Dual motor vs. RWD in winter driving.

[AWDtsla]

A few weeks ago, I got to test my brand new AS3+ tires on my P85D on a steep ice covered driveway. The driveway can't be walked on without slipping...that's how bad it is. I tried the previous week in my prius with tire chains and it was a no go. The Tesla went up without any slippage like it was just the dirt that's under the ice rather than the ice itself.

By far the most capable of the AWD and 4x4 vehicles I've owned. I think tires might make a big difference. The AS3+'s have an excellent ice and snow rating from user surveys on the tire rack. Interestingly, the non plus AS3s have a lousy rating.

After thinking about this for several days, I think this is the the issue: It has responsive torque cut, which gives it the *feeling* of being planted, since it's less likely to have human detectable spin or upset the direction of the car. This sort of works on low traction but otherwise hard surfaces. The real limitation on loose packed surfaces seems to be the inability to direct torque smoothly to each wheel left/right. Loose packed surfaces require consistent spin for optimal traction. My Subaru has 2 vicously limited (NOT viscously coupled) differentials with somewhat of a high preload factor, i.e. if you put both rear wheels in the air, it's quite difficult to turn a wheel by hand, since the opposite side of the differential tries to spin backwards but is vicously limited. This means each side of the differential has a certain amount of torque it will apply in any condition, without viscous locking. Note that the base Subaru's don't have this set of performance LSD's.

TLDR; no limited slip diff's and poor differential braking means bad performance on loose packed surfaces. No Colin McRae tributes in the Model S.

 

[sorka]

After thinking about this for several days, I think this is the the issue: It has responsive torque cut, which gives it the *feeling* of being planted, since it's less likely to have human detectable spin or upset the direction of the car. This sort of works on low traction but otherwise hard surfaces. The real limitation on loose packed surfaces seems to be the inability to direct torque smoothly to each wheel left/right. Loose packed surfaces require consistent spin for optimal traction. My Subaru has 2 vicously limited (NOT viscously coupled) differentials with somewhat of a high preload factor, i.e. if you put both rear wheels in the air, it's quite difficult to turn a wheel by hand, since the opposite side of the differential tries to spin backwards but is vicously limited. This means each side of the differential has a certain amount of torque it will apply in any condition, without viscous locking. Note that the base Subaru's don't have this set of performance LSD's.

TLDR; no limited slip diff's and poor differential braking means bad performance on loose packed surfaces. No Colin McRae tributes in the Model S.

 

[AWDtsla]

First of all, that performance is very weak. See how little torque it was able to send to the other wheel.
Second, stark example of confirmation bias. "Look, that car made it thought!"
Third, barely an inch of snow on the ground, tire makes contact with hard surface no problems.
Fourth, THIS is what it should do, and can't.

 

[sorka]

First of all, that performance is very weak. See how little torque it was able to send to the other wheel.
Second, stark example of confirmation bias. "Look, that car made it thought!"
Third, barely an inch of snow on the ground, tire makes contact with hard surface no problems.
Fourth, THIS is what it should do, and can't.

If you say so, but the only tests I've seen that perform better are with locking diffs. The level of micro torque management on the Tesla is clearly outstanding as I didn't lose traction at all on a steep iced driveway.

 

[AWDtsla]

If you say so, but the only tests I've seen that perform better are with locking diffs. The level of micro torque management on the Tesla is clearly outstanding as I didn't lose traction at all on a steep iced driveway.

Locking diffs suck. Limited slip is what you want.

You can claim how superior the Tesla is all day long, but the fact still remains you can buy a car new for 20-35k, add $800 for snow tires, and have it outperform my car in the snow.

 

[AWDtsla]

...and I guess my Tesla didn't get stuck either in quite pathetic conditions :-/

One negative report is worth 100 positive ones.

 

[sorka]

Locking diffs suck. Limited slip is what you want.

You can claim how superior the Tesla is all day long, but the fact still remains you can buy a car new for 20-35k, add $800 for snow tires, and have it outperform my car in the snow.

Sure, but I don't have dedicated snow tires on my car.

 

[AWDtsla]

Sure, but I don't have dedicated snow tires on my car.

I do.

 

[sorka]

I do.

Yet I made it up a 300 foot 20% grade driveway with solid clear see through ice without so much as a slip on my regular all season tires

 

[AWDtsla]

Yet I made it up a 300 foot 20% grade driveway with solid clear see through ice without so much as a slip on my regular all season tires

I didn't make it more than 20 feet outside my garage door on a 10% grade driveway with a few inches of light fluffy snow, with snow tires.

 

[sorka]

I didn't make it more than 20 feet outside my garage door on a 10% grade driveway with a few inches of light fluffy snow, with snow tires.

Interesting as even my prius does pretty good on unpacked powder on a 6% grade but it couldn't handle the ice even with tire chains.

Do you think there might be an issue with your specific car? Perhaps the wheel speed sensors aren't working as they should?

 

[AWDtsla]

Interesting as even my prius does pretty good on unpacked powder on a 6% grade but it couldn't handle the ice even with tire chains.

Do you think there might be an issue with your specific car? Perhaps the wheel speed sensors aren't working as they should?

I thought so and was about to report it to Tesla, but fortunately there was a lot of ice/packed snow on back roads yesterday, and I was able to test various scenarios, like one wheel on ice, etc, etc. Of course it worked as expected there.

As I said a couple posts above, I think the issue here is with the handling of loose surfaces, for the reasons I detailed in that post. Under those conditions it is not simply a question of not spinning the tires. The tires must spin, and do so consistently.

 

[calisnow]

I didn't make it more than 20 feet outside my garage door on a 10% grade driveway with a few inches of light fluffy snow, with snow tires.

Let's see a video.

 

[Jaff]

Locking diffs suck. Limited slip is what you want.

You can claim how superior the Tesla is all day long, but the fact still remains you can buy a car new for 20-35k, add $800 for snow tires, and have it outperform my car in the snow.

Not from an environmental perspective.

 

[agloutney]

Never been stuck with my RWD 85 with the Pirelli snow tires from Tesla. We had a pretty good dump in Montreal last week and the car was pretty awesome on an unplowed highway at 2am with no one else around to lay tracks. Felt like I was driving a snowmobile through fresh powder. I did lose the radar though as it was pretty much at the same height as the snow I was plowing through. The smooth underside probably helps too. I can confidently say after three Montreal winters that RWD with winter tires is not an issue. That said, I think AWD would be a beast in similar conditions and would definitely get it if I were ordering today.

 

[AWDtsla]

Not from an environmental perspective.

If you really want to go down this road, then maybe even from an environmental perspective. Under such conditions consumption can increase to 500+ Wh/mi. While a gasoline engine is becoming more thermally efficiency since waste heat is being utilized, and EV must consume even more energy for heating. All of a sudden the 3x or so better thermal efficiency is gone. Taking into account pure cost, the fueling cost per mile in my Model S will clearly go over what the $20k car would have. As far as carbon output, will that depends on even more variables. If you go worst case, it's a losing proposition.

I made this observation weeks into ownership, but never bothered to say something because it's against the dogma.

 

[StaceyS]

P85 owner with lots of long distance snow driving. Car has dedicated snow tires. Its done very well. In the summer, its got 21" turbines with Conti Sports on it. Winter, 19" Rials with Dunlop Wintersports. The car feels very stable and predictable in every winter condition I've had it in, from sheet ice to loose snow.

Once had to take our car from Central Oregon to Portland (over the Cascades) for service in heavy snow conditions, and drove back home with a 70D on 21" Contis in similar conditions. Compared to my P85 with snow tires, the 70D with Contis wasn't too shabby. Accelerated almost as good, but stopping and cornering were not as good. Directional stability was also decreased. If the 70D had had snow tires, it would have out accelerated the P85, but then again, both cars have 4 wheel brakes!

We've had a ton of snow this year so far, and with all that snow, very icy roads as well. I've experienced rear-end regen slippage, and in icy conditions I've set the regen settings to low to help mitigate this. Having dual motors would probably help reduce this.

I've never had an AWD car before (mostly because of the fuel efficiency hit you get for the rest of the year when you really don't need AWD), but the Tesla is the first car I'd consider getting AWD for due to the better efficiency on top of the performance.

 

[WannabeOwner]

P90D owner, been driving an S85 loaner in back end of February. No frost nor ice, but wet, damp and some "greasy" roads. On rural roads there is dirt/muds on the road in some places where a truck ran over, and spread!, the verge.

I was very surprised (certainly the first time!!) how the S squirmed during spirited driving, had to lift off lots of times. Never had to do that in the D

 

[TE3LA]

Id like to hear more from experienced owners about whether the dual motor increases services / maintenance costs. I realize Teslas are relatively maintenance free, but dual motor does add quite a bit of complexity molexity fo the vehicle. Any dual motor owners out there have any anecdotes?

 

[wdolson]

I've had mine a little over a year now and no issues. Tesla uses two motors in the Model S/X. The P versions and rear wheel drive versions have a large motor in the back. The AWD versions have a pair of smaller motors. The P version uses one small motor in the front. From all I've read, the smaller motors are more reliable. Almost all the drive unit replacement issues have been with the larger motors, but most of those were with the early cars too.

Tesla's AWD system is quite a bit simpler than ICE AWD systems. With AWD ICE, there is a physical linkage between the single engine and the two drive axles. This adds mechanical complexity as well as weight.

In the Tesla system, the two drive systems are only linked electronically. This makes the system a lot simpler and I have never heard of any software bugs in the AWD control system.

You do have a second drive unit, but each drive unit is doing less work than in the RWD cars.

It's an amazing piece of engineering IMO. 99% of the time in engineering you have to trade off one thing for another, but with Tesla's AWD system the only thing you lose is some frunk space. Everything else is better.