Car with best MPG at 90mph

 They hit 90mph then goes back down a few mph then back up to 90. HF is happiest at 55mph.

I have enjoyed my commute for the last few years- about 1000 miles per week.

Don't really care what the critics say.

I'm wondering if the is a sweet spot has yet to be considered.  Is there something between a C5 and a Prius that has super tall gearing and good aero, entirely possibly with a little larger engine than the Prius?  For instance, a BMW 328d.  It has a 1.88 top gear final ratio while the C5 is 1.71, so not too far off...  What about one of the mid-sized hybrids, their engines are usually a bit larger?

spandak said:

From my experience you're probably best avoiding anything with a turbo. 90 mph in my MS3 is getting close to boost. Mileage drops off fast at that point.

Something that's slippery and has a motor that doesn't mind running higher in the rev range should serve you well. While I have no experience with anything from Tesla I know a Leaf loses power fast on a highway. Like 20% of its estimated mileage disappears. 

FWIW a turbo doesn't make you use any more gas, it just allows you to.    As long as your ECU doesn't put you into a performance/rich mode, gas & air just have to mix to make the torque you need. Then it's up to the tuning of the intake, cams, exhaust at whatever RPM you end up at.

The whole raft of low pressure turbos popular a few years ago work on the basis that the smaller turbo spins up sooner, cutting down on the intake side vacuum that the engine has to work against.  Since it's using largely wasted energy on the exhaust side to build that pressure, it is a net win for mileage over a certain range of engine parameters. They sized the turbos not for big boost but for quicker spin-up and the right range of pressure assist for economy cruise throttle openings.

Tuning of the engine makes a big difference.  My SHO gets its best highway mileage in the 78 to 83 MPH range, better than it returns at 65.  Not high enough for the original poster, it only climbs up to 27-29. But that's around the lower torque peak which is where engine volumetric efficiency is greatest.  (SHO has two torque peaks due to second intake tract opening up, but that's at even higher/less efficient RPM.)

As is being noted, hybrids don't gain very much on the highway because there isn't much chance to convert braking back into watts.  The Prius' smooth shape and small, efficient engine will do about as well as any gas car outside of an Insight.  And it's running near WOT at 90 so the aforementioned vacuum pumping losses are smaller.  Look for not just the cheapest tires but those with higher eco/rolling resistance ratings.

As far as motorcycles, unless faired in heavily they actually don't get the mileage you'd think, their profile/c.d. is not great because of lights, brakes, rider, saddlebags, open wheels, and so on even though smaller frontal area.  Most larger bikes don't get much beyond the low 40's.  And you need a certain engine size to keep up a comfortable 90, particularly with the stated poster's uphill grade.  The Honda NC700 series has a high efficiency twin based on the Fit's motor (IIRC) and is said at Fuelly and other places to get 60-65 mpg though that isn't at 90.  I'd bet it will do better than the Prius though.

Oh, and that Google thing is pretty good.  C&Driver noted a couple of years ago that the

Chevrolet Cruze 2.0L Diesel 6AT

was good for 46 mpg highway, though otherwise not an inspiring ride. It's not a VW, for better or worse.

O.P.'s comments about not wanting to lose in maintenance what is gained in gas savings point out that if what you're after is total cost, you have to track it all.  When I was looking at longer commutes, I pondered a Prius, but when I added up license&reg, insurance, depreciation, and purchase price, I turned around and rebuilt the SHO.  I was never going to do enough miles to come out ahead on costs, much less the loss in driving fun versus guiding an appliance.

Wind resistance increases with the square of velocity.

Road load power increases with the cube of velocity.

As a result I'm highly skeptical of anyone who says their peak economy is at a speed higher than 1500(ish) RPM in their highest gear.

For example, the WR on a car at 78mph is 53% higher than 65mph.  The power requirement at 78mph is 73% higher than at 65mph.  Engine tuning can well be a factor, but I have doubts that any production engine nearly doubles its efficiency 20% higher in the powerband.

Similarly, go on EcoModder and ask how many people are driving at 70, 80 or 90mph to achieve their best economy.  The answer is zero.

Vigo said:

Im sad i didn't get in on this thread from the start. Not enough time to respond to everything before work (evening class)!

TDI's maintenance costs basically always kill any minor MPG advantage vs the Prius. Even the gas vs diesel cost can more than kill it. TDIs are basically never cheaper to run. TDI people will deny this til death, it seems.

I have had the unique experience of doing an extended 90mph run in a 1g Insight. It got 38-39mpg across a completely flat stretch for ~100 miles. Not enough better to offset any of its MANY downsides. I still own a Prius and a 1g Insight and there are very few circumstances i would suggest the Insight to someone over a Prius. 

Also, part of being willing to go 90mph for long stretches is that noone else is around. So this whole idea of being a danger to others because you go 90mph when there's noone else around is foolish. You could argue about the emotional endangerment of anyone who happens to care about the OP if he were in a single car accident, but you'd need to start your own damn thread unless you don't want to be a bigger shiny happy person than the guy you're complaining about. My .02. As a Texan, i understand deserted roads and saving time. And i havent hurt anyone, ever. And i'm still alive. And i still live in Texas. Honestly, many of you should be jealous! 

I won't deny the TDI comment. It's heavily dependent on factors that are difficult to nail down and can vary greatly.  A TDI worked for me simply due to fortunate timing.  The TDI option more than paid for itself during Katrina.  Personally, I wouldn't consider the maintenance to be all that different than a lot of other cars.  A lot of cars have timing belts that need to be changed and doing the job every 100K miles isn't unreasonable. The DIY support for these cars is phenomenal. 

I agree the speed is a locational thing. To someone living in the DC beltway area, the idea of regularly traveling 90 MPH sounds insane - my friends who live down there have to "adjust" when they head back north because they are so used to rarely going much above the posted limit. It's less about perceived safety and more about speeding tickets and speed cameras.  I live in PA and travel the PA Turnpike during rush hour (posted limit is 70). As unlikely as it may sound, 90 MPH can literally be the flow of traffic speed in the left lane.  Accidents are surprisingly infrequent. The worst is when someone gets into the mix who isn't a regular commuter and doesn't know. They get into the left lane doing 75 or 80 and cause a big traffic cluster because they are going so slow.

In reply to ProDarwin :

The OP question was not how to get the best economy over a 90 mile (each way) commute. The question is what cars have decent economy at 90 MPH.  He is obviously willing to give up absolute economy in the interest of saving time.

spandak said:

From my experience you're probably best avoiding anything with a turbo. 90 mph in my MS3 is getting close to boost. Mileage drops off fast at that point.

Something that's slippery and has a motor that doesn't mind running higher in the rev range should serve you well. While I have no experience with anything from Tesla I know a Leaf loses power fast on a highway. Like 20% of its estimated mileage disappears. 

Missed this the first time around. My MS3 is modified to the point where it's quick enough but reliable enough not to risk popping the motor (probably.) On BFG Sport Comp-2's it'll return 33 MPG doing 75 on cruise through a fairly hilly area. I suspect I could have the tuner lean out the tune and hold off the boost a bit longer. Combined with swapping the tires to a lesser rolling resistance setup I bet I could get 36 or so at that 75 and low 30's at 90.

I don't think I'd want to commute 180 miles day in it the way it's setup right now though but when it was more stockish it would certainly have been ok.

If 90 mph is the set speed, then I would think that aerodynamics and gearing would be the most important criteria.  You want something that cuts the air easily, requiring a minimum of power from the engine to do so.  Additionally, you want the engine to be running in the sweet-spot of its power/efficiency curve.  The Hyundai Sonata Hybrid at a Cd of .26 gives up one point to the Prius, but the motor would be running at lower RPM at 90mph, so I think it would be a winner.  

Thought of something on my drive in this morning.

NOISE.

Prius's are stupidly loud wind and road noise, my Mercedes is a good 10-15 decibels quieter on the highway than my friends 2015 WRX on all seasons. Having a quiet car, a comfy seat, and a decent stereo is also important for spending so much time in the car

In reply to pinchvalve :

On that note. I wonder what an Ioniq would do at that speed. It appears to be pretty slippery and the battery pack is claimed to do 50 (late edit)  miles without the engine obviously doing 90 would reduce that number. 6th gear appears to be .767:1.

Jaynen said:

Thought of something on my drive in this morning.

 

NOISE.

Prius's are stupidly loud wind and road noise, my Mercedes is a good 10-15 decibels quieter on the highway than my friends 2015 WRX on all seasons. Having a quiet car, a comfy seat, and a decent stereo is also important for spending so much time in the car

+1.

Amazing how less fatigued I am when I remember to use earplugs in the Miata. 

Another vote for larger engine turning "slow". My 2000 Firebird 3.8 5 speed gets 32 at 80, how much worse would 90 be? Cheap to buy, comfortable etc.. a 6 speed LS1 car would be about the same I guess.

Ian F said:

In reply to ProDarwin :

The OP question was not how to get the best economy over a 90 mile (each way) commute. The question is what cars have decent economy at 90 MPH.  He is obviously willing to give up absolute economy in the interest of saving time.

Yeah, I got that.  See the post above mine.

I gotta think that a TDI would be best, right?  Hard to beat 50 mpg, even with the extra cost per gallon depending on what fuel prices are where he lives.  Around here I think its about even compared to a 40mpg gasser.

I will also echo the aerodynamics part.  The difference between 65 and 90 is significant.  Likely more than doubled, requiring twice the WHP to maintain it.  Anything you can do to cut down the drag has a big payoff.

I for one don't care how fast you drive.  You didn't come here to ask if it was moral, you were asking a scientific question, so I'm limiting my answer to the science of it.

Real skinny tires on equally skinny wheels is likely the biggest aero band for the buck.  Then speed tape and skirts, on a bean or arrow.

Can you talk to your company about telecommuting? Will they let you mine the copper from home a couple days a week?

But, seriously, the Hyundai Ioniq got the best highway mileage of any hybrid we've tested in a while. Hybrids usually make their bones in stop-and-go, but the Ioniq was a beast on the freeway with well over 40mpg.

JG Pasterjak said:

But, seriously, the Hyundai Ioniq got the best highway mileage of any hybrid we've tested in a while. Hybrids usually make their bones in stop-and-go, but the Ioniq was a beast on the freeway with well over 40mpg.

According to the EPA database I linked to a while ago- it's also has the lowest drag according to the track model used for certification. Which is pretty darned accurate.  It's a pretty easy process to sort cars by drag at a speed.  

So is it "ion eye queue" or "ion eek"?

I wonder how much is being budgeted for tickets.

In reply to kb58 :again he’s out west where speed limit is likely to be 80 mph,  10 over seldom warrants a ticket.  

Decades ago I was  doing 105 in Arizona and a cop going the other way just gave me the hand signal for slow it down.  

Obviously he didn’t feel it worth his time to do a U turn and come after me.

Don't think I've seen one in the wild yet, but a 2017 Chevy Cruze diesel with manual trans is EPA rated at 52mpg highway. It wouldn't surprise me if it bested a Prius at 90mph but you'd have to do the math and figure out which would have a lower cost/mile. My guess is the Prius would still come out ahead in that comparison.

2008 s65 amg. Screw it. There's more to life than gas mileage. 

You'll note I am not the one paying for the gas here. 20mpg ftw!

Personally, I wouldn't consider the maintenance to be all that different than a lot of other cars.  A lot of cars have timing belts that need to be changed and doing the job every 100K miles isn't unreasonable. 

I agree that that's perfectly reasonable. The problem is that if you are paying someone full shop price to do your timing belts, you're literally spending enough in timing belts that, for example, by 300k you could have bought a replacement battery pack for the Prius (which it's not guaranteed to need) with what you spent on timing belts (which you definitely DO need). It's not that a TDI has unusual maintenance, it's that a Prius has unusually LOW maintenance. 

The Prius i bought at 217k is now at 262k and i have spent NOTHING on it except to replace the original (i.e. 9 YEAR OLD) 12v battery and install some tires.I have done ZERO maintenance other than oil changes and spark plugs and zero repairs. And neither has anyone else because it still has original every single thing except maybe front brake pads. The front strut mounts are starting to creak when it gets cold, though. 

I think the main problem with this thread is that the OP is already in the best car for the job. Besides a Model S!