Gas Mileage on the Interstate

[ElMonoDelMar]

This year Illinois passed a law increasing the speed limit to 70 MPH on most rural interstates. I am pretty pumped about this considering I drive about 40k miles per year. I know that EPA highway MPG ratings are based on real world driving conditions and aren't optimized for setting the cruse control and taking a nap. Having said that, I am very disappointed with the highway mileage on my 2013 Elantra. In order to get close to the EPA rating of 38 MPG, I have to be driving around 55 MPH. I tend to get around 30 MPG if I push it north of 70 MPH.

My question is this, are there any cars out there that are geared to run efficiently at faster speeds? I understand that air resistance is going to play a major role, but I almost wonder if I would be getting similar gas mileage on the highway in a slightly larger car with a bigger engine. If nothing else, the ride would be much more comfortable and I might not lose that much on my overall gas mileage.

 

[Ferzerp]

My corvette gets better mpg at 70 mph than your elantra....

I can get 31-32 mpg on the highway with cruise control on 70-72 mph (and *much* higher at 55)

 

[ElMonoDelMar]

That's what I suspected. I bet your Vette even handles better in the snow than my go-cart on steroids. It's looking like I need to trade. My Elantra has been disappointing in many ways. I should have researched more before pulling the trigger.

 

[Ferzerp]

Eh. My fiesta, around 70 mph only gets mid 30s. If I speed up and go 80ish it drops down to low 30's. It's just a function of speed. Nothing gets great mileage going fast(er). Going non freeway speeds I can squeeze 45-50 out of it over distances.

 

[ElMonoDelMar]

I know nothing is going to get great mileage with that much drag. The whole point of buying the Elantra was it had one of the highest highway MPG ratings of all of the cars I looked at. With 75% of my driving being fast interstates, I should have skipped the econo-box and got something a little more comfortable. It sounds like I would have been averaging low 30's with either option.

I was really looking hard at a TDI Jetta. I wonder if that would have done any better on a $/mile basis at 75MPH.

 

[Ferzerp]

I really wouldn't sweat it. The difference between 30 mpg and 35 mpg is about 5 gallons per 1000 miles. It really isn't much.

 

[CrackRabbit]

My Sonata is, but the Mazda 6 I have isn't.
On long stretches of highway I've been able to get 38ish mpg.

 

[LTC8K6]

Are you sure it isn't just winter dragging your mileage down some?

Cold air means using a little more fuel, winter blends of gasoline tend to lower mileage a bit, and people sometimes forget about their tire pressures, which drop in the cold air.

 

[ElMonoDelMar]

I'm sure the winter gas is making it worse, but it's been bad all year. The snow storms have got me wishing that I would have gone with a larger/heavier vehicle and not put as much weight on the MPG rating.

 

[dguy6789]

My 2013 Civic gets 35mpg at 85mph

 

[PhoKingGuy]

2010 Jetta TDI was able to get a consistent 45 MPG at 80 mph. Believe it or not.

 

[Herr Kutz]

I just had a 2013 impala rental and if the onboard computer is to be believed, I was getting around 37mpg cruising at 70mph which is pretty impressive imho. At 60 mph it was staying closer to 41mpg.

Conditions and stats:
- Late November to early December - I think the temps must have been in the 40s or so since I had the heater on.
- Driving was mainly on flat roads around New Orleans (e.g. slightly above sea level) with the occasional bridge or overpass.
- 87 Octane Gas (I guess winter blend?)
- 300 hp v6
- The engine was running right around 1600rpm cruising at 70mph with the heater on low.
- The overall mpg as reported by the onboard computer was 27.2mpg when I received the car and it had about 21.5k on the odometer. I put around 1k miles on and was able to bring the car's overall mpg to 28.0mpg.
- I'm no audiophile, but I thought the stock sound system was quite good.
- EPA rated 18/30

I still haven't done the hand calcs, but I wrote down the information in case I need to.

 

[disappoint]

I just had a 2013 impala rental and if the onboard computer is to be believed, I was getting around 37mpg cruising at 70mph which is pretty impressive imho. At 60 mph it was staying closer to 41mpg.

Conditions and stats:
- Late November to early December - I think the temps must have been in the 40s or so since I had the heater on.
- Driving was mainly on flat roads around New Orleans (e.g. slightly above sea level) with the occasional bridge or overpass.
- 87 Octane Gas (I guess winter blend?)
- 300 hp v6
- The engine was running right around 1600rpm cruising at 70mph with the heater on low.
- The overall mpg as reported by the onboard computer was 27.2mpg when I received the car and it had about 21.5k on the odometer. I put around 1k miles on and was able to bring the car's overall mpg to 28.0mpg.
- I'm no audiophile, but I thought the stock sound system was quite good.
- EPA rated 18/30

I still haven't done the hand calcs, but I wrote down the information in case I need to.

Not impressed.

It's a GM car, of course it's awesome.

 

[thedarkwolf]

My 04 jetta wagon tdi auto pulls upper 30s to low 40s with bike rack on the roof going by the Torque app on my phone at 70mph give or take.

 

[ElMonoDelMar]

I just had a 2013 impala rental and if the onboard computer is to be believed, I was getting around 37mpg cruising at 70mph which is pretty impressive imho.

That's another thing that pisses me off about my car. The estimation that the car gives me for my MPG on a given tank is ALWAYS 3-4 MPG higher than what I come up with from the manual calculations from the odometer and gas pump. Take the tank I'm on now, for example. The computer says just a shade over 30 MPG. I know it's going to be closer to 26 or 27 when I fill up the tank and calculate it out. 27 MPG is unacceptable for mostly highway driving on a small commuter car.

 

[kitatech]

I really wouldn't sweat it. The difference between 30 mpg and 35 mpg is about 5 gallons per 1000 miles. It really isn't much.

Using these numbers....
5gal (per 1k) x 3.50 (typical price) = 17.50 x 40 (OP drives 40k/yr) = $700/yr difference.

My 05 Camry I4/stick gets 34-35mpg @ 75mph....(78 on the speedo)

 

[Harrod]

I got 34 mpg in my wife's Maxima between Memphis and Little Rock. I was doing 70-65 most of the time, and followed anything bigger than me.

 

[Jadow]

I drove 600 miles across i-90 in cold ass MN and SD the other day in an toyota avalon with well inflated tires going on average about 75 and got 24mpg

 

[ThatsABigOne]

My 2013 Civic gets 35mpg at 85mph

My 2013 Accord Sport got an average of 30 mpg at 100 mph on a trip from SLC to Moab. On a return trip, I got 28 mpg with same average speed. It was fully loaded with camping gear and 2 passengers. :wub:

 

[tortillasoup]

The Elantra has always had inflated fuel economy numbers. As for finding a car that gets 40mpg @ 70mph, you might want to rent a Honda Accord with an I4 or a Camry I4, do a long trip at your desired speed, then record the MPG. I know the V6 camry is capable of 30+mpg at higher speeds but it requires careful throttle control as just a small adjustment can make the fuel economy drop about 10mpg. Best TPS (according to Scangauge, Torque App) is 19 for the V6 Camry. (Assuming you're not climbing a steep enough hill which will prevent holding that throttle position since you'll lose speed)


The only other car I can think of that will get 40-50+ mpg at 70MPH+ is the Toyota Prius. I don't even want to mention the 2000-2006 Insight because it's a two seater that has an undersized battery pack which = future replacement needed. Otherwise if you're a tinkerer and don't mind, that thing is capable of like 90MPG+ at 55mph.

 

[Jumpem]

The EPA highway test has a maximum speed of 60mph, and an average speed of 48mph. That is why you are not getting close to the rated mileage at 70mph.

I would much rather have the speed limit at 55mph.

 

[nerp]

I get about 34mpg at 75-80 mph. Having 8 gears helps.

 

[deadken]

...
My question is this, are there any cars out there that are geared to run efficiently at faster speeds? I understand that air resistance is going to play a major role...

I think that most of the 'newer' cars designated for the US market have been geared to get the best fuel economy at our 'typical' rated highway speeds. It wouldn't surprise me to learn that cars meant for driving on the Autobahn, etc... are geared for better fuel economy at those higher speeds.

We have had discussions in one of the old car groups that I belong to about getting better fuel economy in 4th gear instead of 5th gear (direct instead of over drive). It used to be than and engine had to 'come on cam' to reach its sweet spot. Which, in our case meaning staying in 4th at a certain speed netted better MPG compared to dropping out of that RPM range and getting worse MPG. I believe one of the biggest factors is the improved HP and TQ profiles, which I believe are largley due to having variable valve timing. Now with VVT, that sweet spot has gotten a lot broader.

I'm not sure that the wind / air resistance plays that big of a difference at the speeds you are talking about. I know it makes a difference, but I'm thinking that the difference between 60 and 70MPH is pretty small. Don't get me wrong, there have been a lot of engine, transmission, and body improvements that all add up. IE: In that same old car group someone was lamenting the loss of drip rails. With todays manufacturing processes and wind resistance goals, we couldn't come up with a car made recently (25 years) that still had them.

I'm going to look up a few of the smartphone applications mentioned here. I'm interested in seeing realtime data as to what is affecting MPG. Can I ask what OBDII BT adapter you guys are using?

For what it is worth, a co-worker of mine LOVES his Elantra. He specifically bought it for the MPG ratings (gas was a bit over $4 at that point). He took his daughter to the dealership and she left with a Elantra when she was ready to buy a new car (hers with a 6sp manual trans). When Valentines day came around he leased his GF a LOADED Veloster to replace her Explorer that was coming off lease. I'm going to ask him how he is making out with the fuel economy on his Elantra next week. This is a 'car' guy so of course we ribbed him a bit that his daughter bought a new car with a manual transmission while he got one with an automatic. He's owned a plenty of classic and muscle cars. It was interesting hearing him go on about how much he loves that Elantra. This thread has me wondering if that car has lost some of its luster by now.

 

[ElMonoDelMar]

What really sold me on the Elantra (other than the inflated MPG ratings) was how large the cabin felt. I am 6'2"/210lbs and with as much time as I spend in a car, interior space was important. I have much more leg room than I did in any of the other cars I drove (Corolla, Sentra, Focus, Cruze, Jetta and Mazda 3). The car is still really comfy to sit in, it's just been a disappointment in most other areas.

The snow handling is horrible. It makes my old Chevy Cavalier feel like an off-road dune buggy by comparison.

I hope your friend is still happy with his purchase, but I would NEVER recommend a Hyundai to anyone after my shitty experience with this one.

 

[Jumpem]

What really sold me on the Elantra (other than the inflated MPG ratings) was how large the cabin felt. I am 6'2"/210lbs and with as much time as I spend in a car, interior space was important. I have much more leg room than I did in any of the other cars I drove (Corolla, Sentra, Focus, Cruze, Jetta and Mazda 3). The car is still really comfy to sit in, it's just been a disappointment in most other areas.

The snow handling is horrible. It makes my old Chevy Cavalier feel like an off-road dune buggy by comparison.

I hope your friend is still happy with his purchase, but I would NEVER recommend a Hyundai to anyone after my shitty experience with this one.

Difference in tires?