Is it normal for MPG to greatly decrease after 70+ mph

I drive 30 miles to work (one way) and 75% of that drive is on highway. I typically haul butt doing 85-90mph down I-10 since it's soooooo early in the morning (I leave for work at 0550) 5 times a week. My trip mpg average is 20-21 mph round trip. I live in Texas Hill Country and it's slightly higher heading to work (usually 22mpg but regularly get as high as 24mpg due to going down in elevation) and slightly lower coming back home, but that's mostly because of slow downs due to traffic then getting back up to speed while going up hills. My tank average is constantly 20.5mpg hand and computer calculated. I am stock except for some cosmetic stuff. The time I see a big difference in my mpg is when it's windy and I am driving into the head wind. That is the biggest detriment to my fuel economy and is also the time I am reminded I am no longer driving my little sports car (2012 Mustang GT) on rails.. this truck is more sensitive to wind and gusts in the handling department.

 

What fuel grade is everyone pumping?
I’m curious if two different grades would show any difference at similar speeds

 

I use 87 octane from reputable stations, and prefer to use "Top Tier" listed stations when I am close to one.

My local Murphy's USA (Wally world) has ETOH free (E0) and they either have a hard time keeping it stocked or just don't order it often enough, but I will occasionally fill up with that (still 87 octane) otherwise I just fill with regular E10 gas.

 

87 octane......and normally Shell.

 

Completely normal. Your mpg will be even worse at that speed when it's cold since the air is more dense.

 

This ^^^^^^^^!!!!!

Cars will get better MPG due to weight and most of all aerodynamic shape.The Tacoma is the most "traditional Truck design" out there, meaning it is a square vehicle with a muscular stance, great for that look, bad for aerodynamics.

 

Just got back from Costco. As I put more miles on it seems to be getting alot better.

 

Agree. Saw one get pulled over Monday by the OHP.

 

Yes. Only place you'll see 20+ consistently is 50mph in 6th gear on flat ground.

 

Yeah it's normal to see a drop past 70ish, but it still shouldn't be as horrible as the mileage you're stating. On my last roadtrip, I was doing 80 in high altitude and was still averaging ~20-21mpg.

 

They exist almost everywhere in western states once out of city limits. Whenever I drive from San Diego, to CO, almost the entire trip is 75mph. And on the way home through Utah, it's 80 almost the entire time through the state.

 

I disagree. TRD OR MT and on my backroads commute home I'm either 4th gear in traffic around 35 or 5th around 40mph and I average 21mpg, with a RTT, and c load duratracs, messured at the pump.

 

Sure. My point was you won't see that past 70. Cruising 40-50 in a tall gear is optimal MPG territory. High speed on the interstate is not.

 

Speak for yourself. Again, I was averaging 20+ going 75+, in high altitude, on often twisty roads and frequent inclines.

 

Access cab sport AT with the air dam. Lot of shit working in your favor for mpg.

 

I still find if fascinating that OR's, purely from what I've gathered from MPG threads (so nothing scientific), seem to typically get significantly worse mileage than Sports (or just non OR's). And I wonder what it is, because I can't imagine the air dam alone makes that much of a difference.

 

From the Taco Factory here in SA the speed limit is 75mph if you head east to Houston, 80mph if you head west to El Paso and 85mph if you head North on 130 towards Austin. And of course even the cops drive 5-15mpg faster than the limit. And DPS has an official 5mph forgiveness buffer. And yes, from my experience gas milage plummets above 65. My diesel VW wagon manages to get 36mpg at 85mph but my truck close to 13mpg. Why my car uses diesel and my truck gas is beyond me...

 

The air dam is definitely significant. People have reported a solid 1-2 mpg drop after removing it. As has already been mentioned in this thread aero is huge, especially at high speeds.

 

Well then I'm glad I've kept my dam on. lol

 

+1 gearing plus aero. Anything above 65mph is where my efficiency drops under 20mpg. 70mpg puts me at about 18mpg flat.

With that being said I can do the White mountains in 4th and still average above 20mpg. Which is awesome