225\60-16 or 245\50-16
 

Is an inch going to make that big of a difference in appearance? I really want the Kumho Ecsta AST's.

Yes.

You will have too much wheel well and not enough tire.

Why not just get those in 225/60/16's?

245/55/16's will be .04% off which is about perfect. If you're getting 245's get 55 series Sidewalls.

245/50/16's are almost 4% smaller, and it will look downright bad.

This is the calc i used.. http://www.1010tires.com/TireSizeCalculator.asp

IT's probably easier to get those tires in 235/55/16's. I had 235/55/16's on my 1995 SLE and swapped them onto my 99 SSEi when I bought it. They were a very good handling tire, but the lifespan was not so great. The brand/model I had were Dayton Daytona's, H-speed rating.

there are no tires in the 245/55/16 size, its just not manufactured by anyone.

You don't want 245/55/16 anyway. You want 245/50/16. They're much closer to the stock rolling diameter. There are alot of tire choices in that size.

can 255/50-16 fit or is the 255 to wide on your year of Bonneville.
a lot of us that have 2000+ cars use the 255/50-17 tire and they fit
in our wheelwell just fine. if the stock tire size is 225/60-16 then the
hieght of the stock tire is 26.6" if you can get the 255/50-16 to fit then
the hieght of that tire is 26", .6" shorter than the stock tire, that would
still fill your wheelwell and if you don't rub the inner wheelwell your
car will handle so much better. again IF the 255's would fit ? :?

ROD

255's will fit with modification to the front wheelwells. I may be mistaken, but there may be minor work needed in the rear as well.

245's rub on SOME 92-99's. Also MAY require modification (removal or hammering of some shrouds/liners/shields).

wren hadn't had his morning coffee yet. While it is true that there are few choices in 245/55/16, BonnieMeMn has the diameters right.

225/60/16 diameter = 26.63" circumference = 83.66"
245/55/16 diameter = 26.61" circumference = 83.60"
245/50/16 diameter = 25.65" circumference = 80.57"

this site can give you a visual comparison
http://www.miata.net/garage/tirecalcold.html