View Full Version : Frame Help. Finding a seat tube angle...

02-10-2016, 10:05 AM
So here's my issue. I live in Korea. I picked this little guy up to play with while I was out here because I thought I saw some potential in the lines, and they're dirt cheap. I replaced the mono-shock with a rigid strut that lowered it about 4 inches, we made some bars, picked up a tank and fender from a cheap supplier in japan, and set up the 21" dirt bike wheel up front. Like most projects, I want this to be cheap, but when I cut off the rear fender struts, what I found underneath was a hot mess. So my thinking, is with the solid strut in place, I can cut off the top loop of my swingarm and cut off the seat tubes, then bend up some new seat tubes, cope them and weld them into the nubs left on the axle plate from the swingarm, hence, making a sort of pseudo hard tail. I know it's a little cheesy, but I'm leaving Korea in 6 months, and the weather's getting nice. I need to get this little dude on the road... All that said, my real question is, how do I calculate the angle to bend my seat tubes? Is there an easy way you've found to work this out?

Shit...so after I wrote all this, I think I answered my own question. I do have a tendency to process aloud, and this happens. What I'm finding is the angle of a "right trapezoid" with the right angles being the frame tube(long base), the axle(side b), and the length of seat tube that is parallel to the frame tube(short base), and the length from the frame tube to the bend is side d. So i need all of these distances. Short base and Long base are parallel, and Side B meets them both at 90 degree angles. I need to find the other two angles. Now I need to figure out how to do that. Any ideas? I seriously suck at math.

This web site http://math.stackexchange.com/questions/620827/finding-the-angles-in-a-right-trapezoid has some formulas, but I've got nothing.

02-10-2016, 10:10 AM
Shit again...I should probably mock it up with bailing wire and then use a damn protractor...make it out of conduit, using that angle to double check, correct, and make it out of the DOM tube. Well, I hope this helps someone else, eh?

02-10-2016, 12:05 PM
Digital levels are a handy way to get precise degree measurements if wanted.