Performance not getting 310 miles promised

[SammichLover]

Yeah, but it's hard to know unless it has been detailed somewhere by Michelin. The width will make a difference regardless (and I'm too lazy to go poke on Tire Rack right now).

The section width is a hair larger on the 20" version compared to the 18" (OE PS4 and also the standard PS4S I use). The tread width is quite a bit wider, a full inch wider. Which is all about the difference between 20" to 18" tires. There is very little difference between the Tesla OE version of the 20" PS4S and the standard 20" PS4S, the Tesla version actually has about 1/4" more tread width, so probably presents a slightly larger front-section.

So you're going to lose a touch with the stock P 20" wheels, beyond just what you don't get with the Aero rims.

 

[SammichLover]

I checked, it is 7.6" tread width for 235/45R18 PS4S and 8.8" for the 235/35R20 PS4S (Tesla version).

See post above for more detail about other options. Given that the section is only 2% wider (9.5" vs 9.3"), and this is just the tires so will be heavily diluted, using the 20" tires will add sub-10 Wh/mi.

Basically it boils down to driver option as to whether or not you get 250Wh/mi at 65mph highway in a stock P in good weather. Even at sea level.

 

[AlanSubie4Life]

The tread width is quite a bit wider, a full inch wider.

I believe that 1.2 inches will make a difference to efficiency, yes. The section width affects the aero as well.

Overall everything seems to line up, anyway.

 

[AlanSubie4Life]

250Wh/mi at 65mph highway in a stock P in good weather

Yikes...not so sure about that one. Splitting hairs, but I suspect that would result in 255-260Wh/mi.

Here is a 237Wh/mi result, but below 60mph. And also with a brisk tailwind for 1/3 of the journey.

Disappointing Range in P3D. Is this normal?

I am fairly sure that 65mph will lead to greater than 250Wh/mi consumption (but it will be close). 75 mph gives about 275Wh/mi.

In any case, 250Wh/mi (indicated) would result in about 290 miles of range for a full 100% to 0% discharge, by my calculations.

EDIT: (Which, agreed, would be quite an excellent result.)

 

[SammichLover]

I believe that 1.2 inches will make a difference to efficiency, yes.

That represents a very small cross-section change, because it is just taper at the edge rather than the full height of the tire.

But of course, if you're running 20" tires then WTF dude?

 

[SammichLover]

Yikes...not so sure about that one. Splitting hairs, but I suspect that would result in 255-260Wh/mi.

Here is a 237Wh/mi result, but below 60mph. And also with a brisk tailwind for 1/3 of the journey.

Disappointing Range in P3D. Is this normal?

I am fairly sure that 65mph will lead to greater than 250Wh/mi consumption (but it will be close).

(1 - (65/70)^2) * 100% = 14% less air resistance at 65mph vs 70mph. It shouldn't be close at all.

 

[AlanSubie4Life]

But of course, if you're running 20" tires then WTF dude?

Just trying to establish the facts, that's all!

I also am trying to evaluate for myself the necessity of road trip tires (and how much they would buy me). Probably would be a good idea because there is the tricky issue of having to make it from St. George to the North Rim and back, and needing to find some sort of charging solution on the North Rim (RV area not going to be something I want to deal with). It'll be easier to manage with more efficient tires, but a problem in either case. Probably not necessary, but also the higher sidewall height would be nice to have.

(1 - (65/70)^2) * 100% = 14% less air resistance at 65mph vs 70mph. It shouldn't be close at all.

If you scale the 275Wh/mi I quoted by 14%, it wouldn't be (that would be 231Wh/mi). But that's not the way it works, as only a small portion of that 275Wh/mi (perhaps 85Wh/mi at the absolute most) is due to aero losses. Zoomit has a model. There are also fixed losses (small of course - I'd estimate about 400W, so only 5Wh/mi at 75mph and 6Wh/mi at 65mph) that reduce with increased speed.

There's no question in my mind that it will be close.

 

[SammichLover]

But that's not the way it works, as only a small portion of that 275Wh/mi (perhaps 75Wh/mi at the absolute most) is due to aero losse

????

That sounds way off. The models I've seen are about 1/2 at (<edit> lower-ish) highway speeds, so more like double that, so it should be at least 20Wh/mi.

<edit> And the flip-side to your discounting the aero component so much is that if you run with that the altitude difference should be a lot less. Either way you cut it, if your P isn't doing 250Wh/mi or less at 65 cruising then there's something else at play, not the car.

 

[AlanSubie4Life]

????

That sounds way off. More like at least double that at highway speeds, so it should be at least 20Wh/mi.

Not sure what you're saying. I modified my statement to be a max of 85Wh/mi due to aero at 75 mph. But I said absolute max (the higher it is the better improvement you can get by going slower). I actually think it is lower than 85Wh/mi @75mph due to aero losses.

My argument? What's the best efficiency you can achieve? It appears to be about 230Wh/mi in the P3D+, at about 35mph (It's probably about 200Wh/mi in the AWD/P3D Stealth with MXM4s). I think we can agree that at this speed of 35mph there are some aero losses, but they are very small relative to 75mph and 65mph.

So, let's say there are 10Wh/mi aero losses at 35mph. That means 220Wh/mi just to move the car. So 220Wh to go one mile. If it's taking 275Wh to go one mile at 75mph, that means the aero losses are something like 55Wh/mi.

That's just rough numbers, I'm not trying to be precise here. Just saying you can't scale 275Wh/mi by 14% because you reduced speed from 75mph to 65mph. There will be nowhere near that much saving (I'd guess it might help by 5-6% or so).

 

[SammichLover]

Not sure what you're saying. I modified my statement to be a max of 85Wh/mi due to aero at 75 mph. But I said absolute max (the higher it is the better improvement you can get by going slower). I actually think it is lower than 85Wh/mi @75mph due to aero losses.

That's bonkers low. That's what I'm saying. Go look at the actual modeling of this people have done. Nothing like that.

Also see my edit above.

 

[AlanSubie4Life]

Go look at the actual modeling of this people have done. Nothing like that.

It would be good to get a link to that (I think @Zoomit has a model and he could chime in). I just have a hard time wrapping my head around why, if the contribution of aero is as large as you say, NO ONE reports better than about 200Wh/mi (230Wh/mi in the P3D+), for modest speeds, for the AWD. I mean, it takes energy to move the car, turn those wheels, overcome that friction.

What do you get at 25mph? According to your original formula, you should get 30Wh/mi (275Wh/mi*(25/75)^2).

Anyway, let's go to a larger number, and let's call the aero losses 150Wh/mi at 75mph (I think this is WAY higher than it actually is), with overall 275Wh/mi, how would that look?

Crudely, it would be: 125Wh/mi + 150Wh/mi*(25/75)^2 = 142Wh/mi (I'm neglecting the 16Wh/mi increase at low speed, from the 400W static power)

Seems unlikely...can you get this efficiency in a P3D+? Or even 160Wh/mi?

The only way this is remotely possible I think is in a RWD running at 35mph (implies 513 miles on a charge). But that vehicle has a better base efficiency, and I would guess can get better than 240Wh/mi @ 75mph.

I know there are EPA coefficients, but do note that those are curve fits, so they can be a little tricky.

Also, note that I am kind of assuming there isn't a significant proportion of losses that scale linearly (not with the square like aero) with speed (there probably are some, but I suspect they are fairly small - but I don't know). The obvious physical contributors are the static power dissipation of the car (400W minimum I think), and the energy proportional to distance needed to physically to move the car (rolling resistance, other friction (drivetrain losses, battery discharge waste heat, inverter efficiency), would fall into this category) - as far as Wh/mi is concerned, this is kind of a "constant", does not scale with speed, and is likely the dominant contributor to the efficiency at low speeds (at very low speeds the 400W static matters of course - even at 25mph it is 16Wh/mi).

It is a good question though, I'd love to know what the actual number is at 75mph - it would make all this scaling so much easier!

I guess I can figure this out for myself if I test carefully, once at 80mph, once at 65mph, over the same course, and make the (small) correction for static losses. No time for that though.

 

[SammichLover]

just have a hard time wrapping my head around why, if the contribution of aero is as large as you say, NO ONE reports better than about 200Wh

People do report sub-200 in LR RWD. It is also why record for insane hypermile of Model 3 is up at 600 miles.

 

[AlanSubie4Life]

Disappointing Range in P3D. Is this normal?

You may be closer than I was.

Based on @Zoomit's statement here, if the efficiency is 275Wh/mi @ 75mph (that's an assumption), his model also says:

"Now let's look at 3P-20" energy consumption at highway speeds. With no wind, just increasing the speed from 75 to 79 mph increases consumption by 6.6%. Decreasing speed from 75 to 71 mph decreases consumption by 6.2%."

I can fit this (neglecting the unknown linear term and any static losses) with:
110Wh/mi + 165Wh/mi (aero) @ 75mph
110Wh/mi + 165Wh/mi *(79/75)^2 @ 79mph = 293Wh/mi (+6.6%)

But, I can't square that with the results at say 30mph (again, a simple model, but...)

110Wh/mi + 165Wh/mi*(30/75)^2 @30 mph = 136Wh/mi

So those other terms must matter - perhaps the fixed consumption is very high...or this is just a model and it isn't quite right....or there is something I am missing.

BTW, at 65mph this model would suggest....234Wh/mi. And 209Wh/mi @ 58mph. Also seems low to me. With the link from early from @Paddy3101, he hypermiled (with a tailwind) and got
237Wh/mi at about 58mph.

So my simplistic interpretation of Zoomit's model is incorrect for sure. There is some other factor at play.

People do report sub-200 in LR RWD. It is also why record for insane hypermile of Model 3 is up at 600 miles.

100% agreed, not surprised at all by that. That's why I specified no one reports better than about that level in the AWD. That RWD is a fantastically efficient vehicle.

 

[Glamisduner]

I'm averaging over 300Wh/mi since switching to 19's and PS4S.

 

[SammichLover]

I'm averaging over 300Wh/mi since switching to 19's and PS4S.

Varoooooom!

Custer SD and back on PS4S + Aeros was 278Wh/mi over the 2700+ miles. A lot of variable conditions in there, of course. But I'm not really one to baby it unless there is an extreme range need.

Lifetime is stabilized around 280Wh, and saw very little change since switching over from the stock MXM4. My guess is they are costing me less than 5%, though a precise number is hard to nail down due to variables.

 

[Glamisduner]

Varoooooom!

Custer SD and back on PS4S + Aeros was 278Wh/mi over the 2700+ miles. A lot of variable conditions in there, of course. But I'm not really one to baby it unless there is an extreme range need.

Lifetime is stabilized around 280Wh, and saw very little change since switching over from the stock MXM4. My guess is they are costing me less than 5%, though a precise number is hard to nail down due to variables.

MXM4's on my car was around 260Wh/Mi. Traveling the same stretch at the same speeds as the PS4S 245/40/19's

 

[SammichLover]

You may be closer than I was.

LOL "may be".

The reason you don't see sub-200Wh/mi reported on the AWD as a matter of course probably has more to do with people not bothering, and difficulty avoiding ever engaging the front motor while hyper-miling. **

I highly suspect that both the D & P have a fairly heavy inflection point in the Wh/mi curve when your choice of cruising speed, in whatever conditions you're driving in, trigger the car engaging that front drive unit.

** I'd actually go out and take a shot at a sub-200Wh/mi extended drive myself for the "fun" of it if I wasn't so sure I'd be bored to tears.

 

[SammichLover]

MXM4's on my car was around 260Wh/Mi. Traveling the same stretch at the same speeds as the PS4S 245/40/19's

That's rim change, as well then? Plus tire profile change that comes with that rim size change.

 

[jerry33]

Yikes...not so sure about that one. Splitting hairs, but I suspect that would result in 255-260Wh/mi.

Here is a 237Wh/mi result, but below 60mph. And also with a brisk tailwind for 1/3 of the journey.

Disappointing Range in P3D. Is this normal?

I am fairly sure that 65mph will lead to greater than 250Wh/mi consumption (but it will be close). 75 mph gives about 275Wh/mi.

In any case, 250Wh/mi (indicated) would result in about 290 miles of range for a full 100% to 0% discharge, by my calculations.

EDIT: (Which, agreed, would be quite an excellent result.)

Depends on wind direction, tires, tread depth, alignment, and road surface. Unfortunately, there are a lot of variables.

 

[jerry33]

That's rim change, as well then? Plus tire profile change that comes with that rim size change.

And the tread compound change, and the tread with change. Lot of changes.