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Offline BikerJan

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Re: Problems with the new LC
« Reply #60 on: July 23, 2013, 04:32:16 pm »

This has got bugger all to do with kickback & "tank slappers" which is induced into the steering by the road surface.
[/quote]

Please advise why the steering induced wobble has nothing to do with road induced wobbles?
 

Offline Slovac

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Re: Problems with the new LC
« Reply #61 on: July 23, 2013, 09:36:27 pm »
 :happy1:
 

Offline AntVan

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Re: Problems with the new LC
« Reply #62 on: July 23, 2013, 11:31:56 pm »
My dealer claims only the very first batch gives head. It makes sense then for Pauli's bike then. Not good, of course.
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Offline GSing

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Re: Problems with the new LC
« Reply #63 on: July 23, 2013, 11:38:29 pm »
Hope they sort it, bike have been with BMW now for two days, and still no news...............

PS - Lucky I have the KTM as backup, never thought that I would ever say that.......... :imaposer:
 

Offline Slaaiblaar

Re: Problems with the new LC
« Reply #64 on: July 24, 2013, 07:23:09 am »
Hope they sort it, bike have been with BMW now for two days, and still no news...............

PS - Lucky I have the KTM as backup, never thought that I would ever say that.......... :imaposer:
Did you ride another GS to feel if it does the same? Can you give some more info on when and how this happens, bike load, suspension setup, when and how often
 

Offline lecap

Re: Problems with the new LC
« Reply #65 on: July 24, 2013, 07:44:04 am »
That video does not show any problem, where is the headshake?

They are trying to prove that the bike is not susceptible to kick back and tank slappers but they don't seem to understand where the kick back comes from ::)


Please advise why the steering induced wobble has nothing to do with road induced wobbles?


I'll try and not make this too technical. :D Please ask if you lose me.

Let's work with a mechanical model:
Your bikes steering physically works like a pendulum: It tends to center itself. It will swing until it's slowed down by friction and centered again if you disturb it.

In the video they disturb the steering by an input from the handlebars. Then they leave the system alone and it does what it is designed to do: The steering geometry and damping of the tire calm down the movement quickly. Every bike will do that, not just a BMW.

Rider / handlebar induced oscillations are rather harmless because your arms have a rather high damping rate and they aren't very elastic. The steering needs a continuous input like turbulent air flow from a leading car or truck or your fluttering jacket to keep a wobble going and simple things like loosening your death grip on the bars, shifting your weight or tapping off or accelerating will quickly cure the wobble.

In our model your arms resemble a very stiff shock absorber. The one end attaches to the pendulum (the steering), you push or pull on the other end.
Pushing / pulling will deflect the pendulum. The high damping and stiffness of your arms in death grip will slow the pendulum down considerably. The steering will take more time to return to the stable & straight position, the bike will start to change its course (like you pulling on the bars to initiate a turn). If you pull on your bars periodically and alternatingly your bike will weave from side to side.

Now we look at the steering and your tire:
Here the situation is completely different. The tire is rather flexible and pretty much likes to behave like a rather soft spring. (Ever seen some high speed footage of a tire going over a bump?) Internal damping is something a tire ideally should have in oodles but you have to build it in using intricate combinations of rubber with layers of fabric and belting made of Kevlar or steel. Too much internal damping and you have a rather uncomfortable fork lift wheel :-\

You hit a couple of potholes - off centre:

Imagine you push and pull the end of a soft spring attached to your pendulum (you grab the tire by its contact patch and twist it against the steering):
Depending on your timing and size of your inputs the pendulum will remain almost stationary or it will start to swing.
As long as your push & pull and the movement of the pendulum is more or less in phase (swings towards you as you pull and away as you push) everything stays neat and controllable: Kick back. A very common phenomenon encountered when riding through potholes and over  bumps, even in sand.
Next you move your input out of phase. Push towards the pendulum as it approaches you and pull as it moves away. If you get the frequency right the pendulum will swing madly. This is called resonance. Transferred back onto your bike: A tank slapper.

Now you have learnt:
The tank slapper is caused by a bump or series of bumps in the road. (One bump very rarely does it).
The damping of the steering has an influence: Front suspension geometry (rake, trail, steering angle, tire diameter and width) and mass.
The damping of the tire has an influence

Final conclusion:
Every bike may tank slap if the right (wrong) conditions come together.
Correct suspension setup and tire pressure does a lot to avoid tank slappers and is the most important cure.
Different type of tires can improve the bike but can also make things worse.
A steering damper can improve a problematic bike but comes with disadvantages. It should ideally act as an ideal (brick wall) low pass filter damping only the resonance of the steering (and above) but have no damping at slower movements. Existing dampers are unfortunately real world ones. Further disadvantages are added complexity and price.
« Last Edit: July 24, 2013, 09:14:41 am by lecap »
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Offline BikerJan

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Re: Problems with the new LC
« Reply #66 on: July 24, 2013, 09:40:00 am »
Thanks for the explanation lecap, Tankslappers is therefore dependant on the natural frequency of the bike, once the tyre induced deviations approach the natural frequency of the bike, the deviations will increase, resulting in a tank slapper.
 

Offline GSing

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Re: Problems with the new LC
« Reply #67 on: July 24, 2013, 08:25:17 pm »
It seems that we have found the problem, and as I thought it was tyre related. They have changed the front wheel and tyre with another brand and the instability was gone. They will change it again with another wheel and tyre tomorrow and run some more tests, if they get the same result, they will change the current tyre with a new one and I can have my LC back.
 

Offline Jondu

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Re: Problems with the new LC
« Reply #68 on: July 24, 2013, 08:36:50 pm »
It seems that we have found the problem, and as I thought it was tyre related. They have changed the front wheel and tyre with another brand and the instability was gone. They will change it again with another wheel and tyre tomorrow and run some more tests, if they get the same result, they will change the current tyre with a new one and I can have my LC back.

Good sivice from BMW?
 

Offline GSing

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Re: Problems with the new LC
« Reply #69 on: July 24, 2013, 08:38:15 pm »
As ALWAYS!!!  :thumleft:
 

Offline Bring It On

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Re: Problems with the new LC
« Reply #70 on: July 24, 2013, 08:54:32 pm »
As ALWAYS!!!  :thumleft:

Glad to hear that thing seem to be coming right here. :thumleft: :thumleft:
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Offline J-dog

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Re: Problems with the new LC
« Reply #71 on: July 25, 2013, 08:43:36 am »
It seems that we have found the problem, and as I thought it was tyre related. They have changed the front wheel and tyre with another brand and the instability was gone. They will change it again with another wheel and tyre tomorrow and run some more tests, if they get the same result, they will change the current tyre with a new one and I can have my LC back.

needed to change the wheel as well?  :patch:
 

Offline Goose

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Re: Problems with the new LC
« Reply #72 on: July 25, 2013, 08:52:57 am »
It seems that we have found the problem, and as I thought it was tyre related. They have changed the front wheel and tyre with another brand and the instability was gone. They will change it again with another wheel and tyre tomorrow and run some more tests, if they get the same result, they will change the current tyre with a new one and I can have my LC back.

needed to change the wheel as well?  :patch:


for testing purposes it's probably easier to merely swap whole wheels than to change a lot of tyres....  ???
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Offline Slovac

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Re: Problems with the new LC
« Reply #73 on: July 25, 2013, 07:27:43 pm »
It seems that we have found the problem, and as I thought it was tyre related. They have changed the front wheel and tyre with another brand and the instability was gone. They will change it again with another wheel and tyre tomorrow and run some more tests, if they get the same result, they will change the current tyre with a new one and I can have my LC back.
If I may ask ... What brand of tyres are giving you the issues?
 

Offline zacapa

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Re: Problems with the new LC
« Reply #74 on: July 25, 2013, 07:52:49 pm »
A different perspective on this:
My R80 airhead is looking to kill me on any bumpy road with a tankslapper of note. It's a monolever BMW and made in 1985. It requires a firm hand and some forethought when hussling through the bends, especially on a bumpy road. Adding spacers to preload the front forks is also a bad idea as your front wheel then has a tendency to loose grip as the bike is not settled enough in the suspension and therefore rides higher which causes the front wheel to loose traction even earlier. Now I don't own a 1200LC, but my recommendation would be to run softer springs in the front for the lighter riders and compensate the rear sag to balance things out. If the bike is settled in its compression stroke by about 1/3 of overall suspension travel things should be good as a starting point. I know the LC is a new age bike and suspension settings are semi computerised which makes things more difficult to find a baseline setting.
Has anyone checked their LC in the different modes to see what suspension sag is with rider onboard. Comeon, we want to see the numbers.
 

Offline HermanH

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Re: Problems with the new LC
« Reply #75 on: July 26, 2013, 06:16:57 am »
If I may ask ... What brand of tyres are giving you the issues?

The Metzeler Tourance NEXT. As the mileage on my LC creeps closer to 5000km, the same is starting to happen!
 

Offline Callie GS

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Re: Problems with the new LC
« Reply #76 on: July 31, 2013, 08:43:55 pm »
Tested my LC and it also give a similar wiggle at 80 kph.
I am just about on 6000 km and I am going to fit a set of Mitas EO7`s
after my trip to Swaziland mid August , will see what happen then.
I don't think there will be to much diff in a 150 and 160 at the back ??
Still an awesome bike !!!
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Offline Slovac

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Re: Re: Re: Problems with the new LC
« Reply #77 on: August 01, 2013, 02:49:07 pm »
If I may ask ... What brand of tyres are giving you the issues?

The Metzeler Tourance NEXT. As the mileage on my LC creeps closer to 5000km, the same is starting to happen!

Swapped my GSA for Elsie last week and have 500 odd km on the clock now. Elsie came with ContiTrailAttack 2 tyres fitted... and even though I have never been a Conti fan, I must say that this set of rubbers are not half bad. Good grip in the dry and in the Cape stormy wet...
I have tried various things with the bike at speeds ranging from 40 kmh to 140 kmh and have not had any headshake. The steering becomes a bit light on the other side of 200 kmh... but I put it down to the bike not really being designed for those sort of speeds... it's not supposed to be a superbike after all.
 

Offline T Rex

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Re: Problems with the new LC
« Reply #78 on: August 01, 2013, 04:28:00 pm »
It seems that we have found the problem, and as I thought it was tyre related. They have changed the front wheel and tyre with another brand and the instability was gone. They will change it again with another wheel and tyre tomorrow and run some more tests, if they get the same result, they will change the current tyre with a new one and I can have my LC back.

Glad it is sorted. I had a similar stability problem when I put E 10' s on my older GS. It started weaving at 120, on tar!! Shows you what a tyre can do.
 

Offline BennNevis

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Re: Problems with the new LC
« Reply #79 on: August 02, 2013, 04:48:21 pm »
I am now on my second LC GS with the following issues that I have experienced first hand, incidentally mine was the first LC to be sold by Atlantic Motorrad.

First bike was replaced after 1st service at about 800km, with BMW SA replacing the bike due to diagnosed gearbox's imminent failure.

This was subsequently resolved by BMW Germany with a finding that the ESA required re calibration, which silenced the grinding gear noise emitted from  the gearbox/diff.

Replacement bike's clutch was inconsistent with bite and lever tension ranging from almost nothing to virtually no lever play. Just after first service, again, the clutch just disappeared in traffic one morning resulting in the bike jerking to a halt in gear at a traffic light.

Dealer found to much hydraulic fluid in the system when they opened it up. They also found the remains of a cleaning rag between the slave cylinder and engine mounting seat!!!

Rear pads was found to be to soft whist doing a trip through Germany and Austria with two of the bikes having to replace their rear brake pads at circa 3-4K kms.

Tyre rumble with the Annakee3 are close to that of off road tires.

Bikes became quite floaty on the Autobahn when exceeding 200km/h with top boxes extended and carrying two weeks luggage in the extended panniers.

Gear engagement from neutral is met with harsh engagement and finding neutral is tricky at best of times.