ST1100 to STealth11 Project

Front end conversion scheme.

Well here is the problem and the imagined solution. After putting some 12,000 miles on the STealth11 I decided to add stock ST1100 hard bags to the rear. This was a great move as far as being able to haul things but a weird glitch popped up as a result. The ST was always very stable and did a good job going down the road at 65-70mph which is my normal cruising speed. However the hardbags caused a vortex to develop behind the bike during certain conditions. Going into a mild headwind and accelerating above 60 would bring on a wiggle which would intensify unless I backed off a bit, then it promptly disappeared. I first tried the Burt Monroe technique of adding 35lbs of lead to the nose of the machine with the idea this would keep the front down and stabilize things.  Wrong there as it proved to mirror Burt's experience which was to do nothing. I then figured it may be due to the fact the wheel yawl from side to side if the body tilts, This is a fact of design with double A-frames the if the body leans the wheels lean also. I thought this may be the problem so I beefed up the sway bar - no improvement. I was somewhat stymied and although the problem was actually quite mild I figured I might as well take the radical shot gun approach and totally rebuild the front end design.

Below is the build on the original front end. Double A-frames off a Yamaha Banshee and wheel hubs off a Raptor.  Shocks were off 1500 Goldswings (2)

My new plan was to remove the A-frames and replace the assembly with a straight axle. The thought here was a straight axle does not suffer from yawl. If the body tilts the wheel remain fixed and do not tilt with the body so stability is maintained, or so I thought (more on this later)

So I set off on the quest, picked up a pile of iron and some more welding wire. Purchased a nice sawsall so I could better chop things apart. I removed the wheels cut up the A-arms and assembled the new design.

To make a long story short, I spent 2 weeks on the design and build. Had to revert to the stock Valkyrie shock as the GL1500 shocks were way to stiff for the new mounting angle. I made the new axle fully adjustable so I could tweak the camber, caster and toe in with just some shims or adjusters.
Well first test ride was a disappointment as the thing wandered all over the road even at 30mph. More caster fixed this however an unexpected problem now arouse. My idea that the initial problem was yawl was incorrect. It is the yawl that keeps the tie rod distance consistent and the change in camber during this tire lean buffers the tendency for the unit to dive into a turn. With the straight axle any body tip results in a mild but noticeable change in tire angle which causes the bike to turn first one way, than due to rider compensation, the other way. I tweaked with steering stem height but only got as far as the unit being drivable at speeds of 70 plus but not without some nervous twitches. I decided this was just not going to work so I am going back to the double A-frame with a twist.

The initial A-frame design had differing lengths of arms. The bottom arms were 2" longer than the top. I plan on building my own arms which. like the Can Am are equal in length. On the old design the camber changed as the arms moved but with this design the camber will stay constant through out it's travel. I also learned the problem initially was nothing more than not enough caster. It is caster which keeps the car/bike traveling in a straight line. It is a compromise though, more caster = more stabile but more feedback in the turns. Less caster less stable but lighter steering.

Here is a link which explains this in pretty good detail (except for toe in) http://www.familycar.com/alignment.htm

Toe in is simple - Camber is used to tip the wheel out a bit (positive camber) this moved the load to the inner bearing which is stronger and usually larger. It also move the impact leverage closer to the swivel or turning center which reduces the effects of a tire hitting an obstruction. This positive camber or leaning tend to make each wheel want to track outwards so toe in just compensates for this by turning each wheel in just a little. Negative camber would require toe out for this reason also.

OK so lets checkout the pictures and see what this all means. Here is the straight axle setup - backwards as this is actually the removal process but you should get the idea and the theory.

From the front you can see the stabilizer bar and shock setup - In this angel you can see the effects of caster and camber.

Below the rear stabilizer which has adjustments for camber also the dual steering dampeners.

First order of business is to remove the body "wings" so I can start chopping out the mounts and weld in new ones.

The top and bottom A-arm mounts will be removed and shorter ones installed - all arms will be the exact same length. The bottom arms will be a fixed triangle shape but the top will be adjustable so I may fine tune the camber as needed.

Here you can also see the sway bar which is a piece 3/4" thick cold rolled steel 32" long. This will stay as is for the new build.

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