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I've been noticing that my RL seams to run real easy right around 50 mph.

That's where it drops into overdrive and the rpms are as low as possible. right around 1200-1500

Any slower, and it hangs in 4th and the rpms stay up around 2k.

I have been getting pretty good mpg driving this way, and when i'm on the highway 55 or 65 limit, I usually hang out right around the limit.

It's been working well so far.
 

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Generally speaking, the most fuel efficient speed for any vehicle with an automatic transmission is the slowest speed in which you can maintain the highest gear with torque converter lockup. The Ridgeline hits this point at around 47 MPH. Once it's there, you can slow down until about 40 before it will downshift back to 4th (assuming 0% grade and no headwind). Keeping it there for any length of time is virtually impossible in the real world. :)
 

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Another thing you can do is drive in the middle lane or the closest to the turns when you can on the freeways, you will short the distance a bit also drive behind a big Rig in long trips to keep the rpms low.
 

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Generally speaking, the most fuel efficient speed for any vehicle with an automatic transmission is the slowest speed in which you can maintain the highest gear with torque converter lockup. The Ridgeline hits this point at around 47 MPH. Once it's there, you can slow down until about 40 before it will downshift back to 4th (assuming 0% grade and no headwind). Keeping it there for any length of time is virtually impossible in the real world. :)
Right you are - 45 mph (47 in this case according to your info.) is correct for the most optimal speed for fuel efficient speed for most modern vehicles.

Anything above this speed and fuel efficiency decreases dramatically. This question was on Jeopardy, we worked it out in college math, and I read it in Consumer Reports some time back. Also, every 200 lbs. of added weight decreases fuel efficiency by about 1%. Most of my in town driving is 45 mph or less, and highway mph is...slightly ...above the legal limit.
 

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Right you are - 45 mph (47 in this case according to your info.) is correct for the most optimal speed for fuel efficient speed for most modern vehicles.

Anything above this speed and fuel efficiency decreases dramatically. This question was on Jeopardy, we worked it out in college math, and I read it in Consumer Reports some time back. Also, every 200 lbs. of added weight decreases fuel efficiency by about 1%. Most of my in town driving is 45 mph or less, and highway mph is...slightly ...above the legal limit.
I'm curious. In your computations, which I totally accept, did the distance traveled ever enter in? I guess what I'm trying to say is that is there a sweet spot for high gear RPM vs distance traveled. It would seem the math applys to a completely level surface. Were we live, terrain must be figured in as most roads are not flat.

I mention this because in our manual tranny high HP car, 6th gear is .5 OD and my best MPG seems to come in the 1500-1600 RPM range which equates to 75-80 MPH. I've always thought the reason this was true was because with a .5 OD, I need enough RPMS/TQ to keep from dipping into the throttle when I hit a hill ...which would increase fuel consumption. FTR....I can easily run slower in 6th, but that doesn't noticably increase MPG.

I could very well be wrong, but it would seem that given the same type of unlevel surface, the RL may need a bit more speed than 47 to accomplish the same. Wouldn't the same principles of RPM/AFR/TQ apply?

Also it was stated that high gear will stay in lockup down to 40 MPH or so. That may be true, but isn't the pcm trying to feed more gas in if you're trying to maintain speed, but dropping speed.....in any gear?
 

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As long as you want to calculate it own down to the gnat's a**, don't forget to consider the fact that engine efficiency curves play a role here, too. Based on my simple answer, you should [in theory] get the best gas mileage by shifting a manual transmission vehicle into the highest possible gear and driving at the slowest speed the engine will continue to run without stalling. Naturally, we know this isn't practical. :)
 

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Another option is 0 MPH. Just standing outside the box picking my nose while I digest all this fancy math stuff...:act029:
 

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I'm curious. In your computations, which I totally accept, did the distance traveled ever enter in? I guess what I'm trying to say is that is there a sweet spot for high gear RPM vs distance traveled. It would seem the math applys to a completely level surface. Were we live, terrain must be figured in as most roads are not flat.

I mention this because in our manual tranny high HP car, 6th gear is .5 OD and my best MPG seems to come in the 1500-1600 RPM range which equates to 75-80 MPH. I've always thought the reason this was true was because with a .5 OD, I need enough RPMS/TQ to keep from dipping into the throttle when I hit a hill ...which would increase fuel consumption. FTR....I can easily run slower in 6th, but that doesn't noticably increase MPG.

I could very well be wrong, but it would seem that given the same type of unlevel surface, the RL may need a bit more speed than 47 to accomplish the same. Wouldn't the same principles of RPM/AFR/TQ apply?

Also it was stated that high gear will stay in lockup down to 40 MPH or so. That may be true, but isn't the pcm trying to feed more gas in if you're trying to maintain speed, but dropping speed.....in any gear?
I expect aerodynamics come into play as well. Your Viper's aerodynamic drag profile is much different from the RL's coefficient of drag. So I suspect the best speed for fuel economy will be vehicle specific rather than speed specific.
 

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Phrases like "picking my nose" and "digest" really bring on ugly images.... :act010:
No worse than blowing snot bubbles. :act027:
 

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I'm curious. In your computations, which I totally accept, did the distance traveled ever enter in? I guess what I'm trying to say is that is there a sweet spot for high gear RPM vs distance traveled. It would seem the math applys to a completely level surface. Were we live, terrain must be figured in as most roads are not flat.

I mention this because in our manual tranny high HP car, 6th gear is .5 OD and my best MPG seems to come in the 1500-1600 RPM range which equates to 75-80 MPH. I've always thought the reason this was true was because with a .5 OD, I need enough RPMS/TQ to keep from dipping into the throttle when I hit a hill ...which would increase fuel consumption. FTR....I can easily run slower in 6th, but that doesn't noticably increase MPG.

I could very well be wrong, but it would seem that given the same type of unlevel surface, the RL may need a bit more speed than 47 to accomplish the same. Wouldn't the same principles of RPM/AFR/TQ apply?

Also it was stated that high gear will stay in lockup down to 40 MPH or so. That may be true, but isn't the pcm trying to feed more gas in if you're trying to maintain speed, but dropping speed.....in any gear?
Can't answer about the "sweet spot for high RPM vs. distance travelled" idea...that was over 20 years ago for me and quite foggy by now. Good question though. The main conclusion I recall was that 45 mph was the optimal speed to maintain if you were running low on fuel and had to maximize the distance on remaining fuel. RPM was not addressed with our project.


Here is an interesting link: http://www.mpgforspeed.com/
with stats from fueleconomy.gov where you can plug in your avg. mpg for any vehicle along with miles travelled daily to see how increased speed decreases fuel efficiency. With these results, the optimal speed for mph is between 45-55 MPH. It does not matter, based on the data, what type vehicle is tested, the results were very similar with MPG decreasing as MPH increases.
 

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Can't answer about the "sweet spot for high RPM vs. distance travelled" idea...that was over 20 years ago for me and quite foggy by now. Good question though. The main conclusion I recall was that 45 mph was the optimal speed to maintain if you were running low on fuel and had to maximize the distance on remaining fuel. RPM was not addressed with our project.


Here is an interesting link: http://www.mpgforspeed.com/
with stats from fueleconomy.gov where you can plug in your avg. mpg for any vehicle along with miles travelled daily to see how increased speed decreases fuel efficiency. With these results, the optimal speed for mph is between 45-55 MPH. It does not matter, based on the data, what type vehicle is tested, the results were very similar with MPG decreasing as MPH increases.

I think engine efficiencies and aerodynamics due to come into play at some point....maybe more so for the example I gave. I would not be able to run in 6th gear at 45-50 MPH....It would be too hard on the drive train and very inefficient. 45 MPH would be 900 RPM. 100 MPH in a Viper is only 2000 RPM. When our car was stock, I could get around 23-24 MPG at 75-80. That did not improve running 60-65 on the 180 miles of two lane roads it takes to get home here. I think the engine efficiencies come into play for us. In other words in order to maintain speed on somewhat hilly terrain.....6th gear at 60-65 is not an optimum gear for going uphill and the pcm feeds in more gas to maintain the speed. At 680 HP and a changed final drive ratio (3.07 to 3.45s)....I can still get an honest 20 MPG all day long on a trip. 22.5 is my best. Not too shabby!
 

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It is interesting how 'efficiencies' can be optimum under the right conditions regardless of how much HP you have under the hood. Factors like aerodynamics, rolling resistance, operating ranges of engines and related gearing can tip the balance under a given condition.
Your Viper is almost idling considering the small amount of throttle it needs compared with a small engined vehicle that may have to work up to 80% of it's power range to maintain the equal of even a moderate cruising speed when going up the same grade.
 

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I've been noticing that my RL seams to run real easy right around 50 mph.

That's where it drops into overdrive and the rpms are as low as possible. right around 1200-1500

Any slower, and it hangs in 4th and the rpms stay up around 2k.

I have been getting pretty good mpg driving this way, and when i'm on the highway 55 or 65 limit, I usually hang out right around the limit.

It's been working well so far.
I've been keeping my ridgeline around 15:00 RP m's on the interstate. Sometimes I have to take it off cruise control and slow down the keep it at 15:00 RPM. But I'll do that but if you do that you'll get the ultimate best gas mileage possible
 

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Those old enough to remember the Jimny Carter days and gas rationing can appreciate the max speed on many roads being limited to 55 mph, ostensibly because the mileage for many cars was optimized at this speed.
 
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