To "D" or not to "D"

[AmpedUP]

I'm interested in the non-performance "D" because of lingering concern about drive unit issues. The S85D drive units will be minimally stressed as compared to all other Model S configurations. I keep cars for a long,long time...and post-warranty reliability is a big consideration.

 

[eco5280]

Fair enough, but know that electric motors have been around for about 1834 so it's not a new technology. Stresses and lifespan of motors is well known and I'm certain accounted for with a monstrously vast margin on these cars.

 

[AoneOne]

As far as the friction of the motor(s) goes: put your car in neutral and feel it roll. The friction is virtually imperceptible.

 

[Ben W]

A year? Going back to the 3% improvement in efficiency, are you talking 30 year expected life and the 3% gives you an extra year? And even that would completely neglect calender life degradation. If part of that 3% came from improved regen, that of course is increasing cycling rather than efficiency so it wouldn't count.

So help me out here - where are you getting a year?

It depends what your threshold is for replacing the battery. If your replacement criterion is, say, the max range dropping below 200mi @65mph, then the extra 3% initial capacity/efficiency (295mi vs 285mi @65mph) combined with lower cycle count will give you about an extra year before hitting that point. This was a huge factor in my choosing the 85kWh battery over the 60kWh. 10 years from now when I might have had to replace the 60kWh pack, my 10-year-old 85kWh pack will likely still have higher capacity than a brand-new 60kWh pack.

Math for the D vs Non-D battery lifetime: Suppose the battery capacity drops 1.5% per calendar year, plus 2% per 100 cycles, and you drive 20k “ideal” mi per year. (ideal = 65mph equivalent). That’s 2.4 fewer cycles per year for the D. (67.8 vs 70.2). Then the D loses 2.86% per year (8.44mi), and the non-D loses 2.90% per year (8.27mi). So it takes 11.25 years for the D to drop to 200mi ideal range, but only 10.28 years for the non-D to reach that point. That’s where I got the year difference from. Plug in your own best-guess numbers, it should come out similar.

 

[David_Cary]

It depends what your threshold is for replacing the battery. If your replacement criterion is, say, the max range dropping below 200mi @65mph, then the extra 3% initial capacity/efficiency (295mi vs 285mi @65mph) combined with lower cycle count will give you about an extra year before hitting that point. This was a huge factor in my choosing the 85kWh battery over the 60kWh. 10 years from now when I might have had to replace the 60kWh pack, my 10-year-old 85kWh pack will likely still have higher capacity than a brand-new 60kWh pack.

Math for the D vs Non-D battery lifetime: Suppose the battery capacity drops 1.5% per calendar year, plus 2% per 100 cycles, and you drive 20k “ideal” mi per year. (ideal = 65mph equivalent). That’s 2.4 fewer cycles per year for the D. (67.8 vs 70.2). Then the D loses 2.86% per year (8.44mi), and the non-D loses 2.90% per year (8.27mi). So it takes 11.25 years for the D to drop to 200mi ideal range, but only 10.28 years for the non-D to reach that point. That’s where I got the year difference from. Plug in your own best-guess numbers, it should come out similar.

Ok - so the bulk of your year came from the extra 10 miles and using a fixed mileage criteria. Fair enough.

I suppose it is worthwhile to come up with a replacement cost estimate - say $15k. Depreciate it out and the extra year is worth $1500.

The reality is for me, I know that 150 would be fine and I'm sure I'll dump the car before 15 years when it might be down to 150. There is also little chance I hit 20k per year so at my usage, it certainly won't be degradation that is a factor in selling the car even if I felt I needed 200 miles. Just for comparison, if I plug in 14k miles/yr, it takes 16 years to get to 200 for a D model and 14.5+ years for a non-D (using your numbers).

So not a factor for most people. What is a factor is resale and like any option, not worth it for that alone (even probably tech package).

 

[wycolo]

The MS doesn't really need AWD, what with its equally weighted tires. What other cars have the same weight all around? That's why they spin rubber and became early candidates for AWD. Nonetheless I expect (hope) to be able to discern differences in handling with the S85D. Plus maybe a bit more efficiency and of course all the fun trying to get stuck in snow.

Adding significantly more power to the MS in the P85D version definitely requires AWD to achieve balanced perfection. The desire for this automotive perfection is basic to the human genetic code; we are destined to accept it unconditionally. Do not ask us to explain why.
--

 

[stevezzzz]

The assumption being that sharing the regen braking on the D will extend the life of the rear tires? I can buy into that line of thinking, but wouldn't it also mean that now the front tires will wear more quickly and likely offset any difference?

I think the benefits to tire tread life come on the acceleration end of things much more so than on the regen end. Max regen on the RWD Model S is 60kW; max acceleration is ~320kW. Unless the road surface is slick, regen doesn't cause much wheel slip, if any. Ddistributing the torque of acceleration over four wheels instead of two could potentially be a big win for tread life, especially on the S85D, since wheel slip will be a much less frequent occurrence. Of course, you have to have good alignment to avoid the known wear problems due to rear toe.

 

[Ben W]

Distributing the torque of acceleration over four wheels instead of two could potentially be a big win for tread life

Very good point. Applying a given amount of torque evenly to four wheels causes MUCH less tire wear than applying the same torque to just two wheels. (It’s highly nonlinear.) A single RWD 0-60 sprint probably causes as much wear as 10 miles of constant-speed highway driving. Replacing the 21” tires every 25k miles instead of every 12k miles could just about pay for the extra cost of the D over its lifetime.

 

[randompersonx]

The MS doesn't really need AWD, what with its equally weighted tires. What other cars have the same weight all around? That's why they spin rubber and became early candidates for AWD. Nonetheless I expect (hope) to be able to discern differences in handling with the S85D. Plus maybe a bit more efficiency and of course all the fun trying to get stuck in snow.

Adding significantly more power to the MS in the P85D version definitely requires AWD to achieve balanced perfection. The desire for this automotive perfection is basic to the human genetic code; we are destined to accept it unconditionally. Do not ask us to explain why.
--

A previous car was a BMW E46 M3. The car is RWD. It came with 18" Z-Rated tires (Michelin Pilot Sport). The car had 49.9/50.1 weight distribution. In the winter, it was totally undriveable with OEM tires. Once I changed the tires to 17" snow tires, it was very drivable.
A (current, for a long time) car was a Porsche 997 Turbo. 19" Michelin Pilot Sport's. AWD. Very unbalanced weight distribution (heavy rear bias). This car was 'driveable' in light snow on the one or two occasions I had to move it that way.

I'd say that AWD likely does make a big difference, even with the weight distribution, but nothing beats having appropriate snow tires in the winter time.

 

[jerry33]

And at $4k, I didn't expect to see many non-Ds. But $5k hit a psychologic barrier for me.

$4K and $5K is less than sales tax and there is potentially more range. Getting the D seems like a slam-dunk if you're purchasing a new car. If you already have a Model S, like I do, the hit on the current car isn't worth it.

 

[wycolo]

A BMW M3 having 50/50 weight distribution is surprising. Maybe you carried lots of junk in the trunk??

My BMW 2002 had almost NO weight on the rear axle [the extent of my BMW experience].
--

 

[randompersonx]

A BMW M3 having 50/50 weight distribution is surprising. Maybe you carried lots of junk in the trunk??

BMW Technology Guide: 50:50 weight distribution

50/50 distribution has been a design goal at BMW for a while, certainly at least since the E46 M3, if not earlier. It's not easy to find the original marketing literature for that model, but it was very clearly stated. Tesla is not even remotely the first car to have a 50/50 distribution.

My BMW 2002 had almost NO weight on the rear axle [the extent of my BMW experience].
--

I also frequently compare the Model T to Ford's new mustang.

 

[wycolo]

I'm impressed and thanks. Compared to the extreme 2002 I'm sure they moved the entire transaxle to the rear and just about everything else they possibly could. 50/50 is quite an achievement for a smallish car like the M3.
--