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"Full-Time" AWD Winter Mode

StealthP3D

Well-Known Member
Dec 12, 2018
9,219
71,035
Maple Falls, WA
It's OBDII code number 4. OBD-II PIDs - Wikipedia
I'm not sure where people get the idea that ICE vehicles can't quickly modulate engine power. They're turning at 1000's of rpm and can control the ignition timing of every spark. Keeping a giant engine idling smoothly is a very tricky problem because the load is so small!

I didn't address how quickly a motor can modulate power (but I will), I spoke to the ability to measure the load accurately, even at very small levels of load such as you might find on ice with a thin layer of water on top.

The link you provided doesn't address the resolution of the torque values. Also, be aware that while modern ICE engines computerized control will reference a torque request value (throttle position sensor) and a torque produced value. The torque produced is very crude. It is a value calculated from the amount of fuel injected, the rpm of the engine, the throttle position sensor, the air mass meter, etc. etc. While there are different fuel injection control systems, and they work somewhat differently, they all have one thing in common, they are simply calculating the approx. torque produced and, especially at very low torque values, it becomes very imprecise. It often doesn't know if the actual torque is slightly positive (slight acceleration force) or slightly negative (slight engine braking). This is only one of the problems with ICE engine control on slippery surfaces.

In contrast, an electric motor has very precise and fast torque feedback and the motor, being lighter and without a bunch of reciprocating pistons, flywheel, etc, can change it's torque much more quickly and with much greater precision. The problem is once a wheel starts slipping because it's being driven too hard, the rpm's of the engine and transmission is higher than ideal for the vehicle speed and these components have an incredible amount of rotational momentum that continues to drive the wheels faster than desired even if the engine control unit cuts power to the engine. The EV motor is much lighter and therefore does not overdrive the slipping wheel for as long after the power is cut. So not only can the electric motor control the torque much more accurately at very low torque values, it also reacts more quickly due to the greatly reduced rotational inertia within the drivetrain.

The weight of an ICE engines crank, flywheel, accessory pulleys, transmission shafts and gears, etc, etc, etc all adds up to a turning mass that is much greater than the wheels they are driving. At low loads, such as on wet ice, all that mass means it's not as responsive to fine control of the traction control. It's far from ideal.

I can't for the life of me understand why you can't see this.
 

mswlogo

Well-Known Member
Aug 27, 2018
6,044
4,666
MA, NH
I didn't address how quickly a motor can modulate power (but I will), I spoke to the ability to measure the load accurately, even at very small levels of load such as you might find on ice with a thin layer of water on top.

The link you provided doesn't address the resolution of the torque values. Also, be aware that while modern ICE engines computerized control will reference a torque request value (throttle position sensor) and a torque produced value. The torque produced is very crude. It is a value calculated from the amount of fuel injected, the rpm of the engine, the throttle position sensor, the air mass meter, etc. etc. While there are different fuel injection control systems, and they work somewhat differently, they all have one thing in common, they are simply calculating the approx. torque produced and, especially at very low torque values, it becomes very imprecise. It often doesn't know if the actual torque is slightly positive (slight acceleration force) or slightly negative (slight engine braking). This is only one of the problems with ICE engine control on slippery surfaces.

In contrast, an electric motor has very precise and fast torque feedback and the motor, being lighter and without a bunch of reciprocating pistons, flywheel, etc, can change it's torque much more quickly and with much greater precision. The problem is once a wheel starts slipping because it's being driven too hard, the rpm's of the engine and transmission is higher than ideal for the vehicle speed and these components have an incredible amount of rotational momentum that continues to drive the wheels faster than desired even if the engine control unit cuts power to the engine. The EV motor is much lighter and therefore does not overdrive the slipping wheel for as long after the power is cut. So not only can the electric motor control the torque much more accurately at very low torque values, it also reacts more quickly due to the greatly reduced rotational inertia within the drivetrain.

The weight of an ICE engines crank, flywheel, accessory pulleys, transmission shafts and gears, etc, etc, etc all adds up to a turning mass that is much greater than the wheels they are driving. At low loads, such as on wet ice, all that mass means it's not as responsive to fine control of the traction control. It's far from ideal.

I can't for the life of me understand why you can't see this.

I must be an amazing driver. I parked an ICE vehicle today, in my garage and didn’t go through the wall or anything.
 

Scott7

Member
Apr 3, 2016
319
358
Wisconsin
For those like me that put certain know-it-alls on ignore, this is a thread full of people agreeing with each other. :p

Maybe I missed it and I know this is an AWD thread, but I’m wondering if anyone can describe how RWD (with winter tires, of course) does in the snow? Specifically does it exhibit exactly the same amount of surprising wiggle before the computer straightens the car out, but using the brakes instead of a front motor?

My i3 does great in the snow with winter tires, but the way it stops oversteer is very abrupt braking of the outside front wheel. It’s totally effective, but doesn’t feel very smooth in my opinion.
 
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StealthP3D

Well-Known Member
Dec 12, 2018
9,219
71,035
Maple Falls, WA
For those like me that put certain know-it-alls on ignore, this is a thread full of people agreeing with each other. :p

I’m wondering how RWD (with winter tires, of course) does in the snow? Does it exhibit exactly the same amount of surprising wiggle before the computer straightens the car out, but using the brakes instead of a front motor?

My i3 does great in the snow with winter tires, but the way it stops oversteer is very abrupt braking of the out front wheel. It’s totally effective, but doesn’t feel very smooth in my opinion.

The RWD Model 3 has more rear-end wiggle in the snow than the P3D. But, just like the P3D, only if you apply too much throttle for the available traction. Of course, with only the rear wheels driven, it's more likely to happen.
 
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Daniel in SD

Well-Known Member
Jan 25, 2018
6,335
9,002
San Diego
I didn't address how quickly a motor can modulate power (but I will), I spoke to the ability to measure the load accurately, even at very small levels of load such as you might find on ice with a thin layer of water on top.

The link you provided doesn't address the resolution of the torque values. Also, be aware that while modern ICE engines computerized control will reference a torque request value (throttle position sensor) and a torque produced value. The torque produced is very crude. It is a value calculated from the amount of fuel injected, the rpm of the engine, the throttle position sensor, the air mass meter, etc. etc. While there are different fuel injection control systems, and they work somewhat differently, they all have one thing in common, they are simply calculating the approx. torque produced and, especially at very low torque values, it becomes very imprecise. It often doesn't know if the actual torque is slightly positive (slight acceleration force) or slightly negative (slight engine braking). This is only one of the problems with ICE engine control on slippery surfaces.

In contrast, an electric motor has very precise and fast torque feedback and the motor, being lighter and without a bunch of reciprocating pistons, flywheel, etc, can change it's torque much more quickly and with much greater precision. The problem is once a wheel starts slipping because it's being driven too hard, the rpm's of the engine and transmission is higher than ideal for the vehicle speed and these components have an incredible amount of rotational momentum that continues to drive the wheels faster than desired even if the engine control unit cuts power to the engine. The EV motor is much lighter and therefore does not overdrive the slipping wheel for as long after the power is cut. So not only can the electric motor control the torque much more accurately at very low torque values, it also reacts more quickly due to the greatly reduced rotational inertia within the drivetrain.

The weight of an ICE engines crank, flywheel, accessory pulleys, transmission shafts and gears, etc, etc, etc all adds up to a turning mass that is much greater than the wheels they are driving. At low loads, such as on wet ice, all that mass means it's not as responsive to fine control of the traction control. It's far from ideal.

I can't for the life of me understand why you can't see this.
I never said electric motors weren't capable of more responsive traction control. I find the traction control in wet and dry conditions to be quite good.
There is not direct measurement of torque of the electric motors either, it must be calculated. High speed torque adjustment on ICEs is done with ignition timing which is plenty fast. I'm not sure why you think knowing the exact value of torque is necessary for a good traction control system anyway.
The problem doesn't seem to be the traction control system though. It seems to be the way to splits torque between the front and rear motors and possibly the interaction of that system with the stability control system. The stability control system uses the brakes and isn't smooth at all. Many ICE vehicles, like my Lexus, have a Torsen center differential which responds faster than any electronic system ever could. But that's all beside the point because we know for a fact that dual motor electric vehicles can have good AWD systems for winter conditions. Many people in this thread have Model S/X and say they work great in the snow!
 

StealthP3D

Well-Known Member
Dec 12, 2018
9,219
71,035
Maple Falls, WA
There is not direct measurement of torque of the electric motors either, it must be calculated.

True, but for all practical purposes the calculated torque values are so fast and accurate they are better than those measured by a load sensor. The same can not be said for the values an ICE calculates.

High speed torque adjustment on ICEs is done with ignition timing which is plenty fast. I'm not sure why you think knowing the exact value of torque is necessary for a good traction control system anyway.

The most slippery surfaces are where the most delicate and accurate systems will shine. An ICE engine cannot even tell if it's applying a slight accelerative force or a slight engine braking force. The electric motor controller/inverter can read this easily. And I've already pointed out the negative effects of a drivetrain with excessive rotational inertia, once the tire spins up past the speed of the vehicle, it must slow down again. Heavier systems give slower and clunkier control when it's very slippery. And having driven plenty of ICE vehicles on very slippery ice, I can tell you the EV's we have are much better at maintaining control on these hazardous surfaces. Even the RWD Model 3.
 

coleAK

Member
Oct 23, 2018
887
597
Alaska
So over the weekend I was talking to a dad one of the u19’s who I coach at the u16-u19 states. Anyway he is a higher up at Totem. The shipping company that has the Tesla account for Alaska. He has got me a deal when I shipped I’m my g500 and LX 570. We were talking about our 3 and He said over the last few weeks they have shipped up a dozen or so model 3 “test cars” gutted with just one front seat. Also mentioned they have shipped up another dozen or so loaded enclosed car transporters which usually means consent/future models, so model Y’s? Everything has been going to Eielson, north of Fairbanks. So looks like more winter testing Is in the works.
 
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matto

Member
Aug 16, 2018
171
120
New York
I didn't read all 11 pages of this thread, but I'll say my snow experience was similar. Aggressive use of the throttle in slippery snow kicks out the rear end a bit. The experience is smack dab in the middle between my RWD BMW (loose rear end, fun) and my 4WD pickup truck (completely stable under acceleration).

It seems like it would be fairly straightforward to add a "snow mode" and that it would be a legitimate benefit for boring people who don't like being sideways while driving.
 
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StealthP3D

Well-Known Member
Dec 12, 2018
9,219
71,035
Maple Falls, WA
I didn't read all 11 pages of this thread, but I'll say my snow experience was similar. Aggressive use of the throttle in slippery snow kicks out the rear end a bit.

Exactly! That's one of the things I like best about the Model 3 in the snow. Most cars prevent you from kicking the rear out a bit no matter how hard you step on the go pedal.
 

matto

Member
Aug 16, 2018
171
120
New York
Exactly! That's one of the things I like best about the Model 3 in the snow. Most cars prevent you from kicking the rear out a bit no matter how hard you step on the go pedal.
Yeah I wouldn't want to get rid of it entirely. But having different drive modes would be cool.

In fact, how about an even more RWD biased mode? Drift mode!
 

mswlogo

Well-Known Member
Aug 27, 2018
6,044
4,666
MA, NH
I had my wife video me in our ice covered driveway the other day.

I floored it a few times on the ice and the video showed no sign of rear bias. Car moved extremely well, it just had small tiny slips from any wheel.

I’d post the video but I don’t like showing my license plate publicly. Too much work to blot out in a video.
 

Daniel in SD

Well-Known Member
Jan 25, 2018
6,335
9,002
San Diego
I had my wife video me in our ice covered driveway the other day.

I floored it a few times on the ice and the video showed no sign of rear bias. Car moved extremely well, it just had small tiny slips from any wheel.

I’d post the video but I don’t like showing my license plate publicly. Too much work to blot out in a video.
Flooring it on dry and wet pavement I also feel the front wheels getting plenty of power, perhaps even too much as the car tends to understeer when pushed. I think it is at small throttle inputs that people are detecting the rear bias. Perhaps the right strategy for accelerating on ice is to keep the throttle at 100% :D
 
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mswlogo

Well-Known Member
Aug 27, 2018
6,044
4,666
MA, NH
Flooring it on dry and wet pavement I also feel the front wheels getting plenty of power, perhaps even too much as the car tends to understeer when pushed. I think it is at small throttle inputs that people are detecting the rear bias. Perhaps the right strategy for accelerating on ice is to keep the throttle at 100% :D

Good point. It was in chill mode. But yeah it would never launch like it does if rear wheel bias happened when flooring it. If it’s a gentle test I’ll have to test it on an icy hill. I might be done with ice and snow this winter. Unless I end up going north.
 

coleAK

Member
Oct 23, 2018
887
597
Alaska
Flooring it on dry and wet pavement I also feel the front wheels getting plenty of power, perhaps even too much as the car tends to understeer when pushed. I think it is at small throttle inputs that people are detecting the rear bias. Perhaps the right strategy for accelerating on ice is to keep the throttle at 100% :D
Isn’t that the old Subaru standard. When it slides floor it. Kidding aside, I have zero slip under acceleration even on solid ice. I’ve gotten used to the rear end wiggle and correct going up hill on ice at a steady speed. The only things that bother me now is the low speed understeer plow on ice and the abrupt cutting of all power on extremely loose or slick. I will day this has been an odd winter not much snow and the roads have been extremely slick compressed ice.
 

SkiCO

New Member
Feb 22, 2019
3
2
Colorado Mtns
You are echoing my feelings exactly! Great article.
As a driver, I enjoy that the dual motor Model 3 is a little tail happy. There is definitely a high “pucker factor” for rear seat passengers and folks who aren’t used to a car getting a little sideways. It’s very different from an automatic transmission Subaru and other vehicles that will reliably understeer instead of oversteering.

That said, the 3 only gets about 15° out of line before it catches itself, so I haven’t felt unsafe in it, even on half-worn MXM4s. I want track mode and snow tires.

Tailhappy is not what you want when you’re on a snow packed interstate in CO. My wife has left her lane on I70 when the tail got loose and this could be catostrophic. The traction control we’ve experienced is garbage for an everyday driver in a snowy climate.
 

SkiCO

New Member
Feb 22, 2019
3
2
Colorado Mtns
I guess the true test would be to put the same tires on multiple vehicles and have them rally up a snowy/icy mountain road. I already know which one would win.

For years people have lamented the way electronic nannies cut power excessively, finally Tesla has fixed the problem by giving the control back to the driver at higher throttle settings while simultaneously improving the TC's stability and grip at lower throttle settings and people complain that the rear end moves around too much on snow/ice at higher throttle settings.

I feel like I've gone into an altenate reality.

It’s not just at higher throttle settings. Steady driving on snow packed Interstate at 40mph with 18” Blizzaks and the rear end breaks loose. Not what I want driving with my kids on the way from Glenwood Springs to Eagle. Create a snow mode for normal people or watch Audi and Volvo/Polestar eat your lunch!
 
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diamond.g

Active Member
Nov 5, 2015
2,421
1,362
Moyock, NC
It’s not just at higher throttle settings. Steady driving on snow packed Interstate at 40mph with 18” Blizzaks and the rear end breaks loose. Not what I want driving with my kids on the way from Glenwood Springs to Eagle. Create a snow mode for normal people or watch Audi and Volvo/Polestar eat your lunch!
Break loose, like you need to counter steer or it feels like it breaks loose but no steering angle change needed?
 

mswlogo

Well-Known Member
Aug 27, 2018
6,044
4,666
MA, NH
Tailhappy is not what you want when you’re on a snow packed interstate in CO. My wife has left her lane on I70 when the tail got loose and this could be catostrophic. The traction control we’ve experienced is garbage for an everyday driver in a snowy climate.

It’s rare I ever see what I call “snow pack” on a highway. If it really is “snow pack” I probably wouldn’t want to go over say 30 mph.

What I call “snow pack” is usually off highway and is often around a series of storms back to back, usually very cold and they just can’t get the roads down to pavement until things warm up. That seems to happen less and less these days with more aggressive chemicals and pretreatment.

Now you could get caught in a blizzard that is dropping several inches an hour and cleaning crews can’t keep up and it starts to accumulate and get packed. But again if that’s happening it’s usually really bad and traffic is extremely slow (e.g. 30 ish mph)

So I don’t quite understand what you mean by snow pack, highway and breaking loose. What speeds are we talking about that your driving on “snow pack”?

Also curious which blizzaks you have and I assume your talking AWD.

I have not come close to that behavior. But then again I don’t travel at “highway speeds” (above say 40 mph) on what I call “snow pack”.

I admit things might be different in CO than I’m used to in MA/NH.

Also could phantom braking (only seen on by me with NOA) or regen braking be triggering it “breaking lose” on your wife?
 
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coleAK

Member
Oct 23, 2018
887
597
Alaska
It’s rare I ever see what I call “snow pack” on a highway. If it really is “snow pack” I probably wouldn’t want to go over say 30 mph.

What I call “snow pack” is usually off highway and is often around a series of storms back to back, usually very cold and they just can’t get the roads down to pavement until things warm up. That seems to happen less and less these days with more aggressive chemicals and pretreatment.

Now you could get caught in a blizzard that is dropping several inches an hour and cleaning crews can’t keep up and it starts to accumulate and get packed. But again if that’s happening it’s usually really bad and traffic is extremely slow (e.g. 30 ish mph)

So I don’t quite understand what you mean by snow pack, highway and breaking loose. What speeds are we talking about that your driving on “snow pack”?

Also curious which blizzaks you have and I assume your talking AWD.

I have not come close to that behavior. But then again I don’t travel at “highway speeds” (above say 40 mph) on what I call “snow pack”.

I admit things might be different in CO than I’m used to in MA/NH.

Also could phantom braking (only seen on by me with NOA) or regen braking be triggering it “breaking lose” on your wife?
In Alaska we don’t use any chemicals or pre treatment to melt snow/ice due to the negative environmental impact. I’m sort of surprised with how liberal MA is that they haven’t banned salt there as well. So I drive on packed snow and ice most of the time around half the year.
 

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