rob_engineer

I've had my 2012 JKU sport with 3.73 rear and manual trans for three months. I have been getting around 17.5 mpg. Some of that has been with highway driving. I have been thinking about mpg vs mph. Today I did about 200 miles of mostly highway driving. Instead of going my normal 70-73 mph, I kept the cruise on about 66-68. Wow, what a difference. My average was 20.5, the highest since I have owned it (5000 miles). I know it takes proportionately more HP to conquer wind as you go faster. Anyone have charts or data showing the mpg vs mph. We basically can use this data as one of the factors in determining how fast we want to drive.

cowboyjeeper

I have a thread stated for gas mileage... it doesn't concern speed so much, I like your idea. But you could look through here to get started... some of the guys have reported their normal driving speeds.

https://www.jk-forum.com/forums/jk-t...format-197541/

From what I've seen once you start getting over 70mph your mileage starts to drop like a rock... 80ish really hurts. But my Jeeps still on order (on a train for delivery ) so I don't have real world numbers to add yet.

ronjenx

Drag goes up as the square of velocity.

I get over 23 mpg when the trip is on 45 mph roads with no stops and few hills.

rob_engineer

So a quick look on Wikipedia gives some answers. Yes, the drag force is proportional to the velocity squared. However, the power required to overcome drag is proportional to the velocity cubed. I wish we had some real numbers such as if I drive the exAct same route I get this much mpg at 50 and this much at 55, 60, 65, 70, 75.

rob_engineer

Here is a link to something I read several years ago when I had a motorhome and gas prices peaked. Some good information in this document.
http://www.catrvclub.org/PDF_Docs/Un...nding_Perf.pdf

keithvegas

There are quite a few variables that are hard to control. Traffic, air temp, wind speed and direction, timing of traffic lights, how aggressive your attitude is. If you are paying attention and understand techniques you can make a big difference. If you recognize traffic is stopped ahead you can ease off early instead of using brakes later. If you fill your tank on a hot day you will lose more to evaporation than on a cold night making you think you are putting more in your tank than you actually are.

Just a few off the top of my head. I'm sure there are many more.

ronjenx

Thanks for posting that.
I'd recalled reading about the "cubed" factor years ago, but missd how it played into the power function.
Power is cubed because, not only is the vehicle going twice as fast through the air, (drag is squared), it's now covering the same distance in half the time; twice the work in half the time.
The time factor is what changes it to a horse power calculation.