So i get my new tires in the mail today and they look fairly wide. Will 255/50/17'* fit on my 2000 bonneville SSEI?

Hmmm....should be close.
245/ 50 R 17 would be the same OD as the stock 235/55/17 tires.
The 255/50/17'* will be about 3/8" taller and 3/4" wider.
I don't really know if they will interfere with anything.

ya...all the tire places are freaking out! *THEY WON"T FIT** OMG!....i'm like try one tire and check so this place its at currently is checking the front.....people make me laugh :P

They should probably fit. They will be a little taller and your speedo will read slower than you are actually going.

So...they fit thanks for all your help No rub or anything. And it looks verrrrry nice.

Would it not throw off the computer and get less MPG?

Should get better actual MPG and your odo will record less miles than you have actually traveled, so your car will retain more value.

So for my car, what tires should I get to do some cheating with my mileage? I already have 235/55/16 instead of the stock 225/60/16

Any tire that has a larger OD than your stock 225/60 16'*, which are ~ 26.6" OD
Your 235/55 16'* are ~ 26.2" OD or slightly smaller than stock.
275/50 16'* would be the same as original size @ 26.8"
If you could fit some 255/55 16'*, they are ~ 27.0" OD.....not even sure if this size is available.
235/60 16'* would be 27.1" OD
You really should consider going to 17" wheels.

What does OD stand for?