Hello,

My brother has a 2002 F-150 4x4 with a 4.6L engine. He recently put a lift on it and is now running 315/75/16 (34.6 inches). The truck came stock with 255/70/16 (30 inches) tires and only 3.31 gearing on a 8.8 axle. This gearing seemed a little high to me but I guess it is only because it is a 4.6L. After I ran all the numbers and did the calculations I came up with that he needed 3.81 gears or something around that. My question is would 4.10 gears be too low for the 4.6L or would that be just right for his truck? Also which companies make the best gears? I've heard yukon makes good ones but more options would be great.

Thanks

 

i have the same problem, same gears and motor in my truck. It wont be too low though, those gears will work good for 35s. I was gonna go 3.73s on stock size tires just to make it nicer to drive, the 3.31s suck for the 4.6. Tell him to go with the 4.10s he wont regret it...

 

thanks for the help! Thats what I was thinking but I just wanted another opinion.

 

4:10's would make a major difference in drive-ability. May look into 4:56's if he is wanting to go any bigger, they work pretty well with anything bigger than 35's

 

i have the same question but i have the 5.4, i just put a 5inch lift on and thinking about regearing. i lost my gas milage and want it back (i knew i was going to loose it) shoud i get the 4.10s with the 5.4 or the 4.56s? from reading some charts and other threads alot of people are real happy with the 4.56s with the 9.75 rear end and 35 inch tires. thanks

 

Go with 4.56 gears. Unless you want to go even bigger with 38s then get 4.88s.

I've been running 35s for 2 years with my 5.4 and 3.55 gears with no problems.

 

With a 5 inch lift and 35's, there is no way you will get your gas mileage back due to aerodynamic and unsprung weight issues.

 

This is a nice logical approach to figuring what you need. So, the next closest ratio would be 373, just slightly lower than your 381.
If you go much lower than that the data sent to the trucks computer will be off enough to affect so many things that custom tuning should be done.

 

I ran my 3.55s after i put a fabtech 6 inch on my truck for about a year and my tranny went out. just installed 4.56s and love it. revived lost power due to the 35 inch tires. would recomend if you run 35s change your gears. it may cost a little but saves you in the long run if your tranny goes out. Almost went 5.13, i think it would have been a moster off the line. just didnt want to risk breakdown.

 

a little formula newtire/old tire x stock gear ratio so a 35/32x3.73= 4.08 so a 4.10 would be the correct formula. lower ratios like 4.56 will add performance and tow power but loose fuel econ.

 

the only thing i would say about that formula is that it doesn't factor in the amount of torque the bigger heavier tires takes to get movin. so over estimating is a better way to go. i know lots of friends that just went 4.10s and barely noticed a difference. I had 3.55s and bumped up to 4.56 and wouldnt go back. my rpms are 2100 at 70. and my mileage didnt change cause the engine isnt working as hard for the power.

 

Thats where any input like the fact you are running 2100 rpm is a big help. the truck feels good witht eh 35s now and 3.73 and would be better with 4.10 but yes if the 4.56 isnt overkilll then thats the route i want to go. also makes a diffrence on engine form 5.4 to 4.6 the 4.6 is a no brainer the 4.56 is better . I had planned on the 4.56 but like i mentioned want feedback on rpms.

 

Use the calculator.

http://www.4lo.com/calc/gearratio.htm

Use 0.7 for tranny ratio if you have an automatic to get rpm's in overdrive. Use 1 for transfer case ratio.

 

I just went on a road trip with my new gears and it turns out I got 2 mpg better in a 200 mile trip up grades and across flats. it did take away my top end acceleration, just takes a little longer to pass but not to bad. but increased my 0-60 time by alot. All and all I like the outcome. Now I am going to do a few things to increase engine horsepower like smaller pullyes, headers and high flow cats. should help top end accerlration...

 

I have an 08 fx4 that came stock with 20's and 3:55's. The tranny is always downshifting and seems sluggish to me. My thought was to swap out gears to 4:10 and keep the stock wheels. Thoughts ? Also, what can I expect to pay?