if you go any wider than 225, you must decrease the profile accordingly.
as Nick said, a 245/50 will be taller than a 225/50 by a bit. not quite an inch, though
when you purchase tires, talk to the salesman. tell him what you want to do, he should be able to point you in the right direction.
as far as i can see, a 225/50 has a 112.5mm sidewall
where a 245/50 would have a 122.5mm sidewall, 10mm taller overall
the correct aspect ratio would be 245/45, that would give you a 110.25mm sidewall
now if you wanted to put a 255 on the car, the correct profile is 255/45r16
for reference: 225/50r16, sidewall profile is 112.5mm
if you wanted a 255/45r16, sidewall profile is 114.75
the problem with tires, though, is they vary. like shoes, or pants.
so, pick tires at your own risk. nothing bad will happen, they may just not look as right as your friends if you choose a different tire.
good luck to you, however.
though i doubt you will need it
hope my rambling helped.....