We are taking a trip to IN later in Sept and are trying to decide if we should take my FJ or my wife's Camry since we are carrying two to four bikes. What happens to the mpg of the Camry when carrying bikes? Does it drop dramatically?

 

Don't fret it, I pull an enclosed 17 ft trailer with 4 Harley Road Kings in and loose 3 mpg, handles it fine.

 

What kind of rack is it? It all depends.

Roof top - you will lose some fuel economy. Hitch mount, probably not much.

Either way you should easily beat the fuel economy of a FJ!

 

rooftop rack will put more weight on the car hence lower mpg, I don't think there will be a dramatic change on the mpg, bikes are not that much weight anyway.

 

Maybe I'm misreading you, but how can it make any difference where the rack is mounted with respect to weight? The total weight is the total weight, regardless of distribution.
The big reason for the drop in FE with a top-mounted rack is increased wind resistance.

 

Yes it is all about wind resistance. I lose 3mpg with one bike on a roof rack on my SAAB 9-5 - it drops from 30 to 27 at 70mph, approx 10%. I would expect a similar loss on the TCH if you have them on the roof - possibly as much as 4-5 mpg with 2 bikes at 70mph.

If you mount them on a hitch-mounted rack it would be a lot less but still have some negative impact as you are still creating dirty air, even if it is behind the car. Might lose 2 mpg. I have not tried a rack on my Prius yet - I just stuff the bike inside - one reason I chose it over the TCH actually.