4 inch, 4x6, and 6x9
a 1991 buick skylark has 4" speakers in the dash and 6x9's in back
1992 is 225/60/16 1991 Buick Regal Limited 3.8 V6 is P205/70/R15.
3 1/2 inch
The 2002 Buick Regal has a V6 engine.
The 2003 Buick Regal has a V6 engine.
The 2004 Buick Regal has a V6 engine.
The 2001 Buick Regal has a V6 engine.
The 2004 Buick Regal has a 3.8 L base engine size.
The 2012 Buick Regal has a 2.4 L base engine size.
The 2001 Buick Regal has a 3.8 L base engine size.
The 2013 Buick Regal has a 2.4 L base engine size.
The 2014 Buick Regal has a 2.0 L base engine size.