Gas Mileage Report

[bobmbx]

Last weekend, I drove from VA to FL and back. Roughly 1000 miles each way. On the way down I had the cruise control on 75 and averaged 18.5 MPG. On the way back the cruise control was set at 80, averaging 16.3 MPG. Thats a whopping 12 percent drop in fuel mileage.

I offer that as evidence that driving north is in fact, up hill.

 

[chuck s]

Air resistance is exponential and once rolling is a major, maybe the major resistance. No surprise that driving faster burns more fuel. I always seem to drive faster on the way home! Air resistance is why it takes obscene amounts of horsepower for even exotic sports cars to reach speeds over 150mph and few can push 200.

On a more practical level air resistance is twice as much at 70mph than than it was at 50mph.

And 14% more at 80mph than 75mph as you just demonstrated.

All in a perfect aerodynamic world. And don't expect your fuel usage to drop 50% if you never exceed 50.

I found during my frequent drives from Cleveland to Gettysburg could be made in the same time with less fuel if I slowed down about 5 mph as I could do it on a single tank of fuel at the slower speed and the time spent at a refuel stop cost more time than I made up with faster road speed.

-- Chuck

 

[Adieu]

Wind n shit.

Also, 80 mph is a bad cruise control setting for most motors in most vehicles, air resistance notwithstanding.... if you have a 5.4 triton, afair its sweet spots are 64, 69, and 74

Whether that's speedo error or its specifically geared and mapped to have specific shift and RPM points corresponding to crusing at 65 70 and 75 as typical speed limits they assumed we'd stay just below, I'm not sure

 

[deweysmith]

I just drove from Montreal to SLC this weekend and most of the time had the cruise set on ~75 (120 km/h) and the computer says I got 14.4mpg.

 

[JExpedition07]

Well with the cold air mass here in the north I’d think driving in Montreal you’d definelty see a drop in fuel mileage. MPG always drops in the cold.

 

[Wahooslayer]

To me, the biggest difference I notice with fuel economy is traffic. Lots of traffic improves mileage due to reduced air resistance (drafting), provided there isn't a great deal of slowing and speeding up. Also, wind direction plays a large role, a 10 mph head wind makes 80 like 90, and vice versa. Tuck in tight behind a semi and watch your mpg go way up.

 

[deweysmith]

Yeah, drafting can help a ton but when Apple Maps says your drive is 35 hours, the difference between 65 and 75 is a precious 3 hours that I don't have to deal with the kids

 

[sjwelds]

Yeah and who wants to stare at the a** end of an 18-wheeler all day.

 

[Adieu]

Drafting can be tricky, if you're used to it in a big lifted truck or low slammed sedan/coupe, beware that vice versa the intuitive following distance and choice of vehicle to draft will actually be COUNTERPRODUCTIVE


You gotta stick yourself in the low pressure zone, depending on your ride height and their ride height some spots behind them may actually be highly turbulent HIGH pressure zones

 

[Frank Wilson]

Drafting can be tricky, if you're used to it in a big lifted truck or low slammed sedan/coupe, beware that vice versa the intuitive following distance and choice of vehicle to draft will actually be COUNTERPRODUCTIVE


You gotta stick yourself in the low pressure zone, depending on your ride height and their ride height some spots behind them may actually be highly turbulent HIGH pressure zones

I thought this was covered on a mythbusters episode years ago.
I think they said you would need to be a couple feet from the lead vehicle to increase mileage.

Using the tank top off method, I am at 11 around town. Highway is a massive leap to 15. But, I'm not adding the correction for the 35's.

Gas hurts, but, I knew going into a V8 El lifted 3/2 and 35's was not going to be a gas sipper. But, I can put a chain around that volt drivers house and drag it down the street

 

[JExpedition07]

Again temperature changes lead to MPG drop as well. In this wonderful cold blizzard spell we are having where my grille keeps getting plugged with snow I’ve watched my avg MPG drop to around 15. Normally highway i get around 17-18 MPG in 4auto and around town it’s usually 15ish. Depending on what your towing has a big effect too, if its a landscape trailer with low air resistance it’s better than an enclosed for economy. Like all of you have pointed out many small things factor in headwind or tailwind, weight, air resistance, speed, traffic, uphill or downhill. I tend not to drive trying to maximize mpg i just drive it as it goes, as most of us do but i know some people who get every last dime out, that being said if it got 12 MPG I’d still love the thing lol.

 

[JExpedition07]

Website glitched and loaded slow and posted my post twice, disregard this one i guess lol.

 

[jeff kushner]

Frank's right....to draft-for-mileage or drafting-while racing......you'd better be tight to the leader....tighter than is safe....like 3-5ft at 75mph behind an 18 wheeler. How many of us are comfortable driving 75-80mph, 4 FEET from the crash bar slung under the trucks rear? If you've never raced on a real live race track and are used to driving & reacting at real speed, not many will be up for it. I've done it but it was very intensive driving and I would never have done it had there been anyone else in my truck. Too many unpredictable variables....

I road raced bikes back in the 70's and at 140-160mph, I had to be w/i 6-8" of the rear wheel of the guy in front to effectively draft him...oh, and I had to "get small".....raising a clenched fist at 160mph INSTANTLY cuts your speed by 5-7mph.....now try to make your Expy small behind that truck.....it ain't safe no way, no how if you do it correctly......

jeff

 

[Adieu]

Frank's right....to draft-for-mileage or drafting-while racing......you'd better be tight to the leader....tighter than is safe....like 3-5ft at 75mph behind an 18 wheeler. How many of us are comfortable driving 75-80mph, 4 FEET from the crash bar slung under the trucks rear? If you've never raced on a real live race track and are used to driving & reacting at real speed, not many will be up for it. I've done it but it was very intensive driving and I would never have done it had there been anyone else in my truck. Too many unpredictable variables....

I road raced bikes back in the 70's and at 140-160mph, I had to be w/i 6-8" of the rear wheel of the guy in front to effectively draft him...oh, and I had to "get small".....raising a clenched fist at 160mph INSTANTLY cuts your speed by 5-7mph.....now try to make your Expy small behind that truck.....it ain't safe no way, no how if you do it correctly......

jeff

False.

Bikes have tiny, aerodynamic profiles.... an expy is essentially a huge brick, as is a semi


Anyway, if you wanna see it in action, just find a semi in an adjacent lane ahead of you and approach it on cruise control +5mph faster than him and pull in behind


Watch your RPMs, first they'll hold steady then they'll spike noticeably as you hit his wake, then drop off below the nothing in front of you RPM as you enter the low pressure zone behind him


Even easier to see if you got an instant MPG readout on a device attached to OBD, or have an instant MPG dial on a car (common on BMWs)

 

[Adieu]

Also, on some cars with more rudimentary cruise control systems, you will accelerate noticeably with cruise control set while pulling in behind a truck

 

[NorthGeorgia]

Just a couple of months ago I drove from north Georgia to central Florida. I got, according to the computer, around 20mpg's. I guess I was lucky? on the return trip is was a tad lower.

 

[Adieu]

Georgia to Florida really feels like you're going downhill pretty much all the time afair

Niiice roads you guys got there

 

[Rusty90272]

If you want to get better gas milage, slow down. Keep it to 60 or 65 and you'll get 19-21, depending on a multitude of factors like head-winds, tail-winds, tire types, etc. These are great vehicles, but driving over 2,000 RPM is the main culprit in bad gas milage.

 

[deweysmith]

Yeah, I get markedly better mileage at 65 but I value the couple of hours I save on the cross-country drive far more than the $20 or so I'll save in gas.

 

[Rusty90272]

Yeah, I get markedly better mileage at 65 but I value the couple of hours I save on the cross-country drive far more than the $20 or so I'll save in gas.

Of coures, time is important and that neccessitates driving faster than 65 mph, as many do, but many are also surprised when they drive fast and can't understand the laws of physics and how come they get sub-standard milage per gallon.

Take care.