5 inch is the biggest you can go on a standard door fitting but if you reach in yo pockets and mod your doors you can go large as you like
In a Peugeot 306, the speakers are located inside the front doors. There should be four wires total, two for the speakers and two for the tweeters.
16.5cm in the front doors
In the doors front and rear.
Front Speakers: 6.5" Component system Rear Speakers: 6"x9"
2 front door speakers 2 tweeters in front doors 2 rear door speakers
Front & Rear Doors take only 6x8 speakers
There are 6 speakers in total; two rear speaker located in the doors, four front speakers; two in the door and two tweeters near the airvents next to the front doors.
5.75 inch speakers are in the front and rear doors
The front speakers located in the front doors I believe are 6 inch speakers. The rear speakers are 6 inch X 9 inch speakers.
6x9 in the front doors 6.5 in the back doors
front speakers are 3.5 inch in the dash. The doors can have 6.5 added in if you want but there are no provisions for them stock
6x8 Door Speakers (Front & Rear)