Turbulence and head shake?

Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by alongat, Aug 20, 2013.

  1. alongat

    alongat Long timer

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    Just came back from a road trip to the motogp at indianapolis and back this weekend - first really long road (interstate slab) trip on my 2012R. Anyhow, the bike performed brilliantly as expected except for...

    Head shake during times of turbulence (like when passing trucks, etc.). Granted, there were windy times throughout the ride and my stock windshield was annoying me (I'm 6'3" and ended up removing the peak visor on my XD4 to reduce the eye-scrambling shake). This head shake wasn't very violent and never happened at any other times, just bothered me when it was happening - kind of unsettling and confidence crushing, etc...Never happened in "clean air". We averaged speeds between 75 - 85 mph, I was using my Jesse cases with no tail bag and they were in the fairly forward position to avoid weighing down the rear end, my 19/17 wheels with Conti Trail Attack IIs (checked pressures - all good at 34 up front, 36 in the rear) and the stock windshield. I raised the preload in the rear to compensate for the added weight of the cases and luggage but nothing altered up front. I'm fairly sure this shake hasn't happened before so I'm wondering if the panniers (either weight or aerodynamics) are causing this.

    Also, I know the following subject has been discussed to death but what are tall people doing to reduce buffeting / wind on their adventures for long trips? I've seen ktm touring windshields (have one, hate it - I think it's rubbish), some really ugly big, huge tall screens and cut-down or short screens either with or without "curved lips". Any pics / info?

    Thanks in advance
    #1
  2. travelsomewhere

    travelsomewhere Been here awhile

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    there are a million opinions on this but my solution was actually a moose shorty windscreen, the stock one will snap your neck. on long trips i have a large aeroflow that i put on top of the moose and remove it when i hit dirt. I wear the same helmet and yes removing it helps, but trust me the moose was the best 50 bucks i spent on that bike.
    #2
  3. Kyler

    Kyler Confused Hack Nut

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    Aero-flow windscreen. I'm 6'5" and this is the shitz. I never take it off. I'm about to head off to Goose Bay this weekend for a 14-day, 5,000 mile ride and wouldn't dream of doing it without it. Yes, it is tall and somewhat fugly. But I'm more interested in a screen that works than eye appeal.

    [​IMG]
    #3
  4. alongat

    alongat Long timer

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    Oh man, but the look of that... :)



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  5. syzygy9

    syzygy9 Been here awhile

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    Kyler, I assume you have the tallest one? I am also considering an Aeroflow but at 5'10 am torn between the short 4" above stock (standard) and the medium 6" above stock.
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  6. Kyler

    Kyler Confused Hack Nut

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    I helped with the prototyping and started with the tallest but ended up cutting it down to the mid-size.

    see this thread http://advrider.com/forums/showthread.php?t=723517 which has links to more threads on this screen.
    #6
  7. Kyler

    Kyler Confused Hack Nut

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    this shows the wind pattern (and this is the tall screen before I cut it down).

    [​IMG]
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  8. syzygy9

    syzygy9 Been here awhile

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    Thanks Kyler, so at 6'5" you find the medium height works for you. By extension that would imply that at 5'10" the standard (low/4") version would work for me. Note that I sit on a sheepskin which raises me an inch or so.

    I have a strong preference for the lowest screen as I do a lot of dirt road riding and don't want to impede my forward view, but I was thinking I could also get a medium screen (6") and drill some lower mount holes to mount the screen lower when I need to. I figure I could drop the screen a couple of inches by doing this, lowering this screen to the equivalent height of a standard (low) screen.

    But I would also like to be able to lower the low screen, so for the really gnarly slow speed stuff, I could drop the standard low screen a couple of inches to 2" above stock giving a better forward view when needed.

    Aaaagghhh decisions?!

    Given your experience with these screens do you think a low screen would work well enough for my height? I am not looking for a completely quiet and serene environment, just reduce the amount of turbulent air shaking my head around. Your viewpoint would be greatly appreciated!
    #8
  9. mjskier

    mjskier Been here awhile

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    I had head shake in turbulence on my SMT. (new bike, first time riding on the road for 15+ years)
    I thought it was something with the bike until I realized that I was hanging to the bar too tightly. It was actually me inducing a front end wobble. Maybe worth trying to relax to see if you don't have the same problem?
    #9
  10. PvtIdaho

    PvtIdaho Deck Spotter

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    For your head shake issue, I've had a similar issue. In a tire thread from '08 I said
    Is that similar to what you experienced? In my case it was with out panniers. I was running a 908 in the back and a 606 up front. That combo is the only time I've had it.
    It seems like most of the head shake threads fall into 3 categories: Decel wobble, Scorpions at 40-50 mph, and high speed shake. But none of those usually involve a 19/17 no knobby set up.

    Ever had any issues with out the panniers or running 21/18?

    You could start some test rides where you vary the rear preload and see if it makes any difference.

    For the helmet buffet issue, besides the taller or shorter windscreen options a taller seat can help. I'm your height with a longer than average torso and I still run the stock screen but have a tall seat (Renazco). It helps but doesn't totally eliminate the buffet. I wear an XD, too, but not on long freeway rides (anymore :D).
    #10
  11. alongat

    alongat Long timer

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    I haven't run the 21/18 with panniers so I don't know if it would happen. I am going to do a run next week (two days, more highway runs) with no panniers, just a Kriega pack or two out back on top and see if anything changes. In clean air (no truck passing, etc), I get no wobble at all regardless of speed whether constant, accelerating or decel...only seems to occur when I'm approaching a truck or other moving object creating turbulent air. I love the shading of the peak of the XD4 but if I'm removing it to avoid eyeball shake, I might as well use my Arai Corsair or AGV GP Tech for highway riding and relegate the XD4 to dual sporting. I also have a Renazco but oddly enough, I found it oddly painful in my middle back - it feels like my Renazco makes me sit just slightly further back than my 990R seat and I'm ever-so slightly "reaching" for my bars; I think it's changing my posture and making me slouch a bit because I found the middle of my back muscles aching. I've actually had very good results riding distances on my R seat with an Airhawk for a bit of Cush and heat isolation so maybe I'll just sell my Renazco. Given my height, I should also consider a set of risers - stock height is a bit awkward when standing up.

    Going back to the head shake, do you think that a "street" steering damper would help? I wonder if the effective reduced trail from the 19 up front exacerbates any inherent shaking from turbulence.




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  12. Kyler

    Kyler Confused Hack Nut

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    Buy the medium and if you don't like it then cut it down. That is easy to do.

    On the head shake issue, I used to get it at about 90 MPH. I always thought it was caused by the screen and panniers. As the second owner, I was unaware the PO installed a lighter rear shock spring. After reinstalling the original spring and servicing the front forks, the head shake went away. I also have a Scotts damper.
    #12
  13. GrenDesb

    GrenDesb Been here awhile

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    Steering damper isn't meant to fix problems.

    Yes it help relax on long loaded run but if your bike isn't setup properly snd handle weirdly, damper is just a plaster.

    Have you set your suspension correctly? Sag and all ?

    Funny two discussion are going on here, steering head shake and thinking head shake.

    #13
  14. GJ990

    GJ990 Been here awhile

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    I'm not sure I agree with you here. Yes it's a plaster (band aid for us in the US), but that's the reason I want one. I happen to like the 908RR tires. They cause head shake. Nothing I can do about it. So the damper helps with that. Perfectly fine solution I would think, no?
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  15. Kyler

    Kyler Confused Hack Nut

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    I put a damper on anything with 3-wheels or less if there is one wheel out front. IMHO, head shake will occur and always at the worst possible time. I consider a damper to be simple insurance. I have one on my 950, my 450, my road-racing sidecar and on my MX sidecar. The only bike I have without one is my trials sidecar.
    #15
  16. Sporting Wood

    Sporting Wood I

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    Check your sag. If the rears too low it'll get a wobble. Also I have found that running 19/17, its best to raise the forks in the trees up to the 2nt line. That ought to correct the bike caused wobble but of course there are many contributing factors. Aerodynamics has never been a strong suit with the ADV. I was once almost blown off the road by a passing semi in NM once...

    As for all day aero comfort, you are right. It has been talked about to death! Everybody's different. Seat height, torso height, what kind of mirrors, windscreen, helmet, etc... I'm 6'2 on a 950S with SuperDuke mirrors, a touratech shorty dakar windscreen, Renazco tall seat and an Arai XD and its ok. No windscreen is better imho, or cut down to just over the dash.
    #16
  17. PvtIdaho

    PvtIdaho Deck Spotter

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    Absolutely. I've got the DirtnBlood risers (don't know if he still makes them) and I could probably use another 1/2" when standing. The risers make a huge difference. I also have Fastway foot pegs in the low position.

    A lot of guys use them. I'd start with the suspension adjustments that have already been mentioned here.
    #17
  18. syzygy9

    syzygy9 Been here awhile

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    After looking at this thread (and the windscreen disgust thread) I took a punt and ended up buying an expensive (to ship to Australia) Aeroflow standard height screen. I am 5'10" / 178cm, average build sitting on a standard seat with sheepskin cover. I suffered terribly due to (my) head shake due to turbulent air coming over the top of the standard screen, made the bike very unenjoyable, uncomfortable and tiring to ride.

    The Aeroflow screen has made a huge difference, a different bike to ride. I was worried as the top of the screen is in my dirt road 'line of vision' but it has forced me to look a little further up the road (as you are supposed to) and I can look through for near obstacles. I cannot emphasize enough what a difference this screen has made for me, YMMV.

    [​IMG]
    #18
  19. mousitsas

    mousitsas Long timer

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    Any vehicle will create behind it a flow pattern which is known as Karman vortex street. Wikipedia has a nice animation of it. This is basically a series of vortices creating a pulsating pressure field, in which you are entering while passing. This field is acting on the side surfaces of the bike which are plenty big. On top of that, these bikes are not famous for being super stable, therefore it is not difficult to encounter what you describe. You could of course improve handling by changing suspension settings, but there is no known remedy that applies for all. You have to experiment with the clickers.
    Panniers affect the overall dynamics and if nothing else, they will slow weave down, but in other cases they might even be the cause of it.
    #19
  20. Two Moto Kiwis

    Two Moto Kiwis Homeless Somewhere

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    We changed our mirrors, I have the opposite prob to you at 5'6.5".

    My XD4 was getting buffeted and it was the stock mirrors, we have a 690 screen on our SE and that works perfect but with the mirror height they sent dirty air to each side of my helmet.

    Given I had a broken neck that is now held together with Ti plates this agitated me big time.

    We fitted mirrors that sit further out (improving rear view) and also lower and that fixed our prob completely.

    I know the adventure is different but something else to consider, maybe take your mirrors off to try it ... food for thought, hope you get sorted.

    mousitsas is right to when you have lanky long suspension travel you do get flex and movement, my 990 SMR, shorter travel etc was rock solid
    #20