marcusgunby
LIFETIME SPONSOR
- Jan 9, 2000
- 6,450
- 2
You guys are very naughty children and im going to tell Jer when he comes back.The teacher will be very cross with you.I can here him flexing his cane right now.
Rocky, rooty trail settings.
- Thread starter MTRHEAD
- Start date
James Dean
Member
- May 17, 2000
- 137
- 0
Some time ago Jeremy said the shim stack actually opens very little, this is very important, to know how far the shim stiffness is really effective.
How do we know??
How do we know??
James D,
EXCELLENT stuff, Man! I've been kicking around the diameter/crossover/bottom shim for a while, but couldn't quite get it to add up. Every time, I'd end up stumbling all over the possible varibles, and give up. So, I'd try to keep the profile the same, but change shim number and thknesses. So, basically, I was fuzzy-mathin' the tapering effect, but correctly computing the thkness factors. It did work quite well.
In a real example, my computation resulted in about a 15% reduction in HS dampening, and the change was quite noticeable. The bike went from "OUCH, this sucks!!!" on the rootsy stuff, to "Ahhhh... What root??" However, I did start to bust a few spokes with my higher speed.
Now, to apply all this to my new RM250.
Shocknut,
Actually, we engineers are kinda boring to listen to, UNLESS you like every last detail picked to the bone! btw, bring your own pocket liner!
Marcus,
Naughty boys, eh? Maybe "we" are the teachers today!
------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"
[This message has been edited by MN KDXer (edited 11-15-2000).]
EXCELLENT stuff, Man! I've been kicking around the diameter/crossover/bottom shim for a while, but couldn't quite get it to add up. Every time, I'd end up stumbling all over the possible varibles, and give up. So, I'd try to keep the profile the same, but change shim number and thknesses. So, basically, I was fuzzy-mathin' the tapering effect, but correctly computing the thkness factors. It did work quite well.
In a real example, my computation resulted in about a 15% reduction in HS dampening, and the change was quite noticeable. The bike went from "OUCH, this sucks!!!" on the rootsy stuff, to "Ahhhh... What root??" However, I did start to bust a few spokes with my higher speed.
Now, to apply all this to my new RM250.
Shocknut,
Actually, we engineers are kinda boring to listen to, UNLESS you like every last detail picked to the bone! btw, bring your own pocket liner!
Marcus,
Naughty boys, eh? Maybe "we" are the teachers today!
------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"
[This message has been edited by MN KDXer (edited 11-15-2000).]
Shockster,
Do you mean "warmer" as in reference to the 15%? Am I hearing to go a little more than that? "Pocket liner" is an engineer stereotype joke, btw. I don't have/wear one either.
The PPS shock on the Polaris sled... I haven't ridden it yet. I bought the sled last April, so I've gone up and down the lawn once, and up + down the trailer. Ask me again in a couple of weeks. My last sled has the Xtra-10, but only the Indy Select shock. Do you have any experience w/ the PPS?
------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"
Do you mean "warmer" as in reference to the 15%? Am I hearing to go a little more than that? "Pocket liner" is an engineer stereotype joke, btw. I don't have/wear one either.
The PPS shock on the Polaris sled... I haven't ridden it yet. I bought the sled last April, so I've gone up and down the lawn once, and up + down the trailer. Ask me again in a couple of weeks. My last sled has the Xtra-10, but only the Indy Select shock. Do you have any experience w/ the PPS?
------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"
I discussed the PPS concept with the GM & Tech Director at Penske when I was there. I had my opinion of it. Upfront I thought it rather strange to throw a hole in your damping curve and all. If you can picture the damping curve of this type of shock compared to the amount of shock travel you can probably see why aggressive riders were lessening the effect or even converting it back to standard design. However, some seem to like it and it would be hard to argue that it is wrong for them. For the aggresive guy, no way! Those wearing drop seat bibs,maybe,yes. Spring selection would be even more critical in my opinion with this shock. Drop me a note from time to time with your impressions. If you ride hard I would guess you will be looking for something better after a good round of objective testing. I can tell you this, the better you can dial your setup to reflect maximum front arm travel the better your ride will be. You know how to do this I assume. Transfer is the key. After that you valve for personal preference. We have to rap on this privately though as some have been getting speared for talking sleds on this site. Proper etiquette and all.
Warmer means in general. 15% would equate to a noticeable change. Figure at least 10% to notice it and maybe as much as 20% for those asleep at the bars. If it's right it's right!
I figured as much about the pocket liner. I was envisioning smocks as well. BTW, does your last name start with a Z?
Warmer means in general. 15% would equate to a noticeable change. Figure at least 10% to notice it and maybe as much as 20% for those asleep at the bars. If it's right it's right!
I figured as much about the pocket liner. I was envisioning smocks as well. BTW, does your last name start with a Z?
slowpokedennis
Member
- Dec 23, 1999
- 24
- 0
Would somebody please explain all this to me in plain english.
This is way over my head. But very interesting.
------------------
Dennis Col Oh
99husqvarna wr250
------------------
Dennis Col Oh
99husqvarna wr250
James Dean
Member
- May 17, 2000
- 137
- 0
In the discussions from the first half of this thread I tried to emphasize the importance of assessing shim force versus deflection rather than looking at shim stack stiffness.
----------------
Here is an example of why: Take half the shims out of the LS stack and put them in the HS stack. The HS stack becomes much stiffer, but does this increase HS damping??
The answer is no - it reduces LS and HS damping force.
Something to ponder.
The stiffness of the combined LS and HS shim stacks is the same and it opens wider for a given force. Sort of like backing off the the shims spring preload. Stiff shims don't always make for high damping force when they are put further back from the compression valve.
James
[This message has been edited by James Dean (edited 11-20-2000).]
----------------
Here is an example of why: Take half the shims out of the LS stack and put them in the HS stack. The HS stack becomes much stiffer, but does this increase HS damping??
The answer is no - it reduces LS and HS damping force.
Something to ponder.
The stiffness of the combined LS and HS shim stacks is the same and it opens wider for a given force. Sort of like backing off the the shims spring preload. Stiff shims don't always make for high damping force when they are put further back from the compression valve.
James
[This message has been edited by James Dean (edited 11-20-2000).]
So if you have gargantuan ports like our buddies at RT brag about do you ever develop enough shim deflection to "crossover" into the HSC - or do you expose enough peripheral port area to bleed off the pressure differential at low shim deflection? (THAT was one "H" of a fine runonsentence.....)
Could this explain the "don't increase the crossover thickness" disciples?
Could this explain the "don't increase the crossover thickness" disciples?
James Dean
Member
- May 17, 2000
- 137
- 0
Mace,
The Race Tech Gold Valves have 3 large openings that expose the shims far more. They will open with less pressure and flow more with comparable shims. Yes, the crossover is exceeded, and generally with a higher speed. I think the valving problems and loss of precise control stem from this higher speed.
The extra flow is usually good for rocks and roots, giving a softer ride. It's not that good when you want more high speed and bottoming resistance. The crossover issue should be handled by changing in smaller increments, say switching from .1mm to .15mm instead of jumping to .2mm.
Either RT or stock compression valves will work well with the right combination of shims. An exception would be a 14mm cartridge rod without extra relief. It flows so much more and is reacted with a larger area that sharp impacts need the extra flow. The advantage of RT is the package of shims and charts for those who want to work on it.
Looking at the charts, I'm surprised that RT isn't showing thinner or thicker crossovers or using thicker .2mm or .25mm shims on the HS stack at the higher settings. This is where the experienced suspension tuner will still have an advantage. Those that I know with RT Gold Valves never hit the right combination in less than 2 or 3 tries. Maybe they're just a picky bunch
.
James
[This message has been edited by James Dean (edited 11-21-2000).]
The Race Tech Gold Valves have 3 large openings that expose the shims far more. They will open with less pressure and flow more with comparable shims. Yes, the crossover is exceeded, and generally with a higher speed. I think the valving problems and loss of precise control stem from this higher speed.
The extra flow is usually good for rocks and roots, giving a softer ride. It's not that good when you want more high speed and bottoming resistance. The crossover issue should be handled by changing in smaller increments, say switching from .1mm to .15mm instead of jumping to .2mm.
Either RT or stock compression valves will work well with the right combination of shims. An exception would be a 14mm cartridge rod without extra relief. It flows so much more and is reacted with a larger area that sharp impacts need the extra flow. The advantage of RT is the package of shims and charts for those who want to work on it.
Looking at the charts, I'm surprised that RT isn't showing thinner or thicker crossovers or using thicker .2mm or .25mm shims on the HS stack at the higher settings. This is where the experienced suspension tuner will still have an advantage. Those that I know with RT Gold Valves never hit the right combination in less than 2 or 3 tries. Maybe they're just a picky bunch
James
[This message has been edited by James Dean (edited 11-21-2000).]
Shrimp on the barbie Jer
Member
- Nov 23, 2000
- 2
- 0
WOW! Guys I have to say that was fun reading. I liked it and think this is a area where your specific expertises can be very much used. I've done lots of math and related in school but frnkly this stuff goes beyound my capablites.(If you want real numbers) (Calc 3) (Or at least ablity to apply it)
The truth is and I have alluded to this before, in many situations I could not produce a number or direct answer for much of anything it just gets to complex. The werid thingis MNKDXER is dead nuts. I have made a point of studing ratio's of all things volumes, realtive displacements etc and created my own (Albiet seceret) propprtions and relations. These numbers are what i use to determine changes but in realality they have evrery thing to do with %'s..
It started along time ago.. Currently Shocknut is working with to see if he can tweak it but it is a program that give a real albiet bogus unit. It was writen by Kevin Stiwell.(Who remmbers him) It gives some good relationships but is no much more than a neat compaison..
It might be neat to let you guy disect it..
As for the piston issuses the seceret is in the low deflections and that is fundementaly why in our shaft speed ranges a low flow piston will perform better than anything else. Are there other issues.. You beet.. So low flow is not the only thing to consider.
What I like about this conversation is its about ideas.. I'm all for that..Thanks for contributing.. I sertianly don't know everything to every degree.. But I make it point to try..This Forum sparks the flame for me and lots of others I know that.
Regards,
JER
The truth is and I have alluded to this before, in many situations I could not produce a number or direct answer for much of anything it just gets to complex. The werid thingis MNKDXER is dead nuts. I have made a point of studing ratio's of all things volumes, realtive displacements etc and created my own (Albiet seceret) propprtions and relations. These numbers are what i use to determine changes but in realality they have evrery thing to do with %'s..
It started along time ago.. Currently Shocknut is working with to see if he can tweak it but it is a program that give a real albiet bogus unit. It was writen by Kevin Stiwell.(Who remmbers him) It gives some good relationships but is no much more than a neat compaison..
It might be neat to let you guy disect it..
As for the piston issuses the seceret is in the low deflections and that is fundementaly why in our shaft speed ranges a low flow piston will perform better than anything else. Are there other issues.. You beet.. So low flow is not the only thing to consider.
What I like about this conversation is its about ideas.. I'm all for that..Thanks for contributing.. I sertianly don't know everything to every degree.. But I make it point to try..This Forum sparks the flame for me and lots of others I know that.
Regards,
JER
James Dean
Member
- May 17, 2000
- 137
- 0
Ideas, yes,
How about a REAL brainstorm.
I have a bunch of ideas floating around on these shim stacks. Math is a strong point too, calculus through differential equations and linear algebra helps. My question is what is the relationship of FORCE (F) to VELOCITY (V) with a shim stack producing stiffness Ks ??? I don't want absolute force in lbs, just a mathematical relationship.
Tell me where I'm wrong because these relationships are a real puzzle for me. See if you can follow.
-----------------------
Starting with a damper having a fixed orifice and a relationship of F= C * V**2 gives a nonlinear increasing resistance to motion. F is force, C is a damping coefficient, and V is compressive velocity.
V**2 is velocity squared or V*V.
With a flexing shim stack C is no longer a constant. It is a function of the pressure exerted on the shims, flexing to reduce the force. So change the name to C(p).
F = C(p) * V**2
Now the tricky part. If the shim deflection doubles, what does C(p) do? The fluid velocity past the shims is cut in half when the damper speed is unchanged. The force was proportional to V**2, so the pressure and therefore force (F) is cut down by 1/4. Does this mean that C(p) is proportional to 1/(deflection)**2? I think its in the ballpark.
Next, consider the shim deflection is close to proportional to force divided by stiffness Ks. This is getting ugly, I know.
The resulting relationship appears to be,
F = (c*Ks/F)**2 * V**2
where c is a constant.
Solving for force as a function of V gives,
------------------------
F = (c * Ks * V)**.66
------------------------
Now substitute your shim stiffness (Ks) as a % change in the stackup to see the change in force from the fork damping. Whew!!
Maybe you engineer types can come up with something better. Try graphing it and things look very interesting. (Also graph F=c*V**2 to get the feel) Next comes crossovers.
James (on the far side)
[This message has been edited by James Dean (edited 11-24-2000).]
How about a REAL brainstorm.
I have a bunch of ideas floating around on these shim stacks. Math is a strong point too, calculus through differential equations and linear algebra helps. My question is what is the relationship of FORCE (F) to VELOCITY (V) with a shim stack producing stiffness Ks ??? I don't want absolute force in lbs, just a mathematical relationship.
Tell me where I'm wrong because these relationships are a real puzzle for me. See if you can follow.
-----------------------
Starting with a damper having a fixed orifice and a relationship of F= C * V**2 gives a nonlinear increasing resistance to motion. F is force, C is a damping coefficient, and V is compressive velocity.
V**2 is velocity squared or V*V.
With a flexing shim stack C is no longer a constant. It is a function of the pressure exerted on the shims, flexing to reduce the force. So change the name to C(p).
F = C(p) * V**2
Now the tricky part. If the shim deflection doubles, what does C(p) do? The fluid velocity past the shims is cut in half when the damper speed is unchanged. The force was proportional to V**2, so the pressure and therefore force (F) is cut down by 1/4. Does this mean that C(p) is proportional to 1/(deflection)**2? I think its in the ballpark.
Next, consider the shim deflection is close to proportional to force divided by stiffness Ks. This is getting ugly, I know.
The resulting relationship appears to be,
F = (c*Ks/F)**2 * V**2
where c is a constant.
Solving for force as a function of V gives,
------------------------
F = (c * Ks * V)**.66
------------------------
Now substitute your shim stiffness (Ks) as a % change in the stackup to see the change in force from the fork damping. Whew!!
Maybe you engineer types can come up with something better. Try graphing it and things look very interesting. (Also graph F=c*V**2 to get the feel) Next comes crossovers.
James (on the far side)
[This message has been edited by James Dean (edited 11-24-2000).]
marcusgunby
LIFETIME SPONSOR
- Jan 9, 2000
- 6,450
- 2
Yes thats what i was going to write-NOT
James D,
OOooh, Man, were you stuck at the in-laws this weekend?
Deep, deep, thoughts you have! Here's a few tidbits of fluid flow you'll also need to factor into your shim deflection vs flow analysis-
a) Fluid flow is not proportional to only the cross section area of the orfice. Factors such as surface edge drag, length of orfice, sharpness of inlet & oulet edges, and viscosity of fluid, are just a few of the considerations which can be a science in itself.
b) The exit side of the piston has some constrictions that are not similar around the entire port circumference. The fluid's escape path is not uniform around the entire orfice.
c) The shim stack does not open parallel to the surface of the piston orfice.
These factors will toss plenty of wrenches into the system and, most likely, confuse most of us waaaay beyond recovery.
Maybe, it's time to put down the calculator and start getting oil on our fingers.
------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"
[This message has been edited by MN KDXer (edited 11-25-2000).]
OOooh, Man, were you stuck at the in-laws this weekend?
Deep, deep, thoughts you have! Here's a few tidbits of fluid flow you'll also need to factor into your shim deflection vs flow analysis-
a) Fluid flow is not proportional to only the cross section area of the orfice. Factors such as surface edge drag, length of orfice, sharpness of inlet & oulet edges, and viscosity of fluid, are just a few of the considerations which can be a science in itself.
b) The exit side of the piston has some constrictions that are not similar around the entire port circumference. The fluid's escape path is not uniform around the entire orfice.
c) The shim stack does not open parallel to the surface of the piston orfice.
These factors will toss plenty of wrenches into the system and, most likely, confuse most of us waaaay beyond recovery.
Maybe, it's time to put down the calculator and start getting oil on our fingers.
------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"
[This message has been edited by MN KDXer (edited 11-25-2000).]
James Dean
Member
- May 17, 2000
- 137
- 0
I aggree with you,
The concept was that whatever percentage change is made to the shim stack stiffness, the resulting change in force will be something less.
(yes, we went to the in-laws too)
James
[This message has been edited by James Dean (edited 11-26-2000).]
The concept was that whatever percentage change is made to the shim stack stiffness, the resulting change in force will be something less.
(yes, we went to the in-laws too)
James
[This message has been edited by James Dean (edited 11-26-2000).]
marcusgunby
LIFETIME SPONSOR
- Jan 9, 2000
- 6,450
- 2
A local suspension guy in the uk has recently got a dyno-im hoping to go over to see him in the next few weeks and have a play.
James Dean
Member
- May 17, 2000
- 137
- 0
I owe you guys a report back on the altered fork valving on my WR. This is what I went with -
(5) 24 X .1mm (was 6 shims)
14 X .1
12 X .1 (new)
24 X .1
22 X .1
20 X .1
18 X .1
16 X .1 (was 16 X .15)
14 X .15
12 X .15
11 X .25
18 X .5
------------
My riding impressions were in tight to medium woods riding with lots of rocks and roots. The forks still had a good firm controlled feel but lost alot of harshness in the rocks and roots. I found myself looking further ahead and riding faster as it was building confidence. It used to make me tense up for sharp hits and the change allowed me to just keep the throttle open more. The few whoops we had were still handled well. I had 2 KTM 520exc's to chase and be chased by during the ride. They had been giving me trouble in these conditions before, but not now. Except when I stalled, those e-start bikes aren't fair.
It's tempting to try softening more, but I didn't feel the bike was holding me back.
My thoughts are that the increased crossover gap (.2mm) was the biggest change, followed by 1 less shim on the LS (6 to 5). The reduced size (12 X .1 - new) on the crossover may not be as effective from a number of factors such as curvature and having a 4 port layout. The 16 X .1 softened the HS slightly also gave a little extra thread coverage putting it back together.
Insights anyone?
James
(5) 24 X .1mm (was 6 shims)
14 X .1
12 X .1 (new)
24 X .1
22 X .1
20 X .1
18 X .1
16 X .1 (was 16 X .15)
14 X .15
12 X .15
11 X .25
18 X .5
------------
My riding impressions were in tight to medium woods riding with lots of rocks and roots. The forks still had a good firm controlled feel but lost alot of harshness in the rocks and roots. I found myself looking further ahead and riding faster as it was building confidence. It used to make me tense up for sharp hits and the change allowed me to just keep the throttle open more. The few whoops we had were still handled well. I had 2 KTM 520exc's to chase and be chased by during the ride. They had been giving me trouble in these conditions before, but not now. Except when I stalled, those e-start bikes aren't fair.
It's tempting to try softening more, but I didn't feel the bike was holding me back.
My thoughts are that the increased crossover gap (.2mm) was the biggest change, followed by 1 less shim on the LS (6 to 5). The reduced size (12 X .1 - new) on the crossover may not be as effective from a number of factors such as curvature and having a 4 port layout. The 16 X .1 softened the HS slightly also gave a little extra thread coverage putting it back together.
Insights anyone?
James
James,
Thanks for the feedback. The 16 x .10 might be a little more significant than you're giving it credit for. Despite that it's lower in the stack, it is closer to the mid point, so its strength is reflected upwards at a fairly good ratio. By dropping to .10, you've essentially went from 3.38 shims of .10 thickness to only one.
The extra crossover shim... Yes indeed, that shim was significant in extending the distance the LS stack flexes before contacting the HS.
Keep careful notes and keep having fun.
------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"
Thanks for the feedback. The 16 x .10 might be a little more significant than you're giving it credit for. Despite that it's lower in the stack, it is closer to the mid point, so its strength is reflected upwards at a fairly good ratio. By dropping to .10, you've essentially went from 3.38 shims of .10 thickness to only one.
The extra crossover shim... Yes indeed, that shim was significant in extending the distance the LS stack flexes before contacting the HS.
Keep careful notes and keep having fun.
------------------
-Vet A Enduro and Hare Scramble Rider.
-Dry tech talker and "known to toss stones"
Jeremy Wilkey
Owner, MX-Tech
- Jan 28, 2000
- 1,453
- 0
Well I'm about usless on this topic, As for the dyno well we are actually in process of building one. The cheaper models have limintations in terms of speed and acelration, so we are designing one that has some of the real exspensive features while saving money one certain fluff type operations. I can only say it is a fun process and that it will be a useful tool in terms of figuruing a lot of the variables, and getting real world numbers.
Jer
Jer
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