Fairing Modifications?

[donpearsall]

At the last BUB, I noticed that my bike leaned to the left starting at about 150 mph and got worse as the speed increased. Of course if I corrected by steering to the right, that makes the lean worse. I am pretty sure it is the fairing (custom made by me) that is causing the problem but don't know where to look for corrections.

Bikes have opposite steering modes depending on the speed, so that is where the confusion is. Since it leans to the left, does that mean there is more drag on the right side causing the front wheel to steer right and therefore lean left? Or could the drag be on the more on the left causing the lean because of more drag on that side?

I guess I am trying to decide if the lean is caused by adverse yaw (flying term), or differential drag caused by assymetrical shape. Can anyone simplify this?

Thanks
Don

[Seldom Seen Slim]

Don:  A few years ago my ZX12R with a Charlie Toy body wanted to go to the left once I got up to 150 and more.  I had to (almost) lean far enough to drag a knee to go straight.  It finally turned out that it wasn't the fairing -- it was that the fairing was mounted just a tad crooked.  The standoffs on the left side were about 2 RCHs longer than those on the right, so the whole front piece of the body was canted left -- and the result was that the bike wanted to go that way once I was moving fast enough for the air to affect things.

It took some simple work with a ruler and hacksaw to make things all better.  I rode the bike at SpeedWeek this year - for the first time in 5 years -- and had no steering issues at all, even though I had taken the body off and fabbed up new supports.  I guess I must have learned something.                                                                             

[maj]

if your bodywork is uneven because its bulging around components it could make a wing of it

uneven positioned body on our 750 gave us wobbles , couple of 1/4 spacers was all it took to fix it , i think it was giving us separation , bodywork with no separation i expect would lean

I think your on track with the yaw , cross wind would feel the same

 

[JimL]

I also had pulling problems with my Charlie Toy setup.  I had to flatten a bulge area, near the left handle bar, by fitting 1/4" solid steel rod stiffeners.  Both sides are very close to even and have very similar flatness.

I added a reinforcement rib, internal, in the front fender.  It was made by grinding the inner glass surface, rigging a duct tape "dam" (sticky side is the layup side), and forming the rib from fibergass tape with epoxy resin.  This keeps the front fender from moving (had major tire rub marks inside, both sides, after running 150 without bracing the fender.)

I should mention that the first correction I made, for gradually increasing "pull" at speed increase, was correcting lateral balance.  I had to add ballast to the left side of the bike to get it to run straight without pushing on the right handlebar.  If the bike has to lean to run straight, gyroscopic precession will be torque against the bars all the way through....faster you go, worse it gets.  The front wheel is trying to fall into the lean.

Right-left balance and straightening the fairing made the bike run very straight this year (except in Saturday wind).  It was running about 165 out the end with just a little early morning side wind on Sunday.

Hope this helps.
JimL

[donpearsall]

Thanks for all of the replies guys! I will check for mounting and balance. The terrible thing is that I can try all kinds of fixes but won't know for a year if they work!!

[SPARKY]

I 25s 

[wobblywalrus]

My method is to take the bike out to a straight flat road with as little camber (cross-slope) as possible or a straight downhill road with similar properties.  The throttle is locked part way open on the level road and I take my hands off of the grips.  The bike should not tilt and you should not need to lean to one side to get it to go straight.

The bike should be stable during all of this.  There are pictures of guys standing on the seats of moving bikes with their arms extended out.

The downhill test is similar except the throttle does not need to be locked.  Return roads on drag strips are good places for a level road test.