I had Bridgestone 165/65-13's on my car for a while. There just about the same as 155/80-12's.
Now i have my spare's on, 185/75-13's out back 155/80-12's in front. There's not much of a difference taking off, on the street of couse. At the drag strip you will certainly notice a change on your time-slip.
I notice it more on the highway at speed. With the big tires, I can just barely push 5th gear. With the small tires 5th gear is no problem.
Try fiddling with this...calculations2.xls