Gas Mileage Mods
Senior Member
Joined: May 2004
Posts: 404
Likes: 2
From: san diego
so i got 3.73 gears, 18" rim with 35" mud graps... my rpms are about 1700 going about 67mph... to reach 2000 rpms i will be going about 73 mph's.... is there a point of diminishing returns regarding engine rpm? i dont have anything to display mpg, so would i get better mpg 1700rpm @ 67mph or 2000 rpm @ 73mph
Senior Member
Joined: May 2006
Posts: 477
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From: NC
Big slick,
Be careful with the 40 PSI on the tires you have. You could very easily wear out the centers. The easiest way to see if you have P series or Load range tires is to look at the sidewall. If it says p275/65/18 or P anything it is a passenger rated tire. If it says LT it will be a load range tire. There will then be a designation of C,D,E. The higher the load range, the more air pressure it will need. For example, my Load range E tires have a max pressure of 80 PSI and will carry well over 3000# each. I run 50-55 psi when not towing. When I hook up to my TT with the tongue weight of 1000#+ I air them up to 70 PSI. I think that 40 in a stock passenger tire will wear out the centers prematurely. Check your sidewall for suggested pressures or max inflation pressures. Do not forget.... air pressure will increase when the tires heat up so check your pressure when the tires are cold.
Be careful with the 40 PSI on the tires you have. You could very easily wear out the centers. The easiest way to see if you have P series or Load range tires is to look at the sidewall. If it says p275/65/18 or P anything it is a passenger rated tire. If it says LT it will be a load range tire. There will then be a designation of C,D,E. The higher the load range, the more air pressure it will need. For example, my Load range E tires have a max pressure of 80 PSI and will carry well over 3000# each. I run 50-55 psi when not towing. When I hook up to my TT with the tongue weight of 1000#+ I air them up to 70 PSI. I think that 40 in a stock passenger tire will wear out the centers prematurely. Check your sidewall for suggested pressures or max inflation pressures. Do not forget.... air pressure will increase when the tires heat up so check your pressure when the tires are cold.
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Joined: Apr 2007
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From: Slidell, LA
Senior Member
Joined: Mar 2004
Posts: 305
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From: Tulsa, O K L A H O M A!
Big pipes flow more, so is bigger better? Answer: absolutely not. Primary pipes that are too big defeat our quest for the all-important velocity-enhanced scavenging effect. Without knowledge to the contrary, the biggest fear is that the selected tube diameters could be too small, thereby constricting flow and dropping power. Sure, if they are way under what is needed, lack of flow will cause power to suffer. In practice though it is better, especially for a street-driven machine, to have pipes a little too small rather than a little too big. If the pipes are too large a fair chunk of torque can be lost without actually gaining much in the way of top-end power.
Grim
Last edited by Grim; Jun 1, 2008 at 11:04 AM. Reason: Added Source
Member
Joined: Sep 2004
Posts: 24
Likes: 0
From: Maryland
Here is my breakdown on gas mileage:
Stock I was getting 14
After K&N and Muffler I made it to a whopping 14.5
With the tires and tuner I jumped to 15.5
The underdrive pullies netted the largest gains and brought me to 17.5
Half of my daily drive is stop and go the other half I am able to set the cruise at 55-60. Looking at doing Efans next.
Stock I was getting 14
After K&N and Muffler I made it to a whopping 14.5
With the tires and tuner I jumped to 15.5
The underdrive pullies netted the largest gains and brought me to 17.5
Half of my daily drive is stop and go the other half I am able to set the cruise at 55-60. Looking at doing Efans next.
Senior Member
Joined: Oct 2004
Posts: 375
Likes: 0
From: Sanford, MI
New tires on Friday!!! I'm not doing it so much for a fuel economy benefit so much as just 'cause I want more of a safety factor (for towing/hauling). I'm upgrading from my "P" designated tires to "LT" tires. I tow a few HEAVY items as well as haul a lot of stuff in my bed so I'm going from P255/70R17's to LT265/70R17's (10 ply).
Since the new skins are a bit bigger, maybe, just maybe, I'll see another tenth or two of better fuel economy if I'm lucky. I'm going to adjust the tire size in my Edge. I know my speedo is 1.5 MPH off on my current setup so I'm going to borrow my dad's GPS so I can dial it in better. Going to take a few iterations but I think it will give me a more accurate idea on what my mileage and miles read while driving.
Current tires barely made it 50,000 miles. I'm getting down to the last bit of tread on them so it is time to head to Bell Tire (they had the best price around here). Unfortunately I have to buy 5 tires (can't forget the spare).
Heh, anyone interested in a virtually unused spare? I had to put it on for 7 miles one day last year when I picked up a nail in one of my front tires.
Since the new skins are a bit bigger, maybe, just maybe, I'll see another tenth or two of better fuel economy if I'm lucky. I'm going to adjust the tire size in my Edge. I know my speedo is 1.5 MPH off on my current setup so I'm going to borrow my dad's GPS so I can dial it in better. Going to take a few iterations but I think it will give me a more accurate idea on what my mileage and miles read while driving.
Current tires barely made it 50,000 miles. I'm getting down to the last bit of tread on them so it is time to head to Bell Tire (they had the best price around here). Unfortunately I have to buy 5 tires (can't forget the spare).
Heh, anyone interested in a virtually unused spare? I had to put it on for 7 miles one day last year when I picked up a nail in one of my front tires.
Senior Member
Joined: May 2006
Posts: 477
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From: NC
New tires on Friday!!! I'm not doing it so much for a fuel economy benefit so much as just 'cause I want more of a safety factor (for towing/hauling). I'm upgrading from my "P" designated tires to "LT" tires. I tow a few HEAVY items as well as haul a lot of stuff in my bed so I'm going from P255/70R17's to LT265/70R17's (10 ply).
Since the new skins are a bit bigger, maybe, just maybe, I'll see another tenth or two of better fuel economy if I'm lucky. I'm going to adjust the tire size in my Edge. I know my speedo is 1.5 MPH off on my current setup so I'm going to borrow my dad's GPS so I can dial it in better. Going to take a few iterations but I think it will give me a more accurate idea on what my mileage and miles read while driving.
Current tires barely made it 50,000 miles. I'm getting down to the last bit of tread on them so it is time to head to Bell Tire (they had the best price around here). Unfortunately I have to buy 5 tires (can't forget the spare).
Heh, anyone interested in a virtually unused spare? I had to put it on for 7 miles one day last year when I picked up a nail in one of my front tires.
Since the new skins are a bit bigger, maybe, just maybe, I'll see another tenth or two of better fuel economy if I'm lucky. I'm going to adjust the tire size in my Edge. I know my speedo is 1.5 MPH off on my current setup so I'm going to borrow my dad's GPS so I can dial it in better. Going to take a few iterations but I think it will give me a more accurate idea on what my mileage and miles read while driving.
Current tires barely made it 50,000 miles. I'm getting down to the last bit of tread on them so it is time to head to Bell Tire (they had the best price around here). Unfortunately I have to buy 5 tires (can't forget the spare).
Heh, anyone interested in a virtually unused spare? I had to put it on for 7 miles one day last year when I picked up a nail in one of my front tires.
Technical Article Contributor
Joined: Dec 2006
Posts: 670
Likes: 0
From: Central Indiana
This works! I drove the same soute to Nashville several weeks ago that I have driven MANY times only this time I ran the speed limit and let everyone fly on by me. Before my mpg was about 14 and after checking it on my return trip at the speed limit, it jumped to 18! I ran the limit every time it changed. Going east into Nashville, it drops from 70 to 65 then 55. As long as gas is, now $4.19, per gallon I won't be speeding.
I ordered a Hypertech Max Energy programmer today. It's supposed to give you more horsepower and torque and 2-6 miles per gallon more fuel economy. I'm getting close to 20 mpg now, but 26 would be 
I know others prefer different programmers, but, I'll let you know how it does.
I know others prefer different programmers, but, I'll let you know how it does.
After years of development the new 2009 F150 get a tremendus mileage increment of 1MPG (that is including a 6 speed transmision)
Hope you can get your money back.
Senior Member
Joined: Oct 2004
Posts: 375
Likes: 0
From: Sanford, MI
Going to a larger tire in diameter will NOT improve your MPG.... it will actually hurt it. You have more rotational mass to get moving. It will also decrease your braking capability.... once again, more rotational mass to stop. It will also hurt your towing performance.... you essentially changed the gear ratio by putting a larger tire on it. Sorry. This is the main reason I stayed at the stock size.... just more plys.
Granted, these are very slight changes and I was hoping for 0.1 to 0.2 MPG better (at best). I'm not going to be at all disappointed if there really isn't a change.
For towing...yeah. I did essentially change the gear ratio. I wish I had a 4.10 instead of a 3.73. For the times I do tow HEAVY items I'll just turn off the O/D and let 'er rip.