Progressive Fork Springs

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Dec 3, 2009
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Kingsport, Tennessee
My Bike Models
Former '82 GL1100 "The Slug"
I know there is a lot of talk about the differences between the OEM fork springs and Progressive fork springs. On my '82, I thought I had OEM springs and last spring, I went and purchased new Progressive springs. Turns out, the '82 already had Progressive springs. My point? I had nothing to compare to. I went ahead and installed them anyway and they did not make any noticeable difference. I kept them installed and put the old set on the shelf.

Fast forward to today. I took the '81 standard for a good shakedown trip today and it has the OEM springs. They seemed a bit soft and can bottom out on large bumps. Today, we swapped out the springs and installed the Progressive fork springs and it made a world of difference! :yahoo:

I have to say, it is really different. I added 12 lbs of air and that was too much. Dropped to 7 lbs and still too much. Let all of the air out and it is perfect! The springs really cushion nicely but provide a good firm ride otherwise. In my opinion, this is a fantastic upgrade and should be considered for the price! ... DQodI28NGg
One of the issues I've noticed with older bikes and even newer ones is that there is an industry that has developed to address handling issues that are directly related to weak/soft suspension.

When I bought my '08 1800, I researched the internet to determine what were the pitfalls if any. Two issues were foremost in a lot of the comments. Weak/soft suspension and tires did not last. I had the Traxion "full monty" suspension installed on the 1800 and it made a significant difference in ride quality and handling.

When I bought my '85 LTD I did the same. I had the suspension upgraded with Race Tech front fork springs and Gold valves (emulators), and progressive 412 shocks in the rear. Significant difference as well.

Suspension on a bike is the same as a car, designed to keep tires on the road, and provide good handling and ride quality. If a person is searching for a way to improve suspension performance with add-ons, IMO not the way to do it. Upgrade with aftermarket suspension or renew with OEM suspension, then look at other issues if necessary.

Just my thoughts on this.

So in your opinion Ernest just changing the front fork springs on the GL11000s to Progressives is not actually enough to improve the front suspension?
[url= said:
Ansimp » Today, 12:36 am[/url]":1a1xbego]
So in your opinion Ernest just changing the front fork springs on the GL11000s to Progressives is not actually enough to improve the front suspension?

Not exactly. What I am saying is, in my opinion, that a suspension system wears out over time and needs to be renewed/upgraded at some point. Changing to Progressive, Race Tech or a suitable alternative will improve the front suspension. This will improve the ride quality, performance and personal safety, and hopefully return the suspension to as close to original as possible. No amount of aftermarket add-ons will or can compensate for a worn out suspension - doing this is addressing the symptoms and not the issue.

Once this is done, if there are other issues, you can address these from a different viewpoint. Point in case regarding springs. Here is a picture of the prop shaft main spring, new and 32 years old:
Drive shaft spring.jpg
Not a lot of difference, just over 1/8 inch, but enough to affect the performance of the prop shaft. Springs are innocuous little items that can be easily overlooked. Even if springs are within spec for length - measured without the benefit of bike load, the spring properties diminish over time, ergo become "soft".

Another case in point is the cars my partner and I drive. We have the KIA Soul, hers a 2016, mine a 2011. The suspension of the 2016 KIA is tight and feels solid whereas the 2011 KIA is a bit more loose and not as solid (my KIA has 98,000 Kms).

This is not to say that some bikes have inherent quirks that are annoying and that people will want to address these issues to get rid of them. My '85 has some quirks that I only notice when I practice slow speed maneuvers such as a figure 8, or u-turns, but since 99% of my riding is not doing this, I'm not concerned.

I also understand why the suspension system is not addressed as necessary, cost, ability to do the work, parts availability, tools, and such. When I got my '85, I had a shop do the work - cost was an ouch but the results were excellent. After 16 months of doing my own work and tackling issues I may never have done previously, I would not hesitate to source the parts and do the work myself. It's a learning curve that I had to go through to understand that I was more than capable of doing the work. If this bike had been an older model car like the 1965 Plymouth Fury I owned, I would not have hesitated to do the work myself.

Having stated the above, I believe that any suspension spring upgrade will improve the performance of the front suspension, bring it back closer to original. If a person is having issues with the front end, renew/upgrade the front fork suspension first then look at other issues.

Short answer is that replacing the original springs with new will improve the front suspension, and enhance the performance and ride quality after which you can test the various weights of oil to fine tune the front suspension. Long answer above.

Just my thoughts and humble opinion.

Just a note.... I replaced the OEM front springs on mine after 15k miles, due lack of 'performance', ie I wanted something sportier. Installed the Progressive springs and increased the weight of the oil, end result much improved. Not to say that I couldn't have more performance with another set up, I wouldn't know unless I tried, just as Ernest stated.
I agree with the points made. Even if our bikes are not on the road, the front fork springs always have a load on them. After 35+ years of sitting and or riding, these springs get a work out. It is a simple upgrade that I believe provides great results.
Red made some excellent points, I obviously wasn't able to compare my OEM springs with new, but the progressive springs made a very big difference in the handling, I also un 0 pounds of air in the front, but 45 in the rear. I primarily ride in the Sierra foothills with lots of interesting roads, the handling improvement was well worth the expense.
Resurrecting an older thread, a lot of time has passed and knowledge of suspension has progressed. This post is for the front suspension only. To address the rear suspension would take an equally long dissertation.

Ansimp asked the question regarding changing out front fork springs. Renewing front fork springs after some 30 plus years with fork springs that are identical to the OEM fork springs will make a difference in the ride of the bike. Any time you renew a part with new there has to be a benefit, some you notice some you don't. The OEM fork springs are probably too soft from a performance perspective, but this does not diminish the benefit of replacing with new.

If you are adding a lot of air to keep maintain the ride close to that of new, good indication that you need to look into new fork springs. You can get straight rate or progressive springs in the same spring rate. Most of us would not notice the difference between the two, so go for the most economical. The OEM springs probably have a 0.8 to 1.0 kg/mm spring rate. A little soft for the GW, so look at a spring rate of 1.1/1.2 Kg/mm - will reduce the amount of air you put in the front forks.

Most GWs do not have a front fork preload adjuster. These can be bought as an aftermarket add-on. I replaced the fork springs on my '85 Limited Edition with Race Tech (RT) 1.0 kg/mm springs. The preload spacer was proud of the upper fork tube by 1" to give the standard GW/manufacturer preload. I also had the RT emulator valves installed.

The preload adjuster will allow you to set the bike sag. Most of us are able to adjust the rear shocks with air or otherwise, and as such 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.

The next issue with our GWs is how the ride feels for our riding conditions. The RT emulator valves control compression damping to absorb bumps and control dive on braking. You set thee spring tension on this valve to control the fork oil flow past it. The more fork oil flow, the faster the compression, the more plush, softer the ride. The slower the oil flow, the firmer the feel and ride. Rebound damping with this system is controlled by the oil flow back into the lower cavity, primarily by changing the fork oil viscosity.

Standard compression damping on a set of damping rod forks is done using three oil chambers, the size and quantity of holes in the lower damping rod, and the oil viscosity.

There are three oil chambers in a standard damping fork configuration. Upper chamber where the fork spring is, the lower chamber where the oil is, and the chamber that is between the damping rod and upper fork tube.

When the front fork spring compresses for whatever reason, the oil is forced out of the lower fork cavity into the cavity that is between the upper fork tube and the lower damping rod. The speed at which this cavity fills or empties is dependent on oil flow orifice size and oil viscosity. Since this cavity is only so big, to control further downward movement of the upper fork tube, the upper fork tube forces the fork oil into the centre of the damping rod through holes in the damping rod that are sized to give a specific flow rate of oil at a specific oil viscosity. 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.

The chamber that is created between the upper fork tube and damping rod must be primarily for normal street riding to take up small street imperfections. Fork oil flows in/out of this cavity on a regular basis to give you a nice ride. There is a top out spring in this cavity. Changing out this top out spring could affect the normal riding rebound of the fork spring, but I would think this would be a lot of work for little payback.

When you start to encounter more severe bumps or holes, the oil chamber created between the upper fork tube and the damping rod the oil flow from the lower oil chamber out to the upper fork spring chamber comes into play. The faster the fork oil can be displaced out of the lower chamber, the better the absorption of the bump/hole, the less jarring you will experience, the more plush the ride. The slower the oil flow, the firmer the feel, the more you feel the bump/hole, and the firmer more harsh the ride.

Rebound damping is the opposite. How fast or slow the fork spring returns to the original ride height by the fork oil returning to the lower oil cavity helps in determining the ride quality. The faster the fork spring returns to the original ride height, the more plush, softer the ride will feel. The slower the fork spring returns to the original ride height, the firmer, more harsh the ride will feel. In a damping rod fork configuration, oil viscosity and number/size of holes in the damping rod are the primary controlling elements.

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.

There are many ways to address the suspension issue. First and foremost, don't think about it, go out and ride and enjoy. Unfortunately, I cannot do this, mostly because I want to know, and then make changes/adjustments - keeps the creative juices flowing so to speak.

Next on the list would be a renewal of what the OEM installed. Freshens up the suspension, should improve the ride quality and performance. Mid life crisis averted.

Now we get to the expensive version(s). Suspension upgrades are generally not inexpensive because it is specialized field, and the market for this is not as robust as that for an automobile, supply and demand comes into play.

Change the front fork spring spring rate, go up to a 1.1/1.2 kg/mm spring rate - can be a progressive spring rate or straight spring rate. Don't believe we are that sensitive to the fork spring rate that we would notice. The fork springs in my '85 Limited Edition have a spring rate of 1.0 kg/mm and are to soft for the application, I have bottomed these out several times. Inexpensive and can be done at the next front fork servicing. Install aftermarket preload adjusters. Two items that will enhance the ride of your GW.

Install emulator valves, knowing that these are for compression damping, not rebound damping. May have to modify the damping rod to suit the install. For the RT emulator valves, the damping rod original holes had to be enlarged and an extra 2 holes drilled for the appropriate oil flow.

Don't forget to address the TRAC braking system when doing an upgrade.

Changing the front fork springs, installing emulator valves, trialing and using different oil viscosities is time consuming work. Need to dismantle the front forks to some extent to adjust the performance of the front forks each time you want ot do a change.

The best is a set of fork cartridges that have externally set preload, and rebound compression damping settings. The best is where each fork has a preload, rebound/compression setting. Second best is where each fork has a preload setting, and one fork controls rebound, the other fork controls compression.

I've probably missed some issues, and could be out in left field, but this is my understanding of the GW front forks. If you have read this far, thank you, if not don't blame you. Cheers
Good explanation Ernest! I can only add this; the Progressive fork springs are already wound tighter than the OEM fork springs for the 1100. Automatic preload! :smilie_happy: