i run 275/45/20 tires
just wonderin what gears i should run

 

4.56 if 4x4. 4.88 if 2wd.

 

What are you trying to achieve? Highway mileage will suffer with shorter gears (4.10, 4.56, etc). City mileage may suffer with taller gears (3.55, 3.21, etc).

It sounds like you're trying to improve low-end grunt, so 4.10s or 4.56s should help. That's a pretty short tire, so your effective rear-end ratio is already short, as well.

 

What gear are you currently running?

With tires that are only 30 inches tall or so, id go with a 4.10 or 4.56. 4.88's are way too low, unless you don't do any highway driving.

If you have 3.92 stock, you won't notice much of a difference to a 4.10 or even a 4.56 jump, and hard to justify the cost.

If you have a 3.55 stock (like I did) then its well worth the cost to jump to a 4.56.

My rpm only jumped from about 1550-1600 to 1950-2000 at 60 mph, and have only seen gains as far as MPG are concerned, but I've got 32" tires.

with our .67 overdrive gear and 30"+ tires, a higher numerical gear ratio like 4.56 will not kill highway gas mileage. It usually stays the same, and improves 1-3mpg in town.

 

With the work done to the engine and the 3K stall and such, it is built for more rpm than stock thus the lower gears.

 

Yeah, unless you plan on moving into performance and speed I would stick with 392s. Wanna race it or get wild? Then 456s would be the deal.

 

Actually, if this is a track truck and a 2wd, 4.88s will give the best launch. But if it doubles as a DD, then 4.56s TOPPS, 4.10s wouldn't be bad either with only 30" tires...

 

4.88's and cruise 65-70 on the highway :P.
j/k

4.56's will be a great medium but with your mods you might not be making the best use of your cams power band since the cam is low-mid range.