clamped mid

ddt clamped mid valve.if i add a 12x.11 bleed shim against the piston,will it affect rebound?my thought is it will be closed over by the stack.it may have some 2 way lag ,i don,t know.

if the smart people here think it will lag and effect the rebound,what would i add to compensate?

i,m going to try a lighter rebound of 20 20 14 18 16 14 12 11 clamp

this is on a kyb fork yz2502st .48 springs with honda hp5 oil.

how does my rebound stack look considering ,the oil used ,the spring rate,and the bleed shim on comp face?

thanks cj

I have the full DDT setup in an '06 YZ450, so it's not entirely a match except in principal. Rather than run a bleed shim as the face shim against the piston, I took a small step toward a bleed by replacing the second shim up from the face with a 16:

Mid was:

20 0.11

20 0.11

20 0.11

16 0.11

18 0.11

14 0.11

11 0.25

11 0.25

17 0.30

SPI 62 Spring

SPI 175 Spring

collar 7.30

Changed to:

20 0.11

16 0.11

20 0.11

18 0.11

16 0.11

14 0.11

11 0.25

11 0.25

17 0.30

SPI 62 Spring

SPI 175 Spring

collar 7.30

With that, I'm running a considerably lightened rebound stack:

20 0.11

18 0.11

13 0.11

20 0.11

16 0.11

14 0.11

12 0.11

10 0.11

10 0.11

The bike is a desert racer, SPI #3 inner oil, stock rates. The goal was to get the fork to be a little more compliant at low speeds on rocky ground without sacrificing any of the brilliant high speed performance of the fork. I think it's an improvement in some ways, but I'm not done fiddling with it yet.

I don't notice a "lag" transitioning to rebound, but I'm not running a lot of rebound, either, so it's hard for me to say. I can't see why it would cause one.

If you are worried about lag or shim deformation you could make a improvised check plate using a smaller shim that will act as a spacer post. For example with a 12.2 (6mm id) and the following shim would be a 20.1 (12mm id). this would give a .1 bleed like you were hoping in the stack above.

I have the full DDT setup in an '06 YZ450, so it's not entirely a match except in principal. Rather than run a bleed shim as the face shim against the piston, I took a small step toward a bleed by replacing the second shim up from the face with a 16:

Mid was:

20 0.11

20 0.11

20 0.11

16 0.11

18 0.11

14 0.11

11 0.25

11 0.25

17 0.30

SPI 62 Spring

SPI 175 Spring

collar 7.30

Changed to:

20 0.11

16 0.11

20 0.11

18 0.11

16 0.11

14 0.11

11 0.25

11 0.25

17 0.30

SPI 62 Spring

SPI 175 Spring

collar 7.30

With that, I'm running a considerably lightened rebound stack:

20 0.11

18 0.11

13 0.11

20 0.11

16 0.11

14 0.11

12 0.11

10 0.11

10 0.11

The bike is a desert racer, SPI #3 inner oil, stock rates. The goal was to get the fork to be a little more compliant at low speeds on rocky ground without sacrificing any of the brilliant high speed performance of the fork. I think it's an improvement in some ways, but I'm not done fiddling with it yet.

I don't notice a "lag" transitioning to rebound, but I'm not running a lot of rebound, either, so it's hard for me to say. I can't see why it would cause one.

What's your street weight and how would your stack differ from a full-on aggressive intermediate/pro MX stack?

I too run the DDT with the EPNP and Clover shim in an 09 YZ450. What exactly does the bleeding of a stack do for you?

Also, what effect does moving the cross-over shim in the primary base shims of the compression valving have?

Are the primary base shims for high or slow speed damping?

Thanks.

What's your street weight and how would your stack differ from a full-on aggressive intermediate/pro MX stack?
175, and to be very general, the stacks for a A/B level MX rider would be stiffer at the face (more base shims).
What exactly does the bleeding of a stack do for you?
Any shim stack that has an adjuster screw on it already has a bleed circuit. In a sense, what the bleed does is to delay the operation of the valve by allowing oil to bypass the valve at low stroke speeds. When the speed increases to the point where the pressure against the valve rises high enough, the stack lifts. Building more bleed into the stack itself essentially is a bit like opening the clicker on that stack a little more. Bleed shims, shims smaller the the face diameter of the piston ports that are placed directly against the piston, let a certain amount of oil volume pass the stack without lifting.

The "bleed shim" in my stack could also be called an early crossover. It allows the bleed circuit to work normally, but the single face shim can lift at the edge soon after the bleed circuit becomes overwhelmed without raising the resistance to oil flowing through the valve very noticeably.

In either case, you can think of it this way: the same clicker adjusts the bleed through both the rebound and the mid valve. The way the mid originally was built, it had "float", which allowed it to lift out of the way until oil velocities where in the mid speed range, so the rebound clicker had not much effect on compression. With the DDT, the mid is clamped by a spring which allows it to "blow off" beyond a certain pressure, but forces it into operation immediately as the bleed circuit hits its limit, and meaning that the rebound clicker affects the early, or low speed operation of the mid a great deal more. The "bleed/early crossover" is a tweak you can use to tilt the balance one way or the other.

what effect does moving the cross-over shim in the primary base shims of the compression valving have?
A valve stack is somewhat analogous to a leaf spring in a truck. The longest leaves act the soonest, and increasing the number of full length leaves gives you a fairly linear increase in basic rate of resistance. As the long leaves bend, they increasingly put pressure on the ends of the shorter leaves, which bolsters the central area of the leaf. Further deflection of the longer leaves is focused more at the outer ends where it is less supported, and this effect works its way up the stack.

A crossover works by putting some space between the first shim or shims, allowing it to deflect as though it were a separate set with a lighter rate until it moves far enough to come into contact with the larger shims above the crossover, at which point it starts to work more like it would have worked without the crossover. The effect is that there is less resistance at lower speeds, but the resistance ramps up once the crossover has been exceeded. The position of the crossover controls how much lighter the early resistance will be, and when the rest of the stack comes into play. The size and number of shims in a crossover also have an effect.

Are the primary base shims for high or slow speed damping?

If you think of damping resistance as a curve, the stiffer the face stack is, the more sharply the curve will rise from lower speeds to high, as I understand it. So you could say "low speed", but it's more accurate to say the the face shims control the "initial damping" rate or response.

a great description , however adding face shims adds just as much hs as low speed , even adding shins after a cross over will act in reverse and add low speed , the reason is the cross over gap closes fairly early in the speed range , so the 2 stage stack becomes "one" fairly early in the speed range

to really separate high and low you would have to put the cross over half way into the taper part

about a 1/2 a year ago I used re-stackor to compare a bleed shim with float.

(I wanted to see id I could get a ddt type setup with no float to behave like it had some float)

according to my restackor sim the bleed shim of course helped to get towards some float but it was far from achieving the type of flow required to simulate float.

The reason was with true float the shims are lifted off the entire flow perimeter of the port with no load, but with the bleed shims, they are pivoting from the center at zero float distance.

Still "you do what you can with what you got". And a bleed shim may be the easiest thing to do. I ended up making a setup with float and final blow-off with the ability to preload the blow off spring or not. but that's another story.

I ended up making a setup with float and final blow-off with the ability to preload the blow off spring or not. but that's another story.

How did that work out for you?

it's nice of course because it gives more tuning options, but it's a lot more work to make than a bleed shim.

I think if you are going to make a bleed shim to emulate float you should run re-stackor to get an idea of what you need. For example, if you are trying to get nearly the effect of running .1mm float you need much more than .1mm of bleed cross-over thickness because it flows much less than .1mm of float. I can't remmeber how much less but I do remember being surprised at how much less.one other point is with float you can have a true check valve (rebound seperation), but with the bleed shim it may not be as seperated.

Re stackor saves alot of time .

it's nice of course because it gives more tuning options, but it's a lot more work to make than a bleed shim.

I think if you are going to make a bleed shim to emulate float you should run re-stackor to get an idea of what you need. For example, if you are trying to get nearly the effect of running .1mm float you need much more than .1mm of bleed cross-over thickness because it flows much less than .1mm of float. I can't remmeber how much less but I do remember being surprised at how much less.one other point is with float you can have a true check valve (rebound seperation), but with the bleed shim it may not be as seperated.

Re stackor saves alot of time .

Union,

Did you use the single spring dell taco or dual spring ddt? You have a ride report by chance? That sounds really interesting.

But is float or bleed the answer for cj's problem? He is having recovery issues during and after successive bumps or hits with his setup. Spring #175 is staying compressed too long and then the fork falls, is what I think is happening.

Cj, actually I like Gray's idea as well with his rebound stack. Its really hard to say until you actually try something. Or like union mentioned, run it through a program to get an idea of what will happen. I've never had this issue on my Mx setup.

I'm wondering if this is an issue of riding style and or excessive weight on the front of the bike, just thinking out loud here.

I have used the ddt in the past, but for this one I made my own because I wanted float.

It works well, but I am going to try more than the stock .25 float (08yz144 enduro racing) I don't have 20 years of riding to compare with so I can't give great feedback , but I've been competing well for the last 3-4 years(top B rider 40+ a.k.a not blazing fast) and am an engineer,and have always revalved all of my bikes myself, so I can see that it works the best compared to other setups i have made,both normal stacks and clamped blow off type ddt. But they were all different bikes/fork types and like I said I don't have massive amounts of other bikes I have competed on to compare to so...

The bike is very good at whoops ,and rarely bottoms, and hitting square edges at higher speeds, but i would like it to be a liitle better on small amplitude square chop, so I will try .35 float next(i think it will smooth the transition on to the mid). One thing for sure is it has the advantage of maximum configurability, clamped or floated,adjustable preload blowoff. The main advantage of blow off other than the obvious pressure limiting is , you can utilize the full port flow area if needed, which is not possible if the stack is fixed. And if one thinks the full flow is too much (i tend not to think so though),you can still limit the blow of travel if needed........too bad all this is not externally adjustable....lol

Just to clarify I wasn't posting with the intent to suggest that float was cj's problem, just trying to give some guidance on what i had noticed in trying to achieve float -like response with a bleed shim.

@grayracer513: Thanks for the schooling! That's the most I've learned about suspension tuning in a single post, perhaps even all-total, since I've been a TT member. It is very much appreciated. You should be an instructor the way you explain things so well.

Another quick question. Perhaps, I'm opening Pandora's box; but what's the advantages/downfall of running a float verses a clamped MV as in the DDT?

I have used the ddt in the past, but for this one I made my own because I wanted float.

It works well, but I am going to try more than the stock .25 float (08yz144 enduro racing) I don't have 20 years of riding to compare with so I can't give great feedback , but I've been competing well for the last 3-4 years(top B rider 40+ a.k.a not blazing fast) and am an engineer,and have always revalved all of my bikes myself, so I can see that it works the best compared to other setups i have made,both normal stacks and clamped blow off type ddt. But they were all different bikes/fork types and like I said I don't have massive amounts of other bikes I have competed on to compare to so...

The bike is very good at whoops ,and rarely bottoms, and hitting square edges at higher speeds, but i would like it to be a liitle better on small amplitude square chop, so I will try .35 float next(i think it will smooth the transition on to the mid). One thing for sure is it has the advantage of maximum configurability, clamped or floated,adjustable preload blowoff. The main advantage of blow off other than the obvious pressure limiting is , you can utilize the full port flow area if needed, which is not possible if the stack is fixed. And if one thinks the full flow is too much (i tend not to think so though),you can still limit the blow of travel if needed........too bad all this is not externally adjustable....lol

Just to clarify I wasn't posting with the intent to suggest that float was cj's problem, just trying to give some guidance on what i had noticed in trying to achieve float -like response with a bleed shim.

thanks for sharing all that Union.

You are right on target with your post. I was off in another direction. I saw cj, post and was thinking about his problem with the ddt.:thumbsup:

@grayracer513: Thanks for the schooling! That's the most I've learned about suspension tuning in a single post, perhaps even all-total, since I've been a TT member. It is very much appreciated. You should be an instructor the way you explain things so well.

To the extent that it's accurate, that's good. I'm really just learning suspensions myself.

As to the DDT question, Dave Johnson, the originator of the design, explains the theory of it better than I could. Read his posts in this thread:

http://www.thumpertalk.com/forum/showthread.php?t=721192

I can tell you that the setup is able to absorb "the big hit" better than anything I've ridden. Especially a hard strike on a fully extended fork, like a landing, or coming down in the whoops too deep. I find myself wondering where all that energy could possibly have been carried off to sometimes. The earlier issue of it lacks a little of the buttery plushness over tiny, repetitive bumps like 'washboards" or small stones, but he's changed things around a bit since, and it's always improving.

the DDT actually doesnt get rid of energy any more than any other fork, but it does it in a different manner for sure , its the opposite to a normal fork,the DDT tries to remove as much energy as early as possible(with clamped mid) and then allow the rest to bleed off via the blow off, this like all setups has advantages and disadvantages.

Ive ridden with it and can say in that respect it does work . I honestly think though the new system like kawi has with the shim stack underneath the clamp shim that allows the midvalve stack to move a bit is a better alternative though . there has to be some form of float or bleed to allow front end to settle in corners I know this for a fact . the DDT cant move as much as it does on a moto application as the forks use too much travel on G outs . Dave is a smart guy and if I were a betting man I think probably in the next year or so he will figure out a system that actually works very well . I've heard many good things about this system on WR forks though .

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