Tyre sizes

[byroncobra]

My car is fitted with Advan 255 50 16s on the rear and 225 50 16 on the front and being a really soft compound semi track tyre i want to keep them aside for track days. Rims are 16 x 9.5 and 16 x 8.

They came fitted to the car when i bought it as a roller and there's issues with the rear guards just scraping the tyre walls when i've a passenger or push hard into corners, this leads me to think that the offset isn't quite correct, but that's another story.

I'm thinking with a lower profile tyre that this may give me less ballooning with the sidewall (the tyre currently sits about 5 to 10mm wider than the rim edge) This should be enough to stop the rubbing I reccon.

There apears to be no such size as 255 40 16, I'm trying to get my head around the changes in profile as treadwidth changes. Can anyone enlighten me on an equivalent sized tyre with a lower sidewall height and subsequent "square" face, should this help solve the scraping problem?

What size sholud be matched up for the front? No clearance issues there.

Thanks

Greg