Unless you own the exact bike that the seat was designed for,
you are entering a custom project (but you already knew that,
right?). This means some fabrication will be required, sometimes
on the chassis, sometimes on the seat, sometimes on both! The
right way to start any decent project is taking the correct measurements,
so here's some hints. We've thrown in some general mounting tips
here for general seat mounting guidelines.
first thing you will want to decide on is what kind of
gas tank you will be using, stock or race? Most race
/ cafe tanks are longer than stock and would take a shorter seat
to match the tank. A stock length tank would use a longer seatpan
to look correct.
style seat are you looking for? Round or square?
Will it match the shape of the tank?
Measure frame rails outside to outside. You will
want to measure, at the minimum, the width at the front, the widest
point, the lenght of the seat pan and the overall length. You
will also want to take a look at the taper of the frame rails.
It doesn't hurt to take as many measurements as you can.
The widest point on your frame might not correspond
with the widest point on the seat. Measure how far back from the
front it is located.