Changing gearing in truck

[Two Bears]

OK,    I am going to buy a 03 f150 4X4 crew cab  know that they get about 15 mpg with stock gears.

Can I change the gearing out to get better MPG? I don't pull anything more than an ATV trailer but would like to get the truck up to 20 MPG if it is possible to do this by changing the gears out.

Once I had a 81 F150 4 with a 351M engine that had a 300 rear end in it that alwaysgot 16-17   MPG and it was my plow truck whih I could plow snow for 12 hours non stop on a tank of gas and never leave 4 wheel drive.

So my thoughts are ....Can I change these stock gears out for 300's and if I can,would I have to change out the front gears too?

What do you all think?

[quickdtoo]

You'd have to swap out the ring and pinion in both the front and rear axles, whether you could reach your mpg goal is another question. I had one done 15yrs ago, cost was about $800 IIRC.

Tim

[R.W.Dale]

OK,    I am going to buy a 03 f150 4X4 crew cab  know that they get about 15 mpg with stock gears.

 If you go to a higher gear with an overdrive trans I will guarantee you you WILL get WORSE MPG. How many RPM's are you turning at your normal driving speed? I'll guess it's less than 1700 rpm. Put higher gears in there and you'll never shift into OD.


 If mpg is a concern forget about a Ford they're fuel pigs only exceeded by Dodges. A similar 5.3 L powered GM truck will be good for another 4 to 5 MPG over the Ford and will run circles around those gutless Tritons to boot. If you go with a 4.8L engine you'll loose some power vs the 5.3 but gain another 2 to 3 mpg

[The Gamemaster]

Just my two cents.

Here you have a man that brags about his horses, but complains about the feed bill.

Just as Krochus said, if you change the gears and it takes the engine out of it's Rpm range it will not get better gas mileage - it will get worse.

A man that worked 20 years at a local Chevrolet dealer bought a used 4 door crew cab Chevy truck from the State of Pennsylvania.  It had 456:1 gears in it and it got about 8 mpg.

He found a set of 411:1 gears and put them in and it went down to 5 mpg!

Your truck is heavy and it takes x amount of energy to move it down the road, especially when you travel at highway speeds.  The manufacturers figure out the best Rpm's for the engine and they program the computer to run the truck at 55 mph at that speed.

When you change the gears, you will also have to change the speedometer gear in the drivetrain and also reprogram the PTM - Power Train Module  - which not only runs the speedometer - it also runs the ABS - which monitors the wheel sensors etc..

My Uncle the school teacher though that by going to a smaller truck - that he could get better gas mileage.  He bought two Dodge Dakota's and none of them got more than 15 mpg.

My Avalanche gets that and it weighs 5400 lbs with all my tools and me in it with a full tank of gasoline - and I don't baby it!  V - 8 (5.3L) with no catalatic converter.

Either pay the man at the pump or park it until gas goes back down below $2 a gallon.

[Buckskins & Black Powder]

keep it at 55. I keep my 92 isuzu rodeo @ 55 most of the time and im averaging 27mpg    No need to waste gas just to get somewhere a few minutes earlier. And dont worry about the horns and rude fingers flying at you. Just remember, you too also have a horn and a middle finger to wave back at them. Along with a smart arse smile on your face. 

[Two Bears]

Thanks for replying guys.
It sounds like it is a poor option to do but I don't understand why the mileage would go down but will have to do some more research on it.

One would think that if you changed everything that needs to be changed out to make it work it would get better MPG's on the highway.

[Keith L]

One of the early responders asked what RPM the truck is running now at highway speeds.  Most of the time axle ratios are computed so at highway speeds the vehicle is just starting on it's best part of the torque curve.  If you gear it higher then the truck will lug when you come to hills, or when passing, or going into a headwind, etc.  This will cause you to get poor economy.  I had a 1990 F 150 with a 300 6 and a five speed.  I went to California with it, and the first day I was driving across Iowa and Nebraska into a head wind.  I insisted on keeping it in overdrive to get better mileage.  The mileage stank.  The next day I tried fourth gear and had much better results with the engine in the right rev range.

If you are good at shifting, and driving it like a truck, you may get some better mileage.  Most of us don't, and even so the increase will likely not pay for the modification.

[R.W.Dale]

 A good example is my Jeep wrangler.

 It had 3.07 gears with a OD transmission, With 31" tires I was turning 1500 rpm at 55mph. With this setup the engine was lugging all the time, I had no power and the MPG was 17.5mpg

 NOW I have the same combination as above save a set 4.11 gears. I now turn 2000rpm at 55mph have all kinds of power and now get 19.7 mpg

 Why do you think this is? With the higher gears the engine had to work harder to propel the Jeep forward thus using more fuel as well as being outside it's optimum torque range. And now with the lower gears the motor doesn't break a sweat pushing the jeep around through the better torque multiplication. The only difference the gear change made in my driving is now I use 5th gear where before I didn't unless I was going 55 or faster, The problem with that is I never drive faster than 55.

 There's a lot more to MPG than just RPM it's generally belevied that piston speed being within a certain range is most important

Gearing for best MPG

Most people think that less revs will equal better MPG. That is not always the case as less revs can also mean more strain on the engine which causes more fuel use. According to a engine design text‚ maximum fuel economy occurs with open throttle and at a piston speed of 1200 – 1500 ft/min. So if you know the stroke of your engine‚ you can calculate the rpm for best fuel economy. Usually comes out somewhere between 2000 – 3000 rpm. Dino provided me with the following numbers. The 4.0L has a stroke of 3.411" and a 4.5-4.8L stroker has a stroke of 3.895" so the numbers would be as follows: 1200-1500ft/min piston speed = 2110-2640rpm on a 4.0, 1848-2310rpm on a stroker. So use the table above to pick the right gears for your tyre size. Above gives the average cruising speed of 65 mph or 105 kph. The more weight you carry the more revs you need to stop the extra fuel use through engine strain. The extra revs is also better for the auto and even engine temperature with less strain and the water pump running faster to circulate the coolant.

 If anything I think Ford trucks already have gearing that it too high for optimum mpg. As the mfg gears them as if everyone drives 80

 

[SHOOTALL]

I HAVE HAD THREE 4 DOOR P/U'S A FORD SHORT BED IN TOWN 19 MPH ON THE ROAD 21-22 MPG , A DODGE LONG BED 16-18 MPG AND A CHEVY LONG BED 18 -20 MPG , ALL HAD CAMPER SHELLS ALL 3/4 TON TRUCKS ALL AUTOMATIC TRANS. ALL WERE DIESEL WITH TURBO ! 

[R.W.Dale]

I HAVE HAD THREE 4 DOOR P/U'S A FORD SHORT BED IN TOWN 19 MPH ON THE ROAD 21-22 MPG , A DODGE LONG BED 16-18 MPG AND A CHEVY LONG BED 18 -20 MPG , ALL HAD CAMPER SHELLS ALL 3/4 TON TRUCKS ALL AUTOMATIC TRANS. ALL WERE DIESEL WITH TURBO ! 

 And that has what to do with gearing a gas engine in a 1/2 ton truck for mpg?

[SHOOTALL]

well i had a 1/2 ton truck with poor gas mileage and thats how i cured the problem ! if ya keep the 1/2 ton then try the tallest tire you can put on it and have the comp. adjusted to the size , as far as 4wd. i had a full size blazer with 308 gears and 350 engine od trans. it got 18mpg on the road , was lousy on the beach or in the moutians on or off rd. its funny how everyone thinks a full size truck can get 50 miles to the gal. but the industry won't let it happen , it must be hard to get all the auto makers to do that world wide ! weight means less mpg , check your truck empty then load it down and check it again ! you will get the picture ! why do you think each of those battle tanks have 4 tankers each comming along behind them ? 50 plus tons don't set the world on fire when it comes to mpg !
i just helped my son change  the gears in his truck , it sets on 39's with a 8 in lift , went to 512's from 410's and with all the tire now the over drive works and mpg went up ! got back in the right rpm range  for power ! we didn't choose the ratio looked it up on a chart ! takes the guess work out of it ! it got better mpg but the cost was as much if not more than a diesel !
if gas engines could get the mpg and deliver the power at the same time why would we be paying extra for a diesel engine ?
thats all it has to do with it , why waste the effort for a maybe when a better way exist ?
You ask !

[R.W.Dale]

if ya keep the 1/2 ton then try the tallest tire you can put on it and have the comp. adjusted to the size

 And watch your MPG drop to even more abysmal lows, Heavier tires with more rotating mass creating an overall ratio so high that it'lll guarantee your trans NEVER shifts into overdrive, YEP a shure fire recipe for great MPG

 I agree that the higher volumetric efficiency of a diesel engine is the way to go......BUT 1/2 ton truck manufacturers are too retarded to put a large 4cyl or small 6cyl turbo diesel in one and not everybody wants or needs a 3/4 or 1 ton truck

[SHOOTALL]

krochus, if you check , new trucks have a listing of tire sizes that work with the computer etc. i have found that using the largest listed i get the best mpg , i run 47 to 50 trucks and i can assure you if the cost of the larger tire did not get off set by the better mpg i would not spend the money ! we buy 20000-30000 thousand dollars of gas a mo. its important trust me !
the tires are less than 20 more each !
wasn't talking about monster truck tires !

[R.W.Dale]

krochus, if you check , new trucks have a listing of tire sizes that work with the computer etc. i have found that using the largest listed i get the best mpg , i run 47 to 50 trucks and i can assure you if the cost of the larger tire did not get off set by the better mpg i would not spend the money ! we buy 20000-30000 thousand dollars of gas a mo. its important trust me !
the tires are less than 20 more each !
wasn't talking about monster truck tires !

 are you running gas trucks or diesel?

[Buckskins & Black Powder]

Heres a good one.

1994 ford f250, long bed, 351w,5 speed, pulling a 1800lb trailer with a 4500-4700lb buick electra. 8mpg hauling this load to denver! Gutless on hills.  Amazing how those big rigs hauling 40-50,000lbs get around 6-7mpg.

Know a guy who bought a 1978 chevy 3500, had a 454 and 4 speed, Hes a buick guy so he pulled the motor, built a fresh '69 430 buick bigblock, mated it to the 4 speed. Hes hauling his 16 foot covered trailer with all his tools, a 70 GS 455 "3600lbs"  in the trailer and hes getting 14.5mpg in the mountains! How? Look up the Torque on a '69 430. Its all made at low RPM where as ford and chevy has always been in the 4000 rpm range VS buicks 2600-3000rpm range. He also put in an RV cam when he rebuilt the motor.

 As for tire size, My 53 ford has a 3.89 ratio rear end, Put 14" Tires on, the final gear ratio works out to 4:11. Put a 15" wheel on and its back to 3.89.  When you put in a low ratio gear like, 4.11 and top it off with a 31-33" tire, Those big tires tame the gears while helping you keep the RPM lower. Put your regular 15" wheels that came factory with those 4.11 gears and you'll be sucking more fuel than ever.

My 71 skylark is getting 3.73 gears but im going with 28" tires to keep the RPM's lower than if i went with a 26" tire.

[Keith L]

I have a 2000 GMC Savana half ton conversion van with a 5.0 liter V8 and an auto trans.  Loaded to the max it gets 20 mpg at 75 mph down the interstate.  With all the aerodynamics of a brick.  Go figure.  My last van was ten years older, a mini van (aerostar) that didn't do as well.  We travel and camp in it, so it is a money saver, considering motels at $60-75 a night.  I have no clue what the rear ratio is, but I am not messing with anything on this one.

[SHOOTALL]

KROCHUS , right now 2 are diesel the rest are gas , the biggest single problem we experince has been rears , ford rears in particular , the last 4 fords we got 3 rears had to be replaced within the 36000 mi wart. one twice , chevy. its fuel pumps around 80000 and dodge has its share of ball joint trouble ! the Toyota's still lack room ! the bottom line , they all break down sooner or later !

[Two Bears]

krochus, if you check , new trucks have a listing of tire sizes that work with the computer etc. i have found that using the largest listed i get the best mpg , i run 47 to 50 trucks and i can assure you if the cost of the larger tire did not get off set by the better mpg i would not spend the money ! we buy 20000-30000 thousand dollars of gas a mo. its important trust me !
the tires are less than 20 more each !
wasn't talking about monster truck tires !

Where can I find this "listing" for tire sizes for Ford or the chart that you talk about?

[SHOOTALL]

most of the time its on the drivers door or in glove box , my chevy.  has 2 sizes listed a dodge i drove had 3 , some of the fords had more . i know the tire dealers have the same chart for listed tires and it should be in the instruction manual that came with the vehicle , now for other sizes check out national wheel and tire out of West Virginia they have more tire we used them when we lifted my sons truck ( for the record i was opposed to the lift , but if it had to happen i wanted to make sure it was safe and legal ) and they had alot of information we gave the mod. truck the lift and they told us what wheels offset and size  that would work !, in VA. , if i down grade a tire on a work truck and it causes an accident VOSHA is going to site me for not having the correct tires along with VDOT , so most reputable tire suppliers make sure on a work truck the don't stray off the chart , I know you can up grade with regard to rating and sometimes when you do you have to switch from standard to metric sizes or vise-versa  i realize people do switch all the time but in a work situation it ain't a good idea !

[30-30man]

I was looking for a 4wd truck for a daily driver for my wife.  She helps with the turkey farm and needed something better than the minivan she was driving.   I test drove a 04 FX4 with the 5.4 Triton.  It felt very underpowered and weak in such a heavy truck.  The motor even seemed to struggle going up the slightest hill. I thought I wanted a Ford because they seem to be able to take the miles.  This thing had an engine that was reported to have 300hp.  My old 97 Ford 4.2v6 felt like it had more power.  After the test drive, I looked back  at another Dodge.  I thought Dodge and gas mileage was as common as cheap gas.  I own a 79 4 wd and a 2002 2wd both with a 5.9 360.  They are both gas hogs. 14mpg max and that is with no load and the wind behind them.  I have to say though  I am very impressed with my wife's 04 Dodge.  I bought a used 2004 Dodge 1500 4wd with the Hemi with 3.55 rear and front gears. I needed the 4wd on the slick boat ramp in my neighborhood.(vacation home)  Many people are going to think I'm lying but I get 17mpg in town and close to 19.5-21 highway.  This has been constant over a month and I am going by the computer up in the console.  I have checked it with pen and paper and the computer is dead on almost.  The best thing about owning a hemi is that you can pass almost everything even a few gas stations.

[SHOOTALL]

my younget has a dodge with a 4.? small V8 gete 18-20 its 4wd but not sure about towing he only tows trl with 2 4wheelers