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the current thinking is for near the 2 inch trail for a trike, but for a heavy road type motorcycle 4 to 6 inches of trail.
the 4 to 6 trail will give too heavy steering on the trike.
I will leave the (why) to someone else! My knowledge of the subject ends here.
If I remember my reading correctly, this is questionable at times, is that with the trike rake, trail, and flop factor all relate to each other.
So when finding a set trail figure one also needs to see what type of flop factor they are creating with that rake and trail figures. Why is there a difference, the most I can remember is that the motorcycle has the ability to lean through corners and a trike has to steer through them. A tighter designed front end gives a better steering than a open elongated one when it comes to a trike. Also when rake angle goes past 45% angle flop factor will start decreasing and that is why 50 plus rake angles do not see flop factor issue's as much.
I do not think one particular item answers the "why" as my mind says a few factors are at play, all was so much inter related to other factors it was a bit much to wrap my mind around it all, but I did it enough to get my project going.
the only thing I see that maybe be questionable, is that the lower part of the shock will move in an outward arc and not be parallel to the fork tubes during its travel. Also it will lessen the shock deflection ie weight supporting ability....this however, may be desirable way to soften the initial part of a bump.I should be pretty close with this iteration. Neck to forks is 2.5" on 45 degree angle with 2" of trail. Rocker is at a 4 degree tilt up at rest. Once I get the back half built, then I'll be able to weigh the front end and see what shocks will be used.
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Well I am not a professional on this, but out of all that I read and looked at I did not see such a design.
Leading link yes, and most all had a wrap around them in the rear for stabability of the longer link arms used.
I did not like the look of the offset flange that made the forks pivot point. All I have seen pivot off the fork tubes. The welding and accuracy would be important as we want those pivot holes to be exactly even and parallel.
What I have read about leading links was that for the shocks to work there had to be a triangle effect between the fork tubes, the shock, and the link arm, hence why the shock is mounted so close to the axle hole.
The above picture showes the offset at the fork tubes causing to pull the shock parallel to the fork tube. this does work, but from what I understood and read you want the rockers to be 90 degrees to the fork tubes in the loaded riding position ( the leading link arms in the pic are much less than that ) and this might be why the triangle layout is needed.
Maybe others will chime in on it, wonder who else has tried this ?
stacebg has built more, and knows more, about leading link systems. From what I understand and have seen it is more the ideal set up ( having your axle height that 1" above the forks pivot point. With springer front ends this is achieved with the rocker and can be a lot more distance, but that is a different design.
Having the front axle a bit higher, probably near that 5 degree angle from the fork pivot point, that 1" higher, allows the shock to follow the decompression stoke when hitting the bump, also it has some pre forward force behind it when you cover the hole. Some would say level and than rider weight would lower fork pivot point below the axle height, but I think that is bigger boys than I. I can blow away in a strong wind, LOL
I did not mean to confuse anyone, heck I could be confused myself.
I just thought having the rear pivot point back behind the fork tube was odd and not a good idea, plus more work that is not needed, but it could have been done so the desired trail was achieved. Just hope all works out for you.