'85 GL1200 Limited Edition Suspension

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Rednaxs60

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Starting a new topic regarding the suspension upgrade of my '85 Limited Edition.

I have mentioned it in my thread, GL1200 Engine Rebuild - Part 5 - Post Getting to the Road: viewtopic.php?f=24&t=14374

Front suspension: Race Tech front fork springs 1.0 kg/mm, RT emulators - 33.5/26.1/17.0
Rear Suspension: Hagon shocks with remote preload adjuster (RAP) - 30 KG spring, 350 mm damper, piston size 18.3 mm

Have some 400 Kms on the rear shocks and think I'm close in having the rear shocks setup.

Having mentioned the above, intend to check the front/rear sag of the bike. This requires a preload adjustment front/rear. At this time my '85 Limited Edition only has preload adjustment on the rear. The other issue is you need to determine the riding profile to get the best setup; ie solo versus two up, or a percentage of both. I will be adjusting the sag on my '85 Limited Edition for solo riding. Will be able to accommodate two up riding because of the rear preload adjustment.

Preload and sag are not synonymous, but preload affects the ride height of the bike and is a necessary component of setting bike sag.

Have the Race Tech Motorcycle Suspension bible that is a very good read. This book has a sag setup procedure that is probably similar to other sag setup procedures, but it is what I have on hand and so far, I understand it.

The recommended required sag is between 1/3 to 1/4 of the suspension travel. To determine the suspension travel, you take all the weight of the front and rear suspension.

For the front suspension, with all the weight off the front suspension and without a rider, you measure the exposed upper fork tube between the triple tree and where the upper fork joins the lower fork tube. This is the L1 measurement. You then secure the bike in an upright position, and with rider on the bike, push down on the suspension and let rise slowly. Take a measurement as you did with L1, and this is your L2 measurement. Next measurement is to lift the front suspension and let settle slowly. Take a measurement as per L1 and L2, this becomes measurement L3.

With these figures, use the formula L1-((L2+L3)/2) to determine the sag. If it is more than 1/4 of the suspension travel L1, the spring is too soft. Increase the preload to bring the sag into spec range. If the reading is less than 1/3 of the suspension travel, the spring is too stiff, reduce the spring preload to bring the sag into spec range. If you do not have adjustable fork spring preload, you may have to get a fork spring with a stiffer/softer rating. The best solution is to get a front fork suspension setup that has an adjustable preload. There are preload caps that can be purchased and found on Amazon and eBay for a reasonable price - least expensive option.

You repeat the above procedure for the rear of the bike as well. You want to set the sag with the minimum amount of preload on the rear shocks and front fork springs.

The second phase of the suspension setup will be adjusting the rebound function of the front suspension. The installed RT emulators require me to disassemble the front forks, remove the emulators, adjust as required, put back in the front fork(s), reassemble, then road test. Rebound affects ride quality and bike performance, as does compression. Too quick a rebound, not good - riding a bucking horse - too little and loose affective shock travel, and if hitting a plethora of bumps in a row, terrible ride quality and bike performance.

Lots to do and finalize. Will do rear first, then get onto the front. Will be talking to my suspension guru at RMR suspensions and determine if Andriani can provide a set of 41 mm front forks for my '85. 50/50 chance of getting a positive response.

More to follow.
 

Rednaxs60

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I have been going through my posts and threads and find that I have a lot of info scattered all over this forum. I'm going to try and bring all my thoughts and posts into this one thread. These are my thoughts and opinion, and could be out in left field, or not. The main point is that this is how I understand the suspension on my '85 Limited Edition.

My GW has no adjustable front suspension, and the rear suspension started out with the OEM air suspension, but was quickly changed. The OEM rear suspension was primarily designed to provide a plush, soft ride with the ability to raise/lower the rear of the bike to accommodate solo and two-up riding.

To upgrade the suspension on my '85 Limited Edition requires a change out of the OEM suspension with newer, modern parts/pieces.

I have explained in my first post what I have done just recently with the install of Hagon rear shocks, and what I hope to accomplish as I go forward. Before I get to adjusting what suspension install I have, a look back at what I have learned may be beneficial.

I'll start with my understanding of the OEM front fork suspension system.

The front fork OEM suspension system is a damping rod system. This type of suspension system has been around for a long time, and does a reasonable job of providing a good motorcycle suspension. This system has limitations, but most of us are content to accept this system with all the drawbacks and limitations associated with it. This is because it really is good enough for the riding we do on our Goldwings. A lot of us buy a Goldwing new and grow old with it, and with this comes the acceptance along the way of the idiosyncrasies that we encounter.

The flip side to what I have mentioned are the people who want to know the what's, why's and wherefores such as myself. Why can't I have a better handling motorcycle even if it is a Goldwing. Why is it thought that suspension set-up and tuning should be the purview of the sports bike crowd, even though some of these sport bike riders have never fully utilized the suspension setup on their bikes.

What are the buzz words regarding suspension, only three or a variant of the three. Preload, compression and rebound damping. Compression and rebound damping can be high speed or low speed, let's keep these two to the basics of compression and rebound damping.

Let's discuss preload. What is it? Preload is the ability to compress the shock spring to set the ride height for the main riding profile and secondly, to provide some ability to adjust for the ride quality and performance if you do not have compression and/or rebound damping adjustments. The caveat here is that you should not compromise shock performance using the preload adjustment. You need shock travel within a specific range to have a good quality ride and motorcycle performance - more to follow on this.

Compression and rebound damping are next. Of the two, I consider rebound damping more important than compression damping. With the right suspension components, this will not be an issue.

Rebound damping is how fast/slow the shock spring is allowed to return to the set ride height. The faster the return, the more plush, softer the ride. The slower the return the more firm the ride will feel. The caveat with the slower return of the shock spring is that if there are a successive number of bumps or holes, you run the risk of the shock spring becoming compacted with limited travel, and then bottoming out a lot. Conversely, too fast a shock spring return over the same road and you could end up with the pogo stick effect, bucking bronc so to speak.

Compression damping has the same consideration(s). Too fast a compression and the suspension may feel plush and soft, where as two slow a shock spring compression and the ride feels more firm.

The main purpose of the motorcycle suspension is to keep the tires firmly planted on the road, and provide a good quality ride and motorcycle performance.

Two key elements to do this are the size/weight of the shock spring and the spring compression rate, generally in kg/mm.

The size/weight of the shock spring is mainly to achieve the desired ride height front/rear, the "sag", so that the motorcycle orientation is neutral, relatively level for the primary riding profile of motorcycle weight, rider, pillion and luggage. To accomplish this, you want to have a shock spring sized so that minimum preload is used to set the motorcycle sag, using not more than 25 to 30 percent of the travel front/rear. The suspension travel specs for my '85 Limited Edition are approximately 5.5" front, 3.9" rear. This would mean that the sag front should use no more than 1 to 1.5 inches of suspension travel. The rear sag would use approximately 1" of suspension travel. If too much preload is applied to achieve these numbers, think about a stiffer spring. Conversely, too little preload and you cannot achieve the desired sag numbers, consider a softer spring.

Once the motorcycle sag is adjusted and correct, the remainder of the suspension setup is using the spring rate within the capabilities of the suspension installed, and concerning yourself with compression and rebound damping.

On to the next post.
 

Rednaxs60

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Let's start with the front suspension, but first let's remember that it is the suspension system that keeps the tires firmly planted on the road, gives us the ride quality we want and expect, and the motorcycle performance as well.

An additional consideration is what is the riding profile. When you order new suspension parts, you may be questioned as to your riding profile, percentage of solo versus two-up riding, motorcycle weight, rider weight - sometimes with riding gear, other times not, any luggage. If the predominant riding profile is two-up, the pillion weight enters the equation. Suspension component manufacturers have amassed a fair bit of data such that the suspension components you purchase are what you need in order to meet your riding profile.

Onto the front suspension of my '85 Goldwing Limited edition.

The front suspension is known as a damping rod fork suspension. There are no external preload, or compression and rebound damping settings. This is unless the owner/rider has upgraded the suspension.

To make any changes to these three design parameters, you need to change out parts, and/or modify the existing design of some/all of the parts. This generally entails taking the front fork assemblies apart, and off the motorcycle.

For most of us, the OEM suspension setup is more than adequate. If you bought your motorcycle new and have grown older with it, you probably don't notice any degradation in the ride quality and performance because you have learned to compensate for any degradation, the way it is. The same issue happens with a new to you used bike. Unless you know what the ride of the motorcycle was before you purchased it, the motorcycle is doing what it is supposed to.

In my case, as with others, I want to know about suspension setup and what I can do to make my '85 Limited Edition ride quality and motorcycle performance better. I know it's not a sports bike, but there is nothing to say that with a few tweaks here and there, that improvement(s) cannot be made.

I would submit that we think of suspension setup and tuning the purview of the sport motorcycle. I would suggest that a lot of sport bike riders know that the suspension can be tuned, but since not a lot is known about it, these riders are content to ride the motorcycle as bought - good discussion item over coffee.

The OEM front fork design is as shown in this diagram with the names of the various components:
Damper forks.jpg
Preload is accomplished by a preload spacer, or a second, smaller fork spring that before the fork cap is installed protrudes a specific distance out of the upper fork tube. Preload is not affected by the fork oil. The amount of preload is dependent on what fork spring you use and the manufacturer's recommendation for exerting preload on the fork spring. The OEM fork spring is rated at approximately 0.8 kg/mm, and gives that signature plush, soft Goldwing ride.

When adjusting the fork spring preload in a damping rod fork system, you must be cognizant of the top-out spring compression. You do not want to compress the main spring to such an extent that you also compress the top-out spring so the top-out spring becomes a solid item and there is no "spring" available to cushion the upward motion of the upper fork tube on rebound.

The preload adjuster, internal or external allows you to set the bike sag. Most of us are able to adjust the rear shocks with air - should be considered a ride height adjustment only, specifically when additional weight outside the riding profile is added to the motorcycle, or by a manual or remote preload adjuster. This can affect the orientation of the bike with a nose up (chopper pose) or nose down (drag strip pose) posture. What you want to achieve with preload is a neutral, level riding posture throughout the riding profile to maximize the suspension travel. To do this you set the sag of the bike such that you use 25% to 30% of the suspension travel for sag adjustment. The suspension travel numbers that I have found for the 1200 GW are front - 5.5 inches, rear - 3.9 inches. This would indicate that you should use approximately 1.4" of front suspension travel and approximately 1" of rear suspension travel.

I have yet to do the sag numbers for my '85 Limited Edition, have mentioned I shall, but have not to date. I would suggest that the OEM fork spring is too soft. This can be proven, and a fork spring change to a spring rate of 1.1/1.2 kg/mm would be better suited for the task. I suggest these numbers because I upgraded the suspension just after I bought my '85 in 2015. Had Race Tech fork springs 1.0 kg/mm springs installed, and I have managed to bottom these out on several occasions. A stiffer spring rate will aid in having a better front end sag, and could provide a better ride quality and motorcycle performance. There are many YouTube videos available to provide you with the instruction s as to how to determine the sag for your motorcycle, books as well such as Race Tech's Motorcycle Suspension Bible - good read for an understanding of how suspension works and what you can do.

My '85 GW has an air system and air can be pumped into the front forks. Setting the sag should be done with a minimum of preload as possible, and with a minimum of air pressure in the front forks. I know this is not what is done, but this is what I would be aiming for regarding the front suspension sag.

Hope this is helpful, and as I have mentioned, it is my understanding of how my '85 Limited Edition front suspension works. Onto the next post.
 

Rednaxs60

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Discussion for this post is what happens inside the front fork tubes. Knowing this has helped me understand what I want to do to the suspension on my '85 Limited Edition.

To understand what is happening, I had to look at and understand the fork oil flow between the three oil chambers. Let's look at the internals of the front forks:
Damper forks.jpg
You will notice there are three fork oil chambers. Fork oil chamber A is the fork oil reservoir for compression and rebound damping. For compression, fork oil chamber B allows the front forks to absorb road irregularities and such, nothing too drastic, and fork oil chamber C allows the front forks to absorb large size bumps and holes.

Regarding the front fork suspension, it is the fork slider that is attached to the wheel that is moving, not the upper fork tube. I mention this because the two part front fork, upper fork tube and lower fork slider operates much the same as a person skiing. Quiet upper body, quiet upper fork tube. The upper fork tube goes down the road not moving and level. The fork slider on the other hand is very active, much like your legs when skiing. Moving up and down absorbing the terrain irregularities, and at a speed that keeps the skis/wheel in contact with the terrain/road at all times.

A different analogy for the above is that fork oil chamber B is for riding down a highway, or a well maintained road. Small irregularities are absorbed because oil is flowing in and out of fork oil chamber B. This fork oil chamber allows for road irregularities such as tar snake and paving bumps and the likes. Not very exciting action going on.

Fork oil chamber C is for the nasty road issues such as speed bumps, lots of compression needed to absorb these nicely, or the potholes that our cities continue to neglect. Need a lot of front fork action to absorb these, hence a lot of fork oil movement.

What happens? When the front fork spring compresses for whatever reason, the oil is forced out of the lower fork oil cavity "A" into fork oil chamber "B" that is between the upper fork tube and the lower damping rod. The speed at which this chamber fills or empties is dependent on oil flow orifice size and oil viscosity. There is very little pressure differential between these two fork oil chambers, so very little oil flows between these two chambers, but enough to ensure an enjoyable ride.

Since the fork oil chamber "B" is only so big, fork oil chambers "A" and "B" can quickly become a combined fork oil chamber with the same pressure being exerted on both chambers when the size of the road irregularities increase. To control further upward movement of the fork slider, pressure increases in fork oil chamber "A" and fork oil is forced into the centre of the damping rod and up into fork oil chamber "C" through holes in the damping rod that are sized to give a specific fork oil flow rate based on the size of the holes and the oil viscosity. The design of the damping rod and the fork oil viscosity resists the compression of the fork spring. Change the oil viscosity, you change the compression stroke - fast/slow. Change the size and number of holes, you change the compression stroke - fast/slow.

Front fork rebound is much simpler to envisage. This is the return of the fork spring to the set ride height by return of the fork oil to the reservoir, fork oil chamber "A". How fast or slow this happens is, again, dependent on the size of the orifices, holes in the damping rod, fork oil viscosity, and the fork spring rate. The spring rate assists in oil flow because as the fork spring returns to the set ride height, a vacuum is developed in fork oil chamber "A". Fork oil chamber "A" increases in size, and the volume difference between the compressed volume and the ride height volume needs to be replenished, otherwise the front fork would collapse. Makes sense to me.

There is a lot going on regarding the front suspension with the simplistic, but quite effective front fork design. If this design is not up to your standard(s), what can be done to improve the front suspension?

The first item on my list would be to renew the front fork springs and fork components. I recommend this because an investment of $100.00 for a set of new OEM equivalent springs, go for the higher spring rates of 1.1/1.2 kg/mm - same cost, with the recommended manufacturers preload setting and oil viscosity should make immediately improve the ride quality and performance.

I would not get too involved in determining whether the front fork springs should be a straight rate, or progressive rate spring. Most of us will not be able to feel the difference between the two. Let your budget and the higher spring rates be the deciding factors.

If the spring is a straight rate spring and the spring rate is 10 kg/mm for example, this spring rate applies throughout the travel of the spring. 10 kgs to compress the spring 1 mm.

If the spring is a progressive rate spring and the spring rate is 10 kg/mm, the spring rate as I understand it is generally the most firm rate of the spring. My understanding of a progressive rate spring is that initial compression is soft, then progresses to medium soft, then medium, them medium hard, then hard, and returns the same way. Something like buying a pillow.

This should result in an immediate new and better front suspension feel.

Have to eventually get to this point, determine what the front suspension sag is. In or out of spec using the 25 to 30 percent of suspension travel rule.

If the front suspension sag is within the 25 to 30 percent rule, good start. If the suspension sag is more than 30 percent, you can try a different preload spacer, increasing the length of preload spacer in 2-3 mm increments. I would recommend only doing this twice, after which you should look into replacing the fork spring size. Fork spring size is generally rated in lbs, noting that spring rate does not affect suspension sag.

If the front suspension sag is less than 25 percent, shortening the preload spacer can be done. This should be done in small increments as well, but you have more flexibility in that you want the preload set to the minimum necessary to achieve the required suspension sag. In this case you can do more preload spacer changes to meet the requirement.

You could try installing an aftermarket preload fork cap. An inexpensive option that allows you to adjust the preload without taking the front forks apart.

Last on the list is changing the oil viscosity. This is primarily for rebound damping. The thicker the fork oil, the slower it flows, the slower the rebound damping, the slower the fork spring returns to the set ride height, the more firm the feel of the front suspension. The thinner the fork oil, the faster the the fork oil flows, the faster the rebound damping, the faster the fork spring returns to the set ride height, the more plush, softer the ride.

All of the above is just my understanding and opinion. Suspension is not a black art, but takes a while to understand and for you to come up with a game plan.
 
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