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Discussion Starter #1
I have a friend that has asked a good question in which I could not find the answer to...

Does the VTM-4 system in the MDX prevent Rollover ?

He said the ML320 has (or will have) a new system available called ESP...Electronic Stability Package. He also claims that FORD will offer this same package on their SUVs in 2001 sometime. He says this system is designed to help stabilize the SUV as it enters into a Rollover by applying power where needed to keep it from flipping.

I looked everywhere, but did not see a focus on rollover from the VTM-4 system.

Thoughts ??
 

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ESP

The VTM-4 does not prevent rollover, I dont think, but rather provides better traction through transfer of torque where needed. The ESP is standard on the ML320 and probably the X5, too. I knew getting an MDX its some safety worthwile feature that I will not get. However, the MDX's wide 66.5 inches track and lower stance is what some claim will help avoid rollover. Its kind of believable but I have yet to see a Crash test (or rollover test) on the MDX to prove its wide track stability on rollover prone maneuvers. Interestingly, on some MDX quality focus group I participated "stabilty control" was one of my safety suggestions so dont be surprised if it shows up on future model MDX.
 

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Discussion Starter #4
This article DOES state that Acura has the Electronic stability control !!!
Towards the bottom in the yellow highlighted section !

Acura really has thought of everything !

I had a feeling that it had it.
 

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Nope. ABC is wrong...

What do you expect from the idiot media? Truth and reality? Ha! :)

ESP helps prevent oversteer/understeer (oversteer contributes to rollovers).
The MDX does not have it. There were long threads on the Edmund's forum about the usefulness of ESP and why the MDX doesn't have it.
 

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Discussion Starter #6
What was I thinking believeing the media !

LOL !

Damn !
 

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The article is talking about electronic stability enhancement system - which is
a very generic term. All the manufacturers have different names for the systems -
ESP, VTM, VDC (Subaru)... Basically, all of them (all wheel drives) do one thing
for sure - shift torque away from wheels that are slipping. In addition, MB's ESP
applies brakes selectively to wheels to avoid slipping and to get control over
the vehicle, plus having a rear differential, it can shift all the torque to a single rear
wheel if need be (which is useful for offroading). I have read that the AUDI's
new Allroad goes one step further - it also adjusts suspension length while
cornering, or if slippage is detected, to gain higher stability/control!

As far as these systems preventing rollover - i think it affects indirectly - an SUV
out of control, skidding all over can eventually tip off! But a higher center of gravity
will always make an SUV more vulnerable for roll-overs...

MDXs wider stance is definitely a key element in MDXs safety along with independent
suspensions.

Check the article on kimmel's index for predicting SUV rollovers in USA today:
http://www.usatoday.com/money/consumer/autos/mauto694.htm

This also lists probabilty for 2000 vehicles - Note, the Odyssey is the best in minivans and
appears along with sedans (acord and prelude are in the same category - 7-9%) And, MDX
is based on Odyssey (odyssey on steroids)

Kimmel says. "If the height is within a few inches of the track width, it makes a big difference."
That's the key difference between MDX and the losers - all other SUVS ;-)
I am curious to know kimmel's index for MDX
 

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Discussion Starter #8
Interesting 411 Bluetooth !

Thanx !

MDX-Obsessed !
 

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Although I wish Acura would have put there VSA system in the MDX you have to remember that no matter how much saferty equipment a car maker puts into a car they can't do a damm thing if you get edjected from the car because you weren't wearing your seat belt. So remember to always wear your seat belt and drive carefully.

Thanks
Evan
 

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Discussion Starter #10
Here..here....I always do that !

:D
 

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Technically, VTM-4 is not stability control. It does provide some of the benefits of traction control, which is a component of stability control.

Stability control systems are actually quite similar. The heart is a computer which computes a number of factors, including yaw rate, vehicle speed, direction, wheel slippage, etc. The system will selectively brake wheels to try to correct an understeer or oversteer situation.

Mercedes' version is called ESP, BMW is DSC (Dynamic Stability Control?), Toyota/Lexus's is VSC, and Honda/Acura's version is VSA (Vehicle Stability Assist).

I'd imagine Acura may add VSA to the MDX in an upcoming model year. It would complement VTM-4 nicely, but it would definitely add to the price.

As far as rollovers go, VTM-4 may help in some cases to prevent loss of control, which leads to rollover. Stability control systems handle some additional scenarios that VTM-4 does not, as do other technologies mentioned here (e.g. the Allroad).

The wider track of the MDX _should_ help too. Unfortunately Acura has not yet revealed how high the MDX's center of gravity is; that's a key to general physical rollover propensity, before you layer on tires, driver behavior, and technologies like VTM-4. The reason I'm cautious about it is that some vehicles which LOOK like they should have a lower center of gravity actually do not (e.g. an ML320 has a lower COG than an RX300).
 

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To the best of my knowledge (after speaking to Acura technical people at length and getting some of their technical excerpts back in 11/00), although the VTM4 system is able to transfer the appropriate torque to prevent side slippage, it serves only as a sophisticated traction control system and was not designed to manage side slippage directly. True stability (side slippage) control requires a set of additional sensors and controls that the MDX definitely does not have. I hope Vehicle Stability Assist (VSA) can be added on later though.

Stability control works to minimize impending side slippage (over and understeering) that can lead to rollover by sensing the onset of side slippage and controlling brakes and/or engine power together. It is is a natural evolution of 4-channel ABS and traction control that can be applied to FWD, RWD or AWD vehicles.

Traction control systems (e.g. VTM4) were designed to detect and manage rotational slippage between the wheels. Side slippage cannot be easily and reliably detected in this way because neither the left nor right wheels may be losing forward adhesion before side slippage occurs. Furthermore, both traction control and 4-channel ABS need to work in concert to reduce the slippage. On the MDX, VTM4 and ABS work independently. Their collective contribution to reducing side slippage is only coincidental and/or subject to the driver's skill or luck.

However, VTM4 may prevent certain side slippage situations that may lead to rollover, though. In the Vehicle Acceleration Torque Control (VATC) mode, torque delivered to the rear wheels leaves more front wheel adhesion for steering the vehicle into and through tight corners.

As an aside, another factor that can contribute to rollover is tire pressure. If the tires do not have sufficient lateral rigidity the wheels/rims can make contact with the road in a side slippage situation and cause the vehicle to trip itself. This certainly contributed to the Explorer/Firestone rollovers. The reduction in tire pressure increases lateral roll of tires.
 

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The sales person told me that VTM-4 system in the MDX prevent Rollover. I don't know and don't want to try... :)hehehee...
 

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This certainly contributed to the Explorer/Firestone rollovers. The reduction in tire pressure increases lateral roll of tires
Lower tire pressure DECREASES the likely hood of roll over precisely because the tires roll instead of the SUV. That is why Ford recommended a lower tire pressure than was typical for SUVs. See http://more.abcnews.go.com/sections/us/dailynews/tiresfrd000820.html or almost any report on the Explorer tire problem. One should be careful when doling out advice to others in this forum about saftey issues.
 

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MDXS said:
This certainly contributed to the Explorer/Firestone rollovers. The reduction in tire pressure increases lateral roll of tires
Lower tire pressure DECREASES the likely hood of roll over precisely because the tires roll instead of the SUV. That is why Ford recommended a lower tire pressure than was typical for SUVs. See http://more.abcnews.go.com/sections/us/dailynews/tiresfrd000820.html or almost any report on the Explorer tire problem. One should be careful when doling out advice to others in this forum about saftey issues.

Back in 1989 Ford discovered and recommended the tire deflation for its Explorer to overcome instability at higher speeds associated with offroad features: high ground clearance and relatively narrow track. Tire deflation lowered the center of gravity, widen the track slightly, increased adhesion, modified the roll characteristics of the tires (and probably produced a somewhat smoother ride too.) But by doing so introduced unexpected variations in the tire performance. Some of these variations may have led to tread separation -- only time (and the courts) will tell.

In the article referenced above, the attorney stated that “Tires will flex more at lower pressure...” I don't disagree with MDXS: reduction in tire pressure increases lateral roll of tires and results in more tire roll and lower SUV rollover. However IMHO, excessive lateral flex allows the rims to come in contact with the pavement more readily (although arguably), tripping the vehicle. Doesn't tire roll eventually lead to the wheel/rim contacting the pavement? This tripping phenomenon was highlighted in a demonstration a few evenings ago on ABC Primetime.

BTW, what advice was I "doling out"? I thought this was a discussion group not a help desk :). However, I apologize to anyone who interpreted my OPINION as advice.
 

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First, It was the Ford engineers that determined lower tire pressure reduced rollover. Second, it is the tires ability to absorb the side force through elastic compression that aids mostly in reducing said rollover. The lowering of the vehicle by lower tire pressure is practically insignificant for reducing rollover. Lastly, I would assume (I'm just guessing here) that the vehicle would rollover long before the tire rims ever came into contact with the ground. I've never heard this being a cause of a rollover.

Also consider that most car rollovers are due to the car hitting a curb or other similar obstruction that catches the tire and flips the car. Some SUV rollovers are also attributable to this.

I don't mean to attack anyone in this group for having an open discussion. Of course, all opinions are welcome. My advice is to be careful when discussing safety issues and try to be clear when stating what is an assumption and what is fact. I would agree that the onus is on the reader more than the writer.
 

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I guess I'm a little confused. Again, this board sounds like people who have never owned an SUV before. The number one prevention to rollover is proper driving technigue. It ain't a sports car so don't drive it like one! I can't imagine that the MDX has a high potential for rollover just because of it's wider footprint and not so high center of gravity. Jeez.. go look at an Isuzu Trooper or something similar. They look like a small gust of wind could blow them over.

.. Still impatiently waiting for my MDX!
 

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MDXS said:
I've never heard this being a cause of a rollover.
For the most part, we seem to be in violent agreement. However, the observation (not assumption) of rim tripping as a factor is based on a demonstration on a recent nationally televised ABC documentary. Before this demonstration, tripping over external obstacles (which the driver has no control over) had been acknowledged as a factor but never rim tripping. ABC may have been mistaken here as they were in their web supplement regarding the existence of ESP (VSA) on Acura SUVs. Nevertheless, there may be something to it.

dancall said:
I guess I'm a little confused. Again, this board sounds like people who have never owned an SUV before.
According to Acura sales and technical teams, Acura targeted existing Acura drivers. Several years ago, they realized that a segment of Acura drivers (non SUV drivers) were looking for something with more utility but with similar performance and quality. Longtime Acura drivers (myself included) began looking at more appropriate family vehicles like minivans and SUVs. Acura had none to offer. The rebadged Izusu Trooper not withstanding. To stem the erosion of their installed base they developed the MDX. Better late than never. It would be interesting to know how many MDX owners are first time SUV drivers though.

dancall said:
The number one prevention to rollover is proper driving technique
May be you or some other seasoned SUV drivers out there can outline what "proper driving technique" is for an SUV.

Originally posted by Acura4Life
Does the VTM-4 system in the MDX prevent Rollover ?
WRT the original thread topic, we have already been in a potential oversteer scenario with the MDX and it performed well. On dry pavement at highway speed my wife (a lifelong sedan driver) was forced to brake and suddenly swerve to avoid some road debris (a set of golf clubs I believe) and back to avoid a slower car ahead. The MDX managed flawlessly. It was hard to say whether VTM-4 played a role since we were decelerating rapidly. The 4-channel ABS may have played a more significant role in this case.
 
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Originally posted by Acura4Life
Does the VTM-4 system in the MDX prevent Rollover ?
WRT the original thread topic, we have already been in a potential oversteer scenario with the MDX and it performed well. On dry pavement at highway speed my wife (a lifelong sedan driver) was forced to brake and suddenly swerve to avoid some road debris (a set of golf clubs I believe) and back to avoid a slower car ahead. The MDX managed flawlessly. It was hard to say whether VTM-4 played a role since we were decelerating rapidly. The 4-channel ABS may have played a more significant role in this case. [/B][/QUOTE]

I would have to say no, VTM-4 had no role in this maneuver. Why? Because VTM-4 (Variable <b>Torque Management</b> 4WD) requires torque, in other words throttle pedal application, to work. Under braking, there is just about nothing going to the system; VTM-4 was in 100% front wheel drive mode since you were not accelerating.

Don't forget also, that VTM-4 doesn't employ steering angle sensors, lateral movement sensors or yaw sensors as stability control systems <b>require</b>. VTM-4 only utilises the ABS wheel speed sensors to detect wheel slippage and as such, it doesn't know if you're about to skid at all.

Hope this helps!
 

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Wen,

Now I understand. I've never heard of a rim coming in contact with the road causing a rollover, but I do not doubt what you saw on the ABC news show is true. I see it can be dangerous to drive an SUV with too low a tire pressure because of this possibility. Thank you for clarifying this. I agree with dancall that the MDX's wide stance minimizes the chance of rollover. This was demonstrated during my test drive when the salesman whipped the wheel to produce a very sharp turn. The MDX stayed well planted.

I do not see how VTM would aid in reducing rollover. Proper driving technique is the best solution.
 
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