Skipping gears with a Manual Transmission

listen...not making this a debate... you should have read my previous post where i clearly stated 1500-1800 works best for me. then you wouldn't have had to ASSUME i meant above 2000

this is what was said...

what you said there is exactly what i said. TOO low of an rpm will work against you when it comes to mileage. that's why i put it in BOLD.

I'm merely pointing out that you tried to correct me by saying something that agreed with my statement. i could care less where the "exact" mark is. I just know that it happens, just like your scanguage told you

I drive mine in 6th as long as my engine will allow it but there comes a point when going up a hill that 6th is going to put you at too low of an rpm and start to cause the vibrations, in which you would be better off in 5th.
Also when the speed limit is 35, 5th gear for me will go around the 1000 mark so i stay in 4th which puts me in the up a couple hundred rpms ...Now do you get what im saying. its exactly what you stated right after me but acting like you were correcting me. there comes a point where too low of an rpm will hurt more than help. exactly what you said.

we were actually talking about mileage when referring to the rpms but I'm fully aware of running low rpms out on the trail. but that's not exactly helping your mileage being out on the trail

 

Well, if there was anyone out there driving around below 1000 rpm, you've helped them immensely.

 

You could get up to speed faster by dropping a gear and ride in a more appropriate rpm range (using the engine's power better) than you could by lugging along in 6th. Your scangauge may show a higher instantaneous mpg as compared to 5th, but with 5th you'll get up to a more appropriate speed quicker. I'm wondering if your overall mileage would actually be lower because you'd be mashing the pedal longer in 6th trying to get up to speed than if you would have dropped to 5th. So for example, say you're lugging 6th gear and you get 1mpg better. Drop it down into 5th and you get 1mpg less but you get up to cruising speed (2000 rpm) in half the distance, at which time you can shift back into 6th for the maximum mpg.

 

I was only stating what I found while cruising. I also found, short of winding the engine to redline, that accelerating quickly, did not have a large overall effect on average mileage (partly for the reasons stated above). My scangauge indicated that the ambient temperature, use of the brake pedal, cruising speed, and general smoothness once up to speed, where the most influential factors, in that order. Acceleration was not really a large factor, because it takes a certain amount of energy to get the truck up to speed, expend it slowly or quickly, it's not a whole lot different.

 

The energy needed to maintain a given road speed and load can be accomplished by different gear and engine speed combos and the scan guage may show little difference in fuel consumption; I dont know what all parameters it considers but usually an engine is most fuel efficient at a certain rpm and torque output.

Definitely there will be be an optimum window where engine wear will be the least for ton / mile produced. That certainly is the finding of research by trucking industry experts. To produce the same horsepower at low rpms requires higher peak torque loading, higher bearing loads and piston thrust loads. Taken to the opposite extreme of running near redline reduces peak thrust loads, but parts start to experience extra loads from G forces which go up on the cube of rpm. The scan gauge doesnt forecast your engine lifespan. That is in your hands (and feet)

The vibration from lugging is a sign of torsional resonance. Do a google on it and see how harmful its effects can be.

 

Not to repeat what everyone else said, skipping gears is good, grinding them however is bad

I was lucky enough to be taught by my dad who is a professional truck driver, and especially a loaded semi truck with a Roadranger 10 speed gearbox and 2 speed rear-end, skipping gears is very necessary You can even shift without using the clutch as long as you get the road speed, rpm and engine load just right, takes a lot of practice and getting the "feel" for it. But doesnt work for every gear combination. I do it in my truck all the time. usually 2-3 or 3-4...

Just use common sense, if it sounds or feels bad, it probably is. Like Tijean said, torsional resonance is bad and lugging the engine or over reving it should be avoided, thats why they gave us 6 forward gears to chose from. Just my .02

 

I think you're correct. I've been looking around the internet and the consensus seems to be that maximum efficiency occurs at the torque peak. So this would seem to indicate that fast acceleration is better for fuel economy as you get it to the torque peak faster. On our trucks, I the maximum torque occurs at 4000 rpm.

 

Most of the time, the highest level of efficiency on a Spark Ignition engine is at the lowest rpm, with the throttle nearly wide open, maximizing volumetric efficiency at any particular rpm. Hence the reason the Prius runs virtually unthrottled, and uses the transmission to vary output to the wheels. The scangauge shows any parameter you want, but it all adds up to absolute MPG (or LHK in Canada). Regardless of all the tech, theories and other factors, on the Tacoma, (4cyl or V6), the most efficient rpms is the lowest rpm, and for smoothness sake, less than 90% load. This also shows how the Tacoma is geared way too short for normal travel speeds.

 

So there seems to be a fair bit of belief that keeping rpms down will give the maximum gas mileage. I will agree with that but throw in the caution that you will start to have tradeoffs on engine wear if you routinely lug the engine heavily loaded at low rpm. You may not get as many miles to an engine.

 

With less than 90% load, it runs smoothly, I find that the auto on my current V6, keeps the engine around 90% load before it will downshift, and as high as 94% load while cruising at highway speed. Then again, the auto had the slip/lock feature (forget what it's called), where it slips the locked torque converter slightly, eliminating most of the vibes from lugging the engine. This is one of the primary reasons auto's can get the same mileage now, they can bog the engine, yet it doesn't shudder through the drivetrain. This is how Toyota sets it up, so I assume it will last a long time, lugging away....