FJR "Dances" with Topcase Installed

[rangerray]

OK, I bought a Yamaha trunk off of E-Bay to mount on my '03 FJR and the bike now "dances," seems to be a little less planted at highway speeds. I thought maybe this was due to my rear tire being worn out, but with a new front and rear tire I still feel this little side-to-side dance when underway at highway speeds. Here's what I have:

230 lb. rider

Avon's, front and rear (although it was donig this prior to the Avon's)

Yamaha Trunk (loaded or empty, still the same result)

Side cases mounted

Stock suspension with default settings (as delivered)

I hope I've explained this annoyance well enough that someone will know what I'm talking about. It's as if the tires are slipping from side-to-side, kinda like what it feels like in a good crosswind. Is there a suspension adjustment that would lessen this effect?

Scott Harrison

Senatobia, MS

 

[GunMD]

I've heard it called the "Givi Shuffle" (Givi being the 3rd party trunk of choice 'round here). Certainly gonna notice it at higher speeds or during windy conditions. It freaked me out at first, but I don't even notice now.

It's normal.

Oh, and "Dances with topcase" may become your Native American Indian name.

 

[exskibum]

It won't occur with a pillion between you and the top case, or as I do on an extended trip, with my tail bag on the pillion seat with the tent inside it and my sleeping bag and Therm-A-Rest pad bungied on top of that. Seems to have something to do with air turbulence mostly.

 

[Rogue]

Totally normal.

2 up you won't have the problem.

 

[KSFJR]

My situation is the same as yours regarding bike and weight. I really haven't noticed much of a change in handling with or without the Givi although obviously there has to has a least a modest amount of effect. However, I ride my KLR 650 Dual Sport quite a bit and that bike will let you know what the wind is up to.

So, I guess after the KLR the effect on the FJR is nonexistent or so modest as to not be a problem. And we do get some wind here in Kansas, however, I have not tried it in a tornado yet. :smilingsmiley:

 

[rangerray]

Thanks. I just needed to know if it was normal. So, I guess that's just the way it is and I will keep on riding the pee out of it.

Thanks all.

 

[RonC]

Interesting. I've had the FJR up to 125 (indicated) with the side cases and GIVI V46 top case and had no shimmy or shake. I have had to struggle a bit to hold it my lane of interstates while passing big trucks.

Like KSFJR, though, my KLR 650 is a real handful in a high wind.

Ron

 

[wallypiper]

I've seen this effect on a VFR and on the FJR.

On the VFR, on the autobahn ( everybody ought to try it once) at about 220 KPH indicated with side bags only, no top case, a very pronouned weave would occur. Dropping back to about 215 would get rid of it.

The FJR with panniers and a top case started to do it, but less pronounced, at about 120 mph. Rock solid at 110, a bit weavy at 120. The locatino of this test is a tightly guarded secret (coughKansascough).

Changing your position on the bike would probably alter the speeds where it happens. Its vortex shedding which creates alternating low pressure zones at each rear corner making the bike lean slightly toward the low pressure side.

The effect is actually used to measure velocity for gas flow and liquid flow applications because the frequency of the pulses is related to the velocity of the fluid.

 

[odot]

Is that kinda like um....pressure is equal and constant in an enclosed system? What's his name? Bernoulli?

 

[Bearly Flying]

What's his name? Bernoulli? tongue.gif

Didn't SHE play the youngest daughter on "One Day at a Time"?

 

[OhioFJR1300]

Just thought I'd put my two cents in on this issue. I had an '05 FJR with a Givi V46 top box. It was very unstable at speeds above 80 MPH. I traded the 05 for an 06 FJR. I kept the Givi box and put it on the 06. So far the 06 is rock solid with the Givi box on it at speeds up to 138 MPH (proven by GPS). So it must have something to do with the year of bike. Anyway I love my 06. :yahoo:

 

[rangerray]

No it's more of a weave; not at all a shake or a wobble. When I take my hands off the bars at whatever speed there is no shake or wobble in the steering area. When I take off the topcase the weave disappears. I can imagine that if you've always ridden with the topcase, you might not even notice what I'm talking about. Like some of the others have said, I'll get used to it with a few more miles.

Thanks for all of the replies!

 

[Toynut]

I would imagine that the net effect of the top case high up in the air stream is similar to a "wing" or tail spoiler/drag chute. It probably acts in a way to add some down force or drag towards the rear of the bike, with the fulcrum effect lightening up the front end. This is in addition to increasing your "profile size" to side winds. A Wilber’s install with some extra rear ride height adjustment may offer some "tune ability" to a limited degree. Your '03 may be due for a shock /spring replacement anyway. I also think that the effect of "loose front end" is greatly enhanced if you load the rear box heavily.

Another tuning option, (consider this one carefully), is to raise your front forks up a bit in the clamps to change the bike's angle of attack. This typically can increase many, (but not all), bikes cornering ability, but does potentially unload the rear tire a bit, depending on your bike model. It's not something to be done capriciously; it's just another tuning option.

The size and angle(tuning block) of your windscreen may also effect the airflow to a point that it may further unload your front suspension/increase buffeting or reshape the air pathway on /around your bike.

These are just a few observations/experiments that I have noticed and attempted on several of my bikes. Your results may vary, of course!