Girder forks...... Stoopid questions? Maybe!

[klogan45]

Just looking at girder forks, rake and trail etc out of interest-these may be real stoopid questions but.......
I understand that that trail can be affected by a number of things, not least of all rake and length of forks.
I have noticed on all the girders that i have seen the upper and lower links are the same length.
The first question is why is this?
The second is this. Surely the trail can be altered by changing the length of the pairs of links.
I have seen various propositions for "ideal" trail ranging from zero to five inches.
What is the "ideal" trail measurement.
My apologies to you knowledgeable monkeys but i really want to understand this malarky.
Regards
K

[terry t]

There's no ideal trail. but in general its about 1 and 2"
the trail on my Goldwing is 1 1/2" and I find that's is fine with and with out a passenger as the trail will alter when the back end goes down

[Olds]

From the little I know of girder design, hear are my own views
The links on girders should ideally be the same but as you say trail can be adjusted, by altering the relative lengths of these slightly. However this introduces some strange changes in steering geometry as the forks move and should be avoided.
The ideal amount of trail depends on a lot of factors. Is it for a trike or bike. A lot of trail on a trike, 4" plus will give great straight line stability but heavy steering, whereas minimal trail 1" or less will give much lighter steering but a steering damper will almost certainly be required.

[triker_Chewie]

http://www.chopperhandbook.com/forks.htm

[BikerGran]

I haven't measured the trail since I had the extended yokes fitted to Gertie but I can now steer with one hand at any speed under and or all circumstances - even over bumps!  And no steering damper required! - but that's with ordinary forks.

[terry t]

I haven't measured the trail since I had the extended yokes fitted to Gertie but I can now steer with one hand at any speed under and or all circumstances - even over bumps!  And no steering damper required! - but that's with ordinary forks.

Same with mine. best thing I done, was have this ezi steer setup made
no more back or shoulder pains after a long run

[BikerGran]

Different setup, same result - less trail! 

[klogan45]

Thanks for the comments and thanks to trikerchewie for the link.
Regards
K