Sorry I've searched, but really didn't find what I was looking for.

I have a 1999 F250 with a 6in lift and 37's on it right now. Its gotten a little sluggish towing so I am planning on swapping out the gears.

As of now I am planning on going with 4.88's or maybe even 4.56's I'm just not sure what gear I want. I guess whatever is best for towing.

My question is, should I replace anything while I am at it? What do you guys think of the gear choice? Any advice would
be greatly appreciated.
Thanks again

Al

 

4.88's with 37's would be great for towing. What gears are in it now? 4.10's? 3.73's?

I'd check out one of the tire/gear ratio charts to see what gear ratio will put you back the gearing that the truck had with stock sized tires.

 

Well it has 3.73s in it right now. Are there any advantages to going 4.88's vice 4.56's?

 

I mentioned this in a previous post a month ago. DCSpecial, an FTE Sponsor here, said 4.30 gears would bring you back to stock powerband with 37s.

FordGuy

 

I kind of feel like when I do my gear swap I want something a little more then 4.30's. I just don't want to regret being too conservative.

 

If your like me bigger tires are an incurrable disease. I WILL be putting 37's on my 79 when the current rubber wears out. And my '05 will get 35's when the current shoes wear out (I still kick myself for not going larger).

Back to the subject at hand.

If your not obsessed with mileage I'd go with at least the 4.56's, they're not to much deeper than the 4.30's. All of the gearing charts DO NOT take in to account the effect of a taller profile vehicle (due to lift adding wind resistance and larger tires adding rolling resistance). I say go a little deeper, especially if you tow a lot. A gear change is to spendy to not get it right the first time.

My wallet and I hate doing things twice!

 

Yup! It would be nice to get it done right the first time around!

 

I didn't see it listed......what motor do you have?

If it's the PSD I'd do 4.30s.
Gas engine I'd do the 4.56s or 4.88s.


37s and 4.88s would be close to the same effective ratio as a stock truck with 31.6" tires and 4.30 gears which was an option with the V10.


I've complied a little chart of sorts that shows how different gear ratios efffect RPMs with different sized tires.

Here's some info I posted awhile back in another post on another forum:

Here's a quick example of rpms with given gear ratios at 70 mph. All rpms listed are for a AOD trans with a .70 OD ratio....so they aren't dead on, but they are close (the 4R100 has a .71 or .72 OD ratio). So, while the rpms aren't 100% on the money it will give you an idea of how each different gear ratio effects engine rpm at 70mph.

tire..............gear...................rpm
31.6"...........3.73....................1943 (stock truck)
31.6............4.10....................2136
31.6............4.30....................2240
34.7............3.73....................1770
34.7............4.10....................1945
34.7............4.30....................2040
34.7............4.56....................2164
36.7............3.73....................1673
36.7............4.10....................1839
36.7............4.30....................1929
36.7............4.56....................2046
36.7............4.88....................2189
38...............3.73....................1616
38...............4.30....................1863
38...............4.56....................1976
38...............4.88....................2114
38...............5.13....................2223

 

Thanks for the info. I actually have a V10, I'm really leaning towards the 4.88's.

 

For everyday driving, Id go with the 4.56 gears.... but of course the 4.88s are gonna make the truck wicked.

 

See thats what I'm looking for.

 

kinda sorta off topic, but is there any way to determine what gears you have by speed and rpm?

 

Are you trying to figure out what your truck has? You can tell by a couple of ways..

1.) tag on the differential. The code on that tag = specific gear ratio
2.) door jamb sticker code

If you have either, we can tell you definitively.

 

well i have checked the door sticker and im not quite sure how to read it really. i do know that my BFGs are 33" dia. and at 70mph the rpms sit just a hare under 2 grand...

 

and as far as the diff tag goes, i didnt know it had one.