I'm thinking of throwing some bigger tires on the s-crew and I would reall rather not spend the money on new gears. I have a 5.4 and I know a 3.73 ratio was an option, but I did not buy the truck new so I am not sure what it has. Is there an easy to find ID tag somewhere?

 

There's an axle code on the driver's side door jamb sticker. Post the code here or search the code list. You can find the "actual" ratio on a metal tag under one of the differential cover bolts. It will be the first numbers on the lower of 2 rows of information.

 

Here is what the axle codes are:
19 = 3.55 open
H9 = 3.55 LSD
26 = 3.73 open
B6 = 3.73 LSD
27 = 3.31 open
18 = 3.08 open
25 = 4.10 open
B5 = 4.10 LSD

 

Thanks, I've got the 3.55 limited slip. Any words of wisdom on the biggest tire to run with a 5.4 and 3.55 gears?

 

If you do any towing or hauling, then I'd stick with a 31" tall tire (265/75/16). But, if you don't, then I'd say a 33" tire would be ok (285/75/16)......

Either way, if you have the stock 255/70/16 tires (~30") you'll have to recalibrate the speedo. It also makes a difference in how the trans shifts as well......

Good luck!

 

I agree with Mitch on the sizing. I have 3.73 gears and 32.7" tires and want more perfomance. What size do you have now?

 

I've got 265/75/17 (31") now and I two around a 3800 lb boat quite a bit. I guess if I want to go with a lift an run a bigger tire, I'll have to suck it up and re-gear. Thanks for the help guys.