Outer Limits 4x4 Board

If u ran the same tyre just in a bigger tyre will it use that much extra fuel.. say 31s to 33s?

the general rule is it will use a bit more fuel around town, and a bit less on the highway

How much depends on the car itself. But once you remember to factor in the speedo error, it's never really a significant amount.

If you put larger tyres on a vehicle and travel a certain distance, the speedo will tell you that is has travelled less distance overall (apart from under-reading the speed as well). If the vehicle uses the same amount of fuel to do the trip and you divide the fuel by the distance, you will apparently get a higher fuel consumption. Most people seem to get caught by this.

Having higher gearing could mean less overall fuel being used on flat country, but in hilly stuff, it probably means moer fuel because the engine will be working harder.

not always, it also depends on gearing.
i actually use less fuel on the 38" TSLs than i do on the 35" BFGs