Now onto the forks

[FuelCooler]

Just remember,Ratchethacks settings are right for Ratchethack only.Everyone has different needs and riding styles which would require different set ups.Dont be afraid to experiment with a different method of setting up your front end.

 

It should be reiterated here that what works for one rider will be complete anathema to another.Find what works for YOU,not somebody else.

 

Thanks BigJ,

Luckily, I do know what I like (some people don't!) and like you said, I will find what works best for me. I am more of a 'one change at a time guy'. I like to see the results of one change before going to the next change. Unfortunately this is my first time through these forks, and I don't know what weight fluid was in them.

He (Ratchethack) and I weigh the same geared up, so our spring rates will be close. The air gap can be different, but I realize I will have to start somewhere! I will probably leave them at 102mm and wrap a ziptie around the tube and see what I am using, travel wise, and back it off accordingly, if needed.

 

 

And one more interesting development as I was in the process of greasing my steering head bearings this afternoon...........drum roll please................trashed bearing cups. Big pit right on center on the bottom, and well worn and pitted on the top. Curiously, it was fairly well greased.

Oh the joy of discovery!

[dlaing]

I measured several things while changing the fork fluid today:

 

Blue locknut (that tightens against the cap):

Rebound Fork- 22mm

Compression Fork- 21.25mm

 

Spring spacers:

RF- 109mm

CF- 110mm

 

Spring (straight wound):

RF- 295mm

CF- 294mm

 

Air Gap

RF-128mm

CF-114mm

 

I am of the belief that fork forces should ideally be balanced. I am not a big fan of this RF/CF design, although it has some advantages for tuning options.

It may make no apparent difference to how the forks ride and wear, but I believe that adding a slightly stiffer spring or more preload to the rebound side is a good idea to help balance the forces. I think your previous Air Gap spread of 128/114 was throwing things further out of balance and could have been causing instability when nearing bottoming conditions.

But I also suspect that the 102mm air gap that you chose maybe too high because it may prohibit full travel:huh2: ....but I don't know for sure. Perhaps a little prohibition is a good thing

[big J]

That's an excellent point Dave,as the fork legs have differing functions,it should be remembered that perhaps differing oil viscosities and levels could be accomodated to suit different riding styles/requirements.

[Guest ratchethack]

That's an excellent point Dave,as the fork legs have differing functions,it should be remembered that perhaps differing oil viscosities and levels could be accomodated to suit different riding styles/requirements.

Dave brought this up some time ago and as I noted back then, I think it's a very good thing to keep in mind for those with asymmetric Marz forks. As Dave noted, they're more configurable than symmetric forks from a damping standpoint, because different fluids can be used in each leg to achieve desired fine-tuning results -- for all those inclined to fine-twiddle such things.

 

Now this is just me, but while I CAN imagine doing this myself (at no particular point in the near-term future) I'd NEVER consider running different air gaps in right and left-hand side tubes!

 

BUT WHY WHY WHY WHY , RATCHET?!?! (...sob...)

 

Take it easy, Grasshopper. . . Don't get all freaky on me now! I'm SO pleased you asked. . .

 

Seems to me that the air spring effect is nothing to be trifled with. Near the end of fork travel on most forks, regardless of how close to bottoming they get on an extra-hard jolt, the amount of force exerted by the combination of the fork springs and air spring can double, and possibly exceed double the force exerted by springs alone at full compression.

 

The graph here demonstrates the principles at work:

 

http://www.peterverdonedesigns.com/oilheight.htm

 

The point being that damping forces are orders of magnitude less than the combined forces of air and spring pressure, and while the Marz forks seem entirely capable of handling damping differentials right and left, I question whether or not they could handle differences of force of several orders of magnitude greater. Damping force differences tend to be greatest at the highest speed of the fork in compression and rebound, where suspension forces due to springs are moderate and air spring rates are very low. This is NOT the case near maximum fork compression. But because the air spring effect is a RISING RATE, the differences right-to-left would be greatest when the suspension forces are greatest at maximum fork compression -- NOT the circumstances where I'd want my fork flexing!!!

 

That's my story, and I'm stickin' to it.

 

BAA, TJM, & YMMV

[big J]

So exactly what does the graph illustrate? Nothing.Lines in a box,no reference to useable baseline data whatsoever.

Your last paragraph is gibberish if you are using the graph as a quantifiable source.How could the engineer? responsible possibly know the torsional strength of the axle used in the Marzocchi fork,for example?

 

Another thing,if you do not strip the damper units in the rebound leg and simply invert,pump and refill,you may have trapped air in the damper cartridge which will render any meaningful measurements and settings total nonsense.Yet I note that you do not strip them,simply invert them which means you have an unknown amount of air,fluid and sediment which you cannot possibly measure lying trapped within the damper unit.

 

I can appreciate that you have done a bit of work on your forks,however your findings are by no means the definitive or final solution.There are as many settings as there are riders.The forks should be stripped COMPLETELY and cleaned thoroughly before any baseline settings can be forwarded with the proviso that THESE SETTINGS ARE WHAT SUIT ME ONLY.

 

In fact,having re-read your last paragraph I would like a further clear and lucid explanation.

 

And try to do it without being patronising or a smartarse.

[Dan M]

 

The point being that damping forces are orders of magnitude less than the combined forces of air and spring pressure, and while the Marz forks seem entirely capable of handling damping differentials right and left, I question whether or not they could handle differences of several orders of magnitude greater. Damping force differences tend to be greatest at highest speed of the fork in compression and rebound, where suspension forces due to springs are moderate and air spring rates are very low. This is NOT near maximum fork compression. But because the air spring effect is a RISING RATE, the differences right-to-left would be greatest when the suspension forces are greatest at maximum fork compression -- NOT the circumstances where I'd want my fork flexing!!!

 

That's my story, and I'm stickin' to it.

 

BAA, TJM, & YMMV

 

 

I think it is unlikely that 14mm difference in air space is going to cause the fork to flex. I also think that different air spring space from leg to leg is about as silly as different spring rates from leg to leg. What you are going to realize is an average of the two. Tuning with different oil viscosities in each leg for compression and rebound damping (spelling OK ratch?) is an option although I don't see it as necessary in most any situation. There seems to be enough adjustment in this area to go from too much to not enough in either fork leg. Having different fluid in each leg to "fine tune" is, well, just a bit over the top.

[Guest ratchethack]

So exactly what does the graph illustrate? Nothing.Lines in a box,no reference to useable baseline data whatsoever.

Your last paragraph is gibberish if you are using the graph as a quantifiable source.How could the engineer? responsible possibly know the torsional strength of the axle used in the Marzocchi fork,for example?

 

Another thing,if you do not strip the damper units in the rebound leg and simply invert,pump and refill,you may have trapped air in the damper cartridge which will render any meaningful measurements and settings total nonsense.Yet I note that you do not strip them,simply invert them which means you have an unknown amount of air,fluid and sediment which you cannot possibly measure lying trapped within the damper unit.

 

I can appreciate that you have done a bit of work on your forks,however your findings are by no means the definitive or final solution.There are as many settings as there are riders.The forks should be stripped COMPLETELY and cleaned thoroughly before any baseline settings can be forwarded with the proviso that THESE SETTINGS ARE WHAT SUIT ME ONLY.

 

In fact,having re-read your last paragraph I would like a further clear and lucid explanation.

 

And try to do it without being patronising or a smartarse.

Uh, BigJ, are you on medication? If not, perhaps you should consider it.

 

Let me see if I've got this straight. You post an illucid, patronising, smartarse "question" and demand a "clear and lucid explanation"..."without being patronising or a smartarse." Have I got that right?

 

Er, well let's see...that's quite a challenge, BigJ, but I'll do my very best.

 

The graph at the link is a conceptual graph, the purpose of which is to illustrate principles that apply to all forks using an air spring. It wouldn't make much sense to put numbers on a graph that apply to a Showa fork, for example, when the principles apply equally to a Marzocchi and Ohlins, as well as to many other makes and models of forks, all with different spring rates, etc., owners of which are actually interested in learning the principles involved -- regardless of numbers that would not apply to all forks equally. The principles are explained at the link in language that the author seems to believe most riders and racers can understand, and they're quite simple. Sorry if it's over your head, Big J.

 

My findings "the final solution"?? Have you been watching WWII movie re-runs?!?!

 

Is there some part of any of my posts where you think I've said that my interpretation of something is the final authority and no other possibilities exist? Can you find a place where I ever dictated (or even suggested) what anyone's settings should be by any specific numbers? I thought I was putting ideas out there on an open forum, along with professional resources for discussion with anyone interested. Uh, wot kind of meds have you got??

 

I find your speculation about wot experience I have with the Marz fork incredibly presumptuous. How would you know wot I've done and wot not?! I've had mine completely down to the cartridges and thoroughly cleaned out twice now, per the maintenance schedule. I've posted here about this numerous times since many years ago, right up to yesterday, I think, when the topic was replacing seals. Per extensive prior posts on this, many don't seem to consider it necessary to do a complete fork strip to change the oil. I happen to disagree, especially for the first oil change, but you see, I happen to believe that everyone's entitled to their own ideas on wot's correct here -- wouldn't you agree, BigJ?

 

Tell you wot, Big J -- I don't remember insulting you, or even exchanging any posts with you. I've no idea wot's crawled up y'er butt, and frankly I couldn't care less. But since you won't, can't, or are otherwise unable to consider the graph at the link I provided, you obviously have no interest in understanding the principles of air spring operation in forks. Failing to comprehend this, of course, it would ALL seem like gibberish to you, wouldn't it?! It would follow that you have no sincere interest in further explanation that you've demanded either, so that's about all I got for now.

 

Perhaps you're looking for some kind of an apology for not posting "WHAT SUITS YOU ONLY"?!

 

I don't believe I'm obliged in the slightest, BigJ.

 

Hope you get better soon.

[dlaing]

I think it is unlikely that 14mm difference in air space is going to cause the fork to flex.

It is the axle flexing that I would be worried about.

This is especially true if the air gap is small enough that the fluid becomes the bottoming point.

It just seems like a really bad idea to bottom on one fork before the other, but who knows, maybe it is well within the range of axle strength. I just would not trust that without knowing for sure.

Presumably FuelCooler's axle is still straight

[Guest ratchethack]

It is the axle flexing that I would be worried about.

This is especially true if the air gap is small enough that the fluid becomes the bottoming point.

It just seems like a really bad idea to bottom on one fork before the other, but who knows, maybe it is well within the range of axle strength. I just would not trust that without knowing for sure.

Presumably FuelCooler's axle is still straight

Now this is just me -- but considering the geometries, it would make sense to me that if the axle is flexing at all under fork compression, you've automatically got a flexing, binding fork.

 

I agree, Dave. I would not want my fork bottoming 14 mm on one side before the other gets anywhere near the same air spring pressure on it. Verdone recommends making changes to both air gaps at the same time in 2-3 mm increments. It's easy to imagine that a 14 mm right-to-left difference in air gap might represent perhaps upwards of 100 pounds difference (or more) at full fork compression, depending on many other factors. Consider that, as Verdone points out, under maximum braking force, the entire weight of bike, rider, and cargo are ALL carried by the fork and air springs. In the case of the Guzzi, this is anywhere from about 700 lbs. to upwards of 800 lbs., depending. If you wound up with a 300/400 lb. or 350/450 lb. (or greater) differential right-to-left, this might be something well advised to avoid. . .

 

I don't think it's possible to reach hydraulic lock with any moto forks. They'd be inclined to blow seals long before they got to this point. Yes, this has been known to happen.

[badmotogoozer]

SNIP

 

In fact,having re-read your last paragraph I would like a further clear and lucid explanation.

 

And try to do it without being patronising or a smartarse.

 

Well said Big J. Your post was neither patronising or smartarse. Rat hopes you will accept BS, mixed with ridicule and obscurity, in lieu of clear and lucid explanation. Seems to be enough for his sheeple to accept.

 

Rj

[Dan M]

It's easy to imagine that a 14 mm right-to-left difference in air gap might represent perhaps upwards of 100 pounds difference (or more) at full fork compression, depending on many other factors.

 

 

Only if you have a vivid imagination.

The difference from 128mm to 114mm is not even 10 percent. At 114 he is already 14mm larger air gap then specified. The larger the air gap, the less air spring effect. With enough air gap, you'll bottom mechanically before any air spring is realized.

[Guest ratchethack]

Only if you have a vivid imagination.

The difference from 128mm to 114mm is not even 10 percent. At 114 he is already 14mm larger air gap then specified. The larger the air gap, the less air spring effect. With enough air gap, you'll bottom mechanically before any air spring is realized.

Good point, Dan. I may have over-imagined and also over-stated the case slightly. But keep in mind that it's a rising rate we're dealing with here, and the curve on the rate graph approaches vertical toward the end of travel, which would also make the DIFFERENCE in pressure a rising rate also -- not simply a 10% difference, but quite a bit more than that.

 

Now I suppose I could be wrong, but AFAIK no suspension Pro in the business would recommend anything other than keeping the levels the same.

[Dan M]

Now I suppose I could be wrong, but AFAIK no suspension Pro in the business would recommend anything other than keeping the levels the same.

 

Couldn't agree more. I called it silly in my first post on this matter.

[big J]

Uh, BigJ, are you on medication? If not, perhaps you should consider it.

 

Let me see if I've got this straight. You post an illucid, patronising, smartarse "question" and demand a "clear and lucid explanation"..."without being patronising or a smartarse." Have I got that right?

 

Er, well let's see...that's quite a challenge, BigJ, but I'll do my very best.

 

The graph at the link is a conceptual graph, the purpose of which is to illustrate principles that apply to all forks using an air spring. It wouldn't make much sense to put numbers on a graph that apply to a Showa fork, for example, when the principles apply equally to a Marzocchi and Ohlins, as well as to many other makes and models of forks, all with different spring rates, etc., owners of which are actually interested in learning the principles involved -- NOT numbers. The principles are explained at the link in language that the author seems to believe most riders and racers can understand, and they're quite simple. Sorry if it's over your head, Big J.

 

My findings "the final solution"?? Have you been watching WWII movie re-runs?!?!

 

Is there some part of any of my posts where you think I've said that my interpretation of something is the final authority and no other possibilities exist? I thought I was putting ideas out there on an open forum for potential discussion with anyone interested. Uh, wot kind of meds have you got??

 

I find your speculation about wot experience I have with the Marz fork incredibly presumptuous. How would you know wot I've done and wot not?! I've had mine completely down to the cartridges and thoroughly cleaned out twice now, per the maintenance schedule. I've posted here about this numerous times since many years ago, right up to yesterday, I think, when the topic was replacing seals. Per extensive prior posts on this, many don't seem to consider it necessary to do a complete fork strip to change the oil. I happen to disagree, especially for the first oil change, but you see, I happen to believe that everyone's entitled to their own ideas on wot's correct here -- wouldn't you agree, BigJ?

 

Tell you wot, Big J -- I don't remember insulting you, or even exchanging any posts with you. I've no idea wot's crawled up y'er butt, and frankly I couldn't care less. But since you won't, can't, or are otherwise unable to consider the graph at the link I provided, you obviously have no interest in understanding the principles of air spring operation in forks. Failing to comprehend this, of course, it would ALL seem like gibberish to you, wouldn't it?! It would follow that you have no sincere interest in further explanation that you've demanded either, so that's about all I got for now.

 

Perhaps you're looking for some kind of an apology for not posting "WHAT SUITS YOU ONLY"?!

 

I don't believe I'm obliged in the slightest, BigJ.

 

Hope you get better soon

 

LOL,well,I dunno about medication,but certainly the whisky bottle I have recently taken out a short term lease on had definite anaesthetic qualities.

 

Anyhow,having reread both our posts,I still cannot believe that Ratchethack,the great defender of truth,wisdom,clarity,reason,blah,blah,would illustrate his main point with a "conceptual" graph. It refers to and concludes nothing,as stated before,it is meaningless lines on a square.To have any meaningful authority,there should be at least a reference to the type of forks used.Are they conventional or USD?Conventional tele's flex considerably more than USD's.What wall thickness of tubing was involved?Are the bending forces indicative of the forces incurred by racing slick type tyres,road tyres or a static tensile load?

Why are the volumes of oil and air fixed?The variables of differing oil/air volumes to maximum chamber volume are not fixed,so therefore any rising rate effect cannot be predicted.Furthermore,no mention of the effects of temperature on the subject,nothing on whether the damping type tested was needle valve based or shim stack,linear or non-linear full compression bump stop,etc,etc,etc??????????It does make a difference,you know.

 

Yeah,I like old war films.

 

You may well have stripped your forks down,but you recently posted that "despite tipping them up at different angles,you didnt think you could get all the old oil out."or words to that effect.That was why I posted that you had to strip the forks completely to get it all out.You have posted quite a few times about draining the forks by inverting them,but I havent seen where you informed that the rebound leg has to be completely to get the oil out.Hence my presumption.

 

I'd still like an explanation,thanks.I am always interested in this stuff,always have been. Since I worked at "Specials",building and testing Harris and Spondon framed machines for road and track,building a ZX-RR superbike-financed by Kawasaki UK,for a TT winner and BSS champion, assisting in set up and development for gawd knows how many proddie racers,it's always tickled me how folk can proscribe what the ideal set up may be.I found through testing that any 2 different riders could have entirely different preferences on the same machine,which makes set up for an endurance racer,where 3 riders share the same bike,highly problematic to say the least.Funnily enough,a lot seemed to depend upon background.Guys coming from Italian or old Brit bikes generally liked a firmer damping profile,guys more used to Jappers liked it softer and "floatier"(technical term )

 

Finally,I've seen the way you reply to Dave and Ryan when you are questioned at length on a subject or been wound up a little and didnt want any of the same,just a matter of fact statement would be nice. It was not intended to piss you off.

 

No apology necessary,thank you.Just a little more clarity perhaps could avoid misunderstanding.

[big J]

Some more random thoughts.

No matter how hard you try,you wont bend an axle Unless you hit something.

 

Whilst a conventional fork,with both compression and rebound damping in the same leg is best set up as one of an identical pair,the separate functions of the Marzocchi fork are possibly a different matter.It could be the case that while static measured volume is identical,displaced volume may vary.The differing displacement characteristics under dynamic load have not been as yet analysed or recorded.There might be a greater spring effect in one leg or the other already?

 

Plenty of motorcycle forks have hydraulic lock on full compression.They're designed that way in conjunction with spring length,rate,damping characteristics,etc.