If you click on the red letter link to coyote7864's best posts
located below the signature photo of my bike
you will access a list of links about many topics of discussion
within the VTXOA 1800 Tech Forum.
One of the links is to the technical specifications of the
various Progressive Suspensions springs.
The springs are of similar spring tension, made to support
bikes of similar weight. The biggest differences between
these springs are the length of each spring.
The stock honda springs measure 12.98 inches when new.
The PS GL1800 springs measure about 13.3 inches.
The PS VTX1800 springs measure about 12.5 inches
so that they are easier for home mechanics to install.
There is a small variation in the spring tension for each model.
It might be 5 or 10 pounds per inch.
Remember these are progressive (variable) springs and
are harder to measure and the amount of the softer tension
versus the firmer tension will vary over the length
of the spring.
For a softer cushier ride you can experiment with the
viscosity of the fork oil or the amount of fork oil contained
in each fork leg.
On their own, with the stock Honda fork oil in
the amounts specified by the Honda service manual,
these fork springs will seem firmer than the stock springs.
The stock Honda springs are also progessively wound,
but the smoothest portion of the springs is also the least firm
and is mostly used up when the rider sits on the seat.
Especially for a rider who weighs significantly greater than
160 to 180 pounds.
There are very few of us who have installed more than one set
of springs in their bikes or the bikes of others.
My recommendations as to which fork springs that a rider should use
for his VTX vary based on the rider's weight and the length of
his pants inseam (leg).
A shorter lightweight guy should stick with the stock springs.
Especially if he is riding a plush thick aftermarket seat.
Someone who weighs over 180-200 pounds with short legs should
get the PS 11-1520 springs designed for the VTX1800.
Someone who is taller and even heavier will be happier with
the PS11-1521 springs designed for the GL1800.
Be aware that it is harder to compress the longer GL1800
springs to fit inside the VTX1800 forks. There are instructions
in bareass172's website how to construct a compressor tool that
will ease the job and make it safer to do if you have to do
the work yourself. I designed and made that spring compressor.
There is also a link in my best posts page of photos of how
my compressor was constructed.
I used long threaded rods, aluminum plate and steel reinforcement ,
but sturdy wood could be substituted for the metal if you only intend
to use the compressor once or twice.
I would recommend the use of two pieces of thick plywood used for
floorboards or roofing (say 3/4 inch thick) or a length of 2x4
as a substitute for the much thinner aluminum plate.
The Valkyrie springs are a compromise and I don't know any forum
members who have tried them, but I think one or two might have.
Probably 90% of the forum members who have changed their forksprings
have used the VTX springs PS11-1520.
Only taller members have been happy with the GL1800 springs.
I am 6 feet 1 inch and weigh 250 pounds and ride the stock
vtx1800 C model seat. My inseam is 33 inches.