BMW K bikes (Bricks)

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KentM

KentM
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When I'm entering or exiting a freeway, I've noticed my '89 K100RS has a kind of waveform that seems to travel through my frame. For a while I thought it must be my suspension going out, but once I started paying closer attention, the wave/wiggle/bounce feels more 'side-to-side' rather than up-and-down. (Side-note: I'm not a speed-demon or major risk taker. Everything I'm describing is experienced at reasonable speeds and fairly pedestrian lean-angles.)

I've owned two shaft-driven R-series before, and am painfully familiar with the lateral torsion those bikes can generate when engine braking in a turn. What I'm trying to describe on the K has some similarities, but a much subtler and longer-lasting phenomenon... (R series produced a 1/4 second jolt, while the K wobble is more like a smooth 1.5 seconds.)

So far, this wiggle seems to be affecting the rider more than the bike. (Meaning that while its a bit disconcerting for me, the bike holds its line just fine.) Furthermore, under any other circumstances, the suspension feels solid/competent. The point is, I don't know how to interpret what I'm feeling. Is this part of the character of the K-series, or is it a symptom of something I need to address? 

Since I'm looking for useful frameworks from which to understand this thing, answers based on wild conjecture, and sober experience are equally welcome.


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'89 K100 RS Special

Code:
“Courage is not the absence of fear, but rather the assessment that something else is more important than fear.”




― FDR
    

Arlina

Arlina
Moderator
Moderator
Bike shouldn't do that.....
I suggest you check some bearings for play, frontwheel, rearwheel, steering and swingarm.


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"Wiggle" on sweeping turns - Bug or Feature? Eu-log10  K1100RS/LT - R1200RT - R1100RS (RIP) - Cagiva SST 350 Ala Verde - K75LT project - K75 Schurgers - K75S
    

Ringfad

Ringfad
Life time member
Life time member
and also tyres.


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"Wiggle" on sweeping turns - Bug or Feature? Ir-log10

   ;BMW; K100RS Style Black 1987 105K Km     ;BMW; K1 Black 1993 60K Km     ;BMW;     K1100LT (Swiss) now a RS     ;BMW; K1 Blue 1990 25K Miles
    

Dai

Dai
Life time member
Life time member
Tyre tread with a depth of less than two millimetres will 'track' badly. Check pressures - 38psi front / 42 psi rear seems to be the consensus around here.


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1983 K100 upgraded to K100RS spec, 1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

moriarti

moriarti
Life time member
Life time member
And if the tyres are Golden Oldies BIN THEM Shocked


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1984 k100 rs red/black VIN  0004449
    

Arlina

Arlina
Moderator
Moderator
Can't see the rim, still have some miles on it Razz Razz Razz


"Wiggle" on sweeping turns - Bug or Feature? 126969592_828158388002847_4786972478537027125_n.jpg?_nc_cat=101&ccb=1-3&_nc_sid=730e14&_nc_ohc=v9h3jcg7QxUAX9q2WfN&_nc_ht=scontent-amt2-1


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"Wiggle" on sweeping turns - Bug or Feature? Eu-log10  K1100RS/LT - R1200RT - R1100RS (RIP) - Cagiva SST 350 Ala Verde - K75LT project - K75 Schurgers - K75S
    

moriarti

moriarti
Life time member
Life time member
affraid affraid more cracks in that than a Politicians answer. BIN TIME

Arlina you ride on canvas  anyway Razz Razz Razz


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1984 k100 rs red/black VIN  0004449
    

8Back to top Go down   "Wiggle" on sweeping turns - Bug or Feature? Empty Wiggle Thu May 27, 2021 8:57 pm

daveyson

daveyson
Life time member
Life time member
Turning on and off a freeway in the US are both right hand turns I think. If you have a preference for turning right, that side of the tread can sometimes be more worn and it probably wouldn't happen on left turns. 

It only lasts 1.5 seconds, that sounds like when you cross a seam in the bitumen at a very acute angle, like going from the on ramp to the freeway.


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11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

gorio

gorio
Silver member
Silver member
@Arlina wrote:Can't see the rim, still have some miles on it Razz Razz Razz


"Wiggle" on sweeping turns - Bug or Feature? 126969592_828158388002847_4786972478537027125_n.jpg?_nc_cat=101&ccb=1-3&_nc_sid=730e14&_nc_ohc=v9h3jcg7QxUAX9q2WfN&_nc_ht=scontent-amt2-1
That tire is like new. It still has the little nubs on the edges. Just keep turning it will be fine.


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1992 K100rs 16v
1997 R1100rt
2006 R1200rt
Past lives
Kawasaki Concours
1976 BMW R90s
1975 Ducati 860gt
1992 Honda VFR750
1985 Honda VF750
1982 Kawasaki 750GPZ
1975 Norton 850 Commando
    

K75cster

K75cster
Life time member
Life time member
You may be feeling the tram tracking road surfaces get when used long term by trucks. You could be feeling the result of too many miles on a straight road and the turn in on your tyre now has an edge to it. Ambient cold at 36psi and put it through some bend swinging to see if you can round the tyre again. Then try to feel it again. Other than that check the final drive for wear by holding the wheel top and bottom and rocking it to see if any movement can be felt. Check swing arm for wear too. If all seems fine move forward and check your steering bearings for flat spots. But hey! onramps and offramps are worn out things at the best of times.


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Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

JSFR80

JSFR80
active member
active member
Those are all good suggestions. When you check your steering head bearings don't just check for looseness but also check for nochiness from a straight ahead position.

    

MikeyD

MikeyD
active member
active member
Some tires have a harder rubber compound in the center than they do on the outside edges. I've noticed sometimes when they get worn they tend to create a scalloping texture that gives me some wobble when I'm banked in a turn. That might be something to check and would indicate it's time for new tires, or give it to Arlina to ride it to the rim  Very Happy. In the photo that harder center strip curves from side to side and in a bank the tire wobbles from high spot to high spot. Let us know what it turns out to be if (I mean when) you figure it out.
"Wiggle" on sweeping turns - Bug or Feature? 20201010


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1985 K100RT (0052390), 1985 K100 (0030066), 2003 K1200GT (ZK01448), 1984 R65, 1984 R80ST, 1974 R90/6, 1976 R90/6, 1997 R850R, 1991 Honda CB250, 1998 Sportster 883
    

92KK 84WW Olaf

avatar
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@MikeyD wrote:Some tires have a harder rubber compound in the center than they do on the outside edges. I've noticed sometimes when they get worn they tend to create a scalloping texture that gives me some wobble when I'm banked in a turn. That might be something to check and would indicate it's time for new tires, or give it to Arlina to ride it to the rim  Very Happy. In the photo that harder center strip curves from side to side and in a bank the tire wobbles from high spot to high spot. Let us know what it turns out to be if (I mean when) you figure it out.
"Wiggle" on sweeping turns - Bug or Feature? 20201010
I use Bridgestone BR45/46 and they are dual compound and prone to this scalloping and wander if run too soft. I find running them at 38psi front 42psi rear avoids this. This gets even more likely if the tyre is aged too much. Check the manufacture date too.


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1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 37,190 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 42,640 miles.

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

Snod Blatter

Snod Blatter
Life time member
Life time member
On the RS in particular it seems to be common, mine starts to get particularly nasty once there is less than around 4mm (!) left on the rear tyre. The front doesn't seem to matter.. My theory is that as the rear wears down it becomes more flexible, which allows this weird oscillating movement to start, and then the weight of the bike flexes the tyre even more and you soon find yourself wondering if you're actually riding some 1950s relic. I have replaced the steering head bearings and the shock and the crown wheel bearing and in the end the only thing that stops it is a new rear tyre. Or going slower..

Moving about in the seat helps as you can keep the bike stood more upright, and putting weight on the inside footpeg often helps calm it down too, and accelerating through the bend can be calmer still but you shouldn't have to put that much effort in to glide round a corner. Sometimes she's just a wobbly old Hector! I've got a Tourance Next to put on soon, I'm really hoping a stiffer radial will help stop it once and for all. By the way I run 40/42 PSI F/R.


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1989 K100RS SE ABS 8v  VIN: 0149214
Others: 1.5 x Honda CBX250RS-E, '94 CB250, '95 TRX850, '16 Z250SL
http://justbikethings.blogspot.co.uk/
    

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