Most fuel efficient speed?

For a speed@ which seems to get good milage for my truck, all stock 275/70 17s, 50-55 seems to knock down the best mpg for me down in heavy air Florida

 

What brand 275's are you running ?

 

All good points, the try not to need your brakes is the best one for people to think about. Almost everything comes back to that, any time you use your brakes you waste momentum.

I've learned every stoplight pattern on my daily commute, and know when to race and when not to to make the next light. Other people making the same commute get all anxious to gun it to the next red light while I cruise right through after they've locked the brakes just ahead.

It is exciting to me knowing it's pointless to race to the next red light that will always be red, so why race. Or I race 10 mph over knowing I'll make the green. Learn the pattern and enjoy the savings.

 

I still am hesitant about the RPM thing. Yeah I am sure it plays in some, but I think the biggest reason why it would appear that the lower RPM saves you fuel is because you typically need more throttle to get to a higher RPM.

For example I was driving up a steep hill the other day with the cruise set at 55 mph (yeah bad practice but I didn't want to go any slower than that). In overdrive I was getting about 10.5 mpg, so I pulled the shifter into 4th. For the first couple seconds I was down in the 8's for mpg, but once it stabled out and the torque converter locked up I bumped up to about 12.3 mpg for the rest of the hill. So I gained almost 2 mpg even though I was running at a higher rpm and it was because the lower gear required less throttle than the higher gear to maintain speed.

Modern fuel injected vehicles do some interesting things to save fuel nowadays, so I think rpm is less relevant. One example is if you are coasting down a steep hill in gear and are over like 2200 rpm (varies from vehicle to vehicle) your engine will actually shut fuel off to the injectors since the momentum of the vehicle will keep the motor running, so in that case you actually want to have higher rpm.

Speed plays a big role too because it takes a lot of energy to push a brick at 75 mph through the air, that is just straight physics right there. Most vehicles get peak economy from 35-45 mph. Just read up on hypermiling and you can learn a lot of interesting things on how to save money on gas. A lot of the big hypermilers are known for taking economy cars and doubling their EPA fuel economy ratings. My little hyundai accent is rated at 34 mpg and babying it on the freeway at 55 mph I can get almost 50 mpg in it.

 

I can't believe if you were using cruise control and going up a steep hill that your slush box automatic didn't drop you into 3rd on it's own. No way it kept you in OD until you downshifted?

With my manual that I can control at 55 I always see better mpg in OD than 4th. More like 19mpg in 5th, and 15 mpg in 4th.

I'm one of those hypermilers you speak of.

Not sure about the accuracy of 2200+ rpm fuel cutoff with an automatic but it's 1100-1200 rpm with a stick.

 

I have 4.88 gears in the diffs haha otherwise yes I would have been in 3rd easy. With the A750F tranny (Toyota 5spd auto) the stall rpm is 1800, so under 1800 the engine and tranny can start to slip a lot more, so the momentum wouldn't keep the engine going as well, so I don't know the exact rpm on the autos but it is a bit higher I believe for that reason.

On a side note, what is wrong with the toyota 4 cyl motors? It seems like in both the 1st and 2nd gens with the v6's get pretty much the same fuel economy. I can still put about 16-17 mpg at 75 mph with oversized tires and really low diff gears.

 

Anything under 2000 RPM. I usually pull 20 or 21 mpg in my commute.

 

Nothing wrong with my I4. 30+ mpg average over 60K with 32-37 mpg at 55 and 27 at 80 in warm weather.

V6 guys want to believe the I4 does about the same. Not true.

 

So was this when pulling hills?

 

Yes

 

Good call. Old school diagnostic ha. Driving with load will teach you those fuel efficient spots for various scenarios and your mpg will increase from driving habits alone. This is one thing that will actually pay for itself.

 

Like posted earlier, I say coast whenever possible!! Don't be the idiot who races up to the stop light to slam on your brakes, then come to a complete stop. You don't get there any faster that way... wasted gas, earlier brake replacement, more engine/transmission wear, and clutch wear is all you get!! I do this everyday, and have made an art of coasting "putting it in neutral" when I can. I just love the feeling of coming to a stop light coasting, just as the light turns green, and fitting right into the speed of traffic. Then just gently accelerate again with traffic having never touched the brakes, and looking for the next opportunity to coast again!!! Good tire pressure makes a big difference for me with oversized tires as well!!! Also some studies have shown that you get better gas mileage running the AC vs the windows down because of aerodynamics! This last point is for those of us in the south at 108 degrees, and high humidity in the summer!!!