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I thought around town "mpg" was supposed be better.

I thought around town "mpg" was supposed be better.

I noticed a long while back that when I am cruising on the highway, going about 75 mph, I easily get an average wh/mi of well under 300,usually in the 270 range. However around town the avg is much higher which I find confusing because you would think that with all the decelerating, the avg would be much less.

For example, yesterday I drove a total of 32 miles, all of which was in town driving, never getting about 45 mph. I used up 11.3 Kwh to go those 32 miles and had an avg. wh/mi of 353. Granted the A/C was running for the miles driven in the afternoon. I have the temp set for 70 and it was 82-85 yesterday.

Is there something I am missing here?

jai9001 | July 12, 2014

I have the same experience.

If you do a lot of stop and go driving, the efficiency suffers.

There is a significant energy cost to cooling and heating in the first few miles.

PleasantonS | July 12, 2014

I get around 280 on the hwy and 310 around town in my P85+. The biggest factor around town is how aggressively you accelerate and how regularly you brake vs. letting the regenerative breaking do its thing. Than can easily be a 50 wh/mi difference.

J.T. | July 12, 2014

The more time spent stopped while using energy (stop lights, traffic) the higher your average will be. Think about it, you're using energy and going zero miles, how can that not affect your average?

zwede | July 12, 2014

Regen isn't 100% efficient or even close to it. I read somewhere that it gives you about 60% back. No idea how accurate that number is, but the point is that although regen is far superior to no regen, it only partially makes up for stop-n-go traffic.

nickjhowe | July 12, 2014

Acceleration is going to kill efficiency. If my math is correct, accelerating from 0-35 mph uses (roughly) the same energy as driving 1/2 mile at 35 mph. If you do 0-35 in 6s, you'd travel 46m. So per unit distance, accelerating to 35 takes 20 times as much energy compared to driving at constant speed.

johncrab | July 12, 2014

I'm expecting this. It's similar to my former XJ-S which was a very heavy car and got truly sucky mileage in town but could get up to 24 on the highway. It's the start/stop that kills efficiency because you have to get all of that mass moving each time. An object at rest tends to remain at rest and an object in motion tends to remain in motion.

Owning two Prii taught me to be a better driver by gauging the traffic, looking farther ahead, learning to sync with the lights, etc. I get 57 winter and 52 summer (high AC load) as a result. I also found that good, economical driving habits are also good, safe driving habits. I'm just more aware of what's going on.

Teach yourself to coast. ICE cars teach us to operate a car like a kiddie pedal car with one foot or the other cranked to the floor at all times. A hybrid or EV wants to be driven differently but it takes better concentration in order to do it.

My habits were so apparent that on my MS test drive the cool Tesla Dude even remarked, "You must drive a hybrid".

romainiacWV | July 12, 2014

It's the physics of starting and stopping a 4600lb car over and over again. On the highway, one you get rolling there is less energy consumed as the cars weight helps to propel it, in the city you lose that efficiency as you have to keep Accelerating the car.

MNGreene | July 12, 2014

As others have said, a higher wh/mi makes sense if you are stopped a lot during city driving, either at lights or on the highway. When driving on suburban roads and highways at 10-50 mph with minimal braking during rush hour, I use about 40 wh/mi less than steady highway cruising.

tes-s | July 12, 2014

The main things that hurt efficiency are speed changes (acceleration), elevation changes, heating/cooling, and wind resistance.

Drive a straight flat smooth country road during the day in good weather with windows closed and hvac off at 30mph with no wind, and you will go a very long distance. Add a 60mph tailwind and you can go forever.

Iowa92x | July 12, 2014

I don't understand the question. Other than hybrids, every car in the history of the world gets better mileage on the highway than in town. Stop and go.

AmpedRealtor | July 12, 2014

Stopping is the enemy of efficiency. Every time you stop, you basically throw away your momentum. This stop and go will rob you of efficiency. If you can time your city drives to hit only green lights, your efficiency will increase. If you see a red light a few blocks away, start coasting and slowing down gradually so that by the time you get to the light it turns green. While annoying the drivers behind you, you would have preserved as much momentum as possible and would have continued through the light without stopping.

Check out some hypermiling techniques, applying them to your city driving will help you improve your efficiency.

jjb94941 | July 12, 2014

It's a pretty reasonable question. Stop and go doesn't necessarily consume more energy than driving at a constant speed.

IF

1. Energy recovery during deceleration was 100% efficient (it's not);

2. One could totally avoid brake use in town (one can't, even though one can minimize it);

and

3. One could avoid being stationary in order to avoid energy consumption while adding no distance (also not possible)

Then one could achieve better gas mileage in town at an average of 30 mph than on the freeway at say, 55 mph.

Of course, 1, 2 and 3 aren't true, so there is a cutoff highway speed below which one can get better energy usage on the highway than in town.

mrspaghetti | July 12, 2014

You can maximize efficiency or fun. Sounds like you've been leading toward the latter :)

Who can blame you?

mrspaghetti | July 12, 2014

Leaning, that is

KidDoc | July 12, 2014

I'm amazed you get under 300 on highway. I usually get 340ish going 75-80 on a fairly flat part of Texas.

Roamer@AZ USA | July 12, 2014

Even at the the highest possible Wh/mi rates it is 20 times better than my ICE so I don't worry about it much.

AndyO | July 12, 2014

I've notice I can get below 300 when in a clump of traffic even if I'm not specifically drafting (I stay at least 2 seconds back). If I'm on the same road by myself it will be around 340.

carlk | July 12, 2014

@J.T. Unlike ICE the motor does not use any energy when stopped though. Accessories, other than perhaps heater, do not use any significant amount of energy.

I too can't get even close to 300 at highway cruising speed, 75~80 in my case.

bonaire | July 12, 2014

EVs are just like ICE cars in terms of mileage. city worse than hwy.

Hybrids "seem" to have higher MPG in city versus highway versus basic ICE cars but the issue is they get poor mpg until their engines warm up. They use a hot engine efficiently when rolling (momentum) and use the battery for the stop-light acceleration to not draw as much gas during the "go" part of stop-and-go.

anthony.dans | July 12, 2014

I've had a P85+ since 3/24 and I'm amazed that @jordanrichard got a range of 270 mi traveling at 75 mph. I drove from Los Angeles to Napa on Highway 5. Starting with a fully charged battery, I had to recharge twice. The trip was approximately 450 miles. The range from my first recharge in Coalinga, CA to where I had a remaining rated range of 5 miles in Livermore, CA was approximately 150 miles. The range from my full second recharge in Fremont, CA to Napa, CA was approximately 75 miles with a remaining rated range of 90 miles. My average speed from the first recharge to second recharge was approximately 80 mph. It was windy and was a lot of the terrain was uphill.

My daily driving is almost exclusively on city streets (no freeways/highways). The rated range when fully charged is 265 miles. Most daily trips average 5 to 20 miles. I average 165 miles per charge.

jordanrichard | July 13, 2014

Iowa2x, the reason for the question is because hybrids run in pure electric tooling around town, until the battery runs low. Since on the highway hybrids run off their engines, their highway mileage is worse than city.

So I presumed the city "mileage" would be better for the MS since there are far more times/opportunities for regen. I guess it's due to not having enough cruising time to lower the energy average from the acceleration.

bent | July 14, 2014

There is a tendency for people to think that EVs are more efficient at stop-and-go than they are on the highway. I think the reason for this is that people keep saying "EVs are so much more efficient in the cities" but then what they are actually comparing it to is ICEs. I.e., "EVs are so much more efficient than ICEs are in city traffic" not "EVs are so much more efficient in city traffic than they are on the highway". In the public mind those two meanings get confused and so you get the misconception forming.

Jonathan D | July 14, 2014

I've found it can be very efficient getting in traffic on the freeway (albeit no less boring). When doing gradual starts/stops in the 10-30mph range I get low Wh/mi usage, it's all gentle accel and regen. Around town if I drive like a granny I can get rated range or better even with stoplight-to-stoplight stuff, but usually if I'm driving around town it means I'm close to home and I don't really care. The cost to recharge the extra 10 miles worth of range or whatever is negligible.

cquail | July 14, 2014

Sounds good compared to my Volt. I used all my battery (9.7 KWH) going 32 miles @ 65 mph with temps in mid 80s a few weeks ago. Tesla a heavier car. Startup from a stop uses lots of juice.

From a Tesla wannabe owner.

bonaire | July 14, 2014

@cquail: I have never gotten that low a mileage in my Volt other than in 30*F weather outside and using some seat heaters. Did you have full-blast A.C. going? I got about 44 miles today in my Volt - a 2011 model using whatever it has for state of charge. One tip to getting more mileage in a Volt or any EV is to finish your charging just prior to leaving. Don't use full blast climate control. And keep your tires at 40-41 psi.

Brian H | July 14, 2014

The comments about accel etc. above are right; all those things work against you in city traffic, and the EPA ratings reflect this, showing ~87MPGe city and ~92MPGe highway. I was surprised on first reading this, because electrics get better mileage at slow speed. That works for you, as does regen. But the frequent changes in speed are a stronger influence.

If you could drive steadily through the city, at say 30mph, catching every light, etc., you'd do better than when driving 80mph on the highway. Fat chance, though!

sule | July 14, 2014

Constant low speed (best around 40km/h or 25mph) is more efficient. This is more common in the city streets than highways. But you also have deceleration (not 100% efficient) and braking (all loss)... And acceleration has its own non-100% efficiency. There are, thus, many factors at play.

During the day my city driving is comparable to my highway driving. When traffic reduces and I relax (nowhere to rush) my city consumption is way better than highway - so good I could switch to use "ideal range" display.

jordanrichard | July 14, 2014

The speed limits where I do most of my local driving, are between 35 and 45. Real world that means traveling between 40-50 mph. I guess the issue is that you can't go more than a half to 3/4 of a mile before hitting another traffic light.

jcaspar1 | July 14, 2014

I get better mileage in town than on the freeway. Freeway at 75-80 I get about 345. This improves a lot with non stop and go traffic. In town going 25-30 without too many stops I can get 515 to near 300.

cantcurecancer | July 14, 2014

Assuming you're not heating or cooling, energy usage during idling is so minuscule that it's not even worth mentioning. Heck, I'll throw in climate control and I bet you the energy "wasted" while idling is not as high as you think

The following is guesswork, but let's very very generously assume

LCDs ~ 50W
Onboard computer systems ~ 200W
Sound cranked ~ 250W
Headlights ~ 20W
Heater full blast ~ 2000W
Misc stuff - 50W

That's 2570W (or 2570Whr per hr)
Which equals 43Whr/min. That's how much energy the accessories are using, thus how much energy is being 'wasted' while idling, assuming the powertrain doesn't use ANY energy while stopped. A minute of idling is equal to 9 seconds of forward momentum (310wh/min = 5.17wh/sec. 5.17 * 9 sec = ~43W)

So let's say you're idling 25% of the time, 15 minutes on the hour. That means after an hour you will have wasted 645W while idling after an hour of driving. That's about 2 minutes worth of forward momentum. That's like a mile in the city?

Get rid of the climate control and drop idling to 10 minutes per hour and you will have 9.5wh/min with wasted energy while idling being about 18 seconds of forward momentum.

And again, I am being very generous with the numbers, unless I made some error somewhere (which is very much possible). But I bet the 17" LCD doesn't even hit 20W, with normal people the heater isn't full-blast but a few minutes until the cabin gets warm. I didn't take into account the energy used for some of the automotive stuff because I honestly don't know how much energy it takes, but I assume it's not much for not long (brakes being applied, suspension raising, etc.)

Don't underestimate how much energy it takes to move a 2 ton vehicle through wind at great speeds. It takes the lion's share of energy every day of the week.

I think the reason it costs more energy around the city is because the regen isn't as efficient as everyone makes it out to be. You're not going to recover the energy spent in drag, rolling resistance, powertrain inefficiency (x2), and the AC-DC/DC-AC inefficiency. But it still beats the hell out of 100% of it going to friction.

Highway w/o regen (coasting) is better than
Highway w/ regen is better than
city w/ regen which is better than
city w/o regen

Tesltoronto | July 15, 2014

Thanks, cantcurecancer. I think you are on the right track.

I have always read and heard that speed is the biggest consumer of energy in a MS. My experience is similar to that of the OP.

I have noticed that I get around 170 W/Km (272 w/mile) when I drive at around 115 Km/hr (72 Mph) vs. over 210 W/Km (335 w/mile) driving in the city. This is without watching the energy consumption like a hawk.

I was expecting the opposite - because we were always told that electric/hybrid cars are more efficient for city driving than highway driving, because theoretically there is no energy consumption when an electric/hybrid car stops at the lights and at slow speeds the car consumes less electricity to move. But I think the other accessories take on a constant amount of energy which was not factored into this calculation.

Bighorn | July 15, 2014

There might be some confusion here equating hybrids with EVs--hybrids are more efficient in the city because they are using more of their electric alter-ego; while on the highway, they're burning gas. EVs are not suffering that disadvantage on the highway.

jchangyy | July 15, 2014

For the sake of comparison, try in-town driving with AC shut off. I see consistent difference of 290's vs. 320s in town with AC off vs. On respectively.

Intros | July 20, 2014

I believe the Leaf is rated higher mpge for city. Tesla, spent more time in the wind tunnel and has less coefficient drag than the Leaf. The mass of a Tesla is larger than a Leaf. I have two Yaris converted EV's that go 145 miles per charge with one third of the mile driven on the hwy at 55-60 mph. If I go hwy at 55-60 mph the whole time the Yaris will only go 130 miles. The Yaris weight is 2750 lbs but is not arrow dynamic. The result is it goes further in the city than the hwy.

I miss my P85+. It has been in the body shop for over 10 weeks. Curse you State Farm.

Brian H | July 23, 2014

Heh! It's aerodynamic, though arrow dynamic sounds like fun.

DTsea | July 23, 2014

Early in morning with no lights I get under 250 wh per mi in city.... but traffic and lights impact it.

jordanrichard | July 23, 2014

I guess the other/better way to look at it with regard to hybrids is not that they do better in the city than highway, but that they do worse on the highway. Since hybrds batteries can't sustain highway speeds, the tiny engines have to do all the work. So you have a tiny engine with next to nothing for horsepower, trying to keep a relatively heavy car going at highways speeds. Since there are obviously no lights, meaning less opportunities to regen, the overall economy is worse.

I also further guess that just as it with ICE cars, what one gets for mpg/range is all defendant on where you live/drive. An ICE in TX will get better mpg than the same model would here in New England due to the temps and terrain. However since one has to generally drive further to get anywhere in TX, you end up using the same amount of gas for one's daily activities. So it's all a wash.

amatiych | July 23, 2014

One week in and still learning to drive efficiently. I get under 290 on highway driving around 65 and average around 310 on a round trip to work that is 80 percent highway.

Driving in Brookyn with short blocks and stop signs can't get below 440

bevguy | July 23, 2014

I have found the biggest problem in urban traffic lies with me, the driver. After decades of ICE driving it is hard to modulate the pressure on the accelerator pedal, keep acceleration very gradual. Another thing is A/C and heating. Current draw for these is time dependent, not mileage dependent. Below 40 mph or so, it's more efficient to drive with windows open and A/C off.

All of these except heating are the same on ICE cars, we just don't notice it because there are no energy used displays and because gas stations are ubiquitous. And as others have mentioned regen is only about 80% efficient, meaning that cycles of speeding up and then regen wastes energy.

Most of the time I don't have to worry about all of this, I can't use all the charge I got at home.

For highways, make it simple. Slow down if you are short on juice. I drive slower in my Tesla than I did in my ICE, it's so nice I am not in as hurry to get there. And I want to avoid any accident that might be remotely my fault. A Tesla owner will be sued for sure.

amatiych | July 23, 2014

bevguy
I am with you its driver's fault. how do you relearn to drive better after driving ICE for 20 years?

ir | July 23, 2014

Hybrids get better city than highway because you are comparing an EV under worst conditions (city) to the best for ICE (highway). The irony is that worst EV mileage is still better than the best ICE mileage.

On a pure EV, you are comparing apples to apples: EV worst in city to EV best on highway. Thus it falls in line with all other pure drivetrains.

Brian H | July 26, 2014

Reminds me of a post by an Italian MS owner who was (very slowly) passed on the highway by a Quattro whose driver was pedal to the metal with gritted teeth determined to "beat" the Tesla ...

Tesltoronto | July 26, 2014

I want to try with the regeneration set to low and see if it makes a difference.

PhillyMomof4 | July 27, 2014

Am I the only person who routinely gets over 400 and doesn't see under 300 unless I've been cruising at 60mph for at least 45 minutes with no AC on? This summer I've been hovering at 405 when I start out every morning, and maybe I'm down to 375 by the end of the day if I've been able to take a road with little stop and go.

Bighorn | July 27, 2014

@Phillymom
400 seems kind of high. My commute is 10 miles but it's about a 400 foot drop. I arrive at work averaging about 180 Wh/m--after the return trip it's up to about 275.

SCCRENDO.Ca.US | July 27, 2014

@PhillyMomof4 Sounds like you enjoy putting your foot down. If you do 80 mph particularly with some elevation that's what you are going to get. But who cares. Enjoy. If you need to conserve range the slow down.

SCCRENDO.Ca.US | July 27, 2014

I average 336 for 40500 miles. Going to work particularly if I am in a hurry with 700 ft elevation I get 380. Coming home I am below 300. If I behave on the way to work I can get below 330

PhillyMomof4 | July 27, 2014

Yeah I used to worry about it but I've only needed to watch my range twice, for day trips. I drive an average of 50 miles a day so my lead foot is not really a problem. I am trying to embrace the regen braking but it doesn't seem to improve efficiency much.

I rarely get to go 80mph and usually am on city roads going 20-40 all stop and go.

Bighorn | July 27, 2014

I think it's probably all the starting and stopping you're doing--I can get to work with only two stop signs. Of course, I take the long way with several lights--riding for the brand.

http://www.jcso1.com/wp-content/uploads/2012/08/Riding-the-Brand.jpg