Gas milage on new gears

[LOGJOCKY]

Ive been looking into changing my gears and Im wondering what kind of milage loss I will be lookin at. I do alot of highway driving but the stock gears suck. I also found that there is a sale on at one of my work suppliers and i can get Front and back 3.73 or 4.10 gears for $225.00 back and $244.00 front.(canadian) so I was gonna do it soon. is this a good price? BTW it will be about a 1/3 less in american funds. Also do I need to change the gears if Im runnin' 33x10.50r15 tires? Thanks in advace.... sorry to ask alot of questions but I have a bad case of the build-up bug lately.

 

[mrboyle]

Not sure on how much it will affect the gas mileage, but if you are planning to run 33's, I wouldn't go any higher than the 4.10's. I'm running 31's w/ 3.73's and the combo works great, but I think the 3.73's would be too high of a gear for 33's.

 

[RTStork]

I don't know how imporytant the gas mileage is to you, but I would go 4.10's if you are running 31's or taller. I have 3.73's and I wish I had 4.10's and my tires are only 29" tall.

 

[KEbert]

Just get a KKM to compensate for the loss of mileage. More power and better mileage from both sides. My god, I can solve any problem

 

[Robert]

Ford must have ran different gear ratios in the earlier transmissions than they did in my '97. My '97 came with 30" tires and 4.10 axle. That combo worked great. Mileage was reasonable and power was excellent. Now that I have 32" tires I am wishing for more gear. My mileage didn't change one way or the other when I went to the taller tires. My new tires are the equivalent to having my stock 30" tires and a 3.89 ratio. I would have to go to a 4.32 ratio to keep my original overall ratio. I would be extremely dissatisfied running 33" tires on a 3.73, 4.10 would be my minimum, 4.56 would be ideal. If the OD gear isn't as low as mine is though a lower ratio might be in order.

 

[LOGJOCKY]

The gas milage itself is only moderatly important to me. The main thing is what kind of RPM's will I be running when Im doin' 120K on the higway( 75m/hr ) I dont want to be runnin over 4000 rpm while drivin. It cant be good for the tranny especially. When I was talkin to the guy at the gear center he told me that it would run around 5000 rpm with 4.10 gears. Is this true? Thanks again

 

[Alec]

From 3.27 gears to 3.73s, my highway rpms went up about 500 on the highway, both in 3rd and OD. My mileage actually improved a bit, though. This is because the engine is in its optimal powerband.

 

[LOGJOCKY]

Are u runnin stock tires? Cause that actuaslly sounds better than going to 4.10s to me. I may only go to a 31x10.50 tire so the 3.73 would work fine I think. What would u think of 8" of lift with 31" tires. might look kind of funny.

 

[Alec]

I have 31x10.50s. And yes, 8" with 31s would look very funny, I only have 2" of lift.

 

[LOGJOCKY]

What size would you recommend with my lift that I plan on doing. Mabye I will just downsize a bit. Mabye only 6"s of lift and 33's. I dont want to go any bigger cause then I will have to go to 4.10's. But if u look on the brightside I will have lots of room for my tires so I wont have to worry about them hitting my fenders.

 

[Alec]

If you're already doing a gear swap and plan on larger than 31 tires, go with the 4.10s. Your rpms will not be at 5000, they'll be ok, especially with overdrive.

 

[LOGJOCKY]

Ok then that is what I will do. Thank you for your input

 

[Robert]

Divide 4.10 by your current axle ratio and then multiply the result by whatever RPM you want to know about. In other words say you are currently running a 3.27 axle and want to know what your new RPM will be when you are currently running 2000 RPM. 4.10/3.27 = 1.25; 1.25*2000 = 2500 RPM. If you want 4.56 instead substitute the 4.10 for 4.56. Using the same example, your RPMs would be 2780 RPM. You need to know what your original ratio is.