Suspension Noticeable shimmy/wobble on my step through fat tire bike

[ramrezz425]

Due to my immense weight of 200 pounds I believe the suspension in the front of my bike is not strong enough and there is no provision to adjust it. I believe it is suspension related. If you see the photos, I put an arrow by the forks showing that there is just a cap on top. Does anybody else out there encounter similar issue and do you have a solution? Is a fork change out a big job thank you in advance for any comments.

 

[DieselTech]

The fork gets play in between the lower shock body & the upper fork shaft/tubes.

 

[DieselTech]

Apply your front brake & hold it, then rock your bike forward & back. Look for play where I circled your fork in blue.

 

[ramrezz425]

Will do! Thanks for the info.

 

[DieselTech]

Will do! Thanks for the info.

Sounds good! Let us know what you find out.

Thanks.

 

[MikeDuf]

Also something else to look at or think about if your forks are gas charged with oil and they are not balanced properly, perhaps from a leaky seal, you can get uneven modulation during the compression and rebound.

That can cause vibration and ultimately wobbling.
Also, what speeds do you get the wobble at?
If only at higher speeds on very flat surface, then it can be like the other post stated if tubes are loose that should be looked at.

And of course the most Elementary item 101 on Fork suspension , is check your fork oil drain it and possibly put a heavier weight.

also check your front wheel for trueness by lifting it up and spinning it, you should not see any wobbling wheel.

The tires look look fairly new from the pictures so I'm not thinking that there is any out of balance issues, but I do see a scuff on the side and if your wheel is bent that is a whole different issue. And that will cause a wobbly ride.
Just my two cents

 

[ramrezz425]

Occurs around 10 miles an hour to 15 mph when making slight steering adjustments

 

[MikeDuf]

Yeah you're probably going to have to put the bike up on a stand and move the wheel and Fork assembly from side to side while having somebody hold the bars and see if you can detect any kind of loose play you might just have a loose head bearing! And that can cause all kinds of nasty things

 

[Atavar]

Sounds like a loose axle to me. Make sure they are both tight.

 

[Annieolnie]

Occurs around 10 miles an hour to 15 mph when making slight steering adjustments

Does it happen if you have locked the shocks out and is it worse when the backof the bike has a load on it? Also, as people have mentioned, there are some scuffs. Did you tip over or have a crash?

 

[m@Robertson]

I think its pretty likely you have what is commonly known as a 'speed wobble'. Also known as a 'death wobble' informally.

It comes from the frame being a little bit flexible. You commonly see it on longtail cargo bikes, but a step-thru frame can just as easily have the same problem. A suspension fork typically makes the situation worse. What happens is the frame flex coupled to the wiggling inherent in suspension fork movement (they flex forward and backward in addition to up and down) creates the wobble more easily.

I had a speed wobble on my Big Fat Dummy until I switched to a different suspension fork, which inadvertently cured the problem. I went from a Rockshox Bluto to a Wren Inverted. This is not the recommended way to fix this problem and I just got lucky by picking a stronger fork.

The more common solution is to use a Cane Creek Viscoset headset. They were designed specifically to deal with this problem. I have Viscosets on both of my Bullitt cargo bikes. My first Bullitt exhibited a horrible wobble at around 18 mph. I was able to stiffen the frame with some side panels and reduced the problem to only occur when I hit a particular washboard stretch of pavement at north of 20 mph. The Viscoset disappeared the problem forever.

There are also motorcycle steering dampeners that get pressed into service, but that is a really DIY thing and involves a lot of experimentation. I used one for a time but hated its limitation on steering travel.

check out the before/after examples in this vid, and note that a lot of the affected bikes in the video are step thrus with suspension forks.

 

[ramrezz425]

The video shows the flex that I am experiencing, The headset appears to be properly mounted into the head stock. Somebody wrote on here that I am experiencing something called "death, wobble" or "speed wobble". It does happen at low speeds and only if I am moving the handlebars slightly left or slightly right then the oscillation starts.

 

[Annieolnie]

Go to Google and search: ebike speed wobble, YouTube. There are videos by Citizen Cycle on the Wired Freedom and a number of them on the Lectric Xpeak, see if it looks familiar. M@ is right. The common solution is that Cane Creek headset. The Xpeak with the top bar doesn't do it, but they have had a continual problem with it on the step thru.

 

[HumanPerson]

https://duckduckgo.com/?t=ffab&q=ebike+speed+wobble,+YouTube&ia=web

 

[m@Robertson]

The video shows the flex that I am experiencing, The headset appears to be properly mounted into the head stock.

The headset would appear to be completely fine if the problem was speed wobble, which does not originate as a problem with the headset. It comes from frame flex causing feedback to the front wheel assembly..

Somebody wrote on here that I am experiencing something called "death, wobble" or "speed wobble". It does happen at low speeds and only if I am moving the handlebars slightly left or slightly right then the oscillation starts.

OK thats a slightly different scenario then, if you induce it by turning the bars. Speed wobble starts all by itself.

I downloaded that video and put it on a loop so I could look closely at it. If you are rocking the whole bike side to side without turning the handlebars, then what I am seeing is the actual fork blades wobbling in place as if they are freaking loose somehow. Concentrate your gaze on the fork bridge versus the relative position of the fender to the right and left fork blades. It looks like the bridge is rocking right and left, but the fender isn't. The only way I can think of that NOT being an optical illusion is if you are rocking the bike side to side, not turning the steering, and there is wobble in the fork blades that comes from that motion.

A speed wobble would be the fork maintaining its relative position to the wheel, and the whole wheel, fork and handlebars wobbling together as one rigid piece (as they should) thanks to a speed-induced wiggle that originates from your bike's rear wiggling (that rear wiggle is pretty much un-felt). Think of it as the bike is wagging its tail, but the result you see and feel is the handlebars wobble. Its demonstrated perfectly in the Cane Creek video.

This is a one-in-a-zillion flaw if it is the former issue, and it resides in the fork being a piece of junk. Horribly dangerous if what I am seeing is not an optical illusion. It would mean the fork blades are rocking independently inside their stanchion mounts instead of being fixed firmly in position.

 

[ramrezz425]

I do have the tire pushed into the corner of my garage and I am moving the handlebars slightly left and slightly right and you could see the flex of those front forks, I am actually over flexing so it could be shown more so on video. But what I'm trying to illustrate is the fact that those forks are kind of weak structural wise if changing the whole fork out is a huge deal then I would rather just sell the bike and look for something a little bit more expensive that has better quality components for suspension.

 

[m@Robertson]

If you are seeing the fork blades wiggle in place from just that simple motion you are doing, then that fork is a disaster waiting to happen. I've never seen anything so bad, and its so bad I'm not sure I am really seeing what I think I am seeing as I can't see how you would not crash with a fork so wobbly.

Changing a fork is not such a big deal, but you need to know what you are doing and have a couple of specialized tools. And a couple of hundred bucks minimum to buy another low cost fork (a for-reals proper fork is going to be US$6-800 which is more than your whole bike is worth I bet). The specialized tool would be the star nut setter, and some PVC to bash on the crown race. Don't spend like $50 on the proper tool for this as a 6-inch piece of 1.25" Schedule 40 PVC will do the job just fine.

 

[HumanPerson]

I had a bike that did similar to that so i just changed to surly krampus forks.
Those were some scary forks all wobbly like that.

 

[Annieolnie]

Can you tell us the make and model of your bike?

 

[ramrezz425]

Can you tell us the make and model of your bike?

Trekcraze T600, rebadged TST/Hovsco.