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sansnombre

Traxxion Kit Tuning

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sansnombre
I installed the kit recently, and it definitely felt better than stock. The harshness of the original was greatly reduced, and it actually felt like I had some compliance up there. 
 
But I'm not using full travel on the fork, not even close. This was great for fork dive reduction while braking, less so for road compliance.
 
My perspective on travel is that on the biggest, nastiest bump you will ever hit while going the fastest you will ever travel, you'll want to just use up all your travel. That's the idea - tune the travel for the maximum hit and you'll be using the appropriate amount on smaller bumps.
 
So I checked it out online and looked for preload recommendations - there was some variance but the windows overlapped quite bit, with ~40mm being about right in the middle for a bike with this amount of travel. This is roughly 30%, again about right from other references.
 
So with the kit installed, I'm getting 32mm for the sag. This makes sense as it's feels too tight and I'm not using all the travel. So I pulled out the spacer rods and carefully removed 6mm from each leg. Popped 'em back in, and the sag is right around 38. Perfect. 
 
Took her for a ride, and it feels significantly better. More compliant, not as harsh off the bottom. And I'm using more travel, but only a little more - about the same as I took off of the spacer. So that's telling me that the designers are really relying upon the exponentially rising rate of the effective "air spring" in the fork and that they have it cranked up to combat brake dive, but it's also limiting travel.
 
For comparison, the standard oil level is 162mm from the top of the tube. The Traxxion kit has it at 110mm from the top of the tube (I'm pretty sure those are the actual numbers; if not, they're close). So we've decreased the total volume height of this airspring by over 50mm! This is about 2 inches, and is quite a bit because the pressure increase is exponential to the volume reduction when compared to other locations in the travel. That is, the change at full extension to 1" compression is significantly less than the change at maximum compression and maximum compression less one inch. So, the air spring is more forceful at the end compared to the beginning, so it has more effect later in travel and less at the beginning.
 
So I pulled about an inch out of the fluid level to reduce that compression, and that did the trick. A VERY compliant, highly-controlled fork action that uses up more of it's travel. Brake dive is slightly increased from before these mods, but still controlled and not an issue.
 
So if you've got this kit and are not using all your travel, take a look at preload at first, and if you want to use more travel and let the fork do what it's supposed to do, consider altering your fluid level and tuning it for your weight, riding style.
 
For racing, there are different considerations. This here tuning advice is for the street.
 
Cheers.
 
 
 
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rick
Well, that all sounds more than a bit familiar. Dropping fluid height in my Andreanis to 150 will sure be cheaper than buying new springs.
 
Think the air gap in my USD Showas is 118mm - but that represents a lot more air as the diameter of the upper tubes is bigger.
 
Might have time before the snow flies to try this.

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sansnombre
True that the original air volume is higher, but the pressure change will be the same as mine as your stroke movement compresses a larger volume per given stroke as well, so it's actually identical.
 
As you know, volume in a cylinder is cross-sectional area times height. If our height is reduced 1/2, we reduce the volume 1/2 regardless of the cross-sectional area.
 
It would be an issue if one had more (or less) fork travel, though. Say you had 6" of potential fork travel and another setup had 4". If your fork moves through 2" of travel during normal usage, the 6" fork has only compressed the volume by a third and increases internal pressure by 50%, while the 4" setup had compressed its volume by a half and its internal pressure would double (ideally), and you'd have more resistance to fork movement.
 
I'm sure you know all this, but for some it might be new info.

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rick
Ya know, I never even looked up what the air gap spec is for our forks OE. Andreani recommended 120mm and that's where I set it the 1st go round. And that was, shall we say, firm. And yeah, what a transformation as dive during a forceful brake application feels so much more controlled.
 
You went from 110 to 135? Mine is now set at 130mm and I still have a bit of harshness and, like you, still have a lot mms travel not used.
 
Considering they gave me springs that are a bit too stiff for my weight to begin with, twotone just a couple days ago, in another post, recommended I drop the fluid level to 150mm. Sounds like a plan.
 
 
 
 
 
 

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pattonme
I think Traxxion has a mis-print to suggest 110. On an SV650, maybe. For the FZ07 140-160 seems to do the trick.
Nice writeup.
 
Oh, ad @rick did you measure fluid height with all the spacers sitting in the oil? Or did you add them and the spring after the fact?

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rick
I think Traxxion has a mis-print to suggest 110. On an SV650, maybe. For the FZ07 140-160 seems to do the trick. Nice writeup.
 
Oh, ad @rick did you measure fluid height with all the spacers sitting in the oil? Or did you add them and the spring after the fact?
Spacers and springs were out, stanchions were to the bottom of the sliders and the damper rods were all the way down such that i had to attach a piece of wire around 'em to pull them back up.  
That's what I've been doing with the Showas except the manual calls for the damper rods to be at a particular height to the top of the tube - It's not all the way down, but close. 
 
 
 

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sansnombre
@rick: I'm actually still fiddling with it. Currently at 135, but I think it's still too high. I took it for a good ride yesterday and although feeling much better, still a little too firm.
 
I'm getting to the point where I agree with the comment above re a misprint. Seems like I'm slowly going back towards 160 as I experiment.
 
That said, it feels much better since the mods, esp the sag mod. That is a very important adjustment, and I know I'm at the slightly firm side there too.

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rick
When I get time and motivation to get back in there, I'm just going to 150mm. Might also give Sonic a call after doing some measuring on the springs. For me, a lighter spring might really be the answer.

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twotone
Measure the movement in the cartridge, and see if you need to remove one of the nylon bushings.

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