High seat -> High Speed Wobble???

[Sunbeemer]

I was trying a high seat on the RR (to solve my knee cramps), and seemed to have picked up a high speed wobble above 90mph. I can start it by giving the handlebars a little snerk, and then the bike starts to oscillate, but not uncontrollably. (OK I know the answer is, "Well, dont' do that, you idiot!" ) It's not a tank slapper, but feels like it could get a bit dicey if I weren't ready for it. What is the cause of this? Does the touring screen vs. the sport screen make it worse?

BTW, are there three seat heights available for the RR, and how can you tell what they are? The high seat I got is 2" higher than the seat that was on the bike when I bought it (used), which I assumed was a standard seat.

Thanks, in advance.

[Paul Mihalka]

In the USA the R1150R came standard with the lower of two available seats, and the R1150R Rockster came standard with the higher seat. The high seat should not cause a high speed wobble, but aerodynamics of a handlebar mounted windshield and a tall body are unpredictable. If I remember well, the Rocksters came stock with a hydraulic steering damper, but not the regular R1150R.

[jamais]

Try increasing the preload on the rear shock. This will put a little more force on the front perhaps solving the issue.

Sometimes you'll get a little wobble if your bike is rear loaded such as heavy bags or 2 up and you haven't compensated with additional rear shock preload.

[NoRRmad]

The higher seat could reduce the dynamic coupling between your body and the bike, lowering the "wobble frequency," and therefore the speed at which it happens... As I understand it, all bikes will wobble at some specific speed, but few can go that fast. If they can, a steering damper will raise the speed at which wobble starts, as will a stiffer suspension. Crank up that preload a bit, see if it makes a difference.

[CycleRob]

Sunbeemer,

A steering damper is needed IF there are stability problems with certain bikes, even when brand new. Sometimes too much mass in the wrong place, or a new non factory windshield combined with a too flexible frame will deliver a speed wobble. There are other contributors like bad wheel, swingarm pivot, steering neck or paralever bearings. Or the Paralever's 2 freeplay adjustments could be excessive. With your 2002 model, I'd blame the windshield for adding trouble to a borderline frame integrity condition. Start at the Paralever freeplay adjustments first. I bet they're a little loose.

[Sunbeemer]

Thanks guys. I'll tighten the preloader and hope that reduces/eliminates this wobble. I've noticed the rear has sagged a bit lately, and found that the preload knob freewheels ~4 clicks before I feel any resistance, so I think it's lost some oil, although there are no obvious signs of a leak. I guess I should refill it but don't know what kind of oil it takes, fork oil maybe? Any suggestions?

[Ric]

Yeah...check your shock, but then....
How old/worn are your tires ?
Check the torque on the wheels, swinger, etc...

There is no way in the world a BMW should get into any kind of wobble, high-speed, slight or otherwise.

[mick Hoff]

Hi
here is a link with pics, detailing adding oil to the preload adjuster

http://members.cox.net/slartidbartfast/ ... ck-oil.htm

on other discussions, they've used jack oil & whatever SAE oil they had around...
Seems no one knows where that oil goes
hope this helps

[owldaddy]

Sunbeemer, Do you have a trunk on the back of your bike? I had a simular problem once after having installed a trunk on the back of my Suzuki. Shortly after that I read an article in "Cycle" about how having a fairing and a trunk interact with eachother, and the results were as you describe. If you do have a trunk, I bet removing it would be a big help. That worked for me. however I kept the trunk, it was to handy to throw away, I just kept my speed down.
Don

[Sunbeemer]

Yup, OwlDaddy, I have a trunk mounted, but I've had it for some time and didn't notice this much wobble before. And like you say, it's handy to carry stuff around in since I don't use a tank bag.

Anyway, I increased the preload on the rear shock and the wobble is much less noticeable, back to the way it used to be (almost non-existent ), so I think the loss of oil in the preload adjuster has affected the ride and I'm going to refill it this weekend.

Thanks again to all who helped, and CycleRob, I've got to do some research on how to check the paralever freeplay adjustment.

BTW, Ric, the tires are still good Pirelli Diablo Strada's (~ 2K miles on). I like 'em!

Thanks for that link Mick, I'd bookmarked that site a while ago, but it got lost in my long list of bookmarks. There comes a point when bookmarking doesn't do much good if you loose them in the clutter -- I'm there!