Nobody has really answered your question with the downsides so here goes:
Ask yourself these questions:
Why would Alfa Romeo, a company that is proud of the fact that it makes driver's cars to be driven and spend a fortune on handling at the expense of reliability of suspension components (which we all know too well about), actually fit 16" alloy wheels as an upgrade on the Veloce models?
Why not go to 17" alloys like most other marques did at the time? It by far a more common size after all!
There is a good reason for everything Alfa did when it came to suspension, wheels and brakes....
Take a good look at the forum, go on.... Do a search for "17" alloy wheel issues"
and you will soon see the shear amount of posts relating to harsheness, buckles etc.
Now do the same search for 16" alloys
and do the math
17" and above belong on a lovely smooth track where you Will
see the benefits...
On British roads and the state that they are in? Well expect to be changing them on a regular basis. "False economy"
for the sake of what? Looks!
How many times do you drive behind an Audi only to see them skew across the road in order to avoid the next pothole shattering their lovely standard 18" alloys? I see it all the time and yes.... I do smile and mutter "what a c*ck".
... Is that what you want?
Then there is the extra wear and tear on already "on the limit" suspension components... the sheer force of an unforgiving pot hole will make a top bush give up the ghost a hell of a lot quicker... so now you have simply compounded the whole problem even further and wish that you had gone for 18" alloys instead as the handling isn't what you expected????
Thats what many owners simply don't understand! get the basics right first.... Your tyre foot print and security of suspension components is all you have between success and failure on the next bend!
So they automatically blame it on the standard alloy wheel instead! Or even worse... the shocks and springs too!
Lets face it... When are you ever going to see the benefit when 95% of the time it's bad roads, traffic, pedestrians, juctions, traffic lights etc... And...... When you do get the chance to open the taps and let the beasty do it's stuff, the 16" alloy is more than up to the task
Been there , done that , got the T-shirt....
And what have I learned?
Well... it's simple... Save the money you were going to spend on alloys and tyres, get the standard suspension bits, brakes etc changed and in tip top condition and invest in good quality rubber and you know what....?
You will find that you can put a standard Alfa in top condition against any 17" alloy shod Alfa with crappy Wan'Li tyres (because the owner skimped after spending so much on diamond cut alloys) on the bends and show it the way home... They will be in the next ditch and wonder how that happened anyway?
Sounds like a rant doesn't it? But it's honestly not, just sound advice as I have tried them all and seen the failures that insue!
Does one inch really make a difference to anyone's life? Ask the missus if it bothers you that much!: