explain this ??

[jerryz]

the s4 weave /wobble above 90mph


i have removed the fairing again so bike is now naked  as fairing was cracking at support bracket  points ,

went for ride today , solo the bike starts the small but perfectly controllable weave /wobble reported by many S4 riders above 90mph , and back end is a little bouncy


BUT 2 up thats my  100lb daughter on the back the bike is completely stable at 100mph plus and a lot more ,       no weave no wobble absolutely 100% stable its a different machine

only a tiny bit of preload added to rear ohlins no other mods ,,,

go solo and weave wobble shimmy returns and rear bouncy returns

I am trying to understand the physics and mechanics of what is going on so i can improve the bike when solo which is 90 % of the time .
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MONSTERMAN

[ducpainter]

I'd check steering head bearings.

[stopintime]

In addition to steering head bearings.... if suspension links are beginning to freeze up - it would be more noticeable with less load.

[Bill in OKC]

One thing that happens with a passenger is you change the geometry of the bike.  When you lower the front the bike is more nimble but also nervous.  Raising the front/lowering the rear (passenger) makes it less nimble and more stable.  'nervous' will also make the bike react to road imperfections.  and again check head bearings.

[SpikeC]

 Have you set the sag at both ends? Lowering the ride hight at the back and raising it at the front sounds like it might help, butt proper sag is the first step.

[Tassie Dave]

I too will suggest rear sag.  That is changing when you add a passenger.

Last century when most bikes had next to no suspension adjustment, I found that if I had the rear set too firm the bike would weave.  Soften the rear and it was fine.

[jerryz]

head bearings are new tapere rollers and in perfect nick and adjustment , forks recently rebuilt , bike handle really nice
apart from the  wobble above 90mph solo??

i think raising the forks by 5mm  might be the answer,   sag at rear will be checked again .

weird that 8 stone extra on the rear made such a difference

[danaid]

 My bike will wobble when the air pressure is a pound or two low.

[NAKID]

My bike will wobble when the air pressure is a pound or two low.

Agreed

[Speeddog]

100 lb daughter will run the head angle out to a more stable number.

And it changes the aerodynamics, and the wobble frequency due to mass distribution.

[jerryz]

also noticed the wobble is less on smooth tarmac  than concrete  washboard highway  ,,,

still dialing it out with a little raising of the forks and playing with aerodynamics of my body over the tank and  suspension adjustments ,,,tyre pressures etc


i also think that the Michelini PR3 on the front is more susceptable to this wobble than the previous pirelli Rosso Corse 2.......as it was rare with that tyre to notice the effect??