"Full-Time" AWD Winter Mode

[StealthP3D]

I'm tempted to put it on my lift to find out... It sure feels like it.

That comment just shows you don't know how AWD EV's like the Model 3 work. An important part of the equation that determines how much power to send to each motor is based upon how much load is on each motor. You are going to learn very little with all wheels in the air.

From an efficiency standpoint it would make sense to send all torque to the rear wheels at low loads.

There are two kinds of torque (or, more accurately, two different places to measure it) when it comes to discussing how power is transferred on a sheet of ice.

There is the torque to the rear wheel axles (I'm ignoring the motor torque, before the gear reduction) and there is the torque applied to the driving surface (by the tire's tread). In a rear-biased AWD like the Model 3 they are two different things. Because without positive torque applied to the front axle, it would be up to the torque applied at the rear tire tread to turn the front tire, axle, gear reduction and front motor. And in an RWD car that is exactly what happens (minus the front motor and gear reduction). The Model 3 powers the front motor before the rear tires slip to avoid using the torque applied by the rear tread in order to turn the front wheels. As the guys working on the CAN bus data continue to map out the data streams, this will become more apparent.

But let's take a step backward. It's obvious that some of you feel the AWD Model 3 has less sure footed acceleration than other AWD cars and, when deeper into the throttle, I agree. That's one of the things I prefer about the Model 3's snow/ice handling because the heavier workload applied to the rear wheels for acceleration helps preserve directional control of the front wheels. And that is a big plus.

Another factor, one that I wrote about earlier deserves a re-visit. It's about how tire wear changes snow/ice grip. I'll copy it below, pay special attention to the part relating to how heavy accelerations on abrasive surfaces (like pavement or snow and ice with embedded sand/gravel) can wear the tread blocks into an unfavorable shape for grip under acceleration. And don't underestimate how the prodigious torque of even the lowly AWD Model 3 can cause even average drivers to wear their tread blocks into unfavorable shapes for good acceleration on snow/ice. Low tire pressures can exacerbate this phenomenon. I believe this is amplifying peoples reaction to the naturally rear-biased nature of the AWD Model 3. Because we all know how addicting that torque can be when we have the traction to use it (and even sometimes when we don't,). You will need to expand the quoted text.

Another factor to consider is that how the car is driven on bare or bare/wet pavement affects snow and ice traction due to the tread wear pattern differences that various driving causes. A tire that is driven relatively normal and conservatively on bare pavement wears into the best shape for overall ice and snow traction. A tire that is accelerated hard, near or exceeding the traction limit but never braked hard has poor ice/snow acceleration but better ice/snow braking. A tire that has been braked hard repeatedly but always accelerated gently will have good ice acceleration but poor ice braking. Tires that have been pushed hard on pavement corners will have reduced cornering ability on snow and ice because of it. Some kinds of winter conditions cause treadwear that naturally reduce traction even when driven with the flow of normal traffic. Pavement that has consistent but reduced traction due to water and coldness can cause micro-slipping even when not being driven particularly aggressively that can cause treadwear that is not favorable to ice snow traction.

None of these tire factors are unique or particular to the Model 3 except perhaps for the tendency of Model 3 owners to make use of the impressive motor torque when they have the bare pavement with which to do so and to limit hard braking due to the ease of regen braking. So Model 3 owners could be inadvertently wearing their winter tires into unfavorable tread wear patterns for ice/snow hill climbing/acceleration.

 

[Daniel in SD]

That comment just shows you don't know how AWD EV's like the Model 3 work. An important part of the equation that determines how much power to send to each motor is based upon how much load is on each motor. You are going to learn very little with all wheels in the air.

The case I would be trying to determine is when there is near zero load (i.e. ice on crappy all season tires).
So if I do this and the rear wheels clearly turn before the front wheels what will you say?
Unfortunately my lift is currently occupied with another project but I'm sure this thread will still be going at least until the end of winter.

 

[StealthP3D]

The case I would be trying to determine is when there is near zero load (i.e. ice on crappy all season tires).
So if I do this and the rear wheels clearly turn before the front wheels what will you say?
Unfortunately my lift is currently occupied with another project but I'm sure this thread will still be going at least until the end of winter.

Maybe you don't understand this because you are in S.D. but on very low traction surfaces it's not about the load you don't have, it's about the load you do have. There is always a load or the power distribution just doesn't matter (at all). It's on ice (where the load is very small) that it matters the most.

I think you have a fundamental misunderstanding of what's required to achieve good traction on ice. It's a very delicate thing which is why EV's can be so superior to ICE. Because the electronics allow very precise measurement of load, even at very small values. There is no comparable ability in any ICE car, at least none that I'm aware of.

 

[mswlogo]

Maybe you don't understand this because you are in S.D. but on very low traction surfaces it's not about the load you don't have, it's about the load you do have. There is always a load or the power distribution just doesn't matter (at all). It's on ice (where the load is very small) that it matters the most.

I think you have a fundamental misunderstanding of what's required to achieve good traction on ice. It's a very delicate thing which is why EV's can be so superior to ICE. Because the electronics allow very precise measurement of load, even at very small values. There is no comparable ability in any ICE car, at least none that I'm aware of.

Block the front wheels and let rears free.

See how much the rears turn before obvious force on the front blocks begins to happen.

I think that would cover it.

 

[ba2002]

Let me guess. You are one of those people who think that because you have AWD all you need are all-season radials?

I mean, it says "ALL" season right?

Michelin xice xi3 are all season right? right?? You are such a good guesser.

 

[StealthP3D]

Michelin xice xi3 are all season right? right?? You are such a good guesser.

Where do you live?

 

[ba2002]

Where do you live?

Minneapolis.

EDIT: Snowy as all get out here - but fortunately (outside of the street i live on) almost completely flat.

 

[StealthP3D]

Block the front wheels and let rears free.

See how much the rears turn before obvious force on the front blocks begins to happen.

I think that would cover it.

The front blocks will be expelled right away. But I'm not sure what that would prove. The best way to test The Model 3 AWD is drive it. Which is what I've been doing all winter.

 

[StealthP3D]

Minneapolis.

And so when you lost it on the freeway on-ramp the other cars were maintaining perfect composure? My experience has been other cars are sliding around while I'm glued to the road. And I don't have the highest grip winter tires.

 

[ba2002]

And so when you lost it on the freeway on-ramp the other cars were maintaining perfect composure? My experience has been other cars are sliding around while I'm glued to the road. And I don't have the highest grip winter tires.

Yes, i had a lexus full size SUV or something in front of me that i was staring at and I didn't see it having any issue at all - plus, the snow was worn almost (but not) completely through to the pavement along the two tire tracks that I was driving along. I was caught totally off guard by the sudden shift of the rear end of my car. And this was not the wiggle I had been complaining about before - this was a 40 degree swing out of the rear that for a split second I thought i was going in the ditch. I'm probably lucky that I didn't panic and try to do something crazy with the steering and/or brakes and the computer had a chance to do it's thing and save me.

I really don't want to change cars, because it's going to cost me $20k+ - but I'm not sure what else to do. I personally don't want to drive a car in these road conditions that has such a tendency to break loose on the back end.

 

[StealthP3D]

Yes, i had a lexus full size SUV or something in front of me that i was staring at and I didn't see it having any issue at all - plus, the snow was worn almost (but not) completely through to the pavement along the two tire tracks that I was driving along. I was caught totally off guard by the sudden shift of the rear end of my car. And this was not the wiggle I had been complaining about before - this was a 40 degree swing out of the rear that for a split second I thought i was going in the ditch. I'm probably lucky that I didn't panic and try to do something crazy with the steering and/or brakes and the computer had a chance to do it's thing and save me.

I really don't want to change cars, because it's going to cost me $20k+ - but I'm not sure what else to do. I personally don't want to drive a car in these road conditions that has such a tendency to break loose on the back end.

You should have your car checked out by Tesla for a software or hardware problem. Because I've tried to kick the rear out that far in all kinds of corners (uphill, downhill, off-camber) and it just won't let me.

Did you have "Chill Mode" on? Because I've never become comfortable enough with it to try that kind of thing in Chill. I'm wondering if there's a programming error that causes this in Chill Mode due to the throttle delay being handled improperly or something - it's not out of the question and it does seem most people who are reporting less than stellar winter driving dynamics are (for whatever reason) using Chill Mode.

 

[ba2002]

You should have your car checked out by Tesla for a software or hardware problem. Because I've tried to kick the rear out that far in all kinds of corners (uphill, downhill, off-camber) and it just won't let me.

Did you have "Chill Mode" on? Because I've never become comfortable enough with it to try that kind of thing in Chill. I'm wondering if there's a programming error that causes this in Chill Mode due to the throttle delay being handled improperly or something - it's not out of the question and it does seem most people who are reporting less than stellar winter driving dynamics are (for whatever reason) using Chill Mode.

You know I do have chill mode on. I was doing it because people were talking about too much torque etc, but I never had the problem in my P90DL (it was heavier and it had a different problem of a great stopping distance, but that was predictable).

I'll turn chill mode off and see if I do any better.

 

[Incredulocious]

I'll turn chill mode off and see if I do any better.

From experience I can say that it won’t matter. And StealhP3D won’t stop telling everyone who experiences this that they aren’t driving properly or don’t know what they’re talking about.

 

[StealthP3D]

From experience I can say that it won’t matter. And StealhP3D won’t stop telling everyone who experiences this that they aren’t driving properly or don’t know what they’re talking about.

I do question why people get their panties in a wad just because the tail kicks out slightly under too much throttle but I have never accused people of "not driving properly". I don't know why you guys are having problems, I'm sure it's not because you have more slippery snow or ice!

 

[coleAK]

Haha. This thread is now 9 pages long and I'm not sure anyone has agreed with you. The Model 3 sticks to the road just about exactly as well as any other car when equipped with the same tires. The problem is the AWD system doesn't apply any torque to the front wheels until the rear wheels slip. This is likely to improve efficiency and handling in dry conditions which is great but unless they can more seamlessly detect rear wheel slippage a mode is needed for snow and ice. It sounds like you may be the only one with a software build that does that

Haha. I’ve been saying this same thing for a while.

 

[StealthP3D]

Haha. I’ve been saying this same thing for a while.

Haha! You were also saying that of course I wouldn't understand the problems you have because living in AK, you have more treacherous conditions, LOL!

Yes, as soon as you get above the 49th parallel the conditions become much more slippery. No wonder the Model 3 AWD makes you nervous.

 

[coleAK]

Our winter has been horribly dry and so I've only driven one time in slush, so can I get more details on this "wiggle?"

I have spent 14 years driving AWD Subarus. I can get a "wiggle" in deep-ish snow (few inches) from a stop. The back end can slip slightly left/right as it hunkers down, then the TCS kicks on, and the car drives straight. This is with 50/50 or 41/59 full-time AWD systems with mechanical center differentials, and rear differentials; Open (08/11 WRX), Viscous (05 WRX) and TorSen (18 STI).

If the "wiggle" is as I described, it may seem abnormal to some people bc you are used to FWD-biased AWD systems. Subaru and Audi (not all Audis) actually drive all 4 tires (50/50 or ~40/60), so the powered rear tires can lose some traction and slightly slip-slide, since there rear is lighter.

Most other companies are really FWD and then at the last second try to send a little bit of torque to the rear, so the rears almost never drive the car forward. Less capable systems.

As I mentioned before our other current cars are a 2010 Subaru Legacy, 2004 MB e320 4matic, LX 570, and the AWD LR 3. Non of them are FWD bias AWD. Over the years the other AWD’s we’ve also had: I got a new Subaru to drive most winters from 1997 - 2004, outbacks Impreza RS, Legacy GT, Wrx’s, Sti. Owned: A6 Allroad, MB g500, 996 turbo. Many had no electronic driver aids. Other than the Porsche all of the other AWD cars mentioned felt more planted and sure footed. All had top level snow tires (most Nokian) and I lived in Tahoe or Alaska.

Again the model 3 isn’t bad. And with (in my opinion) small tweeks to the software it could be better, up there with the best.

 

[coleAK]

Haha! You were also saying that of course I wouldn't understand the problems you have because living in AK, you have more treacherous conditions, LOL!

Yes, as soon as you get above the 49th parallel the conditions become much more slippery. No wonder the Model 3 AWD makes you nervous.

You don’t understand winter and ice like Alaska, Canada, and New England.

 

[StealthP3D]

You don’t understand winter and ice like Alaska, Canada, and New England.

Yes, the molecular structure of ice changes in Alaska, especially if you live near Wasilla. They have Ice houses there where you can buy crystal meth. The ice is amazing there.

 

[Daniel in SD]

Because the electronics allow very precise measurement of load, even at very small values. There is no comparable ability in any ICE car, at least none that I'm aware of.

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!