DailyDrive

It's that time again when gas is creeping up to $4 per gallon, and quite likely will stay there or even go higher for the foreseeable future. So I've decided to figure out what is the optimum speed this old 4Runner is most efficient at.

It is no secret that the largest contributing factor to fuel efficiency (or inefficiency) is air drag. Once you are up to speed and cruising along, it's almost wholly is the air resistance that the engine is fighting.

So using my old trusty ODBII recorder, it wasn't too difficult to figure out how much gas the engine eats at various speeds.



All tests performed on a 3.4L 4x4 AUTO 4.10 rear. The most common set up.

So as it turns out 38mph is about the optimum for maximum theoretical MPG. Blue line shows abstract units of fuel vs. MPH on the X axis. 55mph is about the limit before hitting the upslope of that exponential air resistance curve.

So the moral of the story is, between 15mph and 38mph it should get the same MPG at all speeds, over 38mph it starts decreasing, and over 55mph you are starting to really get diminished return on time saved.

shepherd2111

I guess I need to start leaving for work 20 mins. earlier than I do now....

ChefYota4x4

iTrader: (5)

HAHAHAHAHAHAHA! OMGOSH, that slayed me! lol.

Ok, so, I guess if everyone could drive to work on the freeway at 38MPH, ....we would be getting better mileage than when we drove 60mph... makes sense. However, I live in L.A...... I'd be shot if I tried it, if I wasn't hit with a 750$ Wreckless driving ticket by the CHP, first. lol. <(Oh yes, something LIKE that can and does happen, every day). lol.....

IN all seriousness, .....there was this news report with this guy on that is a "MAX MPG" driver? He turns the car off all the time when on hills or when he can coast, he almost never takes the freeway, unless necessary, and he does all kinds of things that ended up helping him to get like 45% better mileage out of a tank. Can't remember his name. Was actually kinda interesting, ... but again, I'm in L.A., ..... I just see that as paying so much attention to something other than the PSYCHO'S out there, lol. When I slowed down A LOT, and really babied it last tank... I got 230mi. out of 14 Gallons as compared to 190mi., when I was pretty much stomping on it all over town, lol. But even then, 15.5mpg, ...I NEED HELP, something's wrong!!!!!!!

shepherd2111

The people who crack me up are the ones who buy a car like a Prius, and still drive it 80 mph...... Uh, that's not the point..... ! lol

vital22re

iTrader: (2)

Pick up a vacum gauge... it'll help monitor engine load.. lower load... better mpg.

logsurfer

for a vw jetta wagon tdi w/c gets 40 mpg but I came to my senses.. i still love my non-interference engine, and once i do the timing belt package, im set for another 90k.

Hey, at least im not making car payments anymore.

chasekerr23

Also, windows up or down? Back window up or down? Sunroof up or down? Does having a bug deflector for the sunroof help?

I've noticed that if I drive with the windows down and the back window (at the very) up I get a bunch of air resistance. If I crack the back window 6-8 inches, it relieves the pressure, theoretically resulting higher MPG (for the windows down). Wanna prove this anybody?

DailyDrive

Windows up/down is negligible, so doing what is comfortable is more sensible. I'd drive with windows up over 50mph as that seems much more comfortable, even if it were less efficient (which it isn't).

The next best thing after making your car more aerodynamic (which you really can't do to any noticeable degree, without getting crazy) is tire type, size, and pressure.

ChefYota4x4

iTrader: (5)

Far as windows up or down? Hmmmm, I'll tell you what, I bet I've gotten MUCH lower on the MPG when driving through the High Sierras in Summer, because they're down!lol..(No AC, 124*F..... NOT HAPPENING w/out the windows down! lol) It feels like its so much wind resistance, at times, when driving through that valley(Olancha, Big Pine, Etc., on the 395HWY)....that the truck I had at the time was going to lift up on the front end and flip me over backwards. However, I'm sure 'THOSE' types of winds are causing PLENTY of their own damage to mileage, ...windows up or down. But when up, FAR less drag on that Hwy!

tunnelmotor99

Umm...If you drive with the back window down it sucks exhaust in the car. It's really very simple: Don't stomp on the gas when the light turns green to try and race the jerk in the other lane (I keep the RPMs under 2000 when accelerating), follow the speed limit, don't follow too close, don't use the a/c unless absolutely necessary.

2DoorRunner

Ride a bike.

ChefYota4x4

iTrader: (5)

HAHAHAHA, says the Vortec Yota! lol. How is your mileage, btw?

X2 on the mellow driving. Even then, I'm having issues, but as soon as I can find someone that will scope it out, I'll hopefully figure out what's going on..... but still, getting around 3mpg more in the city by just being mellow on the skinny pedal(couple MPH into 1st, 15mph into 2nd, 25mph into 3rd, 35mph into 4th, 45mph into 5th.)

toyota4x4907

I get the same MPG if I rev it out to 5K rpm every acceleration or if I baby it

Check out the MythBusters episode about driving with the windows up with A/C on vs windows down/ A/C off.

I've always been told that going 55 is about optimum for fuel efficiency and ETA.

Prii are fast! I can't win in a race against one . And I've tried on many occasions...!

2DoorRunner

Im not the one complaining about gas prices

And about 15-20 depending on how i drive. No actual numbers though, just going by how fast the gas gauge drops compared to the 22re. Its about the same if i take it easy. And thats WITH 36" swampers and 4.10s compared to 31s and 410s lol

Thread jack over/

ChefYota4x4

iTrader: (5)

Wow, that's pretty good, man! BTW, I wasn't being sarcastic about the "what's your mileage",...I couldn't remember what you'd said in your thread.

Far as gas prices? No comment, lol. VERY loaded topic, already a thread, hahaha ....but fuel economy? Not a bad discussion. I wonder what that 1UZ would get? 17-18? RMA told me, ...can't remember.

DailyDrive

That varies from car to car, a modern Corvette would probably hit its optimum around 70mph, while the 4Runner does it under 40mph.

In theory you should get even better mileage with higher RPMs when the engine is more efficient. Reason why it never translates to real world is because stopping is wasted kinetic energy. Imagine 2 traffic lights and 2 identical cars. One car speeds up slowly, one speeds up fast. The one that sped up fast reached the 2nd light while averaging 40mph. The one that sped up slowly, reached it while averaging 30mph between the lights. Now they are both sitting at the next red light.

One got better MPG than the other because it was going slower.

Taro

I've been averaging 19 mpg with my Taco commuting in L.A. Got 20 on a few tanks.

I have 265/75-16s (with these the speedo is correct, stock size is off inflating mileage) inflated to 38psi. I also drive nice and easy.

My truck has a Leer shell and some extra weight. I also sit about 2.5" high with the suspension.

BigBallsMcFalls

ha I was gonna say 42 mph before looking further in the thread

own one for 12 years you just -know- these things

profuse007

I make 19 miles one way commute everyday with 5 miles non-highway and 14 miles highway yield 17.5-18.5MPG for the past couple of years. The speedometer is a bit off, reading 60mph on dash but 64mph on GPS.

I drive it fairly hard on non-highway and highway. If I drive like a granny w/o revving it so hard, I get consistent 18+MPG. Had once get 21MPG on highway.

okie81

I use my boost gauge, and it's a great reflector of fuel economy

Negative pressure $$$
Positive pressure: $$$$$$$$$