Suspension Tuning - It's a Process!

[MCRIDER007]

Well, yeah. It does add to the confusion, but maybe not in a way you are expecting. The lever is not a preload (ride height) adjustment.
It actually mechanically locks out the softer stage 1 spring, which means that the stiffer stage 2 sporing is in force for the entire stroke of the shock, so in that case the lever actually does change the initial spring rate from soft to a harder spring. I say initial since after XX mm of shock travel (where the soft spring would be coil bound) the rate is then the same.

I see that MCRider beat me to the punchline with fewer words.

While your explanation of how the system works is correct, the devil is in the details. The OEM shock's upper spring, which is locked out in the hard setting, is not a soft spring. Its actually a 1.5 coil spring that is in the 1800-2000 lb. range and as such will never be coil bound. Sounds crazy that the "upper soft spring" is actually much the stiffer spring but that's how springs work when they are stacked in series. If the FJR's shock has a 2000 lb spring on top and a 800 lb spring on the bottom, the soft setting will have a rating of 577.42 lbs and the hard setting will have a rating of 800 lbs. The formula for springs in a series is (a*b)/a+b.

 

[redneckj]

George rebuilt my Penske and it works great.

 

[Fred W]

Well, yeah. It does add to the confusion, but maybe not in a way you are expecting. The lever is not a preload (ride height) adjustment.
It actually mechanically locks out the softer stage 1 spring, which means that the stiffer stage 2 sporing is in force for the entire stroke of the shock, so in that case the lever actually does change the initial spring rate from soft to a harder spring. I say initial since after XX mm of shock travel (where the soft spring would be coil bound) the rate is then the same.

I see that MCRider beat me to the punchline with fewer words.

While your explanation of how the system works is correct, the devil is in the details. The OEM shock's upper spring, which is locked out in the hard setting, is not a soft spring. Its actually a 1.5 coil spring that is in the 1800-2000 lb. range and as such will never be coil bound. Sounds crazy that the "upper soft spring" is actually much the stiffer spring but that's how springs work when they are stacked in series. If the FJR's shock has a 2000 lb spring on top and a 800 lb spring on the bottom, the soft setting will have a rating of 577.42 lbs and the hard setting will have a rating of 800 lbs. The formula for springs in a series is (a*b)/a+b.

Thanks for the correction. Based on that the shock in the "soft" position would be a constant spring rate of 577 lbs/inch for its entire stroke. I was under the impression that the smaller spring would coil bind because the manufacturer specs out the spring rates as two different rates for roughly half the total stroke each. Not sure how you would get the progressive spring rates unless one of the two became coil bound.

 

[MCRIDER007]

Thanks for the correction. Based on that the shock in the "soft" position would be a constant spring rate of 577 lbs/inch for its entire stroke. I was under the impression that the smaller spring would coil bind because the manufacturer specs out the spring rates as two different rates for roughly half the total stroke each. Not sure how you would get the progressive spring rates unless one of the two became coil bound.

That's a good question since the top spring is not going to become coil bound and its unlikely the bottom spring will either since it appears to have about 6 evenly placed coils. Is it possible the FSM is wrong?

 

[someguy]

wow. learning a ton here....

 

[Fred W]

Thanks for the correction. Based on that the shock in the "soft" position would be a constant spring rate of 577 lbs/inch for its entire stroke. I was under the impression that the smaller spring would coil bind because the manufacturer specs out the spring rates as two different rates for roughly half the total stroke each. Not sure how you would get the progressive spring rates unless one of the two became coil bound.

That's a good question since the top spring is not going to become coil bound and its unlikely the bottom spring will either since it appears to have about 6 evenly placed coils. Is it possible the FSM is wrong?

Thinking about this further, it would make sense that the engineers would design it the way you said, so that in the soft position the spring is soft throughout the entire stroke, and in the hard position it is harder throughout the full stroke.
And as I said earlier, that is a very elegant solution to the requirement of needing a stiffer spring when two up loaded, which any shock that only adjusts preload, either manually or remotely, cannot give you.

If only we could select those two spring rates for our own body weights, and also switch damping rates when we switch spring rates, the stock shock might actually be superior to the aftermarket ones.

 

[bigjohnsd]

Fred W makes a point above:

"Using a heavier 10W suspension oil in your forks will not improve your range of adjustment unless you were previously unable to achieve adequate damping when you cranked the adjusters down to full closed (CW). I've never heard of that being an issue with the thinner stock oil. OTOH, by increasing the viscosity of the oil you will be increasing the damping through the non-adjustable "fast response" circuits of the fork cartridge's valves, which will be detrimental to the fork's ability to follow road contours."

Not being a Fluids Engineer, but knowing that there are some here on the Forum, my question is, for a given orfce size, what is the difference in the ability of 5W and 10W fork oil to flow through the orfice athe a given pressure?

My butt dynamic likes the way the Gray Ghost works after the change to the 10W Fork oil, I guess I'm interested in the "Why" and "How" now. Thanks for all of the inputs. I have found trying get to get this dialed in is just as difficult if not more difficult than it was tuning the suspension on my Winged Sprint Car 15 years ago and we were shooting at a moving target, the constantly changing track, then.

 

[Fred W]

As in most things... it depends.

It depends on which 10W oil you used, because they are not all the same viscosity. The Yamaha 01 suspension oil is a known quantity, with a viscosity of 14.57 cSt at 40C. You would want to compare the cold viscosity on fork oil as forks (unlike the rear shock) really does not heat up much past 40C.

Suspension Oils from this representative chart claiming to be "10W", run the gamut from 15 cSt (for Castrol 10W) to 47 cSt (for Silkolene Pro RSF) The actual viscosity will have a lot more to do with how the oil performs dynamically than what is printed on the bottle.

 

[MCRIDER007]

As in most things... it depends.
It depends on which 10W oil you used, because they are not all the same viscosity. The Yamaha 01 suspension oil is a known quantity, with a viscosity of 14.57 cSt at 40C. You would want to compare the cold viscosity on fork oil as forks (unlike the rear shock) really does not heat up much past 40C.

Suspension Oils from https://www.peterverdone.com/archive/files/suspension%20oils.pdf]this representative chart[/url] claiming to be "10W", run the gamut from 15 cSt (for Castrol 10W) to 47 cSt (for Silkolene Pro RSF) The actual viscosity will have a lot more to do with how the oil performs dynamically than what is printed on the bottle.

Agree....but to further answer the question...if the viscosity of fluid A is actually twice that of Fluid B, Fluid A is only going to flow half as much oil as Fluid B if everything else is the same. Most suspension tuners make their money at the track and seem to recommend higher viscosity oil than the designers recommend but I think that is because they have found that higher viscosities are needed to compensate for the higher oil temperatures that are generated in a track environment....and they measure success by lower track times rather than plush rides.

 

[Fred W]

The other part that has far too many variables to answer is: if the viscosity is double, and it flows half as much oil for a given input impact, what does that translate to in measureable or palpable terms.

Answer is that, because it is unmeasurable, and because each hydraulic system is systemically different, the question cannot be succinctly answered. It's a big part of the reason that suspensions and their tuning remains voodoo, and that self proclaimed experts are hard to challenge on their claims.

Which is why understanding what you hope to achieve, and how the variables impact those results, and iteratively changing a tweaking the variables to achieve the results that you feel is your only chance of getting better results than just poke-and-hope (counting clicks) or trusting the aforementioned "experts".

 

[Pterodactyl]

Dave Moss Grey Ghost Suspension Baseline Settings:
Front:

Preload 1 1/2 lines showing which was 1 1/2 lines softer than when I arrived

10 WT Maxima Green Fork Oil!!!

Compression 12 clicks out

Rebound 5 clicks out

Notes: Over the various runs he had me make he noted that I also liked the bike with six more turns of preload in the front. He wanted me to ride it with the softer front to aide in steering. If i didn't like it he told me to add three turns of preload and add one click of rebound, that would put me in the middle of the range I liked.

Rear:

Stock Shock - 36,000 miles - no maintenance done on it.

Spring on Firm - which he said was "Race hard"

He has the rear at 3 clicks out, I came in with 5 or 6 clicks out and the rear spring on Firm.

During the testing and adjustment, I was fully loaded for touring, Front tire at 39# rear tire at 42#, both Panniers were full and the Top Box was on and had a load in it, mostly light clothing. gloves etc.

While we were talking we discussed the very slight cupping on the front tire. Dave said it was suspension related, not tire pressure related. I meant to ask him if the front adjustment had cured the cupping cause but forgot to. I have asked him and am awaiting an answer. I'll add that to this post with an edit when I receive his answer.

Finally got around to comparing my suspension settings to those provided to John by Dave Moss. John and I both ride 2013 bikes and are of the same muscular build. Yes, I know there many variables that cannot be accounted for and that this is like tuning a violin by counting the number of turns on the strings. All that being acknowledged, my comparison of how I have the suspension set to Moss' recomendation to John reveals that I am a suspension tuning savant. All my settings are pretty close to Moss' recommendations and I'm running 10 weight oil. Hey, it's been a long winter.

 

[MBevans]

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Wow, very pleased with all the inputs here, very focussed. Nice!

Fantastic food for thought, and this is one of my first things I will do on my upcoming new (to me) FJR1300A, Gen III.

As I've used Ohlins, Penske, RaceTech and many independent suspension tuners over the years to make my bikes really work in the suspension department...