Hope it helps. You could ... fairly easily I think ... pull some lines and measure trail on a level floor. Pull a string along steering stem axis to floor on level surface, then drop or hang plumb bob against axle, measure on floor the difference.
Not sure that's exact on a stock GL1500, maybe … but I would say close anyway. The standard set up for a
BIKE is not necessarily great for a
TRIKE that does not steer by leaning a tire over.
On a
trike, some trail is good for straight line tracking stability, but excess trail will increase steering effort fast. You will not feel that increase with a
bike so much, as they steer by leaning. The front is more like a caster wheel of a shopping cart with handle bars, and to steer, one leans the
bike over by kicking the tire out at bottom with the first counter steer move
…. on a
trike you steer in the direction of turn and momentum (
inertia) fights you, which is why reducing trail reduces effort.
Below are some pics of a stock (
Black) OEM GL1500 tree set and Champion 6 degree EZSteer (
Aluminum color), you can see difference is in lower tree. Pics from Sep 2004.