caution is warranted here.

At our age it is entirely possible that we have spent most of our lives driving RWD vehicles, or in your case maybe even driving FWD vehicles but never in wintertime conditions.

FWD, or front torque biased AWD can become EXTREMELY HAZARDOUS in wintertime conditions for an unsuspecting or inexperienced driver.

Remember that with RWD if too much engine torque is applied, leading or lagging (engine braking) you still have roadbed traction at the front that you can rely on for recovery efforts. For FWD (or,) once the front wheels lose traction you are totally OUT OF CONTROL!

As a safety measure Cadillac has now moved entirely back to RWD (they couldn't afford to lose any more of their loyal customers). But the previous FWD vehicles with the high torque/HP northstar engine was equipped with an over-running clutch in the tranny so no engine braking was available, and the engine ecu was programmed to INSTANTLY dethrottle the engine upon detection of wheelspin. Cadillac says that the engine was dethrottled if "impending" wheelspin was detected but I can not see how one would detect impending wheelspin.

If you browse the various forums you will find many current complaints relating to almost all of the Toyota and Lexus FWD vehicles regarding complaints of hesitation and/or lack of quick acceleration. My personal opinion is that with the advent of e-throttles the manufacturers are taking action to help prevent loss of control accidents in the above described circumstances.

The most common complaint seemed to be hesitation or lack of quick acceleration response when entering a turn and trying to accelerate simultaneously. This is exactly the prevenative measure I would expect if the manufacturers were trying to prevent loss of control of FWD vehicles where the driven wheels and the directional control, stearing wheels, or one and the same.

Drive the AWD, definite rear bias, BMW X3 or X5 for an example of a really stable AWD platform under ALL circumstances.

Oh, one further note, you cannot safely use snowchains with the RX300/330 or HL as shipped, suspension clearance above the rear tire is not sufficient. Toyota and Lexus both recommend snowchains be used ONLY on the front of there vehicles while simultaneously stating, within the very same owners manual, that an inordinate level of roadbed traction at the front vs the rear can potentially lead to loss of control.

Their example is winter tires on the front with normal on the rear so you can see that snowchains on the front and not the rear would mean an extraordinary disparity between front and rear traction.

I put 1.5" wheel spacers with 17x8 wheels all around on my 2001 AWD RX300 so that I could use rear chains as a first measure and then all four if and when necessary.

Be careful out there.

[4482]

The RX330 AWD is really a FWD vehicle with the ability to route engine torque to the rear if front wheelspin is detected. Lexus uses a different, lower, final drive ratio at the front vs the rear so that the engine torque is heavily biased to the front, 95/5, in normal driving circumstances. If front wheelspin is detected then the front brakes are applied somewhat moderately to simulate roadbed traction and thereby force engine torque to the rear wheels.

If the front wheelspin persists for more than a few hundred milliseconds then the engine will be quickly dethrottled to prevent brake rotor overheating and the resulting warpage.

If you're really stuck, say in mud, after about 45 seconds of wheelspin activity the AWD system will shut down completely long enough for the fractional HP ABS pumpmotor to cool down so it doesn't overheat and fail.

But a note of caution is warranted here.

At our age it is entirely possible that we have spent most of our lives driving RWD vehicles, or in your case maybe even driving FWD vehicles but never in wintertime conditions.

FWD, or front torque biased AWD can become EXTREMELY HAZARDOUS in wintertime conditions for an unsuspecting or inexperienced driver.

Remember that with RWD if too much engine torque is applied, leading or lagging (engine braking) you still have roadbed traction at the front that you can rely on for recovery efforts. For FWD (or,) once the front wheels lose traction you are totally OUT OF CONTROL!

As a safety measure Cadillac has now moved entirely back to RWD (they couldn't afford to lose any more of their loyal customers). But the previous FWD vehicles with the high torque/HP northstar engine was equipped with an over-running clutch in the tranny so no engine braking was available, and the engine ecu was programmed to INSTANTLY dethrottle the engine upon detection of wheelspin. Cadillac says that the engine was dethrottled if "impending" wheelspin was detected but I can not see how one would detect impending wheelspin.

If you browse the various forums you will find many current complaints relating to almost all of the Toyota and Lexus FWD vehicles regarding complaints of hesitation and/or lack of quick acceleration. My personal opinion is that with the advent of e-throttles the manufacturers are taking action to help prevent loss of control accidents in the above described circumstances.

The most common complaint seemed to be hesitation or lack of quick acceleration response when entering a turn and trying to accelerate simultaneously. This is exactly the prevenative measure I would expect if the manufacturers were trying to prevent loss of control of FWD vehicles where the driven wheels and the directional control, stearing wheels, or one and the same.

Drive the AWD, definite rear bias, BMW X3 or X5 for an example of a really stable AWD platform under ALL circumstances.

Oh, one further note, you cannot safely use snowchains with the RX300/330 or HL as shipped, suspension clearance above the rear tire is not sufficient. Toyota and Lexus both recommend snowchains be used ONLY on the front of there vehicles while simultaneously stating, within the very same owners manual, that an inordinate level of roadbed traction at the front vs the rear can potentially lead to loss of control.

Their example is winter tires on the front with normal on the rear so you can see that snowchains on the front and not the rear would mean an extraordinary disparity between front and rear traction.

I put 1.5" wheel spacers with 17x8 wheels all around on my 2001 AWD RX300 so that I could use rear chains as a first measure and then all four if and when necessary.

Be careful out there.

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Thanks WWEST for the detailed information. Looks like I will stick with the AWD version. Makes sense to me.

Thanks again to everyone for your input.

:)

[jgr7]

I'm not sure about the problems with chains in front causing any kind of problems. I do some driving in the snow with 4x4s and I have always put chains on the front only. The front is where you want the traction and turning. The first time four wheelers that I have taken with me thought I was crazy until they see how well it works. Ice on the street maybe a different matter. I think the snow tires in front and regular tires in the rear would cause handling problems much the same as two different tread patterns front and rear would, dry or snow.

Jeff

[Booyah]

All this talk about 330's being crap in the snow is hard to believe! I will know very soon if its a POS! We have already had a quick 6 inch dump a week ago and it seemed to do very well, but when the snow hits and stays Im going to flog the crap out of it and report back. I have a 99 4-Runner I can compare it too.

The first big and lasting snowfall Im going into an empy parking lot and get to know it a little better first--I really want to know how the VSC works and all and how everything reacts.

Funny though the wife says why you have to do that???? Learning the car baby......also some nice play time:) Didnt tell her that though

[wwest]

Sorry, no fun....

At the first instance of wheelspin the brakes will "rattle", if you persist in trying to accelerate anyway the engine will be quickly dethrottled.

Your 4runner can be accelerated and "thrown" into a turn but not the Rx.

[noosense00]

I am new to this board. I thought the AWD RX 330 was split 50/50 all the time? I have also been told for example that the X5 AWD is horrible compared to the AWD RX330 and MDX for example.

Sorry, no fun....

At the first instance of wheelspin the brakes will "rattle", if you persist in trying to accelerate anyway the engine will be quickly dethrottled.

Your 4runner can be accelerated and "thrown" into a turn but not the Rx.

←

[wwest]

Lexus uses a lower final drive ratio at the front that the rear so effective the front wheels will always have higher torque on the application of more power.

The BMW X3, 5 AWD system, definite rear biasing, is one of the very best designs in the marketplace today. Lots of engine lagging torque for quick decleration when you lift the throttle.

Drive one, you 'll love it.

[noosense00]

In reference to the AWD system for the RX330, the lead tech at lexus actually told me that the car is a full 50/50. Neither front wheel or rear wheel biased. I could be wrong, but that is what I was told.

Lexus uses a lower final drive ratio at the front that the rear so effective the front wheels will always have higher torque on the application of more power.

The BMW X3, 5 AWD system, definite rear biasing, is one of the very best designs in the marketplace today. Lots of engine lagging torque for quick decleration when you lift the throttle.

Drive one, you 'll love it.

←

[noosense00]

Please ignore what I just said in the post above. Was reading the other post and now I understand. it is front bias.

In reference to the AWD system for the RX330, the lead tech at lexus actually told me that the car is a full 50/50.  Neither front wheel or rear wheel biased.  I could be wrong, but that is what I was told.

Lexus uses a lower final drive ratio at the front that the rear so effective the front wheels will always have higher torque on the application of more power.

The BMW X3, 5 AWD system, definite rear biasing, is one of the very best designs in the marketplace today. Lots of engine lagging torque for quick decleration when you lift the throttle.

Drive one, you 'll love it.

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[noosense00]

ok. Here we go. After doing some extensive research this is what I found and I hope this answers the question for everyone.

"AWD system splits power 50% front, 50% rear under normal circumstances, shifts power as needed to wheels with the most traction. System has no center differential and relies on traction- and stability-controls to shift power to wheels not spinning. "

According to many sites, the AWD is fixed 50/50 unlike many other SUVs. So basically this is neither front or rear bias.

Please ignore what I just said in the post above.  Was reading the other post and now I understand.  it is front bias.

In reference to the AWD system for the RX330, the lead tech at lexus actually told me that the car is a full 50/50.  Neither front wheel or rear wheel biased.  I could be wrong, but that is what I was told.

Lexus uses a lower final drive ratio at the front that the rear so effective the front wheels will always have higher torque on the application of more power.

The BMW X3, 5 AWD system, definite rear biasing, is one of the very best designs in the marketplace today. Lots of engine lagging torque for quick decleration when you lift the throttle.

Drive one, you 'll love it.

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[jbarhorst2]

The Cadillac Deville series is actually still FWD. The next version will mark its return to RWD. I believe they are using the Sigma platform for this.

Tom

[wwest]

The RX series most definately has a center differrential, an OPEN center differential!

Prior to 04 there was a VC, viscous clutch, coupling, mounted across the two output shafts of the center diff'l which was dropped in 04 in favor of brake modulation for engine torque allocation and/or apportionment.

On a 4 wheel dyno my 01 AWD RX had less than 5% of the engine torque applied to the wheels unless disparate roadbed traction was simulated by the dyno in which case the highest torque measurement obtained to the rear was 25%

That, or course, was with a VC in place.

The new model has virtually no torque to the rear unless front wheelspin is detected and therefore the front brakes are moderately applied to prevent wheelspin and "force" torque to the rear. In the above circumstance if the driver doesn't quickly lift the throttle to alleviate the cirumstance the engine will be quickly dethrottle to prevent brake rotor overheating.

In other words once the system "switches" to AWD mode (moderate front brake application) no significant level of HP/torque can be applied anywhere, front or rear.

[noosense00]

WWest, thanks for the explanation above. Now I understand.