Fork mods discussion - theory and practice

[pattonme]

I don't want to jack any of the existing (somewhat focused) threads with a more generalized topical thread. The intent for this one is to be wide-open and free-ranging. If certain threads develop that deserve their own break-out, we can start a new post and back-ref items from this one I guess.
 
Please familiarize yourself with the following:
 
http://fz07.org/thread/2228/why-forks-pogo-sticks
http://fz07.org/thread/1920/fork-upgrades-compatible-swaps
http://fz07.org/thread/2415/andreani-advanced-cartridge-kit
http://fz07.org/thread/2190/anybody-matris-fork-kit
 
Hopefully I'm not being unfair to anybody. PM me if I missed a worthy thread and I'll update this post.
 
Let's focus on this one http://fz07.org/thread/2682/spring-weight when asking about springs regardless of your weight (nothing wrong with http://fz07.org/thread/2317/suspension-fat-guy but it's splitting the topic unnecessarily, IMO.)
 
I just created http://fz07.org/thread/2711/all-gold-valve-emulator-gve for GVE-related discussions, though more theoretically-minded banter could be hosted here.

[bmwpowere36m3]

You didn't by chance measure a set of stock fork springs?
 
I'd be interested in fork spring rate discussion for particular rider weight. Your fork cartridge kit and valving (are the shim stacks basically out of the donor forks, i.e. stock valving). And thoughts on possible shock options from other bikes.
 
I'm fairly handy with suspension stuff and somewhat knowledgeable. I re-valved my forks and shock (multiple times, a little trial & error) on the DRZ. I used a suspension damping simulator called, Restackor to simulate damping with various shim stacks I also retrofitted a shim stack to the stock checked mid-valve.

[gtmn]

I want to say that traxxion measured the stock springs at 70-75kg
a quick call to dan at traxxion and he can answer and give recommendations
my kit came with 95kg and im 250

[pattonme]

You didn't by chance measure a set of stock fork springs?

 
see post - http://fz07.org/post/38634
 
> I'd be interested in fork spring rate discussion for particular rider weight.
 
Let's use this thread - http://fz07.org/thread/2682
 
> Your fork cartridge kit and valving (are the shim stacks basically out of the donor forks, i.e. stock valving).
 
I developed the shim configuration over the years by virtue of being a repeat Racetech and Traxxion Dynamics customer, disassembling various aftermarket sportbike forks in the same weight class which had been further massaged by various parties to include GP Suspension, ThermosMan, and Lindermann Engineering. Plus looking at what other Netizens had posted as part of their experiments. I then used Restackor to compare and contrast various setups and arrived at "my" configuration.
 
> And thoughts on possible shock options from other bikes.
 
I compiled this list http://fz07.org/thread/1914/shock-upgrades-compatible-swaps but so far nobody has actually pursued any of the candidates, that I know of.
 
<quote>
I re-valved my forks and shock (multiple times, a little trial & error) on the DRZ. I used a suspension damping simulator called, Restackor to simulate damping with various shim stacks I also retrofitted a shim stack to the stock checked mid-valve.
</quote>
 
Excellent! I have the -SM but I wussed out and let a professional re-do both ends.

[gtmn]

now don't get me wrong
I like talkin about this stuff
however
we seem to really be beating the suspension thing down
I think as riders we need to decide how we are gonna ride the bike ( for real )
then how much we want to spend on front, rear or both
I almost feel like the problem is that you cant see or touch the parts in the suspension
we seem to not have a problem spending 1k for exhaust because its a touchy feely kind of product for us and others
there is a lot of vendors that are very happy to help us with our suspension needs
and they are really good at it
and they are a phone call away
also there are members willing to help with set up if you bought the parts to be installed
its not real hard
it just seems that we are not willing to pull the trigger
seriously if you rode one with suspension done then your bikes without mods to the suspension
you would immediately wonder why you didn't start with suspension mods and go home and start calling
 
I am on my ctx 1300 forum and it seems that many on there hate the suspension but they don't know what the problem is
many complaint about how the bike rides but the guys keep spending money on fixes other then the forks
after 168 miles I could no longer take how bad the bike was
I took the forks off that bike and sent them to dan at traxxion and he fixed me up with full adjustable ak20s
the bike is almost a 750lb sport bike now
it is very important to set up your bike for you. not others
a set up bike is so much more fun to ride and so much easier to ride faster and safer
 
I was the same way and thought how can it be so bad
but now after 2 bikes set up it fricken awesome
trust me when I tell you that no one on this or any other forum are gonna worry about every one elses bike set up it doesn't matter to anyone but you
 
as for this post
gold valve kit from traxxion
very firm ride no sharp hits and no crazy brake dive, it is very good
 
please I ask that no one takes any of this personal
its just my opinion
I just know this is gonna go bad for me
 

[mjh937]

@gtmn, I am not sure why anyone would take offense at your post. It seems like a well reasoned and well written opinion. I am still on the stock suspension but it is on my upgrade list (probably for Christmas as I cannot justify the cost (read that as convince my wife) yet). I have the added benefit of my last bike being a mid '80's KZ650 so I do not know how bad this suspension is

[pattonme]

Ok @gregjet, let's discuss orifice size/shape/arc over here so we don't push the Andreani thread off the deep end.
 
> Even an oval of the same crossection area does not flow as well as a round one.
 
I get that (intuitively if nothing else). But if I have a choice of putting a bunch of holes around a circumference, which obviously requires a 'wall' between each hole, surely that flows less than if I were to combine the neighboring holes (2 or 3) into a single orifice? Sure, I'd like to get the full benefit of increasing the area (about 1/2 a hole's worth per wall removed at the diameter and arc-interval we're talking about). Do you have some maths handy that could estimate how much more flow I should get?
 
I'm not sure what the dynamics are vis-a-vis shims and their deflection where it concerns size and spacing of orifices. That's a whole different set of complications.
 

[pattonme]

> "oval" or wedge shaped ports.... However some older ones have round ones. Regardless of their shape, the fluid immediately
> encounters the shim stack and must exert enough force to crack it open and change direction almost 90 degrees
 
I think the reason for the wedge and oval is that it moves the point of force outboard than what it would be if it was a hole. You have all that area right up against the outer edge of the shim exerting pressure as opposed to considerably inboard otherwise. So, basically you can run a heavier shim stack if using arc or wedge. Or maybe the point isn't so much to run heavier but rather pushing on the edge of the shim results in more consistent deflection behavior? Or it's easier to model, perhaps?
 
The thing I noticed about all the pistons I've seen to date is that if you calculate the orifice area, it's much larger than the area if you calculate the 'rectangle' you get if you put the piston on it's edge. Ie. the area between the shim stack and the lip that feeds the thru-hole is often MUCH smaller than the cross-section of the hole itself. I have to wonder, did someone forget to consider both parts of the equation?

[bmwpowere36m3]

I've noticed the same, reverse-side port entrance… is usually smaller. Restackor's site has a LOT of good info on flow entrance losses, port sizing, port shapes, etc… The further out you can put the port edge, the further out fluid is applying force to the shim stack. Which in one sense makes the shim stack softer (longer lever), but more importantly, maybe, loads/deflections the stack in a favorable manor (cones up from the edge). I've seen mid-valves, on CRFs IIRC, were there are just two arched ports:
 

 
The can't imagine making the ports any bigger. With round holes, I feel like you sacrifice port size due to the manor in which the ports are arranged around the piston circumference. The best use of area is a pie-shape port, with minimally thick port walls.
 
I think we can agree… any modern suspension can be tuned to levels exceeding any of our mere mortal riding skills, regardless of port shape.

[gregjet]

Can a non round hole flow as well as a non round one? Of course it can. You just have to increase the cross-sectional area. The trouble is that on round shapes can need to be VERY much bigger. This can be difficult if you have limited real estate to work with. Also the less round the more the fluid velocity effects the restriction. Having said that , A really smart person can use that very difference to design the flow they want without hardware valves. It's just a LOT harder to design. That's why god invented fluidics ( or someone did). A valve that is JUST a shaped hole and does the exact right thing, would be the PERFECT solution .