Wh/mi and why should I care?

[SageBrush]

This is a common mathematical fallacy. It is obvious that it is wrong if you change "25" to "100": doubling the rate of consumption does
not result in no (i.e., 100% less) range. A 25% increase in consumption results in a 20% reduction in range. A 100% increase in
consumption results in a 50% reduction in range. Sparing y'all the real math, a 1/N (N=1,2,3,4,...) increase in rate of consumption
corresponds to a 1/(N+1) reduction in range.

Well said, from the land of Pi

 

[SomeJoe7777]

This is a common mathematical fallacy. It is obvious that it is wrong if you change "25" to "100": doubling the rate of consumption does
not result in no (i.e., 100% less) range. A 25% increase in consumption results in a 20% reduction in range. A 100% increase in
consumption results in a 50% reduction in range. Sparing y'all the real math, a 1/N (N=1,2,3,4,...) increase in rate of consumption
corresponds to a 1/(N+1) reduction in range.

Yes, of course. I was just making the point with rough numbers that using Wh/mi at higher than rated means you get less range. The exact reduction wasn't needed to illustrate the point.

 

[RogerHScott]

Yes, of course. I was just making the point with rough numbers that using Wh/mi at higher than rated means you get less range. The exact reduction wasn't needed to illustrate the point.

Bonus question for the math geeks out there: there is an increase in consumption rate that would yield the exact same reduction in
range; what is that increase, either numerically or symbolically (it is a very special number that has a name [multiple names, actually])?

 

[Clomer]

One thing that always bothered me is that MPG is really miles per gallon of gas. Whereas Wh/Mile is watt-hours per mile. We should actually change MPG into GPM to rate gasoline cars. I know it's just an inverse function, but so many people think that 50MPG is really really better than 45MPG, when in reality it is only 10% difference. In gallons per mile, or gallons per 1000 miles, so 22 MPG = 45 gallons per 1000 miles.

We don't think of EVs in terms of Miles per Wh (or KWh)! 3 miles per 1kwh.

QFT.

When talking MPG, higher is better, and it's because it's distance over unit of energy (bastardizing a gallon of gas as a unit of energy). Wh/mi is unit of energy over distance, which reverses the ratio - this means that lower is better.

 

[CHG-ON]

I really don't care about kwh/mi unless I am pushing my range, which is rare. But I have noticed, with just a 10 degree fall in temps on my commute, my cost to get to and from work has jumped a whopping 23%, from .77c to exactly one dollar! Oh no!.

But honestly, I was a bit surprised to see temps dropping from high 50's to high 40's would have that much of an impact.

 

[whitex]

Ok, not sure why no body mentioned this here. Wh/mile is an average calculated over some distance, so your last 5miles will be different than your last 30miles, your current trip or even car life average.

Rated range tells you how far you can expect to go if you keep it at rated wh/mile (which is under 300 AFAIK).

Projected range is based on last 5/15/30 miles, so it will change as you select different segment distance.

If you do want to compare to ICE, wh/m is not similar to l/100km used in Canada for example (in USA mpg is flipped). You can have a different l/100km or mpg for last mile vs. entire trip.

Bottom line, why is it useful? Same as mpg, you can see how well (or bad) your car is doing compared to what you need and adjust your driving accordingly if needed to make it to your destination with the fuel you got.

 

[kort677]

I really don't care about kwh/mi unless I am pushing my range, which is rare. But I have noticed, with just a 10 degree fall in temps on my commute, my cost to get to and from work has jumped a whopping 23%, from .77c to exactly one dollar! Oh no!.

But honestly, I was a bit surprised to see temps dropping from high 50's to high 40's would have that much of an impact.

do you use your heater when the temps drop?

 

[democappy]

do you use your heater when the temps drop?

I do and saw a similar drop as CHG-ON so I assume he does too. I knew using the heater caused a drop, but I was surprised that getting to the 50s was already enough to reduce efficiency a bunch. I was actually even more surprised to see the battery needing to warm up before accepting regen at what I would still consider a fairly high temperature. I live in NC, so I figured winter impacts to me would be quite low/almost non-existence. Doesn't impact me much, but was different than what I was expecting.

 

[RogerHScott]

jumped a whopping 23%, from .77c to exactly one dollar

Sounds like 2300% to me, but who's counting?

 

[kort677]

I do and saw a similar drop as CHG-ON so I assume he does too. I knew using the heater caused a drop, but I was surprised that getting to the 50s was already enough to reduce efficiency a bunch. I was actually even more surprised to see the battery needing to warm up before accepting regen at what I would still consider a fairly high temperature. I live in NC, so I figured winter impacts to me would be quite low/almost non-existence. Doesn't impact me much, but was different than what I was expecting.

once the heater is on it consumes power, the ambient temp is what regulates how long the heater is engaged. what I do is I limit the use of the heater with the heated seats and steering wheel. once the car's interior is warm that's all I need to remain comfortable

 

[CHG-ON]

do you use your heater when the temps drop?

Yup. I'm a California whimp now. But I think most of the energy is conditioning the battery. I'm beginning to get the power limited popup energy gauge for a second when I start out. I have an uninsulated garage. But it goes right away. So I expect I am right at the threshold. We had a very warm winter last year and this one is shaping up to be cooler and wetter (thank goodness), so It will be interesting to see the change in consumption over time. Last year showed very little change.

 

[kort677]

Yup. I'm a California whimp now. But I think most of the energy is conditioning the battery. I'm beginning to get the power limited popup energy gauge for a second when I start out. I have an uninsulated garage. But it goes right away. So I expect I am right at the threshold. We had a very warm winter last year and this one is shaping up to be cooler and wetter (thank goodness), so It will be interesting to see the change in consumption over time. Last year showed very little change.

keep your car plugged in, it will help

 

[CHG-ON]

keep your car plugged in, it will help

Always do! What Elon says, I do. Except I ain't goin' to Mars. No Tesla service centers.