Lexus Rx400h: Curves With Problems

[othun]

I've heard the rx400h had "little bad movements" in the middle of a curve when the rear engine starts because it's necessary, is it true?

Thanks at all!

[katzjamr]

after i stopped grinning at your post i had to reply with firstly, its never happened to me in 6500 miles of 400h driving, and its my opinion that your comment could only have been made by someone who doesnt own this vehicle and doesnt drive one. i also read three forums daily on the 400h and this issue has never come up from any 400h owner. there are no 'little bad movements' (sounds like a personal problem now that i type it) and to be clear its the rear electric motor, not 'engine'

[wwest]

No, as an example of the correct way the Volvo XC90 AWD system biases the engine torque to the rear until the apex of the turn/"curve" is reached and then starts routing the engine torque primarily to the front after the apex.

The traction coefficient of the front wheels will be at its most stressful prior to and having reached the apex of a turn/curve. On the RX400h the ICE/hydrid drive torque is clearly biased toward the front wheels and therefore the most likely instance for the front tires to lose traction is at the height of lateral + drive torque. The apex of a turn/curve on a slippery roadbed.

So at the instant of approaching the apex on a slightly slippery surface the front wheels slip due to the contact patch being "over-stressed" and as a result the Trac ECU instantly reallocates drive torque to the rear.

The result is probably compariable to the problems with the early models of the Porsche 911, total and complete loss of control.

[Lexus_Jim]

No, as an example of the correct way the Volvo XC90 AWD system biases the engine torque to the rear until the apex of the turn/"curve" is reached and then starts routing the engine torque primarily to the front after the apex.

The traction coefficient of the front wheels will be at its most stressful prior to and having reached the apex of a turn/curve. On the RX400h the ICE/hydrid drive torque is clearly biased toward the front wheels and therefore the most likely instance for the front tires to lose traction is at the height of lateral + drive torque. The apex of a turn/curve on a slippery roadbed.

So at the instant of approaching the apex on a slightly slippery surface the front wheels slip due to the contact patch being "over-stressed" and as a result the Trac ECU instantly reallocates drive torque to the rear.

The result is probably compariable to the problems with the early models of the Porsche 911, total and complete loss of control.

:chairshot:

[RX400h]

No, as an example of the correct way the Volvo XC90 AWD system biases the engine torque to the rear until the apex of the turn/"curve" is reached and then starts routing the engine torque primarily to the front after the apex.

The traction coefficient of the front wheels will be at its most stressful prior to and having reached the apex of a turn/curve. On the RX400h the ICE/hydrid drive torque is clearly biased toward the front wheels and therefore the most likely instance for the front tires to lose traction is at the height of lateral + drive torque. The apex of a turn/curve on a slippery roadbed.

So at the instant of approaching the apex on a slightly slippery surface the front wheels slip due to the contact patch being "over-stressed" and as a result the Trac ECU instantly reallocates drive torque to the rear.

The result is probably compariable to the problems with the early models of the Porsche 911, total and complete loss of control.

Only WWEST would come up with a conclusion like this!!!!!

[wwest]

No, conclusion is really from reading up on the way the new AWD Lexus IS and GS dynamically reallocates engine drive/drag torque away from the front wheels when the VSC's yaw sensor indicates that the front contact patch must be used primarily for directional control.

The IS and GS torque reallocation is pre-emptive and therefore more likely to be a "seamless", smooth transition. On the other hand the RX torque reallocation from front to back is purely reactive and therefore more likely to be quick, instantaneous, and disruptive to driving dynamics.

[RX400h]

I'll bet our RX400h handles better than the early 911s after what I've seen at auto-crosses. The general consensus among the viewers of the event: If you like to do 180 spins, drive an early 911!

[wwest]

I wouldn't disagree, absolutely. But to be fair while my 2001 Porsche C4 NEVER goes out in those conditions intentionally I'b be willing to bet that on most adverse roadbed conditions it would outperform your RX400h, easily.

My 78 SC Targa on the other hand.....

On second thought the 78 has all the advatages of your RX400h, engine weight over the drive wheels. With the right, experienced driver, who knows....

To be fair many years ago I have had the 78 up and over the pass and back in the dead of winter with the roadbed snow packed. Also have driven hundreds of miles on icy roadbeds. But carefully, very carefully.

[RX400h]

I wouldn't call your 01 an "early" 911, but a guy here at work has an 89 911 Turbo - it IS what I consider an early 911.

[larrytrk]

I wouldn't call your 01 an "early" 911, but a guy here at work has an 89 911 Turbo - it IS what I consider an early 911.

Interesting, that so many of us seem to Like 400H's as our second vehicle, after our Porsches.

My 92 C2 is much better in the snow than my 76 911S Targa was, But still dicey, so I rely on the RX.

[Statman]

I can't believe I'm reading a thread comparing the RX400h to a Porsche (any Porsche)...WTF! Are you kidding me? There simply is no comparison and if you can't drive an "early" model 911 give it to someone who can! (I have a '78 930, '80 911SC and an '04 996TT)

Edited January 7, 2006 by Statman

[RX400h]

I can't believe I'm reading a thread comparing the RX400h to a Porsche (any Porsche)...WTF! Are you kidding me? There simply is no comparison and if you can't drive an "early" model 911 give it to someone who can! (I have a '78 930, '80 911SC and an '04 996TT)

Hopefully, you won't ever meet up with an 06 Z06, either on your way to work or on the track. Now if anyone needs a babysitter for one of THOSE bad boys, I'm IN! :)

[Rx330driver]

I can't believe I'm reading a thread comparing the RX400h to a Porsche (any Porsche)...WTF! Are you kidding me? There simply is no comparison and if you can't drive an "early" model 911 give it to someone who can! (I have a '78 930, '80 911SC and an '04 996TT)

Hopefully, you won't ever meet up with an 06 Z06, either on your way to work or on the track. Now if anyone needs a babysitter for one of THOSE bad boys, I'm IN! :)

lol, im surprised you got that username, rx400h. lol lucky :P

[Statman]

Hopefully, you won't ever meet up with an 06 Z06, either on your way to work or on the track. Now if anyone needs a babysitter for one of THOSE bad boys, I'm IN! :)

Already dusted one of those...I do have some mods though

[RX400h]

I can't believe I'm reading a thread comparing the RX400h to a Porsche (any Porsche)...WTF! Are you kidding me? There simply is no comparison and if you can't drive an "early" model 911 give it to someone who can! (I have a '78 930, '80 911SC and an '04 996TT)

Hopefully, you won't ever meet up with an 06 Z06, either on your way to work or on the track. Now if anyone needs a babysitter for one of THOSE bad boys, I'm IN! :)

lol, im surprised you got that username, rx400h. lol lucky :P

I was one of the first "on the list" members, I guess!

Hopefully, you won't ever meet up with an 06 Z06, either on your way to work or on the track. Now if anyone needs a babysitter for one of THOSE bad boys, I'm IN! :)

Already dusted one of those...I do have some mods though

Ah, but the Z06 is $65,000 MSRP. I'll bet a simple supercharger installation would catapult it well beyond your much more expensive car's performance capabilities. Heck, the thing is cranking out 530 HP (derived from dynomometer testing) right from the factory! The supercharger would place its HP up at about 680 HP, all for $75,000. Now THAT's a deal that has no equal!

Edited January 8, 2006 by RX400h

[wwest]

The last weekend in January you can watch as our 2 997 GT3's out run and outlast any Corvettes that show up.

[RX400h]

The last weekend in January you can watch as our 2 997 GT3's out run and outlast any Corvettes that show up.

2005 Porsche GT3:

Type: Flat-6

Displacement: 3600 cc

Horsepower: 380 bhp @ 5800 rpm

Torque: 285 lb-ft @ --- rpm

Redline: 8200 rpm

Performance

0-60 mph: 4.3 sec

Cost: $99,900

2006 Z06

Type: V8

Displacement: 7011 cc

Horsepower: 505 (530 measured)

Torque: 470 lbs-ft@4800rpm

Redline: 7000 rpm

Performance

0-60 mph: 3.7 sec

1/4-mile: 11.7 seconds

Cost: $65,000

At only $42,000, the standard C6 Corvette outperforms the GT3, road and track, according to both Car & Driver and Road & Track magazines. The Z06 is on a much higher plane.

[larrytrk]

The last weekend in January you can watch as our 2 997 GT3's out run and outlast any Corvettes that show up.

2005 Porsche GT3:

Type: Flat-6

Displacement: 3600 cc

Horsepower: 380 bhp @ 5800 rpm

Torque: 285 lb-ft @ --- rpm

Redline: 8200 rpm

Performance

0-60 mph: 4.3 sec

Cost: $99,900

2006 Z06

Type: V8

Displacement: 7011 cc

Horsepower: 505 (530 measured)

Torque: 470 lbs-ft@4800rpm

Redline: 7000 rpm

Performance

0-60 mph: 3.7 sec

1/4-mile: 11.7 seconds

Cost: $65,000

At only $42,000, the standard C6 Corvette outperforms the GT3, road and track, according to both Car & Driver and Road & Track magazines. The Z06 is on a much higher plane.

Boys, let's put the testosterone aside, and get back to the original topic, which I assume was a serious question.

I have experienced low speed engine surges. Slowing down for speed bumps on my street the car will occasionally accelerate slightly, I was surprised and was waiting to see If this would be a problem on an icy street. So far it has happened so rarely, that I have not done any further investigation.

I assume it is a software glitch!

I have not noticed high speed glitches!

[wwest]

"....occassionally accelerate....."

I have noticed, as have many other owners, that the RX300 sometimes "feels" like it is accelerating ever so slightly. But what is actually happening is that the transaxle is upshifting. One of these times is just before coming to a full stop, the transaxle upshifts and the "feel" is somewhat like being bumped lightly from behind.

The other time is during throttle fully closed coastdown circumstances at highway speeds. Here again, the transaxle will often upshift during coastdown giving the "slingshot effect" feeling.

I have proposed that this upshifting is an effort by Toyota/Lexus to improve fuel economy slightly and also possibly to help prevent instances of loss of directional control on an icy roadbed as a result of engine compression braking on the front drive wheels.

I have noticed that on an icy roadbed my ABS is at its most ACTIVE at extremely low speeds. Sometimes I feel as if the RX is never going to come to a full and complete stop in those circumstances.

I know that many other manufacturers have taken what I consider extreme measures to alleviate engine compression braking on FWD vehicles, Cadillac even uses an over-running clutch, and mayb ethis is Toyota's effort in that regard.

My ABS can moderate braking to prevent wheel lockup at low speeds, but it cannot overcome engine compression braking were it to exist. So I can understand why my RX might upshift just before coming to a full and complete stop and only shift down into first once fully stopped.

[katzjamr]

wwest, just curious, where does lexus VDIM play into your thoughts where Lexus states that the system anticipates problems before the threshold of performance loss.