Negative Trail ? ? ?

This video got posted on YouTube December 11 which is only 3 days after this thread was started.  Odd coincidence.  Anyway, relevant to the discussion.

https://www.youtube.com/watch?v=xxfW1UuU-tg&ab_channel=HooptieDoodle

Thanks for adding that video to the discussion Drone, fascinating.

For those who know this stuff, on the scooter, is part of his problem the shock is mounted behind the tire, and not mounted at the same angle as the steering head? Or is that a non-issue?

Wonder if that exotic four hinge leading link that Honda acquired, inspired their newest Gold Wing front suspension. It is a similar way of thinking about suspension.  Maybe they acquired a few of the designers/engineers too. 

I got to 67 without even knowing about it, so I don't think I'll start worrying  about it now.

 For many with sidecar or Trike a bit of rake is all that is needed.

He did make one important and accurate comment. The effects if you go to far with it. The bike will become un ride able as a two wheel.

He kind of just glossed over that .

Very Interesting discussion, and video. Thanks for that!  I have a question, will bringing the fork  tubes  up through the triple clamps, and lowering the front end have any effect on trail? Just curious if for improved handling with a sidecar, and stock tripple trees, if its better to have the fork tubes as long as possible, or bring them up to lower the bike.

Thanks

Rick.

Lengthening or shorting  will raise of lower Front of the bike This would cause weight shifts and a bike that just does not sit right.

When you rake the tree the forks are extended to return the bike back to where it belongs  for heights. that is done with extensions or longer tubes.

The only time you might shove them up is to bring it down after going to a larger front wheel. Or to match up a smaller rear wheel.

In the 60's and 70's it was common to put 6 inch extensions or longer tube on without a rake to try and make it look like a poor mans chopper.

Raked trees were a big budget bite back them and rakes were commonly done by cutting the frame. This also cost money and the bike was trashed for other uses.

For what it is worth, I posted some pics of the LL build, in a separate thread.  I think it may be the build referenced at the beginning of this thread.

You know, it is possible that we measured the near zero trail wrong, but a lot of eyes were on the technique.  A couple of things make me think the actual measured 0.4" of trail may be pretty close to accurate.

1.  Wheel base of the bike starts out at 62" from the factory.  When we finished the build, it was at 66", with the chassis set level with a digital angle finder.  Four inches of wheel base increase might imply a 4" decrease in trail amount, all other things being equal, which they may or may not be.
2. We put a laser through the steering stem to try to spot on a piece of graph paper where the line would hit from @Drone's diagram.  We  then measured axle center line dropped straight to the graph paper.  It showed a small amount of trail, maybe .4" or so.

Now we did not have the wheel on, with the weight of the bike compressing the suspension.  That may introduce some error in the measurement, but probably not a lot.  Maybe another 1/2" or so?

I don't know.  I was pretty surprised at how the rig handled with the theoretically greatly reduced trail.  Chuck tacked everything in position so I could test drive the rig and get the feel of how it handled, prior to finalizing the trail setting.  However, it was so sweet that I had no intention of changing it...

I have read where hack racers like to run close to zero trail, with the idea that they like the steering to be very quick and are not so concerned about being able to relax a little while riding.  I generally won't remove both hands from the bars of anything I ride, however, a few days ago, at about 65mph, I felt the need to zip up my collar.  Zipper was kind of stuck, so I used both hands, with the cruise control on.  I still cannot believe that I can take both hands off the bars without immediately diving into the right ditch, but it does seem possible.

I felt like I learned a lot, going through the LL build process with Chuck Loftkin; I suspect that I am just seeing the tip of the ice-berg, so to speak, but I sure like how my rig handles, now.

Raising the back end with taller shocks or more preload will reduce trail.

I suspect lowering the forks in the triple tree would too since it is in effect making the rear taller than the front thereby changing the geometry in a similar way.

Hal at Metalcraft racing in Houston fixed a DMC leading link that had been built with ZERO trail. If you blinked, boom, you were in another lane. It was super twitchy and you could not take your eyes off the road lest you end up rolled in barbed wire and cedar posts with cows stepping over your carcass. I see why sidecar racers would like it, quick immediate turns with minimal effort.

Hal’s link is adjustable. We ran it out to negative trail once. I tried it on some slow back roads. It sucked. It wandered around sort of picking its own line. My bike stock had just under 4” trail so we adjusted the trail to two inches round about 50% of stock. Result was much stiffer steering at low speed but boy howdy when you got up to 70 it was solid and planted as if on rails. We then adjusted it to 60% of stock trail and for me that’s about all I need. With additional 10% reduction of trail, the steering is quicker and noticeable, especially at speed.

So in my very very limited experience, (3 rigs, maybe 35,000 hack piloting miles)  the closer to ZERO trail you get and beyond, the bike will become less and less controllable the faster you go. Personally, I think reducing stock trail by half would be a good start. But hey, I’m no expert. Each to his own. America, Land of the Free… .

My philosophy on owning Sidecars: You better be Rich or better be able to do all the work yourself. Those that pilot hacks know what I mean. $$$$$