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Compression feel and ICS swap on 09 CRF450R


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Does the compression adjustment on the forks mainly effect the low speed vs high speed damping? Here's my dilemma:

I'm noticing that the stock forks are harsh in the intitial stroke such as when riding over rocks or sharp bumps, so much so that often the front wheel spikes and deflects and feels unplanted, kinda scary and wears me out. Yet on MX tracks I'm using all the travel but not bottoming a ton (but to be honest I do have alot of hard landings because I'm not going fast enough yet to clear alot of jumps at will). I'm on a budget and I'm wondering if going to lighter ICS springs would smooth out those intial spikes, or if I'd be better off lightening the compression clicker although it would seem that would make me bottom too much. I find myself avoiding chop because it goes straight through to my arms. What I'll ultimately do is get a revalve but for now I'm looking for cheaper alternatives.

I'm 174 lb w/o gear, 190 lb with, and I have a 5.3 rear spring (stock was 5.5), and FC link. Forks are stock, MX51 front tire.

Edited by MoreCowbell
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Race sag is 108mm, static is like 42 or so (don't have my notes at the moment), right around what FC recommended when I got the link and spring. I haven't checked to see if there's any fork binding - I assume when you say "R/S" you mean right side? If there was binding wouldn't I feel it as I'm sitting on the bike pumping the forks up and down? Things move pretty freely FWIW. Also FWIW I've only got like 8 hrs on the bike and I'm getting ready to change the fork oil for the first time, could more break in time make a difference?

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Race sag is 108mm, static is like 42 or so (don't have my notes at the moment), right around what FC recommended when I got the link and spring. ?

Seems a bit excessive to me. I never have much luck running that much sag, esp. the static. Seems like most the weight would be sitting rearward and not balanced causing the frt. to feel a little harsh.

doc

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I haven't checked to see if there's any fork binding - I assume when you say "R/S" you mean right side? ?

Yes, it doesn't have to be far off to cause problems, check it like this......

1.Install both forks and set fork height using calipers or a ruler. It is important that fork height be exactly the same for both sides. Tighten pinch bolts to the proper specs (Top: 18 Ft-Lbs | Lower: 15 Ft-Lbs).

2.Before installing axle make sure the end of it (and the edge of axle hole) has not been "mushroomed" from hitting it with a metal hammer. If theres any lip it must be ground off or fork will bind.

3.Install the axle (use rubber or plastic hammer only) and tighten the axle nut to proper spec. If the axle turns while tightening, tighten one right side axle pinch bolt to hold axle in place.

4.Tighten both left side axle pinch bolts to spec.

5.With the left side axle pinch bolts and axle nut tightened, loosen the right side axle pinch bolts. Take a small flat head screwdriver and carefully tap it into the slot between the two right side axle pinch bolts. This will enlarge the axle hole. You will then be able to grab the bottom of the right side fork tube and push it in and pull it out freely. You will be able to see the fork settle naturally into position on the axle without binding.

6.Remove the screwdriver and tighten the right side axle pinch bolts to spec.

If you're wondering if your forks are currently bound up, put your bike on a stand and start this procedure at Step 4.

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Seems a bit excessive to me. I never have much luck running that much sag, esp. the static. Seems like most the weight would be sitting rearward and not balanced causing the frt. to feel a little harsh.

doc

I hear what you're saying, but in this case I don't think that's it as I had the same harsh feeling back when I ran alot less sag, no link, etc. That's why I was wondering if perhaps a simple change in the ICS would be a good cost effective way to get at adding some plushness in the initial stroke without starting to bottom all over the place.

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Going to a lighter IC spring is basically the same as going down in main spring rate - which is what the '09 certainly doesn't need. If anything, your fork is harsh due to an imbalance in the chassis - even with the FC link. I don't know why they suggest so much sag. 105mm should be plenty, BUT at your weight you really need stiffer fork springs. If you keep the fork up in the stroke, they won't feel so harsh on the braking bumps. They feel that way now because your fork is riding too low in the stroke.

Personally, at your weight I would have recommended keeping the stock shock spring and going up a rate with the fork.

Also, the compression adjuster on your fork ONLY affects lo-speed damping.

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Going to a lighter IC spring is basically the same as going down in main spring rate - which is what the '09 certainly doesn't need. If anything, your fork is harsh due to an imbalance in the chassis - even with the FC link. I don't know why they suggest so much sag. 105mm should be plenty, BUT at your weight you really need stiffer fork springs. If you keep the fork up in the stroke, they won't feel so harsh on the braking bumps. They feel that way now because your fork is riding too low in the stroke.

Personally, at your weight I would have recommended keeping the stock shock spring and going up a rate with the fork.

Also, the compression adjuster on your fork ONLY affects lo-speed damping.

Thanks, you mentioned the forks feeling harsh because they're riding low in the stroke over braking bumps. So let me ask you this: what's making me crazy is when I'm just cruising over level and smooth ground (like a trail) but there's spots where there's sharp rain ruts going across or rocks etc, it feels like the forks are high in the stroke (no braking) and still really harsh, I feel every rock and hole spike right thru to my hands and arms and the tire wants to deflect. Even when I'm on the throttle a bit (thereby for sure keeping the forks high) i get the same sensation. Anyway.........you can see my confusion.

Thanks for the input so far.

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Does the compression adjustment on the forks mainly effect the low speed vs high speed damping? Here's my dilemma:

I'm noticing that the stock forks are harsh in the intitial stroke such as when riding over rocks or sharp bumps, so much so that often the front wheel spikes and deflects and feels unplanted, kinda scary and wears me out. Yet on MX tracks I'm using all the travel but not bottoming a ton (but to be honest I do have alot of hard landings because I'm not going fast enough yet to clear alot of jumps at will). I'm on a budget and I'm wondering if going to lighter ICS springs would smooth out those intial spikes, or if I'd be better off lightening the compression clicker although it would seem that would make me bottom too much. I find myself avoiding chop because it goes straight through to my arms. What I'll ultimately do is get a revalve but for now I'm looking for cheaper alternatives.

I'm 174 lb w/o gear, 190 lb with, and I have a 5.3 rear spring (stock was 5.5), and FC link. Forks are stock, MX51 front tire.

Your problem is the mid-valve. No doubt about it.

The velocities and displacements related to these type of hits that you get with rocks and roots is nothing like what you get on most groomed MX tracks.

Now...will changing the IC spring make it better?

Well...yes and no.

The IC spring contributes to overall resistance, or the force required to compress the fork to the next millimeter. If you make any contribution softer, the fork will be...well...softer.

So then it comes down to the matter of what do you change and what is the consequence of making that change. In this case, changing the IC spring could improve sharp impacts to some degree, but will most likely cause the fork to be a bit too wallowing and degrade much faster. I wouldn't do it.

That said, if the fork is not bottoming on the MX track you can try a lower oil level but I think if you want perfection in the rocks you’re going to need to go a little deeper.

:banana:

Uni Dell Taco Kit Description.pdf

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Dave,

What would cause the spike in the midvalve?

So the reason why it is called a mid-valve is because it begins to offer resistance when rod speeds approach a mid-speed velocity.

Mid-valve has nothing to do with position. It's not a "mid-stroke" valve.

Now...how do they achieve such a little device?

Well...the shim stack on the piston is not clamped against the surface as you might see with most dampers. The shim stack can lift (float) allowing the fluid to flow or bleed through the piston with little to no resistance. In other words, the mid-valve does nothing for low-speed movements.

Now...since lift is limited, meaning that the shim stack will only lift so far before it runs into some sort of a limiting device, like a plate or cup, the pressure within the cartridge will begin to build as rod speeds increase beyond a low, mid-speed velocity, (mid speeds can be broken down into low-mid, mid-mid and high-mid).

With that, once rod speeds start to go beyond the upper realm of a mid-speed movement (high-mid) the stack cannot deflect any further and it certainly will not float away from the piston any more. When this happens, the valve starts to lock up, since the pressure generated by the fluid flow is greater than what the valve will flow. Pressure becomes greater on the front than in the back and the conversion of kinetic energy to heat goes way up. Therefore a spike is created and that resistance is obviously transferred into the chassis and the handlebars. The bike lifts or is pushed to one side and there you are hanging on for dear life.

So...float can be good, (but not always) and a mid-valve doing mid-valve like things is good, but high-speed mid-valve lock up is very bad for things like braking bumps, and rocks and roots.

What some tuners will do is allow the shim stack to float further from the piston therefore allowing more flow during the bigger hits, (creating a mid-valve that is more “check plate” like). This does works but then you have a fork that cannot build enough pressure soon enough, which causes the fork to feel too soft and tends to wallow and tends to blow through, (compromises, compromises) as acceleration always precedes velocity.

Does that help?

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Thanks for the explanation Dave, make perfect sense. I am looking forward to trying out some of your products. It will be this winter after the season is over, but that is the best time to play around and tune, right?

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  • 2 weeks later...
S

With that, once rod speeds start to go beyond the upper realm of a mid-speed movement (high-mid) the stack cannot deflect any further and it certainly will not float away from the piston any more. When this happens, the valve starts to lock up, since the pressure generated by the fluid flow is greater than what the valve will flow. Pressure becomes greater on the front than in the back and the conversion of kinetic energy to heat goes way up. Therefore a spike is created and that resistance is obviously transferred into the chassis and the handlebars. The bike lifts or is pushed to one side and there you are hanging on for dear life.

What some tuners will do is allow the shim stack to float further from the piston therefore allowing more flow during the bigger hits, (creating a mid-valve that is more “check plate” like). This does works but then you have a fork that cannot build enough pressure soon enough, which causes the fork to feel too soft and tends to wallow and tends to blow through, (compromises, compromises) as acceleration always precedes velocity.

What about the situation where, after the shims have "floated" and hit the stopper they deflect?

What's to be gained by replacing a single thick shim, say .2, with a couple .1s instead of increasing float? I would expect that the transition point would be the same (float being equal) with a softer second stage of damping.

And what about using a bleed shim as the first in the stack of midvalve shims?

Questions, questions, in a quest for knowledge.

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