Someone help me understand how VSC works...

kdmorse · 12-24-2006, 06:02 AM

And no, I'm not talking about Traction Control - I know the difference.

Just so you know where I'm coming from...

Before my 2006 Prius, I drove a 1995 Saturn Station Wagon, and I drove it for 10+ Years. While it came with fairly crappy tires (The sort of firestone's that got recalled for spontaneous blowouts) - it was always very good to me, and was a very solid, surefooted car. Once the firestones went bald, I put on some of Michelins best, and had been driving on them for the past 5 years. This was also a car with no VSC, early generation anti-lock breaks, and very minor first-gen traction control. And it's what I got used to, got to know the feel of, and could handle in all kinds of weather. I could easily recover if the car began to slip or slide, could easily control turns with a little bit of slip in them, as there was nothing more to it than simple physics, inertia, and friction.

Now, I love my Prius, but it doesn't have the best traction in the world. And compared to what I'm used to, it feels very, very slippery when the roads are wet. (OEM Tires). And there hasn't been too much bad weather since I bought it in January, so I don't have that feel for how it behaves when it starts to slip that I had in my old car. But what happened yesterday freaked me out but good, and *could* have been quite bad.

The roads were wet, and I was making a right turn into a shopping center of of a 55MPH highway. I slowed down for the turn, and would not have said I was driving too fast for conditions - however the fact that the car slipped as badly as it did means that I was driving too fast by definition. I can't actually tell you what my speed was at the moment I tried to turn. As I entered the turn, the car began to slide a little. At this point, I pretty much lost all control. The car beeped at me like mad, lights blinked, and it didn't seem to pay any attention to my attempts to correct it's direction, and I swear it braked on it's own in a way that pulled me to the left, preventing me from completing my turn. ie - it was actively preventing me from turning right, as if it thought turning to the right was the bad thing that was happening. Of course, I had already completed half the turn, so this meant heading into the oncoming lane as I was only able to complete about 45 degrees of a 90 degree turn.

Anyway, having no directional control for a split second (which ain't fun), heading straight towards the curb on the other side of the road, I did the only sane thing I could think of, I slammed on the breaks. The car slowed dramatically, and I was then able to regain control, and I returned to my rightful lane. Fortunately, there was noone exiting the shopping center at that exact moment, because if they had been, I would have driven straight into them.

Yes, yes, I'll take that turn (and all others) much slower next time... Under the circumstances - I'll take them little-old-lady slow.

But my whole question here... is does anyone know exactly VSC is supposed to do for you, how exactly it works? I swear it kicked in after completing half a turn, and then tried it's damnedest to keep the car going in a perfectly straight line, which under the circumstances was about the worst possible thing it could do. I'm quite certain that under those circumstances had my old Saturn started to slip, I could have corrected it and made it round the turn with only a little slide at worst. (Although I'm not sure my Saturn would have slipped at all under those circumstances). Perhaps if I understood the VSC a bit better, I won't end up fighting it for control of the car should something like this ever happen again.

Any advice on understanding it?

(Yes, get better tires, thinking about it)
(Yes, drive slower, thinking about it

)

-Ken

john1701a · 12-24-2006, 08:43 AM

<div class='quotetop'>QUOTE(kdmorse @ Dec 24 2006, 05:02 AM) [snapback]366238[/snapback]</div>

Quote:

I did the only sane thing I could think of, I slammed on the breaks[/b]

To restore grip, the best choice is to press on the accelerator instead. With a front-wheel drive car, you'll actually be able to pull out of the skid. It's pretty cool, after you get past the counter-intuitive nature. Watch the "Cars" DVD. The "turn right to go left" suggestion doesn't make any sense at first either.

Pressing firmly on the brakes is the next choice. Slamming on them is only a last resort.

tumbleweed · 12-24-2006, 11:34 AM

I have only seen the VSC activate a couple of times and both times I did it on purpose, in an empty parking lot just to see how it would react. Both times it simply used brakes and backed off the throttle a bit to keep the car from sliding but the car continued turning at the same radius.

I have never had the experience you describe so I can't really comment on it. You said "As I entered the turn, the car began to slide a little." did it start to slide in the front, the rear, or both ends?

DaveinOlyWA · 12-24-2006, 12:03 PM

gee... dont know how fast you were going??? well... ya didnt get into a wreck and you admit to driving too fast for conditions, so sounds like VSC did its job.

the lack of details really makes any other comments difficult. from your description, you were either trying to make a turn at 40 mph, or were in very slippery road conditions.

what was the road conditions??
weather conditions??
temperatures??
any black ice.??

sounds to me that you entered a completely unexpected handling situation and VSC saved you.

your feelings of panic are normal. in emergency situations only a small fraction of us would handle it with any kind of cool. as soon as VSC takes over, that feeling of having no control is intense.

try using VSC when you are ready for it. that will give you much better insight on its benefits. a few weeks after on snowstorm (illustrated on the Monday night football game bet Seattle and Oakland) i had the perfect opportunity to try VSC. going down an empty hill in Tacoma. temps in the low 30's, road about 80% glare ice, reasonably steep slope. i got up to about 35 mph. then braked, and at the same time did two lane changes over two lanes and back to the middle.

i pulled the maneuver off without any real issues at all. in a car without it, i would have gone completely sideways with the back end leading.

jburns · 12-24-2006, 01:47 PM

<div class='quotetop'>QUOTE(john1701a @ Dec 24 2006, 08:43 AM) [snapback]366264[/snapback]</div>

Quote:

To restore grip, the best choice is to press on the accelerator instead. With a front-wheel drive car, you'll actually be able to pull out of the skid. It's pretty cool, after you get past the counter-intuitive nature. Watch the "Cars" DVD. The "turn right to go left" suggestion doesn't make any sense at first either.

[/b]

Other cars yes but if the front wheels start to slip at all, which they probably will if you are already drifting sideways and hit the gas, the traction control will kill the power. I am very unimpressed with the emergency handling of the Prius. The VSC and traction control become less and less effective the more serious the situation until they actually can prevent you from regaining control of the vehicle.

**Tideland Prius** · 12-24-2006, 02:18 PM

<div class='quotetop'>QUOTE(kdmorse @ Dec 24 2006, 03:02 AM) [snapback]366238[/snapback]</div>

Quote:

And no, I'm not talking about Traction Control - I know the difference.

Just so you know where I'm coming from...

Before my 2006 Prius, I drove a 1995 Saturn Station Wagon, and I drove it for 10+ Years. While it came with fairly crappy tires (The sort of firestone's that got recalled for spontaneous blowouts) - it was always very good to me, and was a very solid, surefooted car. Once the firestones went bald, I put on some of Michelins best, and had been driving on them for the past 5 years. This was also a car with no VSC, early generation anti-lock breaks, and very minor first-gen traction control. And it's what I got used to, got to know the feel of, and could handle in all kinds of weather. I could easily recover if the car began to slip or slide, could easily control turns with a little bit of slip in them, as there was nothing more to it than simple physics, inertia, and friction.

Now, I love my Prius, but it doesn't have the best traction in the world. And compared to what I'm used to, it feels very, very slippery when the roads are wet. (OEM Tires). And there hasn't been too much bad weather since I bought it in January, so I don't have that feel for how it behaves when it starts to slip that I had in my old car. But what happened yesterday freaked me out but good, and *could* have been quite bad.

The roads were wet, and I was making a right turn into a shopping center of of a 55MPH highway. I slowed down for the turn, and would not have said I was driving too fast for conditions - however the fact that the car slipped as badly as it did means that I was driving too fast by definition. I can't actually tell you what my speed was at the moment I tried to turn. As I entered the turn, the car began to slide a little. At this point, I pretty much lost all control. The car beeped at me like mad, lights blinked, and it didn't seem to pay any attention to my attempts to correct it's direction, and I swear it braked on it's own in a way that pulled me to the left, preventing me from completing my turn. ie - it was actively preventing me from turning right, as if it thought turning to the right was the bad thing that was happening. Of course, I had already completed half the turn, so this meant heading into the oncoming lane as I was only able to complete about 45 degrees of a 90 degree turn.

Anyway, having no directional control for a split second (which ain't fun), heading straight towards the curb on the other side of the road, I did the only sane thing I could think of, I slammed on the breaks. The car slowed dramatically, and I was then able to regain control, and I returned to my rightful lane. Fortunately, there was noone exiting the shopping center at that exact moment, because if they had been, I would have driven straight into them.

Yes, yes, I'll take that turn (and all others) much slower next time... Under the circumstances - I'll take them little-old-lady slow.

But my whole question here... is does anyone know exactly VSC is supposed to do for you, how exactly it works? I swear it kicked in after completing half a turn, and then tried it's damnedest to keep the car going in a perfectly straight line, which under the circumstances was about the worst possible thing it could do. I'm quite certain that under those circumstances had my old Saturn started to slip, I could have corrected it and made it round the turn with only a little slide at worst. (Although I'm not sure my Saturn would have slipped at all under those circumstances). Perhaps if I understood the VSC a bit better, I won't end up fighting it for control of the car should something like this ever happen again.

Any advice on understanding it?

(Yes, get better tires, thinking about it)
(Yes, drive slower, thinking about it

)

-Ken
[/b]

Your experience seems to mimic mine on two occasions when we had that snowfall on the west coast at the end of November. On two separate occasions at two different intersections, I understeered and nearly hit the oncoming car (in both cases, there just so happened to be a car in the oncoming lane).

The car did what you described. It understeered (which I think is what you're describing when you said the car seemed to want to go "straight" on instead of turning right), VSC came on (the usual beeping and flashing) and the car corrected itself. I almost gave that girl in the other car a heart attack. She was stopped at the stop sign and I could see her eyes getting wider as I plowed straight towards her car.

So, how does VSC work.

It has a yaw sensor to determine whether you're going off your intended path (under or oversteer). It will retard the throttle and/or apply the brakes to each wheel individually to regain traction.

The best thing I can suggest to you right now is to go to an empty parking lot and re-enact your situation. However, you can substitute speed with steering angle. IOW, instead of going the same speed as the scenario above, just yank the wheel further than usual. That will induce the same characteristics. That way, you don't have to speed and thus can use a smaller parking lot.

Just yank the wheel, let the car understeer and just see how VSC works.

cwerdna · 12-24-2006, 03:32 PM

See my post at http://priuschat.com/index.php?s=&show...st&p=354141.

All cars have their handling and grip limits so it's still possible to spin or go out of control or spin out w/stability control. The Prius isn't a sports car nor does it have very wide or grippy tires.

To the OP: BTW, in the two cases where you used the word "breaks", you should've used "brakes".

donee · 12-24-2006, 05:24 PM

Hi All,

I do not have VSC, but do have a Prius.

VSC works by sensing the car's "yaw". Look down at the top of the car, and imagine the car turning left or right around the an axis through the center of mass (gravity). That is Yaw.

The VSC assumes that when the car is Yaw'ing in oposition to driver command, the wheels are slipping sideways. This may or may not be the case with the stock Prius.

The unmodified Prius has oscilatory yaw response due to chasis flex during high chasis loads. Many of us have replaced the stock floor stiffening plate with the BT Tech plate to help with this situation. Back to the unmodified Prius. The car can yaw dramatically, even with the tires firmly planted. The body flex is steering the tires, and the tires are not slipping, but the steering is yawing the car. VSC will act on it.

I had similar a similar thing happen to me even though my car does not VSC. I was turning to the left on the inside lane of a two lane road, onto a two lane road. All of sudden the car just squirmed into the outside lane, and there was no skiding. Luckily it was early in the morning and there was no other traffic. There was no skiding because of course VSC did not activate (don't have it). I decided that day to order the BT Tech chasis stiffening plate.

As to the comment that the Prius is not a sport's car, well, neither is Saturn SL2 (my previous car) or the OP's SL wagon. But neither of these cars have this problem. All of these cars are similar in weight to the Prius and my SL2 actually used the exact same tire size as the Prius. Because its nearly the same weight as the Prius, and it had 15 inch rims. These identical tires with the same weight on them will slip at the same side load.

Now, what happens when you put an intellegent controller (human or computer) in control of the car during rapid yaw events, and the car starts to squirm. The human driver gets all confused and induces PIO (pilot induced oscillation). The VSC does the same thing, only its steering with differential brake inputs, not steering wheel angle. The basic problem here is the intelligent controllers are used to rapid yaw being due to sliding, not chasis deflection steering. Reacting to the rapid yaw as if its sliding, is the wrong thing to do when the actual cause is Prius body flex misalligning wheel angles. Automatic controls can easily become oscillatory, or drive the system to an out-of-control state (steer the wrong way) when the basic structure of the machine has a non-linear response. Steer left should cause the car to turn left, not right after some load limit is reached (what happened to me).

With the BT Tech plate the car is much more linear in response to steering inputs and does not squirm back and forth under load. I recommend you get one. I actually skidded around a wet curve on the way home last friday, and pulled into a recovery drift with up throttle. No problem. This would have been impossible with a stock Prius. Thank You BT.

kdmorse · 12-24-2006, 07:46 PM

Thank you all for your input.. a few responses...

<div class='quotetop'>QUOTE(john1701a @ Dec 24 2006, 08:43 AM) [snapback]366264[/snapback]</div>

Quote:

To restore grip, the best choice is to press on the accelerator instead. With a front-wheel drive car, you'll actually be able to pull out of the skid. It's pretty cool, after you get past the counter-intuitive nature. Watch the "Cars" DVD. The "turn right to go left" suggestion doesn't make any sense at first either.

Pressing firmly on the brakes is the next choice. Slamming on them is only a last resort.
[/b]

I believe that's exactly what I tried first, as it's exactly what I would have done in my previous car. I think the regular traction control kicked in and stopped me though, and I think that's when VSC started yelling at me. (Very hard to tell, it may have kicked in independently). With all that going on, I had the immediate feeling that attempting to pull out of the skid was *not* working, and shifted to brakes instead. Because of the approaching curb, I didn't really have time to experiment.

The brakes however performed perfectly, no complaints there. They slowed the car dramatically and quickly without locking up, and as soon as they restored proper traction the car turned to the right as requested.

<div class='quotetop'>QUOTE(tumbleweed @ Dec 24 2006, 11:34 AM) [snapback]366281[/snapback]</div>

Quote:

You said "As I entered the turn, the car began to slide a little." did it start to slide in the front, the rear, or both ends?[/b]

Not quite sure how to answer that question. Best as I can describe it, once I was about 45 degrees through the turn, the center of mass of the car wanted to continue traveling in a straight line (at that 45 degree angle), while the car continued to rotate beyond 45 degrees. It seems that the instant the two directions were not the same, VSC kicked in.

<div class='quotetop'>QUOTE(DaveinOlyWA @ Dec 24 2006, 12:03 PM) [snapback]366304[/snapback]</div>

Quote:

what was the road conditions??
weather conditions??
temperatures??
any black ice.??
[/b]

Wet. It had been raining all day, but it had stopped raining some earlier. Just wet pavement, not large puddles. Weather was 55F-60F, so no chance of ice.

Quote:

sounds to me that you entered a completely unexpected handling situation and VSC saved you.
[/b]

I'm not convinced of that, but will withhold final judgment until I understand it better.

<div class='quotetop'>QUOTE(donee @ Dec 24 2006, 05:24 PM) [snapback]366373[/snapback]</div>

Quote:

...
The human driver gets all confused and induces PIO (pilot induced oscillation).
...
[/b]

I'm still working my way through your post - but there was most certainly a left to right shake while this was occurring, as if the car was not 100% sure which way it wanted to correct, or was correcting back and forth in both directions alternatively. It felt very much like the sort of feedback loop that can occur when two separate systems (one computer, one human), are trying to compensate for each other, each end of overcompensating, and nobody wins.

I will have to go find an empty parking lot on a wet day... And I will reconsider the BT plate.

Thanks,

-Ken

Robnerika · 12-25-2006, 09:34 AM

Hi,

This is my first post...hope I'm not violating any protocols....Just bought an 07 with package 2 two days ago. Don't have the car yet. I had heard about the BT tech plate from my boss who has one installed and strongly recommended it. The Prius we bought has the VSC. I'm wondering if adding the plate would help the VSC, work against it, or be unaffected by it? Logically it seems that it would stiffen the chassis and make it less likely that the VSC would be engaged if the yaw was due to chassis twisting. Would you be willing to share your thoughts on that?

BEK

<div class='quotetop'>QUOTE(donee @ Dec 24 2006, 05:24 PM) [snapback]366373[/snapback]</div>

Quote:

Hi All,
I do not have VSC, but do have a Prius.

VSC works by sensing the car's "yaw". Look down at the top of the car, and imagine the car turning left or right around the an axis through the center of mass (gravity). That is Yaw.

The VSC assumes that when the car is Yaw'ing in oposition to driver command, the wheels are slipping sideways. This may or may not be the case with the stock Prius.

The unmodified Prius has oscilatory yaw response due to chasis flex during high chasis loads. Many of us have replaced the stock floor stiffening plate with the BT Tech plate to help with this situation. Back to the unmodified Prius. The car can yaw dramatically, even with the tires firmly planted. The body flex is steering the tires, and the tires are not slipping, but the steering is yawing the car. VSC will act on it.

I had similar a similar thing happen to me even though my car does not VSC. I was turning to the left on the inside lane of a two lane road, onto a two lane road. All of sudden the car just squirmed into the outside lane, and there was no skiding. Luckily it was early in the morning and there was no other traffic. There was no skiding because of course VSC did not activate (don't have it). I decided that day to order the BT Tech chasis stiffening plate.

As to the comment that the Prius is not a sport's car, well, neither is Saturn SL2 (my previous car) or the OP's SL wagon. But neither of these cars have this problem. All of these cars are similar in weight to the Prius and my SL2 actually used the exact same tire size as the Prius. Because its nearly the same weight as the Prius, and it had 15 inch rims. These identical tires with the same weight on them will slip at the same side load.

Now, what happens when you put an intellegent controller (human or computer) in control of the car during rapid yaw events, and the car starts to squirm. The human driver gets all confused and induces PIO (pilot induced oscillation). The VSC does the same thing, only its steering with differential brake inputs, not steering wheel angle. The basic problem here is the intelligent controllers are used to rapid yaw being due to sliding, not chasis deflection steering. Reacting to the rapid yaw as if its sliding, is the wrong thing to do when the actual cause is Prius body flex misalligning wheel angles. Automatic controls can easily become oscillatory, or drive the system to an out-of-control state (steer the wrong way) when the basic structure of the machine has a non-linear response. Steer left should cause the car to turn left, not right after some load limit is reached (what happened to me).

With the BT Tech plate the car is much more linear in response to steering inputs and does not squirm back and forth under load. I recommend you get one. I actually skidded around a wet curve on the way home last friday, and pulled into a recovery drift with up throttle. No problem. This would have been impossible with a stock Prius. Thank You BT.
[/b]

12-24-2006, 06:02 AM	#1
kdmorse Senior Member Join Date: Oct 2005 Location: Germantown, MD Posts: 198 My Car: 2006 Prius Model: Package: #7 Thanks: 0 Thanked 0 Times in 0 Posts Friends: 1	And no, I'm not talking about Traction Control - I know the difference. Just so you know where I'm coming from... Before my 2006 Prius, I drove a 1995 Saturn Station Wagon, and I drove it for 10+ Years. While it came with fairly crappy tires (The sort of firestone's that got recalled for spontaneous blowouts) - it was always very good to me, and was a very solid, surefooted car. Once the firestones went bald, I put on some of Michelins best, and had been driving on them for the past 5 years. This was also a car with no VSC, early generation anti-lock breaks, and very minor first-gen traction control. And it's what I got used to, got to know the feel of, and could handle in all kinds of weather. I could easily recover if the car began to slip or slide, could easily control turns with a little bit of slip in them, as there was nothing more to it than simple physics, inertia, and friction. Now, I love my Prius, but it doesn't have the best traction in the world. And compared to what I'm used to, it feels very, very slippery when the roads are wet. (OEM Tires). And there hasn't been too much bad weather since I bought it in January, so I don't have that feel for how it behaves when it starts to slip that I had in my old car. But what happened yesterday freaked me out but good, and could have been quite bad. The roads were wet, and I was making a right turn into a shopping center of of a 55MPH highway. I slowed down for the turn, and would not have said I was driving too fast for conditions - however the fact that the car slipped as badly as it did means that I was driving too fast by definition. I can't actually tell you what my speed was at the moment I tried to turn. As I entered the turn, the car began to slide a little. At this point, I pretty much lost all control. The car beeped at me like mad, lights blinked, and it didn't seem to pay any attention to my attempts to correct it's direction, and I swear it braked on it's own in a way that pulled me to the left, preventing me from completing my turn. ie - it was actively preventing me from turning right, as if it thought turning to the right was the bad thing that was happening. Of course, I had already completed half the turn, so this meant heading into the oncoming lane as I was only able to complete about 45 degrees of a 90 degree turn. Anyway, having no directional control for a split second (which ain't fun), heading straight towards the curb on the other side of the road, I did the only sane thing I could think of, I slammed on the breaks. The car slowed dramatically, and I was then able to regain control, and I returned to my rightful lane. Fortunately, there was noone exiting the shopping center at that exact moment, because if they had been, I would have driven straight into them. Yes, yes, I'll take that turn (and all others) much slower next time... Under the circumstances - I'll take them little-old-lady slow. But my whole question here... is does anyone know exactly VSC is supposed to do for you, how exactly it works? I swear it kicked in after completing half a turn, and then tried it's damnedest to keep the car going in a perfectly straight line, which under the circumstances was about the worst possible thing it could do. I'm quite certain that under those circumstances had my old Saturn started to slip, I could have corrected it and made it round the turn with only a little slide at worst. (Although I'm not sure my Saturn would have slipped at all under those circumstances). Perhaps if I understood the VSC a bit better, I won't end up fighting it for control of the car should something like this ever happen again. Any advice on understanding it? (Yes, get better tires, thinking about it) (Yes, drive slower, thinking about it ) -Ken __________________ 2006 Black Package #7 Dark Grey Interior Headlight Flasher EV Mod

12-24-2006, 11:34 AM	#3
tumbleweed Senior Member Join Date: Oct 2005 Location: Eastern Oregon Posts: 1,692 My Car: 2010 Prius Model: V Package: Adv. Technology Thanks: 33 Thanked 104 Times in 84 Posts Friends: 0	I have only seen the VSC activate a couple of times and both times I did it on purpose, in an empty parking lot just to see how it would react. Both times it simply used brakes and backed off the throttle a bit to keep the car from sliding but the car continued turning at the same radius. I have never had the experience you describe so I can't really comment on it. You said "As I entered the turn, the car began to slide a little." did it start to slide in the front, the rear, or both ends? __________________ Tom

12-24-2006, 12:03 PM	#4
DaveinOlyWA 3rd Time was Solariffic!! Join Date: Apr 2004 Location: South Puget Sound, WA Posts: 12,375 My Car: 2010 Prius Model: IV Package: Solar Roof Thanks: 24 Thanked 121 Times in 103 Posts Friends: 10	gee... dont know how fast you were going??? well... ya didnt get into a wreck and you admit to driving too fast for conditions, so sounds like VSC did its job. the lack of details really makes any other comments difficult. from your description, you were either trying to make a turn at 40 mph, or were in very slippery road conditions. what was the road conditions?? weather conditions?? temperatures?? any black ice.?? sounds to me that you entered a completely unexpected handling situation and VSC saved you. your feelings of panic are normal. in emergency situations only a small fraction of us would handle it with any kind of cool. as soon as VSC takes over, that feeling of having no control is intense. try using VSC when you are ready for it. that will give you much better insight on its benefits. a few weeks after on snowstorm (illustrated on the Monday night football game bet Seattle and Oakland) i had the perfect opportunity to try VSC. going down an empty hill in Tacoma. temps in the low 30's, road about 80% glare ice, reasonably steep slope. i got up to about 35 mph. then braked, and at the same time did two lane changes over two lanes and back to the middle. i pulled the maneuver off without any real issues at all. in a car without it, i would have gone completely sideways with the back end leading. __________________ My Blue 2010 : Last tank 541.9 @ 49.48 pump (56.7 MFD) 5.54 CPM, 21 MPH, Lifetime:5442.2 miles 56.5 MPG pump. (62.22 MFD) 4.72 CPM. Summer MPG 57.4 Winter: 49.5 My 2006 SPM: Last tank 376.6 miles @38.21 pump (40.8 MFD) 7.17 cpm winter mpg 49.64 summer mpg 53.41 lifetime: 42,563.5 miles 51.5 mpg pump (52.7 mpg MFD) 5.51 cpm My 2007 Zenn total "fuel cost" $166.58 on "about" 9599.7 miles. 1.74 cents per mile (granted i plug in for free at work!!) My Plate: DUALPWR (Dual Power)

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12-24-2006, 03:32 PM	#7
cwerdna Senior Member Join Date: Sep 2005 Location: Seattle area, WA Posts: 2,303 My Car: 2006 Prius Model: N/A Package: #7 Thanks: 26 Thanked 60 Times in 52 Posts Friends: 3	See my post at http://priuschat.com/index.php?s=&show...st&p=354141. All cars have their handling and grip limits so it's still possible to spin or go out of control or spin out w/stability control. The Prius isn't a sports car nor does it have very wide or grippy tires. To the OP: BTW, in the two cases where you used the word "breaks", you should've used "brakes".

12-24-2006, 05:24 PM	#8
donee Senior Member Join Date: Aug 2005 Location: Chicagoland Posts: 2,244 My Car: 2006 Prius Model: Package: #2 Thanks: 2 Thanked 54 Times in 47 Posts Friends: 0	Hi All, I do not have VSC, but do have a Prius. VSC works by sensing the car's "yaw". Look down at the top of the car, and imagine the car turning left or right around the an axis through the center of mass (gravity). That is Yaw. The VSC assumes that when the car is Yaw'ing in oposition to driver command, the wheels are slipping sideways. This may or may not be the case with the stock Prius. The unmodified Prius has oscilatory yaw response due to chasis flex during high chasis loads. Many of us have replaced the stock floor stiffening plate with the BT Tech plate to help with this situation. Back to the unmodified Prius. The car can yaw dramatically, even with the tires firmly planted. The body flex is steering the tires, and the tires are not slipping, but the steering is yawing the car. VSC will act on it. I had similar a similar thing happen to me even though my car does not VSC. I was turning to the left on the inside lane of a two lane road, onto a two lane road. All of sudden the car just squirmed into the outside lane, and there was no skiding. Luckily it was early in the morning and there was no other traffic. There was no skiding because of course VSC did not activate (don't have it). I decided that day to order the BT Tech chasis stiffening plate. As to the comment that the Prius is not a sport's car, well, neither is Saturn SL2 (my previous car) or the OP's SL wagon. But neither of these cars have this problem. All of these cars are similar in weight to the Prius and my SL2 actually used the exact same tire size as the Prius. Because its nearly the same weight as the Prius, and it had 15 inch rims. These identical tires with the same weight on them will slip at the same side load. Now, what happens when you put an intellegent controller (human or computer) in control of the car during rapid yaw events, and the car starts to squirm. The human driver gets all confused and induces PIO (pilot induced oscillation). The VSC does the same thing, only its steering with differential brake inputs, not steering wheel angle. The basic problem here is the intelligent controllers are used to rapid yaw being due to sliding, not chasis deflection steering. Reacting to the rapid yaw as if its sliding, is the wrong thing to do when the actual cause is Prius body flex misalligning wheel angles. Automatic controls can easily become oscillatory, or drive the system to an out-of-control state (steer the wrong way) when the basic structure of the machine has a non-linear response. Steer left should cause the car to turn left, not right after some load limit is reached (what happened to me). With the BT Tech plate the car is much more linear in response to steering inputs and does not squirm back and forth under load. I recommend you get one. I actually skidded around a wet curve on the way home last friday, and pulled into a recovery drift with up throttle. No problem. This would have been impossible with a stock Prius. Thank You BT.