roduction:

OK chaps, sit up straight and pay attention, we’re going back to school! There will be coffee and cake for those who stay the course.

I’ve lost count of how many times I have answered questions about ‘bagger wobble’ on HDF, so this is a description of the rubber mounting system in our Touring bikes, from an engineering perspective, in the hope of improving understanding of what the wobble is and why it happens. I make no apology for this being a long thread, but you can always print it out and read it in bed or in the small room!

It goes without saying that the following assumes a bike in tip top shape. Let us also be clear that many Harley owners have probably never experience the so-called wobble and are blissfully happy with their ride, so for them there is no problem. If you read this and are wondering what on earth it is all about, do not allow yourself to be suddenly gripped with fear!

Let us start with the original rubber-mount system introduced in 1980 and cover the 09-on bikes later.

Wobble 1:

Evos and early TC bikes not only had rubber engine mounts, they also had rubbery swingarm bushings, called ‘cleve blocks’. Some of the bagger wobble reported on these bikes can be blamed in part on them, as they allowed a degree of sideways movement of the rear wheel and swingarm, relative to the rest of the bike. They were dropped by Harley in 2002 and replaced with steel bushings, which cured that aspect of the handling problem. After-market bushing kits are available to replace them on older bikes still fitted with cleve blocks.

Why Rubber Mounts?

Over the decades our bike engines have become progressively bigger in capacity and more powerful. As a consequence the forces inside the engine have become greater, causing more vibration, which in turn is more uncomfortable to us riders and more likely to damage parts of the bike. Norton tackled this challenge back in the 1960s with their Commando, a watershed design, partly because parallel twins are more prone to vibration than our V-twins. In 1980 Harley introduced the FLTs, with their own design of rubber mount system, credited to Erik Buell, which we have all come to know and love!

The approach Norton used in the Commando was to isolate the engine from the frame, using concentric rubber mounts. That system is far from perfect, in part because it didn’t allow the engine to actually move very much. Essentially they addressed high frequency vibration, but not the engine speed ones so well. The beauty of the Harley system is that our engines are allowed to shake, which helps deal with engine speed vibrations, but are also rubber mounted, which helps dampen higher frequency vibrations. That gives us a more comfortable ride, but also has the potential benefit of providing high quality handling at the same time.

Comfort:

Humans are sensitive creatures, despite the tough and rugged image we riders like to have! When man started to employ science in the design of engines and vehicles, we soon learned that if we are going to sit on top of one, the least unpleasant form of vibration is up and down. So our bike engines, solid or rubber mount, are designed to shake that way. When you watch your Harley engine bobbing up and down at idle, that is deliberate! You are watching the laws of physics at work, in perfect harmony with engineering, under man’s control. All is well with the World.

Description:

The engine and trans are bolted together, and the swingarm is mounted directly onto the rear of the trans. Along with the rear wheel this makes up a substantial single Assembly, which is mounted into the frame at three points, of which more shortly. The swingarm axle not only allows the rear wheel to move relative to the rest of the bike, but doubles up as part of the rear mounting.

I will continue to use the word ‘Assembly’ to refer to the combined engine/trans/swingarm/wheel.

Kinematics:

Take a deep breath, we are about to dive into the bowels of your bike!
Statement: kinematics is a branch of engineering that deals with the geometry of motion of moving parts.
Question: what on Earth does that mean and how does it affect your Harley?
Answer: it is at the very core of it and is the basis of the original Harley rubber mount design.
As mentioned, the Assembly described above is mounted in our bikes at three locations:
The rear rubber mounts serve several purposes. The ends of the swingarm axle are fastened to those mounts, which are retained in the frame by the passenger footboard mountings. They support a large part of the weight of the bike; locate the Assembly in the frame, both laterally, vertically and fore and aft; also allow it to rotate up and down, or pitch.
The front rubber mount supports the front of the Assembly and allows it the freedom to move up and down, rotating on the rear mounts. It is laterally supported by a stabilizer link, which prevents the unit from moving sideways at that point, or yawing.
The top support is a simple stabilizer link, which also has several purposes. It doesn’t bear any weight, but allows the Assembly to rock up and down, also back and forth, while preventing it from moving sideways, or rolling.
In all three cases motion is free moving, although the design of the front mount limits the total amount of vertical movement. This is an elegant engineering solution and a kinematically sound design, to be applauded. Unfortunately there is a reservation - there is no stabilizer, to support the rear rubber mounts and prevent lateral movement.

Wobble 2:

The lack of a rear stabilizer is IMHO a serious flaw in the way Harley introduced this design. That comment is entirely justified as every Buell has one, as do all rubber-mount Sportsters, so Harley knows how to do this. It is a mystery why our Touring bikes don’t have one.

This omission is the main source of the infamous ‘bagger wobble’. Lateral forces compress those rear rubber mounts and cause momentary misalignment of the rear wheel relative to the front wheel. The rubber used is stiff and only yields a little. It also is only able to compress to a small degree due to the design, but it is significant and too much.

2009-on:

While Harley continue to use a similar design of rear rubber mounting on their latest bikes, the old single front mount has been changed to a pair that are similar in design to the rear mounts. There are now four rubber mounts instead of three, but instead of leaving only the rear mounts without lateral support, neither front nor rear have a stabilizer.

Frankly, from an engineering perspective, Harley appears to have abandoned the fine principles of the original design. There are many reasons why Harley changed the frame, of which the engine mounting system is only one, however they could have retained the original design and simply added that vital rear stabilizer.

If you sometimes wonder about the handling of your lovely new bike, you have every right to. If you changed from a pre-09 bike to a post-09 one, to get a better handling bike, you simply jumped out of the fire into the frying pan!

Wobble 3:

It cannot be denied that the 2009-on set-up gives improved lateral stability, but it doesn’t cure it. Both front and rear rubber mounts can compress under lateral loads, although the degree of misalignment this causes is improved over the older design.

Stabilizer Kits:

Harley inadvertently created a market opportunity for the custom market, which many brands have filled. The better designs provide lateral support to the rear rubber mounts on earlier bikes, and both front and rear mounts on later bikes would be nice. By providing suitable lateral support, the kinematic principles of the original design are fulfilled.

On both versions of bike, the steering is made more accurate, improving the steering and feel of the bike even at slow speeds, as well as giving better handling at higher speeds. The improved stability improves the riding experience throughout the speed range. The benefits of stabilizers are for all of us, not just those who want to ride fast. However, not all kits are created equal and some designs are superior to others.

Summary:

The original rubber mount design is excellent, but was compromised by the factory, by leaving off the rear stabilizer link, for reasons we may never know. Rubber squashes, which is why we make much use of it in so many aspects of our lives. It squashes on the original bikes and it does on the latest ones as well. Both sets of bikes will ride better with suitable lateral stabilizers.

Finally:

I hope that goes some way to improving understanding of the way our rubber-mount bikes work and why the original design is actually a very good one, only let down by leaving out a vital part. Later bikes are also flawed, so none of our rubber-mount Touring bikes are perfect, or as good as they could be.

Any questions?!

Added later:

If you are looking for the silver bullet, the product I use and recommend is True-Track.

There is also further reading at post #49, for those keen to learn even more!

Everyone please read. This was taken from the touring section.

 

Good stuff here, thanks, should be standard reading for anyone who types "wobble" into any thread!

 

FLHTKONE:

Might be nice to tell folks where you came up with that article.... grbrown wrote and posted it here.... https://www.hdforums.com/forum/touri...e-exposed.html ...

 

True. I thought I read this before. Plagiarism is NOT cool.

 

Try reading the last line...I said it was from the Touring section. NOT PLAGIARISM FOOL!

 

Good read, had no idea, thanks for the info.

 

This and other post only address part of the problem. Why do the sport bikes have no wobble, have way more horsepower per CI than any HD every made and still use counterballancers, and travel at speeds that will never be achieved that a HD never could? The Metrics are very smooth to ride and do not employ rubber mounting.

The stabilizers do work to a degree but are not a real solution due to leverage. Your swing arm is over 26" long with a heavy wheel that is quadrupled in weight at 40 mph due to inertia. Hold a 26" PVC pipe at the end and have a child move the other end while you hold it fast with your hands. Get the idea.

The movie posted on a stabilizer site on how this device will cure a crash happening right in front of your eyes is an insult to my intelligence and a scare tactic accomplished by fraud (movie removed but images are still being used. A rider filmed at the Dragon is shown riding around a corner with his feet up on the crash bars, on one of lowered bikes everyone loves here. Look at the sparks that start at the footrest. The rear wheel is than lifted up and looses traction from the roadway. The Darwin effect is than in play and the rider and bike are erased from the street. No device could/would have helped other than removing the rider from the equation. Lowering a bike reduces your ride height and ground clearance. This means you hit hard parts sooner. Either slow down and make square corners of go into the weeds taking your love ones with you.

Harley improved things in 2014 by addressing the hinged connection on the front fork top triple trees by clamping them and going from a flexible 41mm (actually a 1 5/8/1.625" X 0.165") fork tube to a better 49mm (1.929" X 0.160") fork tube. Due to a thing called cross section the fork tubes are less susceptible to flexing. Take a string of LED lights and tape it onto your forks allowing for stroke on your 41mm fork than put it on to a 49mm fork. Do it at night and have your friend film it with is GoPro or such.

Hinged triple tree/pre-2014 FLT with a fork cap/bolt:
HD has been using a fork bolt that is slip fit through the top triple tree since the HydroGlide was introduced in 1948 & used in 1949. I have no experience with bikes older than that. The fork is slid through the bottom triple tree & goes into a sort of semi-circle cavity and secured in place with the fork bolt that is slip fit through the top triple tree:


To observe the wisdom of this design please have your friend hold your tire in place or use a table wheel clamp and move your handlebar side to side and watch the flex at the triple trees. Go onto a parking lot or such that is free from sand or other debris and splay your feet and travel as slow as you can go. Turn your handlebars 45ş and lock up your front brake without falling over. Watch the forks flex and tweak as your triple trees go askew. What do you think is keeping your bike going down the street where you want it to go other the enormous weight of your front wheel created by rotational inertia.

2014 clamped top triple trees:

In 2014 HD finally started using 49mm fork tubes and a clamped top triple tree. A much better design that previously manufactured. Too bad there was so many traffic fatalities forcing HD to spend more money providing a safer product to the general public.


This is a much better system but at 16 pounds it is heavy and due to HD ever quest of cutting the costs these steering stems are pressed in the bottom triple tree and not welded. It is much cheaper to ship and assemble that way in place of welding them in. Again much better than the pre-2014 but there could be flexing under extreme conditions some of us ride in. Any time you have a pressed fit there is a problem in keeping the produce in alignment under extreme conditions. I believe that if you obey the current speed limit you will never have a problem but some of us do not.

Top triple tree is clamped around the fork tubes holding them in alignment eliminating the triple trees from tweaking due to side load of the tire such as what happens in a sweeping turn on the interstate running at 80+ MPH and your tire hitting a surface imperfection.

I do all of my own work and investigation into products I make. If you use the search function prior you will read where I welded 2 donuts onto a 41 mm top triple tree and purchased 2.4" (I think) extended forks & rode the FLT to prove the deficiency of the HD fork mounting system. In 2006 I started installing cartridge systems into the new new 49mm Dynas and scraped the idea of using 41mm fork tubes in a FLT. I than started working on a 49mm fork system and top clamp system using the same externally adjustable Compression, Rebound, & spring pre-load cartridge system. I have no need to plagiarize, copy someones work, or steal their ideas.

Use your HDF great search function and you will see my work as it evolved.



This is a complete system that there is no other in existence.

 

You're right. My apologies as I had already read it and did not finish your post. But I do think rather than just saying it came from the Touring Section, give credit to @grbrown for all his diligence.