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Discussion Starter #1
I had the opportunity to take Lee Parks' Total Control clinic this past weekend. Among the topics covered was suspension setup. Lee spent some time explaining how to assess proper rebound damping. Lee's technique for assessing proper rebound on forks (also referenced in the Race Tech suspension book - no surprise as Lee is a co-author), is as follows:

- Standing beside the bike, grab the front bars and hold the brake
- push down on the bars hard. Try to direct the force in-line with the forks, rather than straight down.
- as you release pressure, make sure that you neither resist the upward movement, nor pull up on the bars accidentally.
- observe what the forks do.

Ideally, they should rise and then almost imperceptibly settle again. That miniscule amount of settling back down at the top of the stroke is the key. If the rate of rise slows at the end and there's no downward settling, there's too much damping. If they bounce more than once, there's not enough rebound damping. Lee tried this on my currently stock '11 Wee, and about died laughing. I think it bounced 3 times. :thumbdown:

I'm upgrading to some Sonic 0.90 kg/mm springs. After having read TONS on the matter, I understand that there's a big difference in viscosity between different brands of fork oils so I'm at a bit of a loss to identify what brand/weight of oil to run. For reference, there's a table here that shows the cSt @ 40C of various brands of fork oils. It becomes quickly apparent that 10W or 15W means absolutely nothing when trying to assess one Mfgr against another.

So, on to the favor. If you have 0.90 kg/mm springs on your bike, can you please perform the above "bounce test" and report your results, along with brand and weight of fork oil you're using (and it's age)? I'm hoping to triangulate on a decent starting point. I'll likely use either the Red Line or Silkolene oil recommended on the page above, but by knowing what you have, and how it works, I can use the reference table to find the analogous Silkolene or Red Line fork oil.

Many thanks in advance.

-John
 

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i uses the 0.90kg spring.

i use Silkolene Pro RSF 2.5wt with a modified rebound orifice of 1.75mm (instead of stock of around 2.3mm)- why i did that? long story- i had to make the rebound to work with intiminator on compression.

The setup, as far as rebound is concern, is on the lighter side of what i believe to be ideal for riding around the very crap roads around here.a 20% mix on the 5.0wt was already a firm for my liking, but probably produce to ideal stationery test you mentioned

Base on that and the fact most americans seem to like firm setting, and assuming the spring is correct with your weight, i would guess on a stock system, i would use a combination of 5wt and 10wt Silkolene Pro RSF or try the 7.5wt as a starting point. Crappy road riders may like a combination closer to the 5wt end in the Pro RSF range.

What Lee mentioned is a good starting point, you do have to fine tune to your preference. You can start with 5wt and suck out some and fill it with 10wt until you can get the perfect combination for you. - use a spreadsheet for the calculation, as after a couple mix, the calculation gets harder to keep track.

Dont worry, it will take you a few tries to get the perfect combination. Good luck and have fun.
 

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Discussion Starter #3
Thanks AceRider - your recommendation correlates pretty well with Rich at Sonic's recommendation if 10W oil. Since he sells PJ1, I'm assuming he's referring to PJ1 fork tuner (10 wt), which has a cSt @ 40C of 33.9. This is pretty close to Silkolene Pro RSF 7.5W (cSt @ 40C of 37), so I think the right answer lies somewhere in that general range.

I know what you mean about the Intiminators. I had installed a set in a KLR650 I used to own. For all the benefit they provided on compression damping, having to run them with 5W Amsoil hosed up the rebound so badly that it was crazy. I ended up selling that bike, but if I'd kept it I would have ended up either doing what you did with the rebound orifice, or removing them and going with Emulators.
 

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FWIW, if you tear them down completely and clean everything well, as I did, you will find the reassembly takes a few more ounces/ml of fork oil than the normally discussed two pints. You should factor this in to your purchase and mix ratios.
 

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Ideally, they should rise and then almost imperceptibly settle again. That miniscule amount of settling back down at the top of the stroke is the key. If the rate of rise slows at the end and there's no downward settling, there's too much damping. If they bounce more than once, there's not enough rebound damping. Lee tried this on my currently stock '11 Wee, and about died laughing. I think it bounced 3 times. :thumbdown:
Methinks you have no oil in your forks ;)
My stock 08 rebounds very much the way it's supposed to.
 

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Discussion Starter #6
Methinks you have no oil in your forks ;)
My stock 08 rebounds very much the way it's supposed to.
The bike is only ~ 6 months old, and the forks are as they came from the factory, but based on the current performance of the suspension that would not surprise me.
 

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Yeah, well I wouldn't be surprised if the bike had been shipped upside-down....
Checking for oil in the forks is pretty easy.
My buddy bought a new firebird once and found out later t hat it had no oil in the differential; these things happen...
 

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.90 springs
Rebound hole welded shut
15mm unloaded spring preload and zero additional preload w/ adjuster
Race Tech emulators (re-tuned too many times to count...)
7.5wt Amsoil at 150mm


I currently have 7.5 wt Amsoil Shock Therapy and I have the rebound hole welded shut, which really doesn't affect the top (most extended) 1.5" or so of travel. IMO, with my .90 springs set at the current preload, I would not go lighter than this 7.5wt.

I had tried 5 wt, but that definitely was too thin. If I would compress the forks and release, the fork would over-rebound a good 3/4" inch before settling down.

Yes, you want to run the rebound as fast as you can tolerate, but the 5wt Shock Therapy was just too fast in my opinion.

As suggested, I would verify if your bike is set up properly from the factory. Not impossible that it is missing fluid. If the bike was shipped upside, it wouldn't matter at all- the fork fluid would work the same once inverted and cycled several times.

Hope this helps.
 

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Since we both run .9kg spring, I am at a lost to explain how bj,s experience is so different from mine. Emulator an intiminator makes no difference to rebound, all to do with orifice and oil viscosity only... I guess it's really a case ymmv.
 

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AceRider,

You know, I was wondering the same thing- why do you & I find such a difference in our rebound fluids? This stumps me, too.

The dampening system is independent of the rebound, so EXACTLY as you state, our rebound systems should be the same.


So thinking....

Which brand 2.5wt are you using? Do I have less preload maybe? I don't doubt that 2.5 works well for you.

Maybe- The rebound system in those forks are anything but state of the art; Those are really crude internals, pretty much the same as 1970's technology (or lack thereof, but it does work and is common equipment). So, anyway, if your damper rods' diameters and the "moving washers" inside diameter have just slightly tighter clearances than mine, then you would need lighter fluid. The damper rods don't appear to be anything which was manufactured to close tolerances. The internal washer is probably just a stamped component. If my washers are installed with the sharp edge up and yours are sharp edge down, that would make a difference, too. (round or sharp edge from when the punch stamped the part)

I dunno... Maybe this is what happens when we try to make silk purses out of sows' ears? :mrgreen:
 

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BJ,

Amsoil Shock Therapy #10 = 32.1 Cst @40c ; and #5 = 15.7 Cst @40c, so i assume your 7.5 is a mix , approx 24 Cst @40c

Silkolene Pro RSF 2.5wt is 13.6 Cst, 5wt =26.7Cst, 7.5wt =37 Cst , all at 40Cst.

Amsoil Shock Therapy 7.5wt is actually bit lighter than Silkolene PRO RSF 5 wt. Now this would make more sense to me if your rebound orifice is at stock size, based with my experience.

I am thinking this might be because intiminator has a rather tight seal around (even after my mod) the inside of tube where, AFAIK, emulator is very loosely fitted. Perhaps that reduces amount of "free bleed" that's in the stock system due to the large tolerance exist - i am not sure.

BTW, which part do u mean when u say "washer" :
PartShark.com - Motorcycle Parts, ATV Parts, UTV Parts, PWC Parts, Powersports Apparel, Motorcycle Accessories for OEM and Aftermarket.
the only sealing ring i could see is the #14... and it hardly seals on mine when i had them apart last time.

AR
 

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The washer is part of the fork assembly's inner tube and is not available as a replacement part. See the attached pic- the washer is called "check valve".

The seal of the RT would not affect rebound as the emulator has a very lightly sprung check plate.

How much preload do you have on your spring? (unloaded measurement, that is- extended fork, zero force on the .90 spring)? This will be a different measurement than the installed preloaded, as the force of the compressed .90 spring will start to compress the top-out spring under the damper rod.
 

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ok - we are talking about different things - the check valve u are talking about is to enable the fluid to pass freely on rebound travel. Intiminator has the same thing - also lightly sprung. - sorry no pic like the one u have from RT Suspension Bible.

I was talking about the sealing ring on intiminator - AFAIK, no equivalent on emulator - according to Ricor, the reason for that was to stop any "free bleed" introduced by lack of tolerance with the stock damper rod itself, item 13 on the above fiche link. It worked too well for its own good, IMO, and i had to cut the "sealing ring" a little to make sure no additional stiction is introduced by the intiminator.

see the grey sealing ring at the very bottom of the intiminator: it's meant to seal against the inside of tube as the damper rod and therefore the intiminator which sits on top goes up and down ensuring most of the fluid pass through the intiminator shims on compression and check valve on rebound



------------

in terms of preload, I measure with everything on the bike and front wheel in the air and fork caps open. I guess that means the top-out spring is under force (the weight of front wheel and other front suspension items)- it compresses by about 3 mm.

I add spacer and close the fork cap #19 on above fiche, and screw down the adjuster by another 7mm or so. So if i measure the total preload by adding the 7mm and 6mm the fork cap would have push down the spring by the time it is screwed on, this would give a 13mm total preload - i guess u would called this installed preload- does that mean by "unloaded" preload is about 16mm then?

The preload arrangement gives me a rider sag of about 42mm (92kg/202 lbs out of shower) - i would have preferred a little more to give me a bit more negative travel to deal with the crappy road here, but it's a balance act.
 

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Correct, the RT emulator has no such sealing device to help the damper rod's sealing ring with bypassing fluid (item 13 on the fiche). That could account for the Intimidator's need for lighter fluid. The emulator just sits on top of the damper rod and any fluid leaking past "item 13" will not be controled from below.

I didn't say that quite clearly of the washer. The washer I speak of, is the "check valve closes on rebound stroke" in the pic in my last post. However, with your explanation of the Intimidator's sealing feature, that probably makes this check valve tolerances a non-discussion point.

Installed preload vs unloaded... Yes, you have that correct. Sometimes we can get confused depending on how we measure. Your installation is pretty much the same as mine.
 

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Discussion Starter #15 (Edited)
Bazooka Joe and AceRider - thanks for all your work and willingness to share you findings. I've spent a significant amount of time reading all of your posts on the various threads, including this gem of a thread. I've also picked up a copy of the Race Tech suspension bible. I think I've now got a pretty good handle on all the tuning "knobs" available when trying to set up emulators on the Wee.

At the risk of derailing my own thread, I have one lingering question about emulator install. Various folks have reported that if you drill the damper rod holes as shown in the RT instructions, the lower two holes are covered by the oil lock piece. Additionally, I believe that Rich from Sonic has suggested (in a different thread) that the upper two (new) holes will be above the "check valve" referenced in post 12 above in the final few inches of fork travel, such that they inadvertently become additional rebound holes. I wonder if this somehow plays into the symptoms that some people report about rebound being underdamped. So, what's a guy to do with regard to drilling out the damper rods?

Option 1: only enlarge the current two holes but drill no additional holes.

Option 2: enlarge the current holes, and drill two more holes below the stock ones. From the photos I've seen, the oil lock piece does not appear to fit snugly against the damper rod, so these two holes may actually still provide some oil flow (but photos may be misleading). Any thoughts on how much oil flow, if any, these two holes would provide?

Option 3: Enlarge current holes, and drill out two new holes above them, and just live with the fact that rebound will be OK in the upper end of suspension travel, and might go to *$&% at the far end of travel.

Option 4: Drill them as RT suggests.

Thoughts?
 

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my head is spinning from working out the physics - perhaps, if Rich Desmond is looking at this thread, might chime in how it should be measured?
 

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Thinking about drilling the extra holes....
a) The stock damper rod holes are too large for controling low speed compression dampening- this is why our bikes dive so badly with the stock suspension. Meaning, no changes required for swapping to emulators or Intimidators, that is- in regards to low speed compression dampening. But:
b) The stock damper rod holes are too small for high speed compression dampening- this is why the stock suspension hammers so hard on sharp impacts. More flow capacity is required and the stock damper rod holes just don't have enough.
c) So, how much larger do these holes need to be for adequate flow at high speed dampening? Seems to me, that the size and number of holes recommended by Race Tech is just waaaaay over the top.

My thoughts: I think if you added only the two (well, "four" if you count thru both tubing walls), you would have plenty of flow. Compare these holes to the possible orifice in the emulator- there is absolutely no way to flow more fluid thru the emulator than these four holes.
 

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following what BJ says, it follows that as long as the size of damper rod's compression orifice(s) is at least as large as the emulator's orifice area when the blow off plate is lifted, then it is sufficient. - everything else being the same, u cant flow anymore fluid (emulator becomes the new 'bottleneck")

I suppose this still doesnt answer JPK's question - what happens to these enlarged (and/or additional orifices) at full compression - i didnt pay attention when i last had everything apart. - if the whole thing is disassemble, one could see how the damper rod seats on the oil lock piece and the relation with the stanchion on full compression.
 

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In the last inch or so of travel, the fork fluid bleeds between the "check valve" washer and the bottom spacer. This acts as a progressive dampening system to reduce or prevent severe bottoming.

Something of note, though, is that on the return stroke from full fork compression, there is essentially no rebound control when the "check valve" washer is crossing over those drilled out larger diameter holes. Not a good thing, but not very much we going to do about it. Luckily, this is only for a short length of fork travel.
 

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Discussion Starter #20
In the last inch or so of travel, the fork fluid bleeds between the "check valve" washer and the bottom spacer. This acts as a progressive dampening system to reduce or prevent severe bottoming.

Something of note, though, is that on the return stroke from full fork compression, there is essentially no rebound control when the "check valve" washer is crossing over those drilled out larger diameter holes. Not a good thing, but not very much we going to do about it. Luckily, this is only for a short length of fork travel.
You guys are definitely both better at the "numbers" than me (and likely at fluid dynamics), but I did some playing around with numbers. Using pi*r^2 to figure out the area of a given hole, I came up with the following:

RT recommendation of a total of six 5/16 holes = total hole area of 0.460 inches. So, I'm going to assume that any combination of holes that yields the same (or more) total area should flow "enough" fluid (within reason - I don't think a thousand microscopically small holes would flow the same amount due to differences in flow at the edge of a hole vs the center).

Four 3/8" holes = 0.442 inches

Two 7/16" holes and two 3/8" holes = 0.522 inches

You could play with this all day, but what I'm getting at here is that if I drilled out the stock holes to 7/16 inches, and then added two more 3/8" holes below them I'd have more total hole area than the stock RT recommendation. If the oil lock piece covers the two lower holes but is loose enough to allow them to still flow some fluid, this may be enough. This would also be handy if we knew exactly how much room we have above the stock holes and below the "check valve", i.e., what's the max hole I can drill here without it becoming a rebound orifice at the bottom end of fork travel. This would need to be balanced against not putting the hole pairs too closely together and compromising the strength of the damper rod.

Thoughts?
 
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