My xj obviously isn't good on gas Im around 16mpg now but I want to get a roof rack and put my spare on top so I have more trunk storage space. Is having the rack and tire gonna decrease my mpg? I cant really afford to get any worse on the gas

 

Yes anything that changes the airflow over the jeep has the potential to reduce fuel mileage.

 

YES, if you get a rack and put your spare up top you WILL loose fuel economy.
I can feel the drag on the highway, when I throw my spare on the rack.

 

With my spare up top, a LOT of tools that I always carry, 3" on 31's with stock 3.55 gears, I get right at 10 mpg in town. I am looking to regear in the future but for now, I have made my piece with the fact that I drive a 4 wheel drive vehicle with the aerodynamics of a brick.

 

I agree with what the others posted. I have a Thule roof basket and it was very loud before i put the wind guard on it. Its still noticeable, but better...Anyways, i notice the sound and can therefore tell that there is drag...Without a tire haha. With one, there would no doubt be quite a bit of drag

 

You stack a 7-11 on top of a Walmart and the gas mileage will suffer.

 

Not that much.

 

#$%*@ autocorrect. I meant peace, not piece.

 

I put my 31 on top, factory roof rack-it was a noticeable drag on the highway, but now I am used to it. It had a cat **** like smell to it, I couldn't take it anymore.

I've accepted the poor-ish mileage too for this brick. We take the JK if I want "good" mileage-lol.

 

There is a noticeable difference in drag while on the highway with my light bar on

 

Hum.......OP never came back guess he lost interest. The rack and tire really doesn't make a lot of difference on these "Bricks" anyway, if their anything other pure Stock and then it is what it is.

Does anyone know off hand what the EPA avg. city/hiway MPG were on these when new 4x4/4.0/AW4/3.55??

 

What I think I'm hearing everyone say is, "go with a bumper mount for the spare tire." Yes?

 

I don't like the idea of that much weight being bolted to the thin unibody. Eventually, it will stress/crack the body/"frame".

 

I disagree, I think with proper bumper mounts it can support the weight no problem

 

A bumper mount won't decrease the mpg very much if at all though right? Im just doing it on top for now but taking it off when its unnecessary