Interesting experience with the PSM off...
03-07-2013, 02:07 AM
#1
Interesting experience with the PSM off...
Well, I will admit I kind of surprised myself the other the day with the car.
I've been becoming increasingly comfortable with the "soft" limits of my car on some of my favorite spots (at the appropriate times on some very vacant Central Texas Hill Country roads), so comfortable in fact that I can make a DE instructor friend of mine a little nervous in the passenger seat whose mind has been blown by how much grip a 991 S actually has. Let's call it spirited 8/10ths driving on some very familiar roads.
So after doing a little reading up on how the PSM actually works I've been experimenting with how the car feels with the system turned off. (Yes, I know this isn't a very smart thing to do on the street, but I've been doing it in very limited and controlled situations.)
For the first 4 to 5 times I played with the car with it off, there was really not much to comment about. Other then some pretty mild and easily catchable power-on and lift-throttle oversteer in 1st gear corners, the car behaved pretty much as it normally does with PSM on and in Sport Plus mode.
However last Saturday leaving the Grand Am races at COTA I had a different experience. On they way out I was giving a friend his first ride in the car. He asked to give him the E-ticket ride on the way back, so I turned off the PSM to do a little playful low speed sliding around a few of the corners. No big deal. However when exiting one of the corners onto the main road out of the circuit, I admittedly stayed in the throttle a little too long and the car swapped ends almost immediately and promptly drove me straight into the grass on the side of the road. It was bang, bang quick on cold tires. Thankfully there was nothing around to hit and I just pulled back out onto the road without any drama.
I am however confused because, from what I've read about how PSM works, it's supposedly never really "off" and it shouldn't let the yaw angles get that extreme much less nearly swap ends.
Can anyone shed some light here that understands how PSM really works?
I've been becoming increasingly comfortable with the "soft" limits of my car on some of my favorite spots (at the appropriate times on some very vacant Central Texas Hill Country roads), so comfortable in fact that I can make a DE instructor friend of mine a little nervous in the passenger seat whose mind has been blown by how much grip a 991 S actually has. Let's call it spirited 8/10ths driving on some very familiar roads.
So after doing a little reading up on how the PSM actually works I've been experimenting with how the car feels with the system turned off. (Yes, I know this isn't a very smart thing to do on the street, but I've been doing it in very limited and controlled situations.)
For the first 4 to 5 times I played with the car with it off, there was really not much to comment about. Other then some pretty mild and easily catchable power-on and lift-throttle oversteer in 1st gear corners, the car behaved pretty much as it normally does with PSM on and in Sport Plus mode.
However last Saturday leaving the Grand Am races at COTA I had a different experience. On they way out I was giving a friend his first ride in the car. He asked to give him the E-ticket ride on the way back, so I turned off the PSM to do a little playful low speed sliding around a few of the corners. No big deal. However when exiting one of the corners onto the main road out of the circuit, I admittedly stayed in the throttle a little too long and the car swapped ends almost immediately and promptly drove me straight into the grass on the side of the road. It was bang, bang quick on cold tires. Thankfully there was nothing around to hit and I just pulled back out onto the road without any drama.
I am however confused because, from what I've read about how PSM works, it's supposedly never really "off" and it shouldn't let the yaw angles get that extreme much less nearly swap ends.
Can anyone shed some light here that understands how PSM really works?
03-07-2013, 08:48 AM
#2
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Well, only Porsche can give you the real inside story.
Like you my experience is based on experimentation only. In my case I used part of a disused runway so any slipups where not an issue.
My main objective was to learn when and how the PSM interferes and also to try and recognize just where "10" is (as in your 8/10).
The result was that PSM does nothing at all until things get close to the limits and then it interferes in almost a brutal way - definitely no *****-footing around. I uses mostly brake application and throttle retarding for understeer (it does allow some measure of sustained understeer).
With PSM off it is pretty easy to swap ends. You can do it with PSM on as well if you take a lot of momentum into a flick.
It's fun. At least until it comes to replacing the tires...
Rainier
Like you my experience is based on experimentation only. In my case I used part of a disused runway so any slipups where not an issue.
My main objective was to learn when and how the PSM interferes and also to try and recognize just where "10" is (as in your 8/10).
The result was that PSM does nothing at all until things get close to the limits and then it interferes in almost a brutal way - definitely no *****-footing around. I uses mostly brake application and throttle retarding for understeer (it does allow some measure of sustained understeer).
With PSM off it is pretty easy to swap ends. You can do it with PSM on as well if you take a lot of momentum into a flick.
It's fun. At least until it comes to replacing the tires...
Rainier
Well, I will admit I kind of surprised myself the other the day with the car.
I've been becoming increasingly comfortable with the "soft" limits of my car on some of my favorite spots (at the appropriate times on some very vacant Central Texas Hill Country roads), so comfortable in fact that I can make a DE instructor friend of mine a little nervous in the passenger seat whose mind has been blown by how much grip a 991 S actually has. Let's call it spirited 8/10ths driving on some very familiar roads.
So after doing a little reading up on how the PSM actually works I've been experimenting with how the car feels with the system turned off. (Yes, I know this isn't a very smart thing to do on the street, but I've been doing it in very limited and controlled situations.)
For the first 4 to 5 times I played with the car with it off, there was really not much to comment about. Other then some pretty mild and easily catchable power-on and lift-throttle oversteer in 1st gear corners, the car behaved pretty much as it normally does with PSM on and in Sport Plus mode.
However last Saturday leaving the Grand Am races at COTA I had a different experience. On they way out I was giving a friend his first ride in the car. He asked to give him the E-ticket ride on the way back, so I turned off the PSM to do a little playful low speed sliding around a few of the corners. No big deal. However when exiting one of the corners onto the main road out of the circuit, I admittedly stayed in the throttle a little too long and the car swapped ends almost immediately and promptly drove me straight into the grass on the side of the road. It was bang, bang quick on cold tires. Thankfully there was nothing around to hit and I just pulled back out onto the road without any drama.
I am however confused because, from what I've read about how PSM works, it's supposedly never really "off" and it shouldn't let the yaw angles get that extreme much less nearly swap ends.
Can anyone shed some light here that understands how PSM really works?
I've been becoming increasingly comfortable with the "soft" limits of my car on some of my favorite spots (at the appropriate times on some very vacant Central Texas Hill Country roads), so comfortable in fact that I can make a DE instructor friend of mine a little nervous in the passenger seat whose mind has been blown by how much grip a 991 S actually has. Let's call it spirited 8/10ths driving on some very familiar roads.
So after doing a little reading up on how the PSM actually works I've been experimenting with how the car feels with the system turned off. (Yes, I know this isn't a very smart thing to do on the street, but I've been doing it in very limited and controlled situations.)
For the first 4 to 5 times I played with the car with it off, there was really not much to comment about. Other then some pretty mild and easily catchable power-on and lift-throttle oversteer in 1st gear corners, the car behaved pretty much as it normally does with PSM on and in Sport Plus mode.
However last Saturday leaving the Grand Am races at COTA I had a different experience. On they way out I was giving a friend his first ride in the car. He asked to give him the E-ticket ride on the way back, so I turned off the PSM to do a little playful low speed sliding around a few of the corners. No big deal. However when exiting one of the corners onto the main road out of the circuit, I admittedly stayed in the throttle a little too long and the car swapped ends almost immediately and promptly drove me straight into the grass on the side of the road. It was bang, bang quick on cold tires. Thankfully there was nothing around to hit and I just pulled back out onto the road without any drama.
I am however confused because, from what I've read about how PSM works, it's supposedly never really "off" and it shouldn't let the yaw angles get that extreme much less nearly swap ends.
Can anyone shed some light here that understands how PSM really works?
03-07-2013, 09:05 AM
#3
Cold summer tires on a car with its engine stuffed into the rear bumper - you probably don't want to touch that "Please Save Me" button unless you really know how the car will react.
I think the PSM stays off until you apply the brakes - if you stayed on the gas or lifted it wouldn't have intervened, but from your description you were leaving the road backwards regardless.
I think the PSM stays off until you apply the brakes - if you stayed on the gas or lifted it wouldn't have intervened, but from your description you were leaving the road backwards regardless.
03-07-2013, 03:24 PM
#4
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The sensors in any car stability system measure small angles and low angular rates. The system is there to prevent you from getting into trouble, and not saving you from trouble. The system is set up to keep you going straight and/or allowing you to steer away from or out of trouble. In a spin, the system doesn't know where straight is. It's not a 3D navigational system. Just a simple measure and correct system. Think of the stability system as a set of invisible guardrails. It will keep you on the road, but once you go over the rail all bets are off. When you turn the stability system off, the invisible guardrails get tighter, and not wider. It intervenes less at larger angles.
03-07-2013, 07:08 PM
#5
PSM stays off until braking hard enough to invoke ABS. Merely touching the brakes won't turn it on, nor will threshold braking. Only braking that locks up at least one front wheel. From the Porsche website:
For an even more dynamic experience, you always have the option to deactivate PSM. It is automatically reactivated, for your safety, only if you brake harder and either of the front wheels (in SPORT PLUS mode, both of the front wheels) requires ABS assistance. ABS and ABD, however, remain active at all times.
From the sounds of it this never happened, and the system did what its supposed to do when deactivated: nothing.
For an even more dynamic experience, you always have the option to deactivate PSM. It is automatically reactivated, for your safety, only if you brake harder and either of the front wheels (in SPORT PLUS mode, both of the front wheels) requires ABS assistance. ABS and ABD, however, remain active at all times.
From the sounds of it this never happened, and the system did what its supposed to do when deactivated: nothing.
03-07-2013, 07:32 PM
#6
Interesting. I found the same description after I posted.
Net/net is I need to get on a track so I can turn it off and get a good "butt dyno" feel for what the car will do in those situations in a variety of corner types and under varying tire heat / load characteristics.
Just me, but I won't be satisfied I've truly owned this car until I understand and master (relatively speaking) it's behavior at the limit with the PSM off. The track is the only sane place to do that, of course.
Net/net is I need to get on a track so I can turn it off and get a good "butt dyno" feel for what the car will do in those situations in a variety of corner types and under varying tire heat / load characteristics.
Just me, but I won't be satisfied I've truly owned this car until I understand and master (relatively speaking) it's behavior at the limit with the PSM off. The track is the only sane place to do that, of course.
03-07-2013, 07:35 PM
#7
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03-08-2013, 02:40 AM
#8
May I suggest autocross as a much less risky venue than the track? Speeds are lower, and on a well designed course your greatest risk should be you have to clay and polish out a cone scuff. Spin out on a track, everyone gets concerned. Spin out at autocross, everyone cheers. Only thing better is if you can find a PCA Driver Skills event. http://www.pnwr.org/Track/driver_skills/default.asp
03-08-2013, 10:34 AM
#9
Thanks, Chuck. I hadn't actually considered the autocross option. I never really got into that scene before I left for my decade working in Asia.
I've been to Bondurant in the mid 90s (college graduation present from the parents) and I grew up kart racing, but I'm still in the process of getting my mojo back after only riding a motorcycle and not driving for over a decade.
I need to look into joining some autocross events here in the area.
I've been to Bondurant in the mid 90s (college graduation present from the parents) and I grew up kart racing, but I'm still in the process of getting my mojo back after only riding a motorcycle and not driving for over a decade.
I need to look into joining some autocross events here in the area.
03-08-2013, 02:52 PM
#11
Rennlist Member
May I suggest autocross as a much less risky venue than the track? Speeds are lower, and on a well designed course your greatest risk should be you have to clay and polish out a cone scuff. Spin out on a track, everyone gets concerned. Spin out at autocross, everyone cheers. Only thing better is if you can find a PCA Driver Skills event. http://www.pnwr.org/Track/driver_skills/default.asp
03-08-2013, 06:37 PM
#12
Note that PSM takes into account your steering input/angle when it intervenes. PSM will try to stabilise the car in the direction your front wheels point. A Porsche Driving School Instructor once told me that the most common question he got when someone spun off was "Why did not PSM help?" and his most common answer was "Because you did not tell PSM what to do..."
