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Thread: '09 R12GS Odd Slow Speed Handling

  1. #1
    He Who Rests Rots! pfiedler's Avatar
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    '09 R12GS Odd Slow Speed Handling

    My '09 GS has about 6500 miles on it. I'm running Bridgstone Battle Wings (502 on the rear, 501 on the front). Rear tire is a 150/70R17M and the front is a 110/80R19M. Both have good tread depth but seem to be getting "flat" on the top surface. This is for background more than anything.

    What's happening is when coming to a stop and turning right, I get this very unpleasant sensation of the bike pulling to the right as if something had grabbed the bars and was trying to pull the bike over to the right. If I'm applying JUST the front brake (this bike has linked brakes), the sensation seems worse as compared to just applying the rear brake alone...like when slow riding. I mentioned this to the dealer (Max BMW) at the 6K service, but they couldn't identify any problem.

    Has anybody out there experienced a similar thing? Could it be the tires are the problem as they seem to be wearing in a squared-off fashion? Could it be one caliper on the front brakes pulling more than the other?

    I also own a 2012 K1600GT and previously a 2008 K1200GT. I have never experienced such a sensation on either of those bikes or, for that matter, on any motorcycle I've owned in the past.

    Any suggestions will be greatly appreciated. Thank you very much and please ride safely!

    Peter
    Peter Fiedler
    BMWOA #148776
    2012 K1600GT Grey/Silver
    2013 R1200GSW Thunder Grey

  2. #2
    Nickname: Droid
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    Doesn't do the same when turning to the left and brakes applied? Meaning pulling to the left. By all rights it should. The brake calipers get the same pressure at the same time, no delays or reduced pressure assuming no problems with the hoses. If one brake caliper is "hanging up" or dragging then it could be a mechanical issue but not a pressure issue.
    The 2009 GS came with the new Integral Linked-ABS, which is not a fully linked BRAKE system like other linked brakes. From the BMW specs description:
    "The new Integral ABS system applies brake pressure on the front wheel brake solely by means of a hydraulic circuit, thus acting entirely in response to the operating forces applied on the hand lever. This, in turn, ensures a more direct feeling of the brakes particularly important to the sports-minded rider. And now the rider no longer has to get used to any change in control or operation of the brakes when switching over from a motorcycle without ABS.

    The new system naturally maintains the proven semi-integral function, that is automatic activation of the rear-wheel brake when operating the front wheel brake. Pressing the foot brake alone, however, the rider, as in the case of a conventional system, activates only the wheel brake at the rear.

    As with the previous system, the advantages of this integral brake are ideal brake force distribution on both wheels under all conditions, naturally taking load conditions into account, as well as enhanced control enabling the rider to detect at an early point the risk of the rear wheel lifting off when applying the brakes all-out, and to take appropriate counter-action.

    To provide the desired integral function, brake pressure for the rear-wheel circuit is generated and built up by an electronically controlled hydraulic pump. This offers the advantage of pressure management and control completely independent of the front wheel circuit – which is the prerequisite for dynamic, adaptive and, ultimately, consistently ideal brake force distribution to the rear wheel as well as fully independent brake management and control.

    In the event of any deficiencies in the hydraulic pump or electrical components, the rear-wheel brake acts hydraulically as with a conventional system, overriding the integral function. This has no effect on the proper operation of the front-wheel brake, the only difference being that the ABS function is no longer operative in the event of such a deficiency.


    By that description, the front brake operates solely by the application of the brake lever and as I read it, applies "Intergral" function of the rear brake. If you leaning the bike, or with the handlebar turned, while braking you are basically "trail-braking". Trail braking does cause a bike to "turn in, or fall in" more quickly in the direction of the turn. Keep in mind anytime you have the handlebar turned with the front brake applied, there is a force acting at the front tire contact patch which does generate a turning effect at the fork pivot, in the direction of the turn. That, in addition to rear brake application does cause the bike to pivot into the turn direction more sharp, or as you perceive it as "pulling". When you say it doesn't happen with only the rear brake applied, it makes sense because of the reduced turning torque effect at the front tire contact patch, and that the Integral system allows independent application of the rear brake only.

    What is your front tire pressure? On a R12GS I'd say it should be 36 psi or higher, to maybe 40 psi. Low tire pressure, high center of gravity, worn tires, all contribute to the turn-in effect.
    Last edited by ANDYVH; 11-19-2012 at 07:46 PM.

  3. #3
    He Who Rests Rots! pfiedler's Avatar
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    AndyVH:

    Thanks for the very complete response. I was aware of the integral braking system and how it operates.

    The same problem does not occur when turning to the left. I used my GS-911 on the bike today, and I'm getting excellent brake fluid pressure to the front calipers. The components of the ABS and braking pumps all checked out perfectly. A friend, who owns a 2010 GSA, said that perhaps the slider pins on one of the front calipers might be mucked up and may be in need of a cleaning and lubrication. Although easy to dismantle from the bike, I think I'll leave such service to the techs at Max BMW.

    The odd part is this has come on slowly over time and that's what made me think of tires before all else. It's the weirdest sensation...not very comforting. However, once the bike is moving along (over 10-15 mph), it handles wonderfully.

    I appreciate you taking the time to write back. I'll certainly update the forum if and when I'm able to nail this thing down.

    Have a great Thanksgiving and please ride safely.

    Peter
    Peter Fiedler
    BMWOA #148776
    2012 K1600GT Grey/Silver
    2013 R1200GSW Thunder Grey

  4. #4
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    If the bike is truly only doing this to the right, then I would be looking real hard for the problem.

    I suspect tires first. My R1200R has 6,000 miles on it. Tires are too starting to square off. The front feels "heavy" at times like I have a soft tire, but its both left and right. I also can feel the edge when leaning into a turn. Once it gets past a certain point all is well again and the bike feels fine.

    This weekend I went for a ride. Before leaving I checked the tire pressure. I have been running 36/42 like the manual says. Sunday morning it was 40*f when I checked them, rear was 37 psi. I left it there Front was down to 33 psi.

    Bike rode quite well with the leaning problem much less pronounced.

    Perhaps a closer look at your tires. Are they worn even on both sides? Mine wear on the left more than the right because the way I drive. The more worn the tire, the more obvious it is. This is on all my bikes.

    I guess I would be trying changing tire pressure a little to see if it changes the way the bike handles.

    Saying the bike is more stable with just the rear brake on in slow speed maneuvers is totally normal to me.

    Good luck
    David

  5. #5
    Cam Killer marchyman's Avatar
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    Quote Originally Posted by ANDYVH View Post
    What is your front tire pressure? On a R12GS I'd say it should be 36 psi or higher, to maybe 40 psi.
    32 PSI front, 36 PSI rear is specified as the cold pressure for an unloaded, one-up R1200GS by both BMW and most tire manufacturers. OK, they actually specify 2.2 bar and 2.5 bar.

  6. #6
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    Smile

    Quote Originally Posted by pfiedler View Post
    Snip Could it be one caliper on the front brakes pulling more than the other?

    Snip

    Thank you very much and please ride safely!

    Peter
    Are you asking if one sticking caliper can make the bike "pull to the right"?

    Nope, the front wheel and rotors are all one piece. Look at all the bikes with one rotor.

    David

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    Quote Originally Posted by marchyman View Post
    32 PSI front, 36 PSI rear is specified as the cold pressure for an unloaded, one-up R1200GS by both BMW and most tire manufacturers. OK, they actually specify 2.2 bar and 2.5 bar.
    I've run 40/42 for over 200k miles on 7 different 1200GS's. Tourance tires, not EXP's.
    Seems to work for me.
    Marty Hill
    12 GS black/Boxer Cup Replika

    ride till you can't

  8. #8
    Honey Badger Semper_Fi's Avatar
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    40/42 for me

    Ran that on the 08 RT, 10 GT and 11 GSA

    30/32 feels soft to me - YMMV
    2011 R1200 GSA Smoke Grey Metallic Matt
    2009 G450X White
    IBA #35651
    Rogue Moderator

  9. #9
    He Who Rests Rots! pfiedler's Avatar
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    Had the bike checked at Max's today. 2 techs road tested it and didn't find anything out of the ordinary. Checked front end bearings, lock-to-lock for any binding and the front suspension status. All were to specs and working perfectly.They suggested setting the pre-load to "single rider with luggage" which I did and it does seem to improve things. I'm also going to up my PSI to 40/42. If it works for Semper_Fi, then it's good enough for me! (Gezzz...didn't know poetry was lurking in my life!)

    I ALMOST put a pair of PR3s on the bike today, but decided to support a good cause like my wife's Christmas present instead. I think I'll go for those babies in the spring.

    Thanks for the feedback to the question. I'll ride the bike with the changed tire pressures and pre-load and see how it goes.

    By the way...just replaced my stock battery with a Shorai. Simply amazing and sooooo light!

    Have a great Thanksgiving and please ride safely!
    Peter Fiedler
    BMWOA #148776
    2012 K1600GT Grey/Silver
    2013 R1200GSW Thunder Grey

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