Fork Oil Change

[rocketman]

Hi all, I have read this entire thread and found that almost all of the info is re: pre-2003 bikes that have different forks than my 2004 V11. I have  43mm Marz. with rebound damping adj. on both sides and no compression adj. Any info re: these forks? I am geting almost 40% static sag and 25% free sag at the moment.

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Trispeed,

Pardon me Sir, but I need to correct you. It is my understanding the 04 Marz units have both preload adjustment and compression damping. They do not have rebound damping. I too have an 04 bike (LeMans) with the 43mm Marz's and am surprised by these findings. Was also wondering if these issues were just with the older bikes. I am actually fairly happy with my suspension but have never riden an Ohlins suspended Guzzi. Maybe I don't know what I am missing. If I were to make a change the $1000 upgrade is much cheeper than replacing with the ohlins units. But, I'm not convinced yet that it would be all that much better.

 

TXRider,

what year is your bike? Do you know if Traxxion Dynamics' assessment holds true for the 03 - 04 bikes as well?

 

Rocketman

[txrider]

Trispeed,

Pardon me Sir, but I need to correct you.  It is my understanding the 04 Marz units have both preload adjustment and compression damping.  They do not have rebound damping.  I too have an 04 bike (LeMans) with the 43mm Marz's and am surprised by these findings.  Was also wondering if these issues were just with the older bikes.  I am actually fairly happy with my suspension but have never riden an Ohlins suspended Guzzi.  Maybe I don't know what I am missing.  If I were to make a change the $1000 upgrade is much cheeper than replacing with the ohlins units.  But, I'm not convinced yet that it would be all that much better. 

 

TXRider,

what year is your bike?  Do you know if Traxxion Dynamics' assessment holds true for the 03 - 04 bikes as well?

 

Rocketman

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My bike is a 2004 which I pointed out to Traxxion in my original inquirey concerning fork oil level guidelines. Hardy didn't distinguish beween model years nor indicate which model year forks they had worked on.

My thinking at this point still is that $1000 is just too much to spend to get much better fork function. I'll settle for best I can get for a modest outlay of cash, that being the spring purchase. Much as I respect Max and his company Traxxion Dynamics, the major fork upgrade is just too costly.

[Guest trispeed]

Trispeed,

Pardon me Sir, but I need to correct you. It is my understanding the 04 Marz units have both preload adjustment and compression damping. They do not have rebound damping. I too have an 04 bike (LeMans) with the 43mm Marz's and am surprised by these findings. Was also wondering if these issues were just with the older bikes. I am actually fairly happy with my suspension but have never riden an Ohlins suspended Guzzi. Maybe I don't know what I am missing. If I were to make a change the $1000 upgrade is much cheeper than replacing with the ohlins units. But, I'm not convinced yet that it would be all that much better.

 

The manual says it is rebound adj., the adjusters themselves have a little "R" next to them, as well. At any rate , does anyone have experience with a specific spring/ fork oil with this fork? Thanks a lot!

[beauchemin]

ratchethack...... are you now running the Wilbers .7 - 1.0 kg/mm springs?  I'm thinking that maybe I'd give the progressives a go, and swap them this winter.  What spacer length did you settle on?

65749[/snapback]

 

Brian - I don't understand what you are up to... didn't you send your forks to Traxxion to get their AK20 cartridge internals installed? I assume that they would have installed the appropriate springs at the same time. What am I missing? Is the Traxxion solution not Nirvana?

 

Chris

[rocketman]

Trispeed,

Pardon me Sir, but I need to correct you. It is my understanding the 04 Marz units have both preload adjustment and compression damping. They do not have rebound damping. I too have an 04 bike (LeMans) with the 43mm Marz's and am surprised by these findings. Was also wondering if these issues were just with the older bikes. I am actually fairly happy with my suspension but have never riden an Ohlins suspended Guzzi. Maybe I don't know what I am missing. If I were to make a change the $1000 upgrade is much cheeper than replacing with the ohlins units. But, I'm not convinced yet that it would be all that much better.

 

The manual says it is rebound adj., the adjusters themselves have a little "R" next to them, as well. At any rate , does anyone have experience with a specific spring/ fork oil with this fork? Thanks a lot!

65858[/snapback]

 

Trispeed,

My bad, you are correct. It's rebound (So that's what the "R" stands for. I have been self deceived all this time. Now I can play with the adjustment and expect different results. Should of looked at the book before I opened my big mouth.

 

Rocketman

[Guest trispeed]

no problem, Rocketman. I am also pretty satisfied with the overall handling and wonder if our 2004 bikes (with the different forks) wouldn't benefit as much from the modifications suggested for the earlier bikes. Any 2003-4 specific modification experience out there? Thanks!

[rocketman]

no problem, Rocketman. I am also pretty satisfied with the overall handling and wonder if our 2004 bikes (with the different forks) wouldn't benefit as much from the modifications suggested for the earlier bikes. Any 2003-4 specific modification experience out there? Thanks!

65905[/snapback]

 

Trispeed,

It seems to me that Ratchethack has done alot of trial and error learning. He speaks highly of progressive rate springs. I would be willing to give those a try eventually. Springs and fork oil weight and oil levels are your cheapest options. What settings are you happiest with so far. I have my preload at 4 or 5 turns, clockwise (from closed). And zero rebound. I am going to play with the rebound setting some more now that I now what it does. If I remember right the more rebound the harsher the ride. I will try a little bit rather that alot. Maybe 1 to 3 turns.

 

Rocketman

[Guest trispeed]

Hey Rocketman,

I have the rebound at the standard setting of 3 turns out from fully closed and the pre-load 6 turns out from fully closed. (there are 15 turns of preload available and the standard setting is 7 turns out, I believe). It is very plush and smooth over any thing southern california can dish out!

[BrianG]

Brian - I don't understand what you are up to...  didn't you send your forks to Traxxion to get their AK20 cartridge internals installed?  I assume that they would have installed the appropriate springs at the same time.  What am I missing?  Is the Traxxion solution not Nirvana?

 

Chris

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It's not that Traxxion Dynamics is bad, it's more like I'm curious, and spinning wrneches in the garage is cheaper than spending time in the bar....... It's not, really, but I have my wife convinced!

 

I'm just curious to discover what the forks will feel like with optimized damping and progressive-rate springs.

 

Either that or I'll have to break down and screw that supercharge to my car... and I'm still a bit scared of that project!

[BrianG]

Trispeed,

Pardon me Sir, but I need to correct you.  It is my understanding the 04 Marz units have both preload adjustment and compression damping.  They do not have rebound damping. 

 

Rocketman

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Sorry Rocket man, but that's not correct.

 

In fork damping, compliance depends far more on rebound damping than compression damping. Inevitably, when you see only one being adjustable, it is rebound.... with fixed compression... which is actually fixed VERY soft.

[dlaing]

In fork damping, compliance depends far more on rebound damping than compression damping.  Inevitably, when you see only one being adjustable, it is rebound.... with fixed compression... which is actually fixed VERY soft.

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Of course we are talking forks here and not shocks, but

I found it interesting that Hagon shocks have adjustable damping with automatic rebound and compression balance.

I don't know if that is a good thing.

Rebound damping should be set proportionally to spring rate.

Compression damping should be set to the terrain, and it does effect compliance, but it is more difficult to determine what is ideal compared to rebound.

I have trouble even understanding why any compression damping is neccessary if springs are adequately firm.

I have a few ideas, like,

you want more spring rating than compression damping if you have a heavy load,

but if you have a light load, you want a lighter spring rating, but you still want compression damping.

Also the variations between high speed and low speed compression damping provide better compliance over varying surfaces than a spring and rebound damping alone could provide.

I feel my explanation is only scratching the surface.

Perhaps someone could provide a good explanation of why compression damping is necessary.

[Guest ratchethack]

Perhaps someone could provide a good explanation of why compression damping is necessary.

Yes, please. I've always thought that it's best used to work with the amount of rebound damping you're using to overcome the natural tendency of the springs to set up repeat cycling, aka "pogo-ing", and that a little compression damping can allow you to use less rebound damping to "liven up" the fork action for a smoother, more compliant ride. I've always found the best fork action with minimal compression damping, and currently use ZERO on the Marz 40 mm USD with #1 setting on rebound. I've also observed that at ZERO compression damping, you're still getting a "baseline" amount of compression damping, and that you can really notice a difference in it by changing the viscosity of oil.

[dlaing]

I wonder if it might make sense to go with a lighter oil on the compression side????

Something like 5W for Compression and 7.5W for Rebound.

One of the advantages of having Compression and Rebound in seperate forks is that you could do just that.

[Guest ratchethack]

Now why couldn't I think of that?! Since I like ZERO compression damping with my current fork setup, it would make sense to go lighter on that side, so I can use the adjuster for finer tuning - no need to change the rebound side!!!!

 

Thanks, Dave!

 

Have you given any thought to using a long rigid tube of some kind to drain the forks from the tops of the tubes with a vacuum pump? Since I chickened out on drilling, tapping, and plugging my fork lowers (for the 3rd time ), I've been thinking of trying this as a way to get around the dismantling routine. Waddya think?

[BrianG]

Perhaps someone could provide a good explanation of why compression damping is necessary.

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The issue to consider is that the suspension's cycle is, in fact, one 2-sided event. The spring provides the operating "force" on onside, while gravity provides the counter-force on the other. The (more significant) initial motion is the compression event, when you hit a bump. If this force is substantially absorbed by the spring but not damped, the motorcycle receives no upward accelleration that has to be dealt with in terms of handling (nor felt by the rider). The second half of the cycle (rebound) is responsible for the dissipation of the compressive energy the spring absorbed, hence the much greater damping value on this side of the cycle. The damping cycle is a little less than optimal in order to prevent the fork from "pumping up", which is the accumulated travel that would occur if the stroke were not allowed to complete before the next bump. This results in some over-shoot of the fork tube past the neutral point and the second half of the cycle ensues, to damp the remaining energy. With NO compression damping the fork would compress again past the neutral point, and it would take another cycle (or more) to damp the force of the bump. With a bit of comperssion damping it can be finished in one cycle. This is desirable because a completed cycle contributes nothing extra to the suspension's reaction to the next bump.

 

This generally becomes significant in near-limit traction situations, on rough surfaces. That is to say, it's only really a noticable issue when racing on a rough track.

 

Optimal track setting for springing results in near-full-fork-travel when the rider brakes as hard as he can. Optimal compression damping is indicated when the rider bounces his weight on the properly sprung fork, and the fork overshoots to an "above-neutral" position on rebound , and then settles quickly on compression, just to neutral , with no need for the initiation of a second rebound cycle.

 

Typically you will find the right springing first, by measuring unloaded and loaded sag values. Then you will set the compression damping to zero and ride the track to determine proper rebound damping for the rough bits, trying to set a little as is reasonable. Then you will set the compression damping to what is needed to kill the second rebound cycle, as mentioned above.

 

Street bikes need not be damped this closely, and in fact will feel plusher with a bit of a second damping cycle. Which is good if you like the ride of a Harley or a Lincoln...... but not so good if you like the ride of a Sport Bike or Sports Car.