Forums

Wind Effect on Model S Range at Highway Speeds

Wind Effect on Model S Range at Highway Speeds

Anyone have reliable data on how a significant head wind (or tail wind) can effect the range of the model S at highway speeds (65-70 mph) over a distance of at least 100 miles? I know wind (10-20 mph) can significantly effect your mileage in an ICE car.

UnshodBob | 10 juni 2016

The "weather variation" tab on evtripplanner shows the effect of a 5 mph head or 5 mph tail wind. I put in a trip from Corona CA to San Diego CA which is about 95 miles actual distance. I didn't set any specific car or other options. It said about 95 miles used with a tailwind, about 105 miles used with no wind, and about 120 used with a headwind. That tab is blank until you enter a trip, and it shows USAGE, not RANGE per the note at the bottom. I'm not sure how accurate it is, but people say it is a good program overall.

Bighorn | 11 juni 2016

A headwind is comparable to driving that much faster i.e. driving 70 mph with a 10mph headwind is similar to driving 80 mph. Don't know the coefficient of drag from back to front.

snively2011 | 11 juni 2016

I can give you a qualitative answer but nothing quantitative.

Driving through Wyoming and South Dakota was absolutely BRUTAL on my range. Sustained 50 mph winds just destroyed my efficiency. We were stopping at every supercharger, charging for a long-ass time, and driving just under the speed limit to make it through those states :)

Bighorn | 11 juni 2016

South Dakota is notorious for poor efficiency even without wind. I think it relates to the road surface. Efficiency runs between 400-450Wh/m or about 100Wh/m more than expected.

Ruby110 | 11 juni 2016

@Bighorn: Ah, that explains it! I had poor efficiency numbers crossing SD the last couple of days. One day the wind was out of the northeast and the next day out of the southeast. We were traveling west. I thought is was only the wind effect.

Passing through Sheridan today. Any efficiency loss expected?

Bighorn | 11 juni 2016

@Ruby
I find that WY has about a 10% SOC penalty vs the 25%SOC of SD. You definitely need a 30% buffer in SD or you're either turning back or going 30 MPH under the limit. The algorithms may not account for the fact that the speed limit was boosted to 80 MPH. I may see you around if I don't go check out the new Yellowstone chargers:)

kortlander | 11 juni 2016

common sense will tell you that driving into a headwind will use more energy, driving with a tailwind will require less. my real world experience this past winter was that heading west on I70 into a very strong headwind required at least 25% more energy than if there wasn't any headwinds. on the return trip I was doing 75+ mph and only using 245 wh/miles with a similar tailwind. you'd be wise to plan for this on any road trips you might take

stevenmaifert | 11 juni 2016

Not easily quantified, but a headwind is a significant range killer and should be factored into your trip planning. Charge to 100%, keep an eye on your watt hour per mile consumption, and slow down if necessary to make it to your next charging opportunity.

Ruby110 | 11 juni 2016

@BH: FYI. Leaving Gillette in a few minutes.

Bighorn | 11 juni 2016

Enjoy those Bighorn views!

Ruby110 | 11 juni 2016

A head wind example: we left Sheridan with a projected arrival of 30%. Not too long into the drive the percentage began dropping. When it dropped to 15% projected I slowed down to 65 from 80. That stemmed the flow and I waited for a truck to come along. It took dozens of miles but when it did I sort of drafted it. When the road turned west the wind became a cross wind. So with 37 miles to go I went back up to 80. Arrived with 21% remaining.

Ruby110 | 11 juni 2016

@Bighorn: Very nice meeting you. I'm going to have a drink at one of those restaurants you recommended!

SbMD | 11 juni 2016

A Bighorn view to the second power :)

Bighorn | 11 juni 2016

@ruby
Great to meet you and your wife! Those precipitous drops in anticipated arrival SOC fortunately usually level out at about the 30 mile mark. There was quite a gale that blew in after you left though!
Cheers!

rg22.vanhorn | 11 juni 2016

Here are some real numbers... just for wind/ speed drag (no rolling resistance, no elevation gain/ loss, no acceleration, no other inefficiencies..):

Tesla Consumption

Effect of Drag (Air Resistance) on Consumption

Drag Force

F = Cd*ρ*V2*A/2gc

F = Drag Force
Cd = Drag Coefficient
ρ = Density of Air
V = Velocity
A = Drag Area (Frontal Area)
gc = Dimensional Conversion Factor

Power

P = F* V = Cd*ρ*V3*A/2gc

Consumption = Power (Watts)/Speed (mph)

Cd = 0.24 Tesla Website
ρ = 0.0765 lbm/ft3 Assummed constant. Density is a weak function of temperature and alititude.
A = 25.2 ft2 Tesla Website
gc = 32.2 lbm-ft/lbf-s2

Speed Power Consumption
(mph) (kWatts) Watt-hr/mile
10 0.03 3.1
20 0.25 12.3
30 0.83 27.7
40 1.97 49.2
50 3.84 76.8
60 6.64 110.6
70 10.54 150.6
80 15.73 196.7
90 22.40 248.9
100 30.73 307.3

Power is proportional to speed cubed.
Consumption is proportional to speed squared.

Consumption due to drag goes from about 110 Watt-hr/mile at 60 mph to 150 Watt-hr/mile at 70 mph to 197 Watt-hr/mile at 80 mph.
Consumption due to drag at 50 mph is about one-half consumption at 70 mph.

Ruby110 | 11 juni 2016

@rg22: So my takeaway is I experienced a double whammy. High speed limit (80mph) and high headwind.

@BH: Yeah, I experienced the leveling off in South Dakota but it also fluctuated up and down by several percent. I thought that was strange.

In this instance I was ok until it dropped to 15% and we still had about 100 miles to go.

quassinoid | 11 juni 2016

Thanks for all the good responses to my question. This is a good forum with nice people.

ram1901 | 11 juni 2016

Now imagine the impact it has on a less efficient, high drag, ICE vehicle heading through SD.
Bet fuel economy goes from 24 mpg down to 16. Just pickin' a number out of the air... but
point made...

Bighorn | 11 juni 2016

@ram
On less efficient vehicles. it isn't as pronounced. Imagine your Tesla averages 300Wh/m and then the headwind adds 100Wh/m--your efficiency now only allows you to travel 75% of normal. Then consider an ICE which might have an efficiency of 1200 Wh/m when conversion of energy is considered--the 100Wh/m penalty of the wind only drops the efficiency by around 7.5%. Same concept applies to the relative expense of using the AC or heat, the latter of which is compounded by the fact that heat is a byproduct of the ICE and must be produced resistively by the Tesla.

shs | 12 juni 2016

There is a very nice app described on the Tesla Motors Club Forum that will get the windspeed and direction from the web (as long as you have cell signal) and display it relative to your travel direction as a head wind or tail wind. It also picks up and displays elevation and rate of climb - very cool!

https://teslamotorsclub.com/tmc/threads/tesla-winds-and-elevation-web-br...

It is a bit complicated to set up, and is best done at first on your laptop, but once you have it working in the car’s browser window and save it as a favorite, it is very easy to access in the future. Or in my case, since I rarely use the browser for anything else, it will come up by simply selecting the browser. No more looking for flags while traveling up and down 99!

barrykmd | 12 juni 2016

ram1901 | June 11, 2016
Now imagine the impact it has on a less efficient, high drag, ICE vehicle heading through SD.

Not an issue with gas stations on every corner.

Bighorn | 12 juni 2016

@barry
A corner requires that two roads cross--not very common in SD:)

Ruby110 | 12 juni 2016

I just set up the browser app. I'm looking forward to trying it tomorrow leaving Missoula. I wish I had had this going from Sheridan to Billings a couple of days ago. Although I'm getting better at "reading" the weeds along the roadway.

Earl and Nagin ... | 13 juni 2016

@Bighorn,
Good point. I'm guessing that proliferation of plug-in vehicles in rural areas isn't because of trepidation towards having to plan fueling stops since folks out there have to do so with gasoline already. I suspect the economics and vehicle types that are electrified today are more likely the driving factors.

AoneOne | 13 juni 2016

@Bighorn: Are you sure about that relative efficiency of an ICE in a headwind? Surely using waste heat from an ICE minimizes the effect of cold weather, but a headwind requires more power to be delivered to the wheels. If the fuel-to-wheels efficiency is, arbitrarily, 20%, why would that value change for a head wind vs. normal air resistance, rolling resistance, etc.

According to the example on https://www.fueleconomy.gov/feg/driveHabits.jsp, 30 MPG @ 55 MPH becomes 20 MPH @ 80 MPH.

Polybius | 13 juni 2016

I have taken a few long trips and it really did not matter. You will likely not be in the wind the entire time.

Tropopause | 13 juni 2016

I'm still waiting for Trip Planner to account for winds. Then we'll be sitting pretty!

Bighorn | 13 juni 2016

AoneOne
That's a good point and one I don't have a solid answer for. I don't know if the inefficiency of an ICE is linear as increasing power is requested. Would a headwind raising the power required by 100Wh/m require 100 or 200 or 400 Wh/m at the engine--I don't know.

The other aspect that makes EVs seem more affected is the magnitude of the change in miles available. If the effect of the wind were identical in percent degradation, it has a much greater impact on miles one can travel. Say a 100MPGe EV suffers a 25% loss due to wind, that's a 25 mile impact per "gallon" whereas a 20 MPG ICE would only see a 5 mile loss per gallon, which may go unnoticed given the fuel capacity.

CraigW | 13 juni 2016

Bighorn,
I will be driving from Cheyenne to Bozemen at the end of this month in an S70D. the only gap that would possibly give me trouble would seem to be Lusk to Gillette. Any suggestions or comments?

CraigW | 13 juni 2016

P.S. What I have found is that - without taking wind into effect - driving over 75 mph yields more time spent at the supercharger than gained because of driving at the higher speed. This is a general observation over 3.5 years of driving a Model S.

Nowadays I just set autopilot on 75 and leave it alone, unless I am on my last leg of the day.

Bighorn | 13 juni 2016

@Craig
I've made that leg several times in a P85+ that range charges to 250, so maybe comparable to yours? Lots of desolate sections that would lend themselves to slowing down without impeding flow, if necessary. The last bit on I90 is 80 MPH but you'll have an excellent sense of your reserve by then. Agree about 75 MPH being a sweet spot. As I recall, the trip planner was making largish jumps in estimated remaining SOC. It would be 20% then 12 and back to 20 again. Don't know if it relates to connectivity or what. I don't remember having to economize.

PV_Dave @US-PA | 15 juni 2016

ICE inefficiency is certainly not linear. If it was, then "pulse and glide" wouldn't work as a way to boost efficiency. Most ICE vehicles' peak efficiency is at a power level above what's required for steady-state cruising without wind.

Straight headwind is like adding to your speed, straight tailwind means drag as if subtracted, but cross winds on average also cause increased energy use. And if driving at a constant speed, the increase in energy from the headwind is much greater than the same decrease in energy from the tailwind, so if you had 50% pure headwind and 50% pure tailwind, you come out significantly behind having no wind at all. Add in the fact that the wind is frequently NOT pure head or tail, and wind causes a pretty significant increase in energy use in most cases.

dleidy | 15 juni 2016

My X burns about 425 going 70, when I draft a trailer at the same speed with the cruise distance set to 1, the power usage droves below 250 Wh/mi. Drafting is hugely beneficial for range. Just pick a trailer with big mud flaps and don't do it on a dirty road to avoid rocks.

DonS | 15 juni 2016

On US 101 between Gilroy and Atascadero,CA, I have learned to charge 15% more for the northbound trip. The windmill lined up directly with the road direction indicates the headwind northbound is straight on every time.

David Trushin | 15 juni 2016

A few years ago i sent tesla a suggestion that they put an air speed indicator into the big screen apps. I'm not an aeronautical engineer, but it seems like a strategically mounted Bernoulli tube would do the trick.

ShockOnT | 15 juni 2016

Two things about speed affect your range:
1. Air drag
2. Friction associated with the wheels (tire warming, bearings).
The air drag is by far the dominator at highway speed, because it goes up by the cube (3rd power) of speed. So a doubling of airspeed requires 8 times more power.

Your airspeed is your groundspeed plus headwind (or minus tailwind).

Note that only the forward or backward component of the wind is added. The sideways component would add very complicated losses (vortex generation, micro changes to tire footprint etc) but could be ignored.

mooneytune | 15 juni 2016

As a private pilot and soon to be Model S owner, I have to say this is fascinating to me. Planning a long distance drive in a Tesla is almost exactly the same challenge as planning a long distance trip in a plane. Wind radically effects your efficiency (in the plane's case ground speed vs. air speed) and knowing where you can stop to top of the fuel is critical, especially in the more remote areas of the country.

I guess the main difference that all pilots will tell you is that you don't get to pull your plane over on the side of the road when you screw up and run out of fuel!

JAD | 15 juni 2016

@mooneytune, you also can't fly at 25 mph and more than double your range when needed :)

bb0tin | 16 juni 2016

@Bighorn
You said "A headwind is comparable to driving that much faster i.e. driving 70 mph with a 10mph headwind is similar to driving 80 mph."
No it isn't.
Increasing your speed increases your rolling resistance.
Increasing the headwind by the same amount does not. (to any appreciable degree)

T90KWH | 16 juni 2016

@bb0tin - no doubt you are correct that rolling resistance is also increased bur BH didn't say 'equal to', but 'comparable to', because the air resistance is by far the dominant factor.

T90KWH | 16 juni 2016

bur = but!

Bighorn | 16 juni 2016

@bbottin
I know you argue for argument's sake. Please provide evidence in the form of formulae to support your assertion that speed has any meaningful impact on rolling resistance in this real world example.

bb0tin | 16 juni 2016

@Bighorn
You said "I know you argue for argument's sake"
You are incorrect.
I argue because I believe that the opposing viewpoint is incorrect, based on evidence and reasoning.
I never argue a position I do not believe is correct.
I try never to hold an opinion unless I have evidence and reasoning to support it.
"I don't know" and "I have no opinion on that" are said by myself many times in real life.

I would request that after you read these links you acknowledge that what you posted was incorrect.
http://machinedesign DOT com/automotive/understanding-rolling-resistance-car-tires
https://en.wikipedia DOT org/wiki/Rolling_resistance

PS:
I also understand why you asked me for the evidence supporting my statement.
Please provide evidence for a statement you make next time I ask.

bb0tin | 16 juni 2016

@T90KWH
You said "bur BH didn't say 'equal to', but 'comparable to', because the air resistance is by far the dominant factor"
You are incorrect as can be determined from the links provided above.

bb0tin | 16 juni 2016

People can establish that what I said is correct if they own a bicycle and it gets windy where they can ride.
Wait until you have a windy day, say a 50kph wind, and ride into it. You are likely able to maintain 20-25kph on your bike. Now try and ride 70-75kph on a still day. You will not not be able to do so. You will not even be able to maintain 50kph.

GHammer | 16 juni 2016

bb0tin, you are incorrect. The aerodynamic drag increases by the square of the velocity while rolling resistance increases linearly. Google aerodynamic drag vs. rolling resistance and you will see many sources with a variation of this graph.

bb0tin | 16 juni 2016

@hammer @OR-US
Your graph supports what I said, not the other way around.
Rolling resistance increases with vehicle speed.
Rolling resistance does not increase the same with a head wind.
The links I provided explain this.

PV_Dave @US-PA | 16 juni 2016

@bb0tin: You are correct that tire drag is not affected by wind speed in any meaningful way. And thus, the total drag of a 70 MPH car in a 10 MPH headwind is not equal to the total drag of an 80 MPG car.

HOWEVER, @Bighorn didn't say equal, he said comparable. Have you done the math to compute figures for both cases? And what do you consider to be the definition of "comparable"?

I suspect that the two cases are close enough that "comparable" is a reasonable adjective. If you disagree, please feel free to do the math and present the results here. Certainly since aerodynamic drag goes as speed squared while tire drag is linear, there's no question that aerodynamic drag at that speed is much larger than tire drag. But if you don't do the math and quantify your interpretation of "comparable", then you're not proving anything.

GHammer | 16 juni 2016

@bbOtin. OK, now I understand what you are trying to say. You are picking nits. Bighorns statement in the practical world was absolutely accurate, the contribution to increase of overall drag due to tire rolling friction is negligible compared to air speed drag.

bb0tin | 16 juni 2016

@PV_Dave
I have provided links so you can do your own calculation.
I have also explained how you can do your own empirical test by riding a bike.
I am not going to do the calculation, or the experiment, for you.

Pages