You will want the 60 inch belts for the front and probably for the rear too.
I just installed seat belts in my Amphi (as in yesterday). I hadn't even sat
in the seat yet, so I just went out and tried them.
I have a 40 inch waist
. With 60 inch belts in the front, I have about 6
inches of belt adjustment left. A 72 inch belt might fit me, but would
definitely be too big for my wife.
The rear is a bit more difficult. This is because, as far as I know,
Amphicar never had rear seat belts installed at the factory. Thus, you must
design your own attachment method (I can send pictures of mine if you want).
With most any attachment method I can think of, 60 inch belts should be what
you want. With my method, 60 inches is actually a bit long. However, if you
decided to do something like tie the belts to the rear swing arm tube (a nice
solid location), then you would probably need 72 inch belts to allow for the
knot. Note, I do NOT recommend that you tie a knot in the seat belt, it
would weaken the belt significantly.
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