Vibration at specific speed

[Joepi5]

Hello,

For some time now my 2010 GS has a strange vibration between 35 & 45 mph, I've been on a quest of finding the source of this and fixing it. As I can't imagine it's normal. Also I can't pinpoint or remember if it's always been here or started somewhere during the last year. This one is still relatively new to me (got it last year).

Feels like the bike is moving up and down, like with a bent wheel. Happens when cruising at that speed or when slowly/gently accelerating through it, when accelerating hard I can't feel it. The frequency is quite low, didn't measure but it's noticeable individual 'bumps'. Leaning the bike has no impact on this.

With the throttle closed on deceleration I also can't feel it. While standing on the pegs it's unnoticeable. Lowering the preload or loading the bike more makes it less noticeable.

It's most noticeable in third and fourth gear, slightly less in second and fifth, but still noticeable.

Things checked and/or replaced:
- changed wheel (from spokes to cast), remounted the same tires, tires are next on the list to replace. The rear one has some squaring in the middle. They are continental trail attack 3 tires.
- checked and double checked wheel straightness on both the wheel and the wheel+tire
- rebalanced the wheels
- changed all the oils, everything came out clean without glitter
- swapped the final drive for a newer one off of a R9T, with low mileage
- swapped out the drive shaft for the motorworks rebuildable one (this does make slight rubbing noise somewhere near the front boot, but it doesn't noticeably drag, it all feels smooth. Anyone else notices this with there GS?)
- had the ESA shocks rebuild
- rebuild the rear brake caliper and fitted a new disc
- checked tightening torque on the frame mounting bolts.

Is there anything besides the tires I can try or check? Or should I just accept that it's there and part of my bike? It doesn't really affect the riding. Had a blast touring through the Eifel, Luxembourg and the Ardennes last weekend! So I'm planning on keeping riding it until something breaks and then fix it again.

 

[littleade]

Has the rear tyre got a flat spot on it?

 

[Joepi5]

Has the rear tyre got a flat spot on it?

Last Thursday I checked the roundness on a static balancer by spinning it over a clamped spirit level. It wasn't 100% round, it had some up and down movement. But nothing out of the ordinary, haven't yet had any tire that is 100% round.

 

[squibb34]

You've dealt with the driveshaft, which is often the culprit, so I guess it just has to be the tyre.

2 mm is generally accepted as the max run out. The last time I had this issue was with a new tyre - initially I thought it must be carcass distortion, maybe stored badly or damaged in transit, but it turned out to be so tight on the bead that it hadn't quite seated correctly.

 

[Joepi5]

Turns out it is the drive shaft. I replaced the OEM one with a Motorworks one, which was a little bit shorter than stock. I don't mean to say it's a bad product in general, but it doesn't suit my bike.

I'm a big heavy dude (135 kg in riding gear). This coupled with stiffer springs and freshly rebuilt shocks. The need to have it in 1 helmet/luggage ESA setting because lower than that means I still scrape the crash bars on the ground when riding.

This all means that the swing arm angle is steeper than what is generally the case, with this angle the slightly shorter drive shaft is too short which leads to the up and down shaking sensation. This is futher proved by increasing shaking when on the highest preload setting (even steeper swingarm angle). And almost no shaking on the lowest preload setting (swing arm closest to horizontal.

So I'm trying to get the Motorworks shaft returned and looking to get an OEM one back.

 

[fraserwaters]

I’m in Norway on a tour and my 2012 is doing exactly the same thing. I put it down to tyres or wheels but could it be the driveshaft? The bike is carrying 90kg with me and the luggage on, and I fitted Pirelli scorpion str tyres last week and had them balanced by a reputable independent.

 

[Joepi5]

Could be the driveshaft.

Fitted a brand new BMW driveshaft yesterday. After a short test ride my GS no longer feels like a rocking chair at the specific speed.