Suspension Adjustability -ES vs A

[Bill Lumberg]

From softest to firmest, is the overall range of suspension adjustment the same between ES and A models? I know one is incrementally adjustable from the dash, and the other is manually adjusted, but from soft for solo to 2 up with gear, is my top and bottom end the same on a '14 or '15 bike?

 

[Fred W]

No. Not the same at all. Apples and Oranges, I'd say

Front fork on the 3rd Gen A models has a dual rate spring with variable preload. 1st stage (first 67.5mm of travel) is .85 kg/mm and second stage is 1.02kg/mm. Springs are compressed 11.7mm when installed and the preload is adjustable by 15mm.

Front fork of the ES models has a single rate spring of 2.04 kg/mm in an upside down configuration, no variability of the preload only damping. (Because the FSM shows springs in both sides, I have to assume that the 2.04 is for the total of the two springs otherwise that would be far too stiff.) Springs are compressed 10mm when installed.

A models have a 2 stage rear spring but the spring rate specs are screwed up in the manual. It says the 1st stage is 976 lb/in and the second stage is 1952 lb/in and when you lock out the 1st stage (with the hard position lever) the force goes to 976lb/in. That has to be wrong. I would say that the second stage is 976, (which is pretty darned stiff) and the first stage is something less than 976.

ES models say the single rate rear rear spring is 685 lb/in, but of course you have the ability to vary the preload and the damping.

 

[Bill Lumberg]

Thanks Fred.

 

[MCRIDER007]

No. Not the same at all. Apples and Oranges, I'd say

Front fork on the 3rd Gen A models has a dual rate spring with variable preload. 1st stage (first 67.5mm of travel) is .85 kg/mm and second stage is 1.02kg/mm. Springs are compressed 11.7mm when installed and the preload is adjustable by 15mm.

Front fork of the ES models has a single rate spring of 2.04 kg/mm in an upside down configuration, no variability of the preload only damping. (Because the FSM shows springs in both sides, I have to assume that the 2.04 is for the total of the two springs otherwise that would be far too stiff.) Springs are compressed 10mm when installed.

A models have a 2 stage rear spring but the spring rate specs are screwed up in the manual. It says the 1st stage is 976 lb/in and the second stage is 1952 lb/in and when you lock out the 1st stage (with the hard position lever) the force goes to 976lb/in. That has to be wrong. I would say that the second stage is 976, (which is pretty darned stiff) and the first stage is something less than 976.

ES models say the single rate rear rear spring is 685 lb/in, but of course you have the ability to vary the preload and the damping.

I think if one were to remove the springs and actually test them the results may be significantly different than what is in the FSM. My experience to date is that the front fork rates between the A and the ES seem to be the same. Are they single or dual rate....they feel like single rate but it will be easy to see once they are removed. I don't know what the "compressed when installed" actually means, I haven't had to compress the main spring on any cartridge fork I have ever changed the oil on....damper rod forks usually do require main spring compression to re-install the caps. The damping adjustment designs on the A and ES are quite different but seem to give the same overall results. I would expect that if the forks were put on a shock dyno they would have very similar damping curves.

I wish someone would measure the shock springs and find out what they really are. The A shock has two springs in series but even if the FSM is correct on the individual spring rates, the standard calculation for springs in series doesn't work because each of the springs has its own base installed preload. My best estimates, comparing a 800 lb spring on my 08, measuring sag, and adjusting the sag numbers to compensate for claimed base preload, is that the "soft" setting has about a 780 lb effective rate and the "hard" setting is about a 950 lb rate.

Comparing the A spring rates to the ES single spring rates gave some strange results that "did not compute" at all to the FSM claimed ES 675 lb spring rate. I can say that the A model on the hard setting had the same sag as the ES model (on the 2up with luggage preload) with a 365lb load....which was achieved by about 22mm of preload on the ES vs 12mm of preload on the A model. As the load increased the ES sag increased about 20 precent faster than the A sag. After doing further sag comparisons between the ES and my 800 lb spring on my 08, it appears the ES spring rate is also around 800 lbs. I don't have any test data on the range of relative damping between the A and ES shock but both most seem to work the best with the damping in the middle of their respective ranges.

 

[Fred W]

I don't know what the "compressed when installed" actually means, I haven't had to compress the main spring on any cartridge fork I have ever changed the oil on....damper rod forks usually do require main spring compression to re-install the caps.

"Compressed when installed" is the difference between the free spring length and the installed spring length. I'm not sure what you are talking about. I have never not had to compress a fork spring (cartridge or damper rod) when installing the spring. Every fork I've ever touched you need to push the spring down (a little) while threading the locknut down on the top of the spring spacer. There is definitely some coil preload there.

If the FSM is correct about the fork spring rates then the "A" fork should be slightly softer for the first little bit until what's left of the soft rate gets coil bound. The stiffer rate is essentially the same as the single rate spring in the ES. Most of whatever spring preload is applied would be taken up by the softer spring section.

But I am certain they borked up the specs on the A shock springs. There is no way the spring is 1952 lb/in. That would feel like a hard tail when on the "hard" position. And then they screwed it up and gave the softer (976) spring rate as what remains when you put the lever to hard. I think whoever compiled the data for the specs section just goofed.

 

[MCRIDER007]

I don't know what the "compressed when installed" actually means, I haven't had to compress the main spring on any cartridge fork I have ever changed the oil on....damper rod forks usually do require main spring compression to re-install the caps.

"Compressed when installed" is the difference between the free spring length and the installed spring length. I'm not sure what you are talking about. I have never not had to compress a fork spring (cartridge or damper rod) when installing the spring. Every fork I've ever touched you need to push the spring down (a little) while threading the locknut down on the top of the spring spacer. There is definitely some coil preload there.

If the FSM is correct about the fork spring rates then the "A" fork should be slightly softer for the first little bit until what's left of the soft rate gets coil bound. The stiffer rate is essentially the same as the single rate spring in the ES. Most of whatever spring preload is applied would be taken up by the softer spring section.

But I am certain they borked up the specs on the A shock springs. There is no way the spring is 1952 lb/in. That would feel like a hard tail when on the "hard" position. And then they screwed it up and gave the softer (976) spring rate as what remains when you put the lever to hard. I think whoever compiled the data for the specs section just goofed.

I know what "compressed when installed" means, I also know that if anything needs to be compressed to get the fork cap on then it is going to be the lighter of either the main spring or the top out spring....and the top out spring is usually the one that gives. The next time I have the forks off I'm going to measure the distance between the top of the spacer and the top of the fork tube and see how much the springs have to compress to get the cap on.

I think the FSM is correct about the individual spring rates. Both springs are used in series in the "soft" position, only the lower spring in the "hard" position. The upper spring is the 1952 lb spring, it only has about 1.5 coils and the gap between the coils is huge. The formula for measuring the weight of springs in series is A*B/A+B which in this case computes to 651 lbs. However, that formula isn't accurate if the springs are preloaded and it appears from the FSM that each spring is preloaded. As I recall, when Traxxion measured the GEN1 shock springs, they found that the actual spring rate in the soft position was higher than calculated rate.

 

[Fred W]

I know what "compressed when installed" means,

OK, you (just previously) said that you didn't know what I meant.

I also know that if anything needs to be compressed to get the fork cap on then it is going to be the lighter of either the main spring or the top out spring....and the top out spring is usually the one that gives. The next time I have the forks off I'm going to measure the distance between the top of the spacer and the top of the fork tube and see how much the springs have to compress to get the cap on.

I've heard you mention this idea before about the top out spring being weaker than the fork spring, but always just let it go. The top out spring is only in compression when the fork leg is topped out, which only occurs when the bike is unweighted. Even when the bike is just sitting there under its own weight the main spring is somewhat compressed and the fork is not topped out. So increasing the preload adjustment at that point most certainly increases the compression entirely on the main spring (not the top out spring). The only time the the top out spring would be more compressed by increased preload would be when the bike it completely unweighted.

So that thing that you screw into the top of the fork most certainly increases the preload under the practical conditions of having the bike sit on the suspension. What it does on the center stand is insignificant except to the folks measuring sag numbers.

Don't forget that the spring needs to be compressed some (just a little) to get the lock-nut and cap threaded onto the cartridge's damper rod. Then when you are threading the cap into the upper fork tube you also have to compress it a little more, just to get it started. Then, the distance of the threads of the cap compresses it even more. Yes, these compressions may be occurring on the top out spring, but once you put the weight of the bike on the fork all the weight and distances will be on the main fork spring.

 

[MCRIDER007]

I've heard you mention this idea before about the top out spring being weaker than the fork spring, but always just let it go. The top out spring is only in compression when the fork leg is topped out, which only occurs when the bike is unweighted. Even when the bike is just sitting there under its own weight the main spring is somewhat compressed and the fork is not topped out. So increasing the preload adjustment at that point most certainly increases the compression entirely on the main spring (not the top out spring). The only time the the top out spring would be more compressed by increased preload would be when the bike it completely unweighted.
So that thing that you screw into the top of the fork most certainly increases the preload under the practical conditions of having the bike sit on the suspension. What it does on the center stand is insignificant except to the folks measuring sag numbers.

You need to re-think this entire issue. First of all, the adjuster at the top of the caps is a ride height adjuster rather than a preload adjuster because it doesn't begin to compress the main spring until the resistance of the top out spring is greater than the resistance of the main spring. If you were only compressing the main spring then the length of the entire fork would stay constant....which it doesn't. If you measure sag on a weighted spring and then change the preload, the sag (spring compression) appears to change on a 1 to 1 ratio but what is really happening is that the adjuster has also changed the length of the fork. Its difficult to see and measure on conventional forks when they are on the bike but very easy to see and measure on inverted forks. The ratio of the fork length change to the adjuster change on unweighted forks is determined by the ratio of the resistance of main spring to the top out springs.

Jeff Ashe enlightened me on this issue when he stated that the FJR preload adjuster looked like it was changing the preload but wasn't....and I could not figure out what he was talking about until I put ZX-14 forks on my C14 a couple of years ago and could easily observe and measure what actually happened when the adjusters were used. The ZX-14 forks have very long top out springs that are also pretty soft. If you change the adjuster by 15mm, it compresses the top out springs 15mm, does zero to the main spring, but the fork becomes 15mm longer. Sag doesn't change at all but since the fork is 15mm longer the ride height and steering geometry does. The C14 forks have much stiffer top out springs, they are half the rate of the main spring so a 3mm adjuster change results in the top out springs compressing 2mm and the main spring compressing 1mm. The length of the fork changes by 2mm rather than 3mm.

The FMS page 2-11 that I have (for the 13A) states the fork spring free length is 345mm and the installed length is 322.8mm, a difference of 22.2mm....that is a whole lot of compression. You may be right about having to slightly compress the main spring to get the lock nut on the damper rod but any additional required compression to screw in the cap would probably be on the top out springs, and it would be a minimal amount and not nearly as much as the FSM states.

For those reading this and completely scratching their heads, preload means compressing the main spring and shocks are much different than forks. Shocks do not have top out springs but do have a fixed length and the spring is in a confined space. All modern cartridge forks have top out springs, usually external to the cartridge on conventional forks and internal (inside the cartridge) on inverted forks. When cartridge forks are reassembled and you pull up on the fork tubes, the fork tubes feel like they are fully extended but are actually bumping up against the bottom of the top out springs. When there isn't any weight on the forks and you turn the cap adjusters clockwise you are applying a force downward on the main spring but an equal force upward on the top out spring. If the top out spring has less resistance than the main spring then it will compress and the fork length will increase. On a weighted fork the top out spring may be as Fred said "out of play" but the fork still has the ability to lengthen if the cap adjusters are extended. The main spring is not going to compress further due to pressure from the cap adjuster until it is in a confined space....and that will not happen as long as the fork has not fully compressed the top out spring and can increase in length.

Back to the original question of whether its necessary to compress the main spring to put the forks together, I have always been able to easily start the cap threads by hand and it appeared that there wasn't any spring resistance to seat the cap but maybe there is some spring compression at the end of the process. If so, I think it is much less than what is shown in the FSM.

 

[Fred W]

No, I'm sure that I fully understand what's going on here.

First off, spring preload is synonymous with ride height. That is all that spring preload does on any fork. It doesn't make the spring any stiffer. It just alters the height that the fork will sit at (dynamically) within the fork's stroke, for a given weight load. Once the fork has weight on it it is no where near that top out spring, so the only thing the adjuster will have done is push down on the main fork spring more (or less).

The fact that the fork elongates under no weight due to the compressing top-out spring does cause issues for measuring your sag values because (as you mentioned) the fork's unweighted length will increase. So attempting to use the standard sag recommendations will not work out right. You'd want your measured dynamic sag to be larger than the standard 1/3 of stroke to compensate for the top out spring. But it is still raising the ride height, which is what you want when you up the preload.

I think if we had some alternate means to measure the sag without using the fully extended fork as the reference it would make more sense since all we are trying to do is set the correct ride height.

As for the spring being compressed during assembly, I recall putting a little compression on to get the spring on the cartridge, and a little more just to start the cap into upper tube, and then the number of threads of the cap is probably at least 10mm or so... Would have to add it all up next time I'm in there.

 

[MCRIDER007]

As for the spring being compressed during assembly, I recall putting a little compression on to get the spring on the cartridge, and a little more just to start the cap into upper tube, and then the number of threads of the cap is probably at least 10mm or so... Would have to add it all up next time I'm in there.

I plan to do the same. I thought that getting the lock nut on the damper rod was a matter of lifting the damper rod rather than compressing the spring. Once the lock nut is on the damper rod, the cap screws on the damper rod without any additional lifting or compression, and the fork tube easily meets the cap threads without any additional spring compression. I would think that any required spring compression to fully screw in the cap would be absorbed by the top out springs but I am going to take some measurements the next time and see what is really happening.

Another thought, at least as far as the FJR is concerned, is that we have been working with different spring lengths and/or spacers. Aftermarket springs are rarely the same length as the OEM springs and if the spacer length is not adjusted accordingly then compressing the main spring may be required to put everything back together....and I can't remember my experience the last time I put a OEM FJR fork back together.

Inverted forks are quite different and compression of the main spring is absolutely necessary both to take it apart and put it back together since the spacer blocks easy access to the damper rod lock nut and when you try to lift the damper rod you are fighting the internal top out springs. I think you would have to actually measure the main spring after the cap is screwed on to determine the installed length.