I'm putting together a 1980 CB900C Sidecar rig and have two different front fork assemblies. The 1980 fork has the axle directly below the forks. I also have a 1981 fork with a leading axle ahead of the fork. As I understand it, the one to use is the leading axle fork. I have also discovered that the triple trees are quite different. With the 1980 triple trees mounted, I measured a fork tube angle of 28-1/2 degrees. I switched to the 1981 upper and lower triple trees (both times using the 1981 leading axle fork tube assemblies) and measured a fork tube angle of 26 degrees. While the conparison measurement of angle was accurate using a Central Tool magnetic angle gauge, the exact final angle will change slightly because the front of the bike was raised slightly to lift the front wheel off of the ground for disassembly. Do I want to use the triple trees with the least (26 degree) angle?
Posted 12/10/2004 10:56 PM (#5612 - in reply to #5609) Subject: RE: Fork angle question
Location: Middleburg, Pa
Trail is measured by running an imaginary line down through the steering head to ground level. Then another, vertical, line is run from the center of the front axle to ground. The difference in these two points is trail. Less trail = less steering effort.
For the least trail with the stuff you have it would seem like the greater angled triple trees in combination with the forks that have the axle in front of the downtubes would do the trick.
Do a mock up and do some measurments and see what you get.
Click on the link below and it will take you to Doug Bingham's site, sidestrider.com, and a good illustration of how to measure trail. http://tinyurl.com/4nnrh
Hope this helps,
Posted 12/11/2004 5:48 AM (#5616 - in reply to #5609) Subject: RE: Fork angle question
Location: Southern Minnesota
Wow, Now I understand! I'm sure glad I stopped working on the project and got this advice. I'm sure it will make a difference on the steering effort of the rig. I've printed the information from the sidestrider website and will run through the measurements tonight just to show myself the effects of the two different sets of triple trees. Thank you for taking the time to answer my post.