regearing
 

heres my set up
98 f150 4x4 5 inch rcx lift 35 inch mickey thompson baja mtz with the 4.6 v8 with 245000km wat gearing should i do thta will increase my mpg i drive about 50km a day. also how much will it affect my mpg.

What gears are you running now? I would go with 4.56's. I'd also look into a programmer\tuner. You will get some improvement in performance, mpg's and your speedometer will be calibrated correctly to recognize the change in tire size\gears.

I agree

im running stock gearing if that helps im not 100% sure of what stock is and most of my driving is at 90km/h will 4.56 gears make my rpm too high while cruising at that speed.

You need to find the axle code. You can commonly find it on your door jam. Post it up here to find out what you have. I am betting you have 3.55s. The larger tires make up for the ratio change, so you will be fine as far as RPMs go. Highly recommend programmer too. Honestly your mileage will probably not improve a whole lot, but your power will with the gear change.

4:56s and 315/75/16s got me pushing 2,300ish rpms at 70-75mph.

ok thank you very much fro everyones help once i get the money together i am going to buy the 4.56 gears thanks again everyone. Another question tho is will the programmer affect the life of my engine with so many km on it because my dad put one on his 2001 gmc 2500 diesel and it messed up his towing abililty after about 150 000km with it on his turbo was shutting off and then the truck just wouldnt move with a trailer on it. any help will be greatly appreciated.

my axle code is h9

All the programmer does is change shift points,spark advance, and timing. Theres nothing to worry about. It just uses power that your stock "tunes" or settings wont allow for, because Ford set them to be acceptable to everyone. For example, some people like smooth shifting, where as, others like a firmer, crisper shift. I really like the Edge because I can monitor just about everything thats going on with the engine as well as mpgs and all that. I have 4:56 and 315s and my edge says that my average miles per gallon is 15.8. That is mixed driving, and my ratio mile per mile is almost 1:1 so I would tend to think thats pretty accurate.

H9 is 3:55LS if I remember correctly.

thank you for all the help guys especially b2therad im definetly doing the gears but im gonna wait and save up for the programmer

No problem!