Saturday, February 15, 2014

Bonneville 2010 Yahoo!

So we left off with the bike having been roughly assembled after getting the bodywork back from paint. Chris Cosentino swung up to finish assembling the air-shifter he designed and fabricated, while we started to pack up the trailer. Fast forward to the salt and the bike looked something like this:

Once again we had a punch list to address which burned most of Sunday and half of Monday. The darn thing just wouldn't steer and would flop over the second you started to correct the steering. The harder i tried to ride the bike the worse it got. We fixed it, with three solutions all happening at once on our makeshift workbench so it was hard to say which solution was the effective one. So the three steering solutions were:

1) Reverse the steering linkage; Why pray tel? The bike was originally steered with two vertical levers/handlebars connected to the steering arms via push-pull control cables. Note the black control cable in the picture above, this is the original chassis from 2006. I was never thrilled with this system even though it was mechanically very convenient in connecting point A to point B. There was about .125 of play in the steering system due to the cables movement in the cable housing, it worked and the play was hardly noticeable at speed, but it bugged me.

In this photo you can see the cables have been replaced by rigid aluminum rods with rod end bearings at either end providing a very direct link to the steering arms with no slop in the system. If you look closely you can see the original mounting holes for the steering linkage at the bottom of the handlebars which is below the pivot which was correct for the steering cables but not the rods. The rods needed to clear the moving swingarm so the steering arms were rotated 180 degrees and now reside above the swingarm reversing the input movement. Here's the rub; i kept the same mounting points on the handlebars so the steering is now reversed. I didn't think this would be an issue as most steering input happens on this bike with body english and i figured i would get used to it. So we moved the mounting point above the handlebar pivot point. While i don't think this was the culprit it certainly didn't hurt. I would like to move the rods to the originol mounting point, to reverse the steering, as an experiment next time we are on the salt.

 2) Adjust the trail; Prior to arriving at the salt I decreased the trail from 5.0 to 3.5 inches as an experiment. On the right side of the front hub, see photo above, there is a tab pointing downward which is welded to the wheel spacers. These white spacers key onto the kingpin/steering axis and by rotating the spacer the kingpin angle changes which changes the rake which in turn changes the trail. The original chassis was slow to react to steering input, no doubt the low center of gravity played into this as well. With the new longer chassis I feared the extra wheelbase and weight would make it steer even slower so i thought less trail might speed up the steering a bit but it didn't seem to be working so we added 2.0 inches of trail . Again, like the steering linkage I'm not quite sure if this was the solution as i have not played with this adjustment on its own. If it ain't broke, don't fix it.

3) We found black rubber on the interior of the fender where the tire was rubbing. I believe this 'smoking gun' is what steered us in the right direction, excuse the pun. The bike had no self righting characteristics and and as i mentioned before would just flop over once the front wheel received or didn't receive input. The wheel was binding up enough to stop self righting but not enough to lock it up.

After all three changes were implemented we had a motorcycle that steered really well. The following video shows before and after; before i was sick to my stomach and after you will see i am happy enough to run around in circles. The team worked really well through this problem and we beat it.

It took a couple of runs to figure out the shifter system which needed a battery and CO2 giving us two more variables to contend with. Simplicity had always been the mantra when designing the bike but this added complexity seemed necessary due to the ergonomics involved at the footrest area. Shifting up and down with a thumb push of a button was really cool, Thanks again to Cosentino Engineering.
That's me and Cosentino in the photo, I'm really happy with the shifter and he.......well he looks uncomfortable.
Next blog entry, we set a record!