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Optimal speed for gas mileage

#1
Most people say around 55-65 MPH is best as far as fuel efficiency is concerned. It's certainly true that going faster dramatically decreases your gas mileage, particularly over the speed of 70. Most people blame the transmissions and say they need deeper overdrive gears, and while the transmission makes a huge difference, most new cars do in fact have very deep overdrive gears, and the mileage still dips considerably as you approach the speed of normal traffic on your typical freeway. Turns out that the wind drag makes a pretty significant difference all on its own, and I decided to put a lot of that to the test in my new ride. 

My 2007 jetta, 5 cylinder 2.5 liter is pretty nice. Snagged another steal on it and paid 2400 for it with 60K miles, and it's clean inside and out with no mechanical issues whatsoever. EPA claims it gets around 19 MPG in the city and 28 on the highway. 

Granted, I have yet to own a single car yet where I didn't exceed the gas mileage estimates. I don't necessarily drive like I'm in the Indy 500, but I don't drive like a grandma either, so I'm a little pleasantly surprised by this. In the city, I do generally average only around 20 MPG or so (a little better back home, usually closer to 23). But on the highway, rolling at 70 MPH or so, I get about 30-32 easily, sometimes a hair better. A noticeable amount better than the EPA's estimates, and without dipping down to an unreasonably slow speed. 

It's a small sedan, and most compact cars do a little better than this, but for a car that isn't specially designed with fuel-economy in mind, 18-20 in the city, 30-32 on the highway isn't bad and is definitely liveable. But for a car that's the same size as my corolla, I wanted to see how far I could push it. 

I noticed that around 50-52 MPH or so, my mileage was a good bit better than I expected, and even in the city (if I was driving at a good time and didn't hit a lot of red lights), my mileage was actually a little better than it was on the freeway. Turns out that around this speed in my jetta, it will easily average about 36-38 MPG. Took it out on the open freeway and put it in cruise control at about 55-60 MPH or so in the evening, got about 35 miles to the gallon. Not bad at all for a 2.5 liter engine that's only rated for 28 MPG on the highway.  

Did a little quick research, and it turns out there's an explanation for this, despite the super deep overdrive gears in most newer cars. Wind drag is basically the result of your velocity/speed squared. So increasing speed from 70 and going up to 85 miles per hour increases your wind drag by around 33% alone. Based on those calculations, my car would only get about 20 MPG or so roaring at 85 MPH. I can get away with that easily in my civic and still not dip below 30 MPG, but in my Jetta, I think I'll be staying below 70... 

Interesting stuff indeed. EPA estimates can in fact be beat. And pretty easily at that. 
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#2
interesting, It's not often I get to go above 70 here unless I'm way out in the boonies, but I do notice I get much better gas mileage in how I drive as well as the speeds I commonly travel at.
my accord btw get's similar ratings to your corolla on average now that I'm much better practiced and gentler with it, surprisingly on the highway I do notice a 3 to 5 mpg drop when my CB radio antenna is up, the speed limit is 65 until you get most of the way to denver and I usually flow with traffic which typically goes 70 to 75 outside of rushhour.

on the other hand, I usually pick up trucker chatter on the highway so it's a tradeoff
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