i have a set of 33" 12s on my jeep that are like new and i dont drive my jeep. thinking about swapping them to my 90 with the 4.9. right now im running 31" 10/50. what kind of performance loss will i get by doing this. how far off will my spedo be.

 

33x12.00 will rub the radius arm (assuming its stock backspacing)

You shouldnt see a performance decrase, i have a bddy with a 3'' body lift and 33's and his scoots along just fine

speedo should only be off a tiny tiny bit but nothin to worry about

 

The speedo will be off a fair bit but that's not your biggest problem.. you need 4.10 gears in the axles or it'll be one giant slug.

 

I can answer this for you cause that is what my truck looks like. (33-12.50-15's)

The tires rub on the radius arms at full lock. I have never driven in Arizona but in Florida I can make a U-turn using 3 lanes total (turn lane and 2 opposites) and not get any rub from it.

My speedo is about 7mph off above 35mph.

My fuel mileage is down to 9mpg (4x4 with a C6 and 3.55 gearing) and no offense to him, but Conanski likes to point on that my stuff is all thrown off because of the tires but I know how I calculated it and I am 100% positive it is correct.

Also, I have the acceleration of a semi but once I get going I can run 85 all day long (then I run out of fuel... ha)

So, I think that is what youre looking at.

 

so it will work but my gas mileage will drop. im getting almost 16 mpg so it wouldnt be worth it, not at the price of gas.