I'm told part of my poor gas mileage problem is because I'm running on 32x11.50 tires. Why do bigger ones get worse mileage?

 

I would say its just more weight to turn. more weight = more effort from the drive train.

 

More rubber on the road equals more resistance too. Tread design could also play into resistance.

 

ANOTHER FACTOR

A larger diameter tire also has a larger circumference and travels farther wth each revolution. Your odometer is calibrated for a specific dia/circumference tire. The larger tire will throw your MPG computations off a little making it appear that you have traveled a shorter distance (based on the odometer reading /fewer revolutions) on a tank of gas.

Going from a 31 inch dia. tire to a 33 inch dia tire effects the actual distance rolled by approximately 6 % as an example.

Example: So if you are using 33 inch tires and the odometer is calibrated for smaller 31 inch tires and the odometer reads 300 miles you have actually traveled 318 miles. Say you used 30 gal of gas to make this hypothetical trip. The MPG calculation will be 10 MPG, it is actually 10.6 MPG

 

Friction. That's what you bought them for, for more traction, which is more friction on the road surface. Pump as much air in them as the sidewall allows, and it will help, but give you a rougher ride.

 

Bigger is always better!

 

My dad just put a new set of tires on his Ranger. They're filled with nitrogen and they're supposed to get about 1/2 mile per gallon better than regular air.

 

without the proper gears(axle) itll pull harder on the drive line cousing the engine to work harder resulting in more feul used

 

I have an 86 with a 460 I want to put bigger tires on it will I see a huge mileage difference currently getting right at ten mpg

 

If they are wider also, with a rough tread, yes you will see a loss in mpg.

 

Unless going to a bigger diameter tire is improving your effective gearing - e.g. if you have a 4.11 axle now, & drive at higher speeds

 

Mine are filled with nitrogen as well. Almost 80% Nitrogen, 20% Oxygen, and aproximately 1% of other gases...

In other words regular old fashioned air we breathe...

I'm not too optimistic on 100% Nitrogen filled or nitrogen enriched anything... Tires or Gasoline

 

How do I know what the gear ratio is. This truck has a lot of non stock parts but i cannot be sure they did anything with the gearing

 

Larger tires also lift the truck, allowing more air turbulence under the truck, increasing drag and reducing efficiency.

Generally, larger tires are heavier which as unsprung weight adversly affects handling as well as acceleration [slower] and braking [longer].

If you want to play [increased traction, looks, etc.], you have to pay!

 

If there is no longer a readable tag on the axle - lift ONE wheel off the ground & mark both the tire & the driveshaft.
Turn the wheel exactly 1 revolution & count the turns of the driveshaft.
Divide the driveshaft revolutions by 2, & that is your ratio.

For instance -

If 1x wheel revolution gives you 7x driveshaft revolutions - you have a 3.55 (or 3.54) axle ratio.
Or 8.25 revolutions would mean a 4.11 axle, & so on.