The gear ratio is the number of times that driveshaft turns for every one wheel rotation. So, a 3.73 axle means that the driveshaft spins 3.73 times with one rotation of the rear wheels. The higher the number, the more power is sent to the wheels, but it will hurt your mileage.

A lower axle ratio (like a 3.08 or a 3.31) will increase your mileage, but hurt your power.

Tire sizes are opposite, big tires are better for mileage, worse for power. Small tires are better for power, worsr for mileage.

 

Thanks Tim, that explanation was what I expected but It was good to hear someone comfirm my suspesions. Thanks for the help.



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White 1999 F150 4X4 XLT Regular Cab, 5.4L Short bed, 373 Rear, Towing & Off Road Pkg, 6 Disk CD, Keyless Entry

Mods Include : Superchip, Flowmaster exhaust, Chrome bed rails, Full window tint. Triton boats tag on front - BASS sticker in rear glass

 

The difference between the 2 ratios is less than 5% and is probably insignificant in terms of mileage, unless you do a lot of open highway driving and even then is going to be less than 1 mpg. The difference in acceleration is equally insignificant, maybe a couple of tenths in the 1/4 mile and nothing on the street. With a 4X4 you're already lugging around a lot of dead weight (until you get into the dirt) and large diameter tires, so more gear is definitely better.

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'95 Ranger 4.0 auto 2wd swb.
moving up to an F-150 in 2000.
joined to learn about what works and what doesn't

 

I have a 373 ratio in my 99 4X4. Others have
355. I understand what the difference is but what effect does this ratio have on MPG or MPH. Does the lower gear ratio help in MPG but hurt in MPH? Or should I say pick up or power of the vehicle. Most of the 4X4's seem to have the 373. Any easy way to explain this?

Thanks

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White 1999 F150 4X4 XLT Regular Cab, 5.4L Short bed, 373 Rear, Towing & Off Road Pkg, 6 Disk CD, Keyless Entry

Mods Include : Superchip, Flowmaster exhaust, Chrome bed rails, Full window tint. Triton boats tag on front - BASS sticker in rear glass





[This message has been edited by Triton (edited 06-25-1999).]

 

Triton
I beleive that the 3.73 is associated with the 5.4 and is part of the "off the road" package which includes a different size tire.Bigger rear gear plus bigger tires probably makes for minimal MPG from a 3.55 with smaller tires.
Paul

 

I figured as much. Thanks for the responses guys. I dont think anything can help the mileage on this rig unless I get out and push. Is OK though, gas is cheap in Georgia compared to most states and I like the extra umph.



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White 1999 F150 4X4 XLT Regular Cab, 5.4L Short bed, 373 Rear, Towing & Off Road Pkg, 6 Disk CD, Keyless Entry

Mods Include : Superchip, Flowmaster exhaust, Chrome bed rails, Full window tint. Triton boats tag on front - BASS sticker in rear glass

 

fin2lean,
the 3.73 gears are optional, my truck has them and I don't have the ORP package. My wifes '99 Ranger has the same gear set with the 3.0 engine, and they too were optional.

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'97 F-250 L/D Lariat S/C, 4x4, 5.4, E4OD automatic, 3.73 gears, 4 wh. ABS and 4 wh. disk brakes, gray leather interior,keyless entry w/alarm, outside: white w/gray rocker section, sliding rear window, tow package. Mods- Ford running boards, Ford ventsahdes, Color-matched bug deflector, AVS tail light covers, Tuff Liner bed liner, unknown brand of cat-back exhaust system (previous owner installed).

 

What swaybars actually do (aside from reducing sway):
The grip available at a tire is a function of the vertical load (weight) that it carries. As load is shifted from one tire to another, the tire which receives the weight gains grip but to a lesser amount than the tire which gives up the weight looses grip. adding a swaybar or replacing an existing swaybar with a stiffer one allows more weight to be transferred from the inside wheel to the outside wheel in a corner. The result is that a stiffer front swaybar causes the front end to lose grip and causes the vehicle to understeer or "push." A rear swaybar causes more weight to be transferred to the outside rear wheel, causing the rear end to lose grip and the vehicle to oversteer or "get loose." All US passenger vehicles with the possible exception of the Vette and the Viper have huge amounts of understeer built in and can stand to be loosened up a lot with no danger.
Trucks are a slightly different story, with their very stiff rear springs and extreme front weight bias, they can be VERY twitchy in hard cornering situations. Even as softly sprung as the current F-150s are, this is still true. Adding a rear sway bar to reduce sway is a good idea, but you probably want to consider a stiffer front bar as well to "balance" out the suspension. Look at the Lightning where Ford added a much stiffer front bar to offset the stiffer rear springs and the rear bar. BTW the stiffness of a swaybar is proportional to its diameter to the 4th power (d**4) so very small increases in diameter give big increases in stiffness (e.g. a 1.25 inch bar is 2.44 times as stiff as a 1" bar). Check Steeda for sway bars. They are a road-race oriented Mustang shop, but they market handling and power stuff for the F-150 as well

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'95 Ranger 4.0 auto 2wd swb.
moving up to an F-150 in 2000.
joined to learn about what works and what doesn't

[This message has been edited by StrangeRanger (edited 06-29-1999).]

 

Iggy
Actually we are both right. According to Kelley Blue book and all related sites it can be an option. No two wheel drives get it,only 4x4's and no work trucks, they have to be XL's,XLT's,Lariat's. As soon as the Off road package is combined with the 5.4 the 3.73's become part of the package. From all the sites I just looked at, Kelley's and carprices.com,and couple of others it appears that when you get the two (ORP and the 5.4)the third (3.73's) comes with it. I may be wrong. Boy did you every try to read one of those options list and try to understand it. I need some aspirin.:-0
Paul

 

To all,
A myth that I have recently disproved is that a lower gear ratio will always cost you mileage. I had a stock 3.55:1 ratio in my truck and was displeased with the very low rpm at cruising speed and had a desire for more launch so I changed to a 4.10:1 gear and believe it or not I picked up 1.5 mpg. I just recently made a 1,000 mile trip with the first 500 averaging 20.5 mpg. The second half was lower because the wires on the back of the IAT sensor broke inside the insulation and I could not find it until I got home. Anyhow it raised my rpm closer to the power band and I am very pleased with the change. By the way I consistantly get 17.5-18.5 mpg in town.
Later and God Bless!!!

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Jim
Bright Red, 97 f-150 SC flareside,4x2,4.6,auto tranny, Mobil-1, Superchipped, Airaid, .999 tuned TPS, 3 chamber Flowmaster with custom dual outlets at bumper, JBA headers, Hellwig swaybar, steel cowl induction hood(non-functional), Magnecor 8mm wires, Plat-4 plugs, B&M Shift-Plus(no help if chipped), A.R.E. hard bedlid, Laverne nerf bars, American Racing 8x16 with 315-55-R16 B.F. Goodrich Sportruck TAs, 4.10:1 Precision Gears, ASP performance pulleys,Monro-Matic Plus shocks.

 

To all,
A myth that I have recently disproved is that a lower gear ratio will always cost you mileage. I had a stock 3.55:1 ratio in my truck and was displeased with the very low rpm at cruising speed and had a desire for more launch so I changed to a 4.10:1 gear and believe it or not I picked up 1.5 mpg. I just recently made a 1,000 mile trip with the first 500 averaging 20.5 mpg. The second half was lower because the wires on the back of the IAT sensor broke inside the insulation and I could not find it until I got home. Anyhow it raised my rpm closer to the power band and I am very pleased with the change. By the way I consistantly get 17.5-18.5 mpg in town.
Later and God Bless!!!

------------------
Jim
Bright Red, 97 f-150 SC flareside,4x2,4.6,auto tranny, Mobil-1, Superchipped, Airaid, .999 tuned TPS, 3 chamber Flowmaster with custom dual outlets at bumper, JBA headers, Hellwig swaybar, steel cowl induction hood(non-functional), Magnecor 8mm wires, Plat-4 plugs, B&M Shift-Plus(no help if chipped), A.R.E. hard bedlid, Laverne nerf bars, American Racing 8x16 with 315-55-R16 B.F. Goodrich Sportruck TAs, 4.10:1 Precision Gears, ASP performance pulleys,Monro-Matic Plus shocks.

 

Chaplain
I'm sorry but I must disagree with you on this. If this was all that we had to do then we wouldn't need to have overdrives in our vehicles to get better gas mileage. It sounds like you have a nice truck with a lot of modifications to it, including different size tires and the rear gears. After you installed these two items you did get your speedometer/odometer recalibrated didn't you? If not then your mileage that is displayed and the mileage you traveled would be quite a bit different.
Paul

 

fin2lean,
You may disagree if you like,I can only report to all what I experienced. In regards to the tire size and speedo correction, yes I did correct the speedo for the 4.10 gears, I had to get the gear special from Steeda because Ford does not make a 23 tooth gear (you can read all about this in another post about speedometer recalibration). The tires are the same height so no change there. I am a Reserve Sheriff Officer as well and we have a nice little tool that I check accuracy with if you know what I mean. I check my mileage every tank and keep track of the driving conditions each time so I am confident in my information. I beleive that lugging aroun 1600-1700 RPM was causing me to use more gas, now I am running around 2100 RPM which puts it in the edge of the power band. I don't know what will happen to my mileage now since I just finished putting my blower on this evening, I will post after some testing.
God Bless!!!!

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Jim
Bright Red, 97 f-150 SC flareside,4x2,4.6,auto tranny, Mobil-1, Superchipped,Supercharged(Powerdyne), .999 tuned TPS, 3 chamber Flowmaster with custom dual outlets at bumper, JBA headers, Hellwig swaybar, steel cowl induction hood(non-functional), Magnecor 8mm wires, Plat-4 plugs, , A.R.E. hard bedlid, Laverne nerf bars, American Racing 8x16 with 315-55-R16 B.F. Goodrich Sportruck TAs, 4.10:1 Precision Gears, ,Monro-Matic Plus shocks.