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Old 01-22-2018, 06:47 PM   #176
SoapBox
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It's refreshing to see so many people on here who understand how open diffs work these days.

My oh my how many fights we've had on here trying to convince people what is actually happening when one wheel is on ice spinning, and the one on the pavement is still.
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Old 01-22-2018, 06:52 PM   #177
SoapBox
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Is it me, or can the system really only work when you're not actually in a full-on understeer condition? AKA, would this actually help you on a track at 10/10ths, or just when you're briskly driving on back roads?

If I'm experiencing true understeer, my outside front tire is already maxed out. It has nothing more to give. Sending more power there is simply going to make matters worse.

I bet if we looked at the algorithm, if the car is truly out of front end grip, it wouldn't ramp up torque across the front. That's the opposite of what you'd want to do.

The more one thinks about it, this seems like it will only tighten your line when you're not maxed out laterally. Which isn't helping you at the track or at least not very much if you're hustling.
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Old 01-22-2018, 07:20 PM   #178
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Quote:
Originally Posted by SoapBox View Post
It's refreshing to see so many people on here who understand how open diffs work these days.

My oh my how many fights we've had on here trying to convince people what is actually happening when one wheel is on ice spinning, and the one on the pavement is still.
I learned the hard way with open diffs........older Jeep, stuck across a deep rut with diagonals either on ground or in the air....
No going anywhere.........center diff lock was broken so all 3 were open.
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Old 01-22-2018, 07:35 PM   #179
Boggie1688
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Originally Posted by SoapBox View Post
Is it me, or can the system really only work when you're not actually in a full-on understeer condition? AKA, would this actually help you on a track at 10/10ths, or just when you're briskly driving on back roads?

If I'm experiencing true understeer, my outside front tire is already maxed out. It has nothing more to give. Sending more power there is simply going to make matters worse.

I bet if we looked at the algorithm, if the car is truly out of front end grip, it wouldn't ramp up torque across the front. That's the opposite of what you'd want to do.

The more one thinks about it, this seems like it will only tighten your line when you're not maxed out laterally. Which isn't helping you at the track or at least not very much if you're hustling.
I've had it come on during the clover leaf getting on and off a freeway. Since I originally started this thread, I've upgrade my front brakes. I now have squeaky pads. Which means, I have an audible squeal when the system comes on. This happens at the autox too. Depending on the course design I can bump into the torque vectoring. Some of the guys have come around asking why I'm on the brakes coming out of the corner. In the instances where the system comes on, I'm understeering but its not terrible. The understeer you get here is very manageable. I also choose lines that allow me to go wide open without worry about terminal understeer into a wall.

In any case, I bring that all up because I know the system come on when I'm understeering and pushing. Does it know that I've used all available grip? I don't know. How does the system know how much brake pressure to apply? (there can be any combination of brake pads with different coefficients of friction) Again, I don't know. I'm sure the car can see relative wheel speeds, my steering angle, actual direction of travel vs desired.

It would be cool to better understand how the computer decides to active PTV and how it modulates it. The only downside I see to a system like this is during a track scenario where you might start to overheat the brakes, melt the pads and/or boil the fluid.
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Old 01-22-2018, 07:42 PM   #180
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Originally Posted by Charlie-III View Post
I learned the hard way with open diffs........older Jeep, stuck across a deep rut with diagonals either on ground or in the air....
No going anywhere.........center diff lock was broken so all 3 were open.
Lol, me too. It made me put Detroit lockers front and rear which then created other problems both on and off road (it pushed in the mud and wanted to change lanes every time you shifted on the road). The benefits almost outweighed the drawbacks, but this was a short wheelbase TJ. If I was still Jeeping a daily driver Iíd go selectable (ARB probably) front and a Detroit Truetrac in the rear, although then you have electrical or air lines that can be damaged. No free lunch thatís for sure.
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Old 01-22-2018, 07:46 PM   #181
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Originally Posted by Boggie1688 View Post
I've had it come on during the clover leaf getting on and off a freeway. Since I originally started this thread, I've upgrade my front brakes. I now have squeaky pads. Which means, I have an audible squeal when the system comes on. This happens at the autox too. Depending on the course design I can bump into the torque vectoring. Some of the guys have come around asking why I'm on the brakes coming out of the corner. In the instances where the system comes on, I'm understeering but its not terrible. The understeer you get here is very manageable. I also choose lines that allow me to go wide open without worry about terminal understeer into a wall.

In any case, I bring that all up because I know the system come on when I'm understeering and pushing. Does it know that I've used all available grip? I don't know. How does the system know how much brake pressure to apply? (there can be any combination of brake pads with different coefficients of friction) Again, I don't know. I'm sure the car can see relative wheel speeds, my steering angle, actual direction of travel vs desired.

It would be cool to better understand how the computer decides to active PTV and how it modulates it. The only downside I see to a system like this is during a track scenario where you might start to overheat the brakes, melt the pads and/or boil the fluid.
So you find yourself faster with the ATV on the short auto cross courses? I would have thought turning everything off and pitching the car into the corners and then hammering the throttle would be quicker in a short course situation.
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Old 01-22-2018, 08:19 PM   #182
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Originally Posted by JRowland View Post
So you find yourself faster with the ATV on the short auto cross courses? I would have thought turning everything off and pitching the car into the corners and then hammering the throttle would be quicker in a short course situation.
Car is on a **** ass alignment with 5 year old BFGood Rival S. and slides like a pig everywhere. I never tried turning it completely off. I daily the car, so doing anything with the alignment seems like a waste.

I'll give it a shot next year, if I find time to take the car out to the autox. I have another car I compete with, so the WRX goes if I can lock out the class in points.
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Old 01-23-2018, 12:08 PM   #183
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Originally Posted by Boggie1688 View Post
To be clear, there are two types of understeer:

1. You enter a corner carrying to much speed, and you exceed the grip of the front tires. This causes understeer.

2. You apply the throttle to early in a corner and/or too much throttle, you exceed the ability of the front tires to provide both lateral grip and forward acceleration. This causes understeer.

The Subaru torque vectoring system cannot work without power from the engine. As a result, it cannot help understeer scenario #1.
Your examples are the exact same thing. In both cases you have exceeded the load capacity of the contact patch at the front tires and can't support the desired lateral forces. Understeer is understeer. You can get into the situation different ways, but the cause is always exceeding the friction circle at the front tires.


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Originally Posted by SoapBox View Post
I've been a PCA instructor for about 10 years now. Off the bat I will say that their modern stuff has gotten so good that I agree with you at least to some extent. Big difference between your traction control (and particularly the higher threshold modes), and that found on the cars we're discussing here.

That being said, I think you're under estimating what even an average weekend warrior is capable of after a good amount of seat time. A half-competent student should be probing the limits of the chassis (at least mid corner off) half way through a weekend. Personally, once a student learns the line, demonstrates good car and track awareness, I'm encouraging them to turn the TC off if they are getting into it often. At that point, it's holding them back. Not only from learning proper car control, but also from outright speed and the fun that comes with hustling a car near its limits. <-- maybe that applies much more to older cars with older systems...as again, i agree the newer/high end stuff is good.
I spend most of my days thinking about and worrying about the average driver. All of our software DFMEA's and ISO26262 hazard analyses deal with the knowledge, reflexes, and skills of the average driver. Working in the auto industry and having the chance to work with various product engineers, vehicle dynamics engineers, high performance drivers, and true racing professionals I can confidently say that I am not underestimating the average driver. Maybe I underestimate the subset of drivers who actually attend a track day or autocross, but not the true "average" driver.


I think we are getting at the same point though. With enough seat time and skill development you can justify turning off the nannies. Learn the line, learn more about the car, then turn off TCS. Learn to deal with wheel spin and over/understeer which it may induce and then think about disabling ESC.


Quote:
IMHO, one of the most fun aspects of driving a car at 10/10ths is "keeping the ass end where it's supposed to be". And that's the very thing you admitted to handing over to the car. It's sort of a shame when people put the resources into acquiring a car with outstanding balance and composure, get out on the track, but never get to experience it because they're sitting on the TC all day. Not speaking to you directly, just in general.

Isn't car control the reason we're all ultimately out there?
This makes perfect sense when one can afford to write off the vehicle. If you are tracking your daily driver or any vehicle which you haven't fully paid off I don't think it makes financial sense to disable the features which can help save you from a very expensive mistake. We're all out there to have fun, but wrecking the car ruins the fun.


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Originally Posted by Boggie1688 View Post
For the torque vectoring we are speaking of, it is only under power. The computer will apply slight braking pressure to the inside front wheel.

Why? How does this work and why is it called torque vectoring?

The WRX has an open diff. It always has a 50/50 torque split. Which means the maximum torque either corner can have, is equal to the lowest. Usually this is the inside wheel because you start to spin it. IE: Go around a corner, and you spin the inside wheel. Let say it is only taking 25lb ft to spin that inside wheel. Because it is an open diff, the outside wheel can only put down 25lb ft too.

Now the brake can be used to increase the amount of torque required to rotate the wheel. The computer can lightly apply brake pressure to the inside wheel, bringing the torque up from 25lb ft to 100lb ft. Now the outside wheel can now have 100lb ft. The inside wheel is not putting an extra 75lb ft torque into the road. The extra 75lb ft is be used to overcome the friction provided by the pad. You burn pads and create heat. However, the outside wheel which has the grip and the ability to put more than 25lb ft torque to the road, can now get more torque.

The exercise is about increase the torque sent to the outside wheel, by simulating more load on the inside wheel. Is this real torque vectoring? No. I would consider this more like torque recovery.

Is is not actively moving torque side to side. It is just trying to help recover torque to increase what is available to the outside wheel. A problem caused by the inherent design of an open diff. Note the outside wheel can take more torque but is being limited by the spinning inside wheel.
Didn't we already discuss this? What you are describing is generally referred to as a brake-based limited-slip differential (BLD). Brake-based torque vectoring (BTV) is a different feature and can work off-throttle as it's just a tweak of what is already known as ESC...dragging the brake to slow the inside wheel and develop yaw. The difference is that BTV might only utilize 100-200Nm of brake torque where ESC corrections are in the 1000Nm range for faster and more significant correction.


Quote:
Originally Posted by SoapBox View Post
It's refreshing to see so many people on here who understand how open diffs work these days.

My oh my how many fights we've had on here trying to convince people what is actually happening when one wheel is on ice spinning, and the one on the pavement is still.
Agreed!
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