Originally Posted by
tonski
Yea I'm aware of that, the reason bicycles measure it that way is because it the bend in the fork changes effective rake angle. Please start thinking, I'm not going to spoon feed you information anymore or respond to your idiotic responses because you refute physics. Look at the colorful picture and explain how the orange rake has more trail.
Obviously not to scale but any rational thinking person [and perhaps even you] can see a trend.
The illustration has one problem - the head tube angle didn't change when the OP changed the fork.
Therefore both forks (both "axle points", i.e. orange and red) need to use the original (red) head tube angle as the basis for measuring trail.
The red point is closer to the red axis than the orange point. The orange point has more trail.
Rake lets the axle vertical line to "catch up" to the headtube axis line. More rake moves the axle forward, reducing trail.
A 90 degree head tube angle (like a shopping cart) is unusable unless you get trail somehow. The way to do this is to have a "backwards rake" fork. This is how shopping carts work - 90 degree angle, negative rake, and boom, the shopping cart wants to go straight when you push it. Derny track bikes have the same thing, essentially vertical headtubes with negative rake forks.
Trail = stability = goes in a straight line.
Headtube angle = quicker turning
I forget the frame company but the ones that sponsored Spago's team in the early 90s, they had insane head tube angles (75?) with almost no rake. Although this seems counter-intuitive, the small rake made for more trail. If they increased the rake, there'd have been less trail.
Shorter height fork will decrease trail, increase headtube angle, and put slightly more weight on the front end (all extremely minor, granted). This could explain the quicker handling. On one of my overbuilt frame/forks I cut 5 mm off my lower head tube and perhaps 2 mm off my fork crown in an effort to quicken handling. It didn't make a huge difference.
cdr