Hello, i am looking for some help with selecting a new gear ratio. I have a95 f150, 4x4 302. The truck currently has 285 tires and i really doubt i would ever go bigger. The truck is a auto and sometimes it seems its real slow to get going from a dead stop. I assume this is sure to the larger tires and not a tranny problem. I have been told this is fixed by changing the gear ratio. I have no idea of what size, what you lose, what you gain or what to expect rpm and millage wise . any help is much appreciated

 

What gears do you currently have? What type of driving do you do? HWY? City? Town? Do you tow alot?

 

I'm sorry i don't know the current gearing, how do i find out, most of my driving is highway/around town.i really don't drive it much at all really. I live a mile from work and i have abother truck i use so i can baby my toy. Its was bought mostly for fun and going to the hunting club, about forty miles away mostly straight highway. Only towing i do is a four Wheeler, small john boat and maybe a trailer of yard trash from time to time

 

Well way to find out is sometimes theres a tag on the diff cover, most of the times there isn't. So at that point you will have to count the gears inside your rear diff. I would assume you have a 3.73 or 4.11 from the factory. to get better off the line you would want to go up in gears. Say you had a 3.73 or 3.55 than you would want a 4.11. Now for highway driving you want a lower gear say a 3.55 or 3.73 if you have 4.11s. Lower gears will drop your rpms on the highway, higher gears will increase the engine rpms.

Clear as mud right.

 

Huh? Lol, i really just want it to drive like it did with original tires size with the 285. Isn't there a way to calculate that with the new tire size, seems factory was a happy medium of highway versus get up and go

 

Yes but you need to know what size gears are currently in you axle. Than when you know that you will know what gears you need. And the joys of being 4wd is you have to change both front and rear gears

 

Ok the tag says...5 844 B Second line... 3 55 88 2k23 that's 3.55 gears right. Original tire size was proably 255 or 265

 

Look on your door jamb sticker for the axle code, you then should be able to find a code chart that will tell you what it is, that is if you want to verify what the rear diff tag says. There are probably several charts floating around on here.

 

Should mean you have a ford 8.8 rear end with 3.55 gears. So than I believe 4.11s would be the equivelant

 

To calculate for the correct gear ratio for bigger tires the formula is simple. Take the larger size tire diameter and divide it by the old tire size diameter. For example, if you had 30" tires stock, and lifted it and put 35" tires on it.

Then (35/30) = 1.166667

Take this number and multiply it by what your stock gear ratio was, so if you had 3.55 gears stock

Then (1.166667*3.55)= 4.14

So, you would want to have 4.10s or 4.11s, whatever is available, to get back to how it was before.

For you, I am not sure that the 285s you are running or will run are big enough of a difference to even warrant a gear ratio change, it is expensive to regear two axles. I may be wrong though, if the truck originally had some really small 235s on it or something, than a 285, depending on the aspect ratio could be a pretty big jump in diameter.

 

You have 3.55 gears.


LOWER gears are HIGHER #s, as in 4.10s, 4.56s.

HIGHER gears are LOWER #s as in 3.08s, 2.73s

With a 285 upgrade from the stock, a 4.10 would get you close to stock overall gear ratio. If you want a little bit more get up and go, put 4.56s. It will make your highway rpms a bit higher, but not too bad with a overdrive.

 

My truck for example, needs a lot more gear than it has, it has a very underpowered engine and large tires, 4.10 gears are what it had stock, it needs at least 5.13s. Luckily for me, I do have a very low first gear in my ZF to get the thing rolling.

 

Ok just checked, the door sticker says the truck came with 235s what does that do to the question

 

OnlineConversion.com - Tire Size Conversion

This will help you for the tire size and then do the math thats stated above

 

My math came out to 4.30, what available size is close to that