Hi Jake,
The guys above have got it covered pretty well.
Unzipping/zipping was always a recommended option before you dropped or lowered your top, but at the same time, was not mandatory, and could be avoided if you so chose, without any glass damage happening. The owner always had an option in that sense. That said, i have never unzipped the top before lowering it, and have never had any issues as such.
In my case, i believe there are three golden rules to prevent glass breakage ..............................................
1. NEVER drop the top with (ANY OBJECT SOFT OR HARD) sitting in the well liner area, or under the well liner area that would make the well liner floor protrude upwards.
2. NEVER drop the top when the car is parked outside and is stationary, and there is a strong wind blowing in any direction. ( i did that, and busted my glass)
3. NEVER try to drop the top when your car is in motion, FORWARD OR REVERSE.
Lastly, i had a new Robbins top installed several years ago, and the black pinpoint fabric by design is thick, stiff and rigid, so every time i drop the top, i go to the trouble of stopping the dropping process halfway, then walking around the car and manually tucking in the folds as the top progressively goes back down to full drop travel. This helps position the glass correctly (avoiding potential breakage), and prevents any undue stress put on my glass and as well as the fabric. Definately worth going to the trouble to prevent potential damage. Softer chosen vinyl tops, should not present this potential problem from occurring.
Hope that helps,
Greg
