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Harley Speed Wobble, Tank Slap, also known as the Death Wobble

Hoople has you covered with the alignment and a rear stabilizer solved my wobble problem on my 05 RG. You have an additional problem and that is the size of the windshield on your RK. With bike aligned I had the wobble with my 94 FLSTC (large windshield), and after talking to several MSF trainers they taught me how to handle the wobble. It really takes some courage the first time you have to do it, but it does work. First you have to loosen your grip on the bars as fighting the wobble just makes it worse, next you have to increase your speed (that's the scarey part). The bike will find it's center and than you can slow down. Try to relax and don't fight the bars, your reflexes can't keep up with the occillation. I have the TWR rear stabilizer but the progressive and several others work the same way. The progressive and TWR do not hang below the bike like the trutrack.
 
I have just bought a 2001 Ultra and experienced wobble,the alignment is correct according to the manual,and is offset by about .5 inch, to the right , depending on which expert you talk to ,this is correct, a friend told me the tire pressures in the manual are too low, and advised running 40 in the front and 42-44 in the rear, this did seem to help alot , however now I feel every little pebble etc., I will however be installing a rear stab. system when I can afford it.
 
Very sorry for your loss....All the touring models I have owned have had this condition ,it has been my biggest gripe with the touring bikes and I have taken a lot of time and effort looking into this, I put my bike in to this condition at least once everytime I ride my bike ,As Hd Don explained you need to stay calm and not panic , Ive put my bike through this wobble hundreds of times its second nature to me now , and it seems to be more apparent on curved grades either up or down,and (depending on your tire condition) that will determin the speed that the wobble will occur, as far as the fix all here are correct with the info they provided but , I would like to add that the stock shocks and tire wear plays a big part also at least this is what I have found, stock touring bike with a new tire the conditions will happen about 80 mph, now put about 35% wear on that tire and the wobble will start at about 65-70 mph after 50% wear the wobble will start at about 60-65 mph. Now take that same bike and add a tru-track- or progressive system with a new tire your in the 90 to 95 mph range before the wobble starts at 35-40 % wear you wont see wobble till around 80mph after 50% of tire wear the wobble will begin in the 65-70 mph range, now add a good set of shocks with good rebound and with a new tire its gonna take everything it can handle but the most incredible thing I have found with adding a good set of shocks is that over the whole tire wear range, when the wobble occurs it is not as violent it give you the feel of more control hence not hitting your panic button. If you run your touring bike hard and fast as I do I suggest its somthing you learn to control so you dont panic , Like I said I put my bike in this condition pretty regular because of the relationship with tire wear plays a big part of what speed the wobble will start,this way it does not startle me ,to me its not IF its when it will happen .its like putting your bike in a brake lock up condition and learning how much force you front brake can handle ,and on rear brake lock up learning to handle the skid pattern of your bike .these are not ifs they are when it will happen and being in control with out going in to pannic mode ,
 
I had this happen earlier this summer with my 2000 Road King Classic. Travelling 75 mph on the expressway the front wheel went from vibrating to shaking to wobbling in a span of 5 seconds. I backed off the throttle (did not brake) and the bike finally calmed down when it got below 60 mph. I was lucky in that there was no other traffic and didn't go down. Found th reason for my event was a combination of low air pressure in both tires and loose spokes in the rear wheel. I was guilty of neglecting proper maintenance on my bike - a mistake I will not make again. I also intend on replacing the stock laced spoke wheels with solid cast, replace tires when worn, and carry a pressure gauge to check tire pressure before each ride.
 
catfishon said:
not had this happen on my harley but i did have a 79 goldwing with full fairing that would start to wobble anytime i went fast and let off the throttle to fast. im pretty sure this was all due to the fairing and as long as i gave it more throttle it would stop . i would then back it off slow and it was ok .
but it would always scare the (EDIT) out of me.
sorry to hear of your loss.

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Had a similar incident on my 83 Goldwing, same exact thing, at about 45-50 mph she just started shaking, handlebars went haywire, I muscled it and gently slowed and it vanished, I excelerated up and down trying to see if I could make it happen again to see if i could isolate what caused it, i could never recreate it, but it happend about 3 times int eh 15 years I had the bike. I even had the Fork stabilizers (Chrome of course) installed, still happend. Never could figure it out...had mag wheels with fairly new rubber first time it happened on a straight stretch warm dry road.
 
Firstly, Gary I am very sorry for the loss of your brother.

I have experienced the speed wobble, and been reading and thinking about this (never a good thing;). On my bike there are two types of handling 'anomalies', and I suspect that the two are mixed up:
One is a slow/soft swinging type of movement occurring in high-speed corners. It is predictable, repeatable, and really not that much of a problem once I got used to it - a 'feature'.
The other has only occurred a couple of times, but is scary. It is a violent higher frequency wobble that leaves me totally out of control. Not sure when it happens, but it seems to be connected with uneven surfaces and acceleration in turns. What I think kept me from crashing, was easing off the throttle while loosening my grip. Once on a jap bike I managed to accelerate through the wobble - on my tourer I did not dare as I was afraid it would take too long, crashing before getting through it.

My theory is that the first one is a rear wheel steering issue that can be cured by stiffening up the rear swingarm pivot to frame connection by whatever means. The other one, is a 'classic' wobble that I belive is something totally different.
Question: The FXR is famed for its great handling compared to other Harleys. Looking through a 1987-1990 parts book, it is clear that the FXR and FLH are basically identical bikes when it comes to the frames and engine/trans/rear swingarm system. Why are we not hearing complaints about FXR handling?
Could it be that as it is a lighter bike the rear steering never happens? While the 'real' wobble is connected to the front geometry being totally different on the two models, coupled with a weight distribution difference in the two.
The FXR has the traditional negative offset fork legs (fork legs in front of the neck) and more rake. The FLH has positive offset, but a steeper rake. This gives a large trail, but combined with a 'light' front-end at speeds it could be causing wobbling.
Not sure if others agree, but I often get a very 'light' feeling from the front that seems more pronounced when my windshield is on...
There is probably not an easy cure for this, but I believe in well maintained suspension, tyre pressures, and possibly a touch tighter neck bearing than the manual calls for (like I saw someone else suggest - I will try next time my nacelle is off).
 
Hey everyone,

I've been reading into this subject and have found that on race-bikes, the biggest cause for high frequency wobble is due to the nature of our front end suspension.

I think race bikes pose a good source of problem finding because they push these machines further than anyone of us, and are constantly improving to get faster around the track, so they know what they are doing..

The biggest weakness about telescopic forks is the fact that they are connected to eachother only at the triple tree and the wheel. There is a large area between the wheel hub and the triple trees which is mainly unsupported (except for a fender mount) on most bikes. This makes it possible for the suspension to flex. I can understand this better when I imagine going straight down the road and hitting a bump which is only affecting part of the tire, say only the right side of the front tire. This bump can (will) flex the wheel to the left since the force of the bump is applied mostly to the right shock and there isn't anything substantial to keep the structure rigid.

Now if you think about this, this flexing of the wheel is what you do when you turn as well, and thus the bike will behave as if a sudden steering input is given. If this is not stabilized, the speed wobble can occur. This also explains why this is more likely to happen in a turn, there is already some flex going on by the turn itself, and bumps just add to the effect!

Race bikes solve this by using steering dampeners, inverted forks, smaller wheel sizes and short shocks (I guess that's why radical front ends never made it to the GP's). What we can do is install a fork brace, to give the front end some more anchor points.

I hope that someone finds this useful.
Take care,

p.s. off course steering head bearings etc play their part as well, but this would then be a maintenance issue.
 
The more I research the theory about tank slapping and how it happens, the more complex the answers become. There are many theories on how & why it happens and what can be done to reduce the chances of it happening. But what is very interesting is that in several examples during conducted studies of tank slapping, it has been found that if the rider is thrown from the bike, the bike will upright and become completely stable once again. Think about that for a second. If the riders weight was theoretically Zero, tank slapping could not occur. That almost concludes that the fundamental geometry of the bike is correct since once the bike rids itself of the real problem (the rider),, all is well.

It seems to be that once the riders weight goes out of phase with the bikes weight (the bike swings left while riders weight is swinging to the right) it is all over and there is nothing that will stop it. It now becomes a self feeding, positive feedback oscillation, where the riders swinging weight becomes the positive reinforcement.

If the riders weight is high in relationship to the bike frames center of gravity your chances for uncontrollable tank slapping is far greater than if the riders weight was close to the ground.

I truly feel & believe that what we HD riders experience (rear steering wobble) is not the same as true "Tank Slapping" (a violent positive feedback oscillation) that a metric racing bike will experience.
 
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