Maybe I am gettting to wrapped around the axle and thinking to hard.

When a manufacture builds a vehicle and installs a gear ratio of lets say 3.55, what tire size do they use as a baseline?

Naturally as you increase tire size your gear ratio changes, so if they offer a tire size ranging from 235 to 265, what are they basing there choice of axle ratio off of?

Confused?

 

my truck came with 2.73's and 25in tires

 

You sure about that?

Anyway, they choose the ratio and tire saize combination that would give the best balance between fuel efficieny (since that's what it's all about these days) and power.

 

manufacturers are more than likely making the ratios to comply with epa standards for gas mileage, etc..... yada yada yada

to give a vehicle the "off road package" they usually offer different axle ratios- 3.73, 4.10 , 4.30 , 4.56 and also larger tires.and some stickers that make you think you can do anything.
the manufactures usually find a good mix of on/ off road performance, enhanced more to on road driving and fuel economy.
not many people i know actually take a new truck " off roading" other than driving down a graded forestry service fire road. i see lots of people with lifts, big tires but the truck never sees any off road other than pulling over for an ambulance or fire truck
thats my theory, because actual "off road" vehicles are usually older, and custom tailored to the driving they will be doing by the owners- i.e. rock crawling or mudding.
so with that in mind what the mfr. has to offer and what you need for your driving style, the aftermarket world is for you. my $.02

 

The gear ratio does not change simply by putting different size tires on. All that changes is RPM's per MPH.

 

The gear ratio in the differential does not change, but the overall effective gear ratio does. That's what he meant.

 

I have the so called off road package but all that was available was 3.55