• Apr 14, 2010
The latest blow to the formerly sterling reputation of Toyota came this week when Consumer Reports gave the new Lexus GX460 a "Do Not Buy" rating. It's not often that CR gives its worst rating to a vehicle and it's never happened to a Toyota or Lexus product before. In light of recent recall woes, Toyota is taking this news very seriously and has stopped selling the Lexus GX while it investigates the issue.

The reason for the dire rating is what CR considers a major safety risk with the new GX. During the publication's handling tests, the CR drivers experienced significant oversteer (the back end of the vehicle sliding sideways) before the electronic stability control intervened and brought the SUV back under control.

Cornering oversteer is something automakers try to avoid, except on high-performance sports cars. On SUVs with a high center of gravity, this is an especially serious problem because if the vehicle hits a curb, shoulder or other impediment while sliding it's more prone to roll over. During a previous test with the Toyota 4Runner, which shares its basic platform with the Lexus GX, CR didn't experience the same problem. Follow the jump as we examine some possible explanations for the disparity between these two SUVs.

When electronic stability control systems (ESC) were first adopted in the late-1990s, they went on high-end luxury vehicles followed by Sport Utility Vehicles. SUVs have a higher center of gravity than cars and thus an increased tendency to roll over. The rollover tendency is exacerbated when the vehicle is sliding sideways and ESC was found to have a significant mitigating effect on rollovers. As a result, ESC is almost universal on SUVs and crossovers now and will be fully required for all vehicles by 2012.

According to Toyota spokesman Bill Kwong, while the 4Runner and GX share a frame and basic dimensions, there are substantial differences between the two. The Toyota is only available with a V6, while the Lexus has a V8. The Lexus also carries considerably more standard equipment, and as a result the GX is over 600 pounds heavier than the 4Runner. Their suspension setups are also substantially different. Therefore, the two SUVs can be expected to behave quite differently on the road.




According to test engineer Jake Fisher at Consumer Reports, they do two different emergency handling tests. The first is a double lane change to evaluate obstacle avoidance maneuvers. In this test, the GX had no problem at all. The second test is a handling course set up on a paved vehicle dynamics pad. The course has a variety of different types of corners with a total length of just over a mile. The maximum speed through this course is typically no more than 50 mph.

The CR engineers generally do two laps of the course. Over the first lap they drive through at speed, exploring the limits of the vehicle without doing anything unusual. On the second lap the drivers push harder to see what happens in more extreme conditions. One of the tests is too see what happens when the driver lifts off the throttle mid-turn. Drivers of classic Porsche 911s or Corvairs are all too familiar with the results.



Most modern vehicles will simply understeer straight ahead at the limit. The GX, on the other hand, suddenly swung its rear end sideways. The ESC did not immediately intervene and bring it back in line. Instead, it responded late and because of the degree of instability, it brought the vehicle to a complete halt. Just to make sure this wasn't a problem with one particular vehicle, CR procured a second example that exhibited the same behavior. This is particularly surprising because Toyota/Lexus products have a reputation for having overly aggressive ESC systems that tend to intervene early and often.

Fisher also confirmed that the brakes were not applied when the oversteer happened, which rules out the possibility of the electronic brake force distribution (dynamic brake proportioning) applying the rear brakes too aggressively, which could have caused the oversteer.



There are several factors that could be coming into play here. First, Lexus engineers seem to have tuned the GX suspension in such a way that makes it inherently unstable in lift-throttle conditions. This can be done through a combination of spring and damping rates, bushings, tire choices and suspension geometry. It's possible this was done to try to make the handling more responsive and then rely on the ESC to keep things under control. As long as the ESC is doing its job, there's nothing wrong with this, but if the electronics don't do the job, drivers will have a real problem.

On the electronic control side, several things could be at play. It's possible that the engineers simply didn't calibrate the software properly for the characteristics of the GX. When developing vehicles, there are always a set of performance requirements defined with standard tests for verification. It appears that Lexus engineers and their ESC supplier may not have included a mid-corner lift in their test regimen and thus never experienced this behavior. If so, this is a major oversight on the part of Toyota/Lexus. In that case, the ESC could be applying too much brake pressure on the inside front wheel, which could make the problem worse.



Another related software issue is filtering and calibration of input signals. ESC relies on signals such as steering angle, lateral and longitudinal acceleration, yaw rate (the rate of rotation around the vertical axis), brake and throttle position, among others. All of these sensors can experience drift and noise based on vibration, temperature and age. Accelerometers can also be fooled by factors like banked turns. The engineers incorporate algorithms in the control software to zero and adjust these signals if the vehicle is not moving. They also derive signals from each sensor to cross check the others. There is also software that filters out noise from electrical or vibration sources.

If a filter is too aggressive it can result in delays causing the instability to not be detected until it is too late. If a zeroing or self-calibration algorithm is not functioning properly it can have the same effect. It could be a combination of any or all of these factors. Without instrumenting a vehicle, we can't say for sure, but Fisher and Kwong both told Autoblog that Toyota engineers have been in contact with CR engineers in the past two days and are investigating the situation as you read this.

In addition to software, it's also possible that it could be an issue with the ESC hydraulic control unit (HCU). If the HCU can't build brake pressure fast enough, it might not be able to apply enough brake pressure to keep the vehicle under control.



One other possible scenario is that the brake calipers might be knocking back more than expected during repeated cornering. Under lateral loading, the pistons in the brake caliper can be pushed back, which then requires more brake pressure to be applied before braking force is generated. ESC typically compensates for this by pre-charging the brakes, which brings the pad up to the rotor before the brakes are needed. This can typically be corrected with a software calibration change.

So how can Toyota fix this? Most likely it can be corrected by a software update to the ESC. The extent of the software updates is unknown at this time. If it only requires revised calibrations, the fix could come pretty quickly, perhaps within days. If it requires algorithm changes, more extensive testing will be needed and it could take longer. It's also possible although far less likely that Toyota may have to resort to a hardware change that could involve new springs, dampers, bushings or anti-roll bars. Either way, Toyota/Lexus engineers will surely be taking a fresh look at their ESC performance requirements in the future, and until a fix is found, the stop-sale on the GX will continue.


I'm reporting this comment as:

Reported comments and users are reviewed by Autoblog staff 24 hours a day, seven days a week to determine whether they violate Community Guideline. Accounts are penalized for Community Guidelines violations and serious or repeated violations can lead to account termination.


    • 1 Second Ago
  • 105 Comments
      • 4 Years Ago
      So Toyota is not doing boring cars anymore, while the media are still trying to kill it.

      Yes the driving dynamics is to be corrected, and yes, if it wasn't Toyota everything would have been much more quite.
      • 4 Years Ago
      As much as I hate CR, that was a crazy nice drift!
        • 4 Years Ago
        And some people are saying that Toyota doesn't make fun cars anymore... acceleration + powerslides... That's what I call the "fun" formula.
        • 4 Years Ago
        I thought the same thing!

        Ken Block! Your new drift machine is here.
        • 4 Years Ago
        That's one bad#$ drift right there! I was hoping the driver would gas it once he regained control to finish off that corner. I, for one, would love to see that thing compete in Formula Drift.
        • 4 Years Ago
        Seriously, power out!
        • 4 Years Ago
        Seriously. They should have turned the ESC off completely and kept going!
        • 4 Years Ago
        Yeh...it drifted to a halt!
      • 4 Years Ago
      As much as I hate CR, that was a badass drift.
        • 4 Years Ago
        +1... Epic.
        • 4 Years Ago
        It's hard not to imagine how this would have been handled by CR had Toyota not been crowned 2010's Whipping Boy car company.
        I'm just astounded by human nature; it's become a veritable witch hunt.

        Would this have been handled the same two or three years ago?
        • 4 Years Ago
        Isn't the GX a rebadged Toyota Land Cruiser and not the 4Runner?
        • 4 Years Ago
        I want one of those now. Just to drift it!
        • 4 Years Ago
        @ Lee

        +1

        Damn man you are so quick!!!
        • 4 Years Ago
        @rgt4488:

        You're thinking of the LX. The GX is in fact a 4Runner sibling. But, ya know, seen one overweight luxury SUV, pretty much seen 'em all.
        • 4 Years Ago
        Introducing..the Lexus GX-F
        • 4 Years Ago
        that suv is badass. they should brand it as a sport SUV.
      • 4 Years Ago
      Some crazy JDM drift-action going on right there... which might be cool in a Nissan Z or FL-A, but not so much on a top-heavy SUV.

      Seems like it should be fairly easy to fix with a software update... not that I can really see a good reason to every buy a vehicle like the GX anyways.
      • 4 Years Ago
      I thought that was a feature?
        • 4 Years Ago
        No, it's not a MacBook.

        Well, a Don't Buy is pretty good. Just ask the Bluth family.
      • 4 Years Ago
      What would happen at higher speed? Say, at 80 mph on the highway... Remember the original Audi TT?
      • 4 Years Ago
      Again the basic is unsufficient engineering, especially extensive simulation of all possible situations, time cost testing and taking appropriate corrective actions like change of vehicle's hardware and software. And here is high end SUV, one of most expensive!
      • 4 Years Ago
      i am no expert, but i rather slide the tail around and halt then understeer into a tree....
      • 4 Years Ago
      It's time to give Consumer Reports a "Do Not Buy" rating.
      • 4 Years Ago
      I'm pretty sure I drifted a Grand Cherokee a hell of a lot longer than that the last time I got stuck with one as a rental, I don't see CR bagging on those things.
      • 4 Years Ago
      That is some nice drifting action. Maybe this will kill the SUV craze, and people will drive cars again.
      • 4 Years Ago
      "Under lateral loading, the pistons in the brake caliper can be pushed back, which then requires more brake pressure to be applied before braking force is generated."

      That is incorrect. The same brake pressure always results in the same braking force. (There are a few assumptions made in that statement, but they're pretty reasonable ones.) Knockback will result in increased pedal travel, but not pedal force or brake system pressure.
    • Load More Comments