Wind drag

[05SportV8]

First of all let me say I am a little nuts about gas cost and fuel efficiency.
Recently I have kept my eye on my driving habits and their impact on MPG. I have spent 2 weeks doing a little research on my own.

I do a 25 mile round trip every day to work on a flat straight road.

I can put the 4runner in cruise control 95% of the length of the trip. There is a gas station around where I live and there is another one at the end of my trip where I had filled the tank back so I could get real numbers on used gas.

I have repeated the following events 3 times to have some sort of average.

Trt ----------------- MPG
cruise at 40 mph ---- 19.2
cruise at 50 mph ---- 20.3
cruise at 65 mph ---- 18.1
cruise at 70 mph * -- 16.7
cruise at 50 mph ** - 15.4

* done only once (speed limit is 55mph, so I did not want to risk another trip at that speed)
** done on severe wind 35 mph against driving direction it should translate into a 85 mph trip

Ok now some observations:

Best efficiency was obtained at 50 MPH. Based on wind drag I thought that 40 mph will be even better MPG. But I was also looking at the rpm. At 50 mph the V8 goes at 1500rpm. At 40 it is around 1300 rpm. I guess the efficiency of that engine is hurt at such low rpms.

Air drag was a great deal of influence on MPG. I can

 

[OUTRNNR]

Nice observations...I was always curious about what the most efficient speed to cruise is.

Just to clarify, is this road you take to work relatively level? I'm assuming it is because I'm sure you would've listed if it was uphill one-way.

As for the difference in cruising between 40-50 MPH my theory there is the difference in gas you are saving between 1300-1500 rpms doesn't make up for the fact that you are driving 10 mph slower, thus accumulating less miles per gallon of gas consumed.

Don't tell me you actually drove all the way to work going 40 mph in a 55?? Did you actually leave earlier to accomplish this test? Or is this just an extrapolation from a shorter test?

Either way, nice work.

 

[05SportV8]

Hi Outrnnr,

Answer to your questions:

I live in Iowa, which is fairly flat. The road I take is leveled to the point I dont think there are more than 10-20 ft of difference in eleveation start to finish. There is just one small river crossing at the very end of my commute.

Yes I drove the car on cruise at 40 mph 3 times. Yes my mother was called a few times.

Yes again, left home 15 minutes earlier those days.

Fuel used was 89 octane 10% ethanol on a 4R with 12k miles on it.

With respect ofthe drop at 40 mph, I wonder if I keep the car in 4 instead of D and again at 40 mph if that improves MPG by having the engine a higher rpm. However I don't think is practical, just for curiosity sake. I'll post it if i do that part.

Cheers.

 

[Northof49]

So if it used less gas at 40mph would you actually drive to work everyday at 40mph? Or even 50 for that matter?

 

[biglatka]

I've actually observed the same gas mileage vs. speed measurements (although not as scientifically as 05SportV8). The sweet spot is somewhere between 50-55 mph. My mileage was manually calculated but you can correlate the results well if you assume the computer is off by 7% on average. At 70+ the mileage really starts to fall off, look at the readout as you increase up through 70 to 80 (watch out for Smokey too). You have to remember that, everything else being approximately equal, the air drag goes up with the square of the velocity. I also agree that other things must be factored in at 40 mph and below. BTW, at 40 mph you should be in fifth gear. It's time consuming and not much fun to drive at 50 on a road with a speed limit of 70 though. One of the reasons I traded my SR5 V6 for the V8 SE was for the engine and X-REAS, and I wouldn't get to appreciate the added power much if drove for maximum fuel economy.

 

[Uneek]

Good findings.

I've read in several articles that 55-60mph are the optimal speeds for maximum fuel efficiency, just because many vehicles today have their aerodynamics designed around that. Old DMV envelopes use to say 55mph saves lives and gas.

I was under the impression that if I'm going slower, my RPMs are lower, but I'm driving longer vs. if I'm going faster with higher RPMs, I'm driving a shorter amount of time. Your findings prove that the drag is that much more significant.

 

[jeober]

Do you think Toyota might have optimized the top gear for the EPA hwy MPG?

 

[kimboy]

Not knocking on you for your efforts, but, some other variables that may not have been taken into account are.

Cruise Control: it takes energy to operate, I say you lost a little power in your experiment, however, the loss was negligable because you used it at all tested speeds.

Windspeed and direction: - nuf said here. Everyday's a little different.

RPM's: Did you monitor the status of the rpm's for each trip? I guess the gear ratio/ air to fuel mixture affects your outcome.

Good job.

If I traveled 55 on a highway, I'd be dead meat

 

[Koz]

Cruise Control: it takes energy to operate, I say you lost a little power in your experiment, however, the loss was negligable because you used it at all tested speeds.

You've got to be kidding! How much gas mileage do you think he lost?

Koz

 

[teotwaki]

If we really thought that the cruise control module would make a significant impact we could calculate the numbers. It is a matter of the alternator's efficiency and the fuel consumed to power the little cruise control module. I used to know an off-road racer that had electric clutches on his alternator and air conditioner compresser in his pre-runner. On his dash he had an engraved sign that said "disengage a/c and alternator above 100 MPH!"

I offer the following for the fun of the discussion.

Lets say for the moment that the tenth of a watt of power consumption was not negligible. If you recall that the 4Runner is fly by wire, i.e. no mechanical throttle linkage, I would offer up that the cruise control saves power. The cruise control has a tighter closed loop response than a human, reacting to micro-changes in vacuum variation, thus making many small finite adjustments. Humans tend to react slower, requiring a larger press on the gas pedal which makes the throttle servo move more, thus consuming a larger amount of power.

I can say that I have seen cases on an uphill where I can manually work the throttle without causing a huge transmission downshift and subsequent jump in engine revs. which the cruise control is prone to do. As they say YMMV...

Anyhow, you could also save fuel by turning off the daytime running lights, 250W stereo, Nav system and so on and save even more fuel over the long haul. Or buy a Prius!

Not knocking on you for your efforts, but, some other variables that may not have been taken into account are.

Cruise Control: it takes energy to operate, I say you lost a little power in your experiment, however, the loss was negligable because you used it at all tested speeds.

Windspeed and direction: - nuf said here. Everyday's a little different.

RPM's: Did you monitor the status of the rpm's for each trip? I guess the gear ratio/ air to fuel mixture affects your outcome.

Good job.

If I traveled 55 on a highway, I'd be dead meat

 

[Koz]

The cruise will INCREASE the mileage by only using the required amount of fuel to maintain a constant speed. The amount of fuel for electrical power is nothing you could even measure.

Koz

 

[AlexJet]

I was doing some calculations myself. I have to go from Toronto to Ottawa a few times, so I measured some numbers for myself. There are two roads there, one is a highway (461km ~ 290miles), and another is a country road (407km ~ 250miles). If I'm going on a highway at 110km/h (~70mph) I'm using 3/4 of my gas to one way; on a country road trip with approximately 90km/h (~55mph) I'm using my tank for both ways. The time is equal in both cases ~4h10m. I've done this trip more then 5 times each way last year. That's my figures.

 

[RickyCRX]

Really, you guys are spending way too much time and effort on this.

If you REALLY care about gas mileage, you completely bought the wrong vehicle (which is why the 1-2mpg difference between V6 and V8 argument is so comical; if you really cared about gas mileage, you would have bought something that got 30+mpg).

Ricky

 

[Northof49]

Really, you guys are spending way too much time and effort on this.

If you REALLY care about gas mileage, you completely bought the wrong vehicle (which is why the 1-2mpg difference between V6 and V8 argument is so comical; if you really cared about gas mileage, you would have bought something that got 30+mpg).

Ricky

It's unbelievable really.....there are 6 threads relating to fuel economy on the FIRST PAGE of General Discussion.

For what it is, the 4Runner gets good mileage. In the grand scheme of vehicles that actaully get good mileage, it's pretty shitty! I drove across Canada basically floored in my Matrix and got almost 40mpg......

All of the argueing and testing in the world won't make these things even return 30mpg. How many discussion do we really need to establish that a 4rth gen 4Runner basically gets 20mpg??



PS: Not harping on this thread specifically.....it just bewilders me how much discussion stems from the fuel economy of a large, powerful 4x4.

 

[biglatka]

Well, I kinda enjoy reading these threads on mileage, wind drag, how cold weather affects mileage, etc., finding them interesting and informative. As far as I'm concerned, the more topics and thoughts the better. If others don't like or are bothered by them the solution is simple; don't look at them. Each to his own. Peace

 

[RickyCRX]

Well, I kinda enjoy reading these threads on mileage, wind drag, how cold weather affects mileage, etc., finding them interesting and informative. As far as I'm concerned, the more topics and thoughts the better. If others don't like or are bothered by them the solution is simple; don't look at them. Each to his own. Peace

:whipping2

Just like beating a dead horse.

It's a god damned 4100-4500lb SUV depending on what drivetrain and trim level you purchased and has the aerodynamics of a brick wall. Just DRIVE it. The manner in which you drive these things matters a whole heck of a lot more than what conditions you drive it in. If you are one of those people that hits your brake pedal every 20 seconds because there is a car somewhere in front of you somewhere on the same road you're on, you'll probably get the worst gas mileage. If you look ahead, plan your acceleration and braking accordingly to be more efficient, it will reward you with better gas mileage, longer brake pad life, less wear and tear on your transmission, etc. All of those factors have a LOT more to do with your overall cost of ownership than checking to see if a certain ground speed/air speed affects mileage.

You want to get the absolute best mileage possible? FORGET the cruise control. DO NOT use it; it will NOT give you the best gas mileage possible unless you are on absolutely flat terrian through your entire trip. The fact of the matter is that the cruise control makes the engine work harder on uphills and lets it 'coast' on downhills, wasting a TREMENDOUS amount of energy. If you've ever done any serious mountain biking, you will know what I'm talking about. You want to build up speed 'for free' on a downhill and essentially 'coast' up hill. Cruise control does the opposite.

Buy a vacuum gauge (boost gauge) and install it on your vehicle; T it into a vacuum line off of the intake manifold. Maintain the highest level of vacuum possible at all times and I guarantee you will get the best gas mileage possible no matter what conditions you drive in. After a little while, you will be able to tell when are the best times to apply throttle and when are not.

But please, everybody, PLEASE stop beating this dead horse. These aren't "record breaking gas mileage" vehicles. You should have known that before you bought it; if you didn't clue into that before you wrote the check, please go shoot yourself now.

Ricky

 

[Koz]

The best mileage will be achieved with the cruise set at 50 mph.

Koz

 

[HuntRunner]

At least you didn't capitalize His name, but He is my God too....no need to use His name in vain. Thanks
Sorry if I broke the rules moderators and administrators, but I could not let this one go.

 

[RickyCRX]

The best mileage will be achieved with the cruise set at 50 mph.

Koz

:dammit: You can't make a blanket statement like that. Did you not read a single thing I said? Set the cruise at 50mph in the mountains of Oregon or Washington and you will be lucky to get 15mpg out of it because the transmission will be downshifting to 3rd gear CONSTANTLY!

Ricky

 

[RickyCRX]

At least you didn't capitalize His name, but He is my God too....no need to use His name in vain. Thanks
Sorry if I broke the rules moderators and administrators, but I could not let this one go.

Gee, I am sooooo sorry to offend you. I didn't capitalize it for folks like yourself.

People in this world need to grow tougher skin, too. *grumble*

Ricky