Is Rx300 "awd" A Scam?

[wwest]

In the alternative......

I use the quietest tires I can buy with absolutely no conern for adverse roadbed traction.

But with a set of snowchains at the ready and no reluctance on my part to put them to use.

The most common use is for getting around all those SUVs helter-skelter on the roadbed, or not.

[J.B]

RX330............AWD.........

The 04 RX uses an OPEN center diff'l and different final drive ratios F/R to bias the engine torque to the front by a rather large factor, say 98/2 F/R**. AWD engine torque apportioning is provided by braking any slipping wheel(S). With the front wheels "natively" achieving such a large portion of the torque AND having to handle the lateral torque during turning it is extremely unlikely that the rear wheels will have encounter a slipping condition.

What that means to you is that the ONLY time any significant level of torque is routed to the rear wheels is upon Trac braking application (to limit slippage) at the front followed fairly quickly by engine dethrottling if the driver doesn't react quickly and lift the foot feed.

** The RX300 used less desparate F/R final drive ratios (~3.12/2.98) than the RX330 (~3.48/2.92) and had 95/5 F/R torque biasing (actual 4WD dyno measurement) so I would assume the RX330 is closer to ~98/2)

wwest

I am a little confused with your front/rear differential ratios:

You say that the older RX300 have a 3.12/2.98 ratio, which equates to a 95/5 front/rear. I calculate that this gear ration should equate to a 52/48 front/rear ration (where a 3.02/3.02 would provide a 50/50 ratio).

You also say that the RX330 have a 3.48/2.92 ratio, which equates to a 98/2 front/rear. I calculate that this gear ratio should equate to a 58/42 front/rear (where a 3.20/3.20 would provide a 50/50 ratio).

The last fun we had in a snow covered iced parking lot demonstrated that all four tires were throwing similar rooster tail of snow, suggesting similar torque applied to all four wheells.

Thanks

JB

[wwest]

I have known, heard, of any way to calculate torque ratios from final drive ratios. You may be right, I just simply don't know.

My numbers are taken directly from a 4 wheel dynamometer where the 01 RX300 indicated a 95/5 F/R torque ratio unless there was many tens of seconds of disparate F/R rotation rate to activate the VC fluid and then it rose to not quite 75/25 F/R.

[tds]

I guess another way to look at the AWD/FWD issue is to compare the RX300 AWD with a FWD car. The last time I had my RX300 in for maintenance they gave me an ES300 for a loaner for the day. Now the ES300 is a FWD vehicle, so I turned off the traction control and gave full power when the light turned green. I had to fight the steering wheel against torque steer and I got lots of wheel spin. This is typical of a FWD with high horsepower...no matter how good a job they try to do they just cannot completely eliminate torque steer.

Now, on my way back from the dealer after picking up my RX300, when the light turned green I again gave full power (i.e. gas pedal on the floor). There was no torque steer (i.e. zero) and no wheel spin (i.e. Zero). So I guess my question is, if the RX300 AWD is really only a FWD, why do I not get the torque steer and the wheel spin I should get from a FWD vehicle (traction control did not kick in either). The answer is clear. The RX300 is definitely an AWD vehicle.

It doesn’t matter how the ratio is split front to back. All that matters is how the vehicle performs, and it performs as an AWD in dry weather, on snow, on slippery roads or anywhere. I am very happy with the job Lexus has done with the AWD (although I am less happy with some of the squeaks and rattles).

[RonLex]

When you live in Tahoe or Incline Village you use chains for stopping and controlling your RX300/330... The steep hills and sharp turns are very dangerous and tire chains or cables are a must...

Also, not all RX300 and RX330 SUVs are AWD...... :D

[SW03ES]

And I have zero torque steer on my ES300 ;)

[tmastres]

So RonLex, do you put the chains front or back? This may sound silly but if you read this entire thread you'll actually see a difference of opinion. Just curious for some empirical data.

[tds]

And I have zero torque steer on my ES300 ;)

←

SW03ES: Sorry it took so long to reply to your post, but it has been quite a while since they kept my RX300 overnight (actually 3 days while they remove the resonant vibration in the headliner, fix the dashboard squeak (twice now) and remove the 'chirp' noise from the rear seats). <_<

Anyway, Lexus gave me a loaner 2004 ES300 (I have it in my garage at the moment). Now I have been testing this car for torque steer for the last 2 days. I don't know why yours does not have any torque steer, but on this one, at full power and full acceleration (from a stop), I frequently have to wrestle with the steering wheel to keep it going in a straight line. Lexus may have done an excellent job with minimizing any torque steer inherent in the drive train, but they cannot factor in pavement and road variations. Under full power if one wheel gets less traction (say a bit of gravel on one side of the road, a touch of oil on the other side, or a rut in the road) then one side of the front wheel drive will pull more than the other and you have...torque steer. The only way to remove this is to separate the drive wheels from the steering wheels (i.e. rear wheel drive).

Under low and moderate acceleration I can detect no torque steer, but under full acceleration it is definitely there.

Incidently, I am very impressed with the power and acceleration of this ES300.

[SW03ES]

You have an ES330, the ES330s I've driven have noticable torque steer, it must have something to do with the extra torque or the powerband (the ES330 has an updated motor from my ES300 and 30pounds or so more torque).

Also, try it with TRAC off, what you might be feeling is the trac system kicking in to control wheelspin.

[jgr7]

Would the rear wheels on the rx300 ever get much power to them if chains were used on the front? My thinking is that unless you were trying to spin the wheels, using chains on the front of this type of awd would make the rear wheels almost never receive much power IE the front not loosing traction no need for the rear wheels to pick up the slack.

I'm not sure if the system is the same but my Honda C-RV has what they call real-time four wheel drive, front drive until the wheels spin then some power is sent to the rear. If you floor it in the rain you can feel the front start to slip and then stop when the rear gets power, this takes less than a second and stops all loss of traction.

My thinking is that chains on a front wheel drive car are more for stopping and turning than traction, except in ice conditions where nothing much helps.

If you live in snow country I would think that a set of snow tires and cheaper wheels would be the ticket for every day driving in the winter, save your good stuff for dry weather.

Most all the 4-wheeling I do in the snow is off road in 4wd trucks I always put the chains in the front unless I'm in mud then its all wheels. This even goes for the 33,000 lb 4x4 trucks that I have to take off road although they have duel rear tires. If the snow is real deep I will chain up both ends, this helps when you have to plow through the deep stuff. I work for the power company and have to go to the nasty places to restore power, I'm not doing this for fun although it is.

Jeff

[BadBrad]

I drive my AWD up into the snow several times a year (usually at least once a year in a blizzard) and never even come close to needing a chain-up. But I do frequently pass a number of motoring geniuses with front wheel drive cars putting tire chains on their rear tires. :chairshot:

I will say that I found the tires that Lexus equips the RX with to be total crap in the snow. Git yerself some Michelins with an M+S rating (and not those stupid marketing gimick "SUV" tires).

[SW03ES]

Lexus equipps their cars with poor tires all the way around...

[wwest]

There's snow, and then there is SNOW!

Anyone who has skiied in various areas throughout the US will understand immediately.

Driving on the cold, dry, powdery stuff is much like driving on 3 inches of loose sand. Almost any RWD, or even a FWD vehicle, even with summer tires will do fine.

Out here in the nearby environs of Seattle we have what we refer to as Pacific Boilerplate.

Anyone idiot enough to put only front chains on in this stuff would soon find themselves being dug out of the nearest barrow pit. Think for a minute about why in our mountainous regions truck-trailer rigs must use drag chains during the winter.

And then think about what happens when you need to slow or stop quickly with front chains ONLY, especially driving down a slippery incline.

Bye now....

[jgr7]

One thing we know for sure is that in the snow or ice, SPEED KILLS. Take it slow and easy and leave youself pleanty of time and room for stopping. And keep your insurance paid up.

Jeff