Seat Pan

One thing I learned when I was head judge in the Rat’s Hole Show in Daytona and Sturgis is that a seat is often the weakest part of many very well built motorcycles. I am not talking about the color used or even the material employed. I am talking about the seat not fitting perfectly to the frame, not being symmetric or being afflicted with wrinkles because of poor seat pan preparation.

Some upholstery shops do seat pans. Others refuse and will do only the pure upholstery job. My opinion is that the bike builder should prepare a pan for a custom seat. A seat pan being “part” of the frame, it’s our responsibility to make it right. Steel pan or fiberglass? It’s very controversial. We do both and each has advantages and disadvantages. Steel pans require metal fabrication skills to make them fit perfectly to the rear fender. The pan must be very smooth when doing thin seats, like on most top custom motorcycles. If not, all imperfections, sooner or later, are going to push the foam (even high-density foam) and create weird wrinkles and crooked stitching lines. Fiberglass seat pans don’t require any particular skills and can be built by any builder working in his garage. Fiberglass can easily be smoothed out to create a perfect base and sanded for perfect adjustments. The danger is that fiberglass seat pans have a tendency to retract when curing (usually the first 48 hours), creating an imperfect fit to the rear fender (back of the seat pan retracting). But there are several ways to avoid or correct this problem. Because this story is about helping the largest number of non-professional builders, we decided to show a fiberglass seat pan fabrication.

To get started, buy 2 gallons of fiberglass at the closest auto store, find two paint brushes (no, you will not be able to reuse them) and a roll of foil. Cut a piece of thin cardboard for the sitting part. Cover it with foil and continue up the fender (no cardboard is used on the fender part of the seat because cardboard will never fit perfectly to a curved shape). Be generous with the foil, covering more than the seat area. Cut pieces of fiberglass cloth to imitate the shape of the seat. Then, using a brush, soak the fiberglass cloth with resin. Let it dry 24 hours. The day after, do a second coat of resin using extra hardener for fast curing. Wait 24 hours more. Then with a thin felt pen, you can draw your seat. To trace a perfect curve for the back seat, I use …my welding rod.

Remove the pan and give it its definitive shape by cutting it with a small cutting wheel. To be certain that the back seat has a perfect symmetry, we cut a piece of paper imitating the back seat. We fold it in half. Right away, we know where the cutting wheel has to work again against the fiberglass. Sand the top of the pan for a smooth finish.

To hold the seat in place, it’s very simple. The pan being installed on the frame, drill two holes in the front at the place where the front tube extends to the seat. Drill through the fiberglass. We drill only one hole through the fiberglass in the back fender. Then we fiberglass three button head bolts into the three holes. Your seat can now be dropped into place. It will never move while riding and it will not need any tool to be removed. Our seat pan fits like a glove.

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