Huge difference, large mpg loss 65 mph to 70 mph. Any idea what may be causing it, my gears?

[HeySkippyDog]

I commute 5 days a week on my 5.3L/6 speed, been doing it for years. Did it on a 2014 double cab and a crew cab. Crew cab was a few hundred pounds heavier.

Really didn't notice much difference in fuel mileage between the two to care about.

Bear in mind, I'm in Florida and the road is flat as can be. We get windy days, but I've never paid attention to that. But wind can be pretty restrictive.

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[swathdiver]

10 hours ago, HeySkippyDog said:

I commute 5 days a week on my 5.3L/6 speed, been doing it for years. Did it on a 2014 double cab and a crew cab. Crew cab was a few hundred pounds heavier.

Really didn't notice much difference in fuel mileage between the two to care about.

Bear in mind, I'm in Florida and the road is flat as can be. We get windy days, but I've never paid attention to that. But wind can be pretty restrictive.

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What do you mean flat?  What about all them hills (highway overpasses) every mile or so?  

 

There does seem to be a slight grade to I-95, we get less mpg going north and better heading south, generally speaking.  The grade is contrary to prevailing winds, on the east coast anyway.

[L86 All Terrain]

I was getting readings of 10.5L/100km (22.4usmpg) on stock tires. When I put on my 33x12.5 10 plys I get on average 13L/100 (18mpg) at 65mph if I up it to 70-75mph I am looking at 15.5L/100 (15mpg). 33x12.5R20, CAI, 6.2L 8L90e 3.23. It seems to shine when im on the slower secondary roads at around 40mph, I can get it to 19-20mpg

Edited October 18, 2019 by L86 All Terrain

[TXGREEK]

I was getting readings of 10.5L/100km (22.4usmpg) on stock tires. When I put on my 33x12.5 10 plys I get on average 13L/100 (18mpg) at 65mph if I up it to 70-75mph I am looking at 15.5L/100 (15mpg). 33x12.5R20, CAI, 6.2L 8L90e 3.23. It seems to shine when im on the slower secondary roads at around 40mph, I can get it to 19-20mpg

Loss of mpg’s will definitely happen every time you’re adding larger tires. Considering my truck is lifted, running heavier wheels and tires, I’m definitely good with what I’m getting. Mostly depending on wind activity, I’m averaging 18-20 mpgs on the highway at 65-70 mph, 17-19 mpgs at 70-76 mph.




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[L86 All Terrain]

^ Yeah nice truck. Lots of members here will tell you they have a 6" lift on 35's and get 24mpg at 75mph, it's just not the case. But comparatively my current truck has about the same mileage as my old 1998 350 on 29" highway tires, and I have nearly double the HP on tap. My 2010 5.3L on 33's was better than my current 6.2L on 33's.  

[swathdiver]

11 hours ago, L86 All Terrain said:

 My 2010 5.3L on 33's was better than my current 6.2L on 33's.  

But nowhere near as fun when you stomp on the gas pedal!

[HeySkippyDog]

What do you mean flat?  What about all them hills (highway overpasses) every mile or so?  [emoji3]
 
There does seem to be a slight grade to I-95, we get less mpg going north and better heading south, generally speaking.  The grade is contrary to prevailing winds, on the east coast anyway.

Hell I can't tell. Been driving it for years between Eau Gallie and 46.

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[swathdiver]

21 hours ago, HeySkippyDog said:

Hell I can't tell. Been driving it for years between Eau Gallie and 46.

Nice area, good times at the Titusville Rifle and Pistol Club.

[m3n00b]

With my 6" lift and 35x12.5s I get about 22mpg at 60, 20 at 65 and about 17 between 70 and 75.