Udi's shimmed boxxer

KW - Wait until you ride my '08 ATA with a very major damping mod that it will receive soon. I think you'll be impressed at what a proper shimmed damper can do.

My take on this recently is that LSC or compression immediately from zero speed up to whatever your blowoff point is just causes spiking on super high speed chatter that is mostly absorbed by your tires and translated into your suspension at a lower shaft speed. What you want is mid-speed support with a mellow levelling off to highspeed for rocks and larger edges. There are easy ways to get there with shim tuning, but the point is that the midrange and the transition point and duration is far more critical to tune than the high speed or low speed. Just my observations...

Edit: Your 07 ATA still has compression damping with the adjuster backed all the way off still. They're made to provide useable damping for all springrates and rider weights, so they are still useable for a normal sized rider at the lighter end of the range. Remove the damper and drill out the compression port to something huge if you want to experience no compression damping hehe...

This thread reminded me of Rennie talking about his Boxxer setup on the Santa Cruz site. He said something about running no compression damping at all, and I thought it was a mistake, but after reading a bit I suppose it makes sense.

It's probably because he runs so heavy of a springrate (I hear he likes his stuff set up stiff, even for his weight) that he doesn't get much brake dive and can tune the high speed compression and bottoming just through the air chamber size. Just a guess though.

Bicyclist said:

This thread reminded me of Rennie talking about his Boxxer setup on the Santa Cruz site. He said something about running no compression damping at all, and I thought it was a mistake, but after reading a bit I suppose it makes sense.

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That really depend how you ride. Or just your best feeling with the bike. Also remember that Rennie use hard spring rates.

I don't know. I was the type of guy (before) that ran a MZ 66 or a 888 Rc and I was so happy because it was smoth and with a lot of movement. Now, that i'm a competitive rider i'm the oposite. I want to run the LSC almost full. More is better for me right now.

Hacktastic said:

KW - Wait until you ride my '08 ATA with a very major damping mod that it will receive soon. I think you'll be impressed at what a proper shimmed damper can do.

My take on this recently is that LSC or compression immediately from zero speed up to whatever your blowoff point is just causes spiking on super high speed chatter that is mostly absorbed by your tires and translated into your suspension at a lower shaft speed. What you want is mid-speed support with a mellow levelling off to highspeed for rocks and larger edges. There are easy ways to get there with shim tuning, but the point is that the midrange and the transition point and duration is far more critical to tune than the high speed or low speed. Just my observations...

Click to expand...

Exactly. Kind of what I've been saying. I'm open the idea of a better execution of the concepts. I just haven't ridden anything that makes me think we're there yet.

Hacktastic said:

Edit: Your 07 ATA still has compression damping with the adjuster backed all the way off still. They're made to provide useable damping for all springrates and rider weights, so they are still useable for a normal sized rider at the lighter end of the range. Remove the damper and drill out the compression port to something huge if you want to experience no compression damping hehe...

Click to expand...

I'm going to drop some 3w oil into it this week (I've got 5 right now). I'm pretty happy with how the 888 works, I just want my totem as supple. But I'm not going to screw with the damper on that one because I may put it up for sale once that boxxer comes out.

The totem I'm keeping for a long enough while that I don't mind screwing with it a bit. Plus I've already got a box of totem goods that I can easily return the thing to stock bits. Seeing Udi's pics just got me thinking.

I mentioned it before but I'm going to be down in mammoth this weekend. Be cool to get some runs with you if you feel like making the drive.

Hacktastic said:

My take on this recently is that LSC or compression immediately from zero speed up to whatever your blowoff point is just causes spiking on super high speed chatter...

Click to expand...

Rant on...
Where did this fear of LSC come from? My guess is adjusters that don't actually do what they claim. Anyway, spring rate is the most important adjustment you can make, but LSC is by far the most important damping adjustment. With those 2 spot on you could almost forget about the rest. I exaggerate but I need to offset this silly idea.

Rant off..

MttyTee said:

Rant on...
Where did this fear of LSC come from? My guess is adjusters that don't actually do what they claim. Anyway, spring rate is the most important adjustment you can make, but LSC is by far the most important damping adjustment. With those 2 spot on you could almost forget about the rest. I exaggerate but I need to offset this silly idea.

Rant off..

Click to expand...

I'd say it's a combination of things, the LSC circut (and the fork in general) being too crude to effectively function with an adjustment, the range of LSC control being not-appropriate, and what you said about the adjuster/circut not really doing what it's supposed to if it's really controlling LSC.

I don't think you can call any one adjustment the "most important", with excessively fast or slow rebound it doesn't matter what your compression is set too, with insufficient high speed you'll spike a lot, especially at high speeds where you need control (not to be confused with the high-shaft-speed hits that you are encountering), and so on. If LSC is done correctly it can be beautifull (my avalanche), but otherwise the "adjustment" can screw up a lot too, and for the longest time MTB dampers haven't been complex enough to warrent the adjustment, or for it to really do what it's supposed to IMO.

Every manufacturer has a different idea of what range "low speed" falls into. I just think that the low speed needs to be very very soft to let the fork even get into its travel otherwise it just causes harshness as it starts off the top. It's the motion after that point that you want the damping to have the effect on, which is (by most definitions) the midspeed. The highspeed is where it gets "yanked" into the travel, and is usually controlled by the blowoff support behind the shims, or the springrate behind a ball valve, etc..

Hacktastic said:

Every manufacturer has a different idea of what range "low speed" falls into. I just think that the low speed needs to be very very soft to let the fork even get into its travel otherwise it just causes harshness as it starts off the top. It's the motion after that point that you want the damping to have the effect on, which is (by most definitions) the midspeed. The highspeed is where it gets "yanked" into the travel, and is usually controlled by the blowoff support behind the shims, or the springrate behind a ball valve, etc..

Click to expand...

That sounds kind of like TPC+, wouldn't you agree?

Hacktastic said:

Every manufacturer has a different idea of what range "low speed" falls into. I just think that the low speed needs to be very very soft to let the fork even get into its travel otherwise it just causes harshness as it starts off the top. It's the motion after that point that you want the damping to have the effect on, which is (by most definitions) the midspeed. The highspeed is where it gets "yanked" into the travel, and is usually controlled by the blowoff support behind the shims, or the springrate behind a ball valve, etc..

Click to expand...

I think you are mixing up speed and position here.

Hacktastic said:

It's probably because he runs so heavy of a springrate (I hear he likes his stuff set up stiff, even for his weight) that he doesn't get much brake dive and can tune the high speed compression and bottoming just through the air chamber size. Just a guess though.

Click to expand...

relative to his weight, Rennie actually runs his suspension pretty soft. Just watch practice at a world cup (or check out Earthed) and you'll notice lots of different setups being used by everyone. I watched Peat and Rennie follow each other down the same section of St. Anne last year and Rennie's fork was burried in the bottom of it's travel while Peaty's was riding noticeably higher (could be spring rate or compression settings). same deal with his rear suspension. And then there are guys like Fairclough who weighs about 150lb and runs 160 psi in his fork.

Best thing to do is understand what the adjustments actually control and how it translates into how the fork feels over diffrent terrain. and then keep trying new settings until you find what works for you.

Gotta gree with MttyT on the LSC adjustment being most important. And i think the faster you go the more you start to appreciate what it does.

General Lee said:

Gotta gree with MttyT on the LSC adjustment being most important. And i think the faster you go the more you start to appreciate what it does.

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I think rebound is the most critical adjustment of all really, you can ride a fork with no compression damping but having no rebound damping makes a bike dangerous to ride.

However, I do agree that the faster you go, the more you appreciate what LSC does - when you're hitting corners, g-outs, and most critically, really steep stuff so hard that your arms are threatening to collapse under you, having more LSC is such a massive benefit.

That said, if your arms are as weak as mine are right now, hitting stuff that hard isn't difficult at all!

Socket said:

I think rebound is the most critical adjustment of all really, you can ride a fork with no compression damping but having no rebound damping makes a bike dangerous to ride.

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Rumor has it that Myles won the Mt Snow Norba in 2000 with a completely blown rear shock (something was making a racket when he came by me) so I guess you could argue neither are absolutely needed, but I would agree if I had to pick one to be with out I'd keep me rebound. Though while externally adjusting a damper I tend to leave rebound till last.

Point was, I've tuned for people riding XC, DH, MX, SX, and even some guys on Harley's (blush) and by ADDING LSC to the majority of their set ups they come back raving about how much more supple the bike is and how much more controlled the ride is.

Socket, Lee, Udi and the rest know what I'm saying but to the others.....don't be afraid of damping!!!!! It only encourages manufacturers to continue to sell sub-par dampers with adjusters that don't do much or don't do what they claim.

...and don't change any of your adjusters based on how it feels while bouncing in a parking lot

MttyTee said:

Rumor has it that Myles won the Mt Snow Norba in 2000 with a completely blown rear shock (something was making a racket when he came by me) so I guess you could argue neither are absolutely needed.

Point was, I've tuned for people riding XC, DH, MX, SX, and even some guys on Harley's (blush) and by ADDING LSC to the majority of their set ups they come back raving about how much more supple the bike is and how much more controlled the ride is.

Socket, Lee, Udi and the rest know what I'm saying but to the others.....don't be afraid of damping!!!!! It only encourages manufacturers to continue to sell sub-par dampers with adjusters that don't do much or don't do what they claim.

...and don't change any of your adjusters based on how it feels while bouncing in a parking lot

Click to expand...

my bike feels like rubish in the parking lot. well, it feels balanced and smooth but it has so much LSC that it just feels harsh when it not being ridden hard. if i take my dh bike trail riding it feels like sh*t, but once up to spped it's great. same sort of thing applies to modern dh geometry; a 63 degree head angle is fantastic for racing fast, but it makes the bike a real chore to handle when you are just coasting along.

I know some of the setting a few of the world cup guys run who are the same weight as me but i could never get away with it. Comparitively speaking i'm just way too slow.

General Lee said:

my bike feels like rubish in the parking lot. well, it feels balanced and smooth but it has so much LSC that it just feels harsh when it not being ridden hard. if i take my dh bike trail riding it feels like sh*t, but once up to spped it's great. same sort of thing applies to modern dh geometry; a 63 degree head angle is fantastic for racing fast, but it makes the bike a real chore to handle when you are just coasting along.

Click to expand...

Exactly the same here... lots of people bounce on my bike and whinge about it being way too firm with the compression, but it's hard to argue with the actual on-track results.

Socket said:

Exactly the same here... lots of people bounce on my bike and whinge about it being way too firm with the compression, but it's hard to argue with the actual on-track results.

Click to expand...

Can you imagine Robbie Gordon wheeling his trophy truck out of his million dollar trailer and hopping up and down on the bumper, then crawling under the truck to click his dampers. Amusing thought.....:biggrin::biggrin:

MttyTee said:

Rumor has it that Myles won the Mt Snow Norba in 2000 with a completely blown rear shock (something was making a racket when he came by me) so I guess you could argue neither are absolutely needed, but I would agree if I had to pick one to be with out I'd keep me rebound. Though while externally adjusting a damper I tend to leave rebound till last.

Point was, I've tuned for people riding XC, DH, MX, SX, and even some guys on Harley's (blush) and by ADDING LSC to the majority of their set ups they come back raving about how much more supple the bike is and how much more controlled the ride is.

Socket, Lee, Udi and the rest know what I'm saying but to the others.....don't be afraid of damping!!!!! It only encourages manufacturers to continue to sell sub-par dampers with adjusters that don't do much or don't do what they claim.

...and don't change any of your adjusters based on how it feels while bouncing in a parking lot

Click to expand...

Right now i'm really liking the damping that the 5th element provides me. It feels amazing for pedaling in downhill sections an also when you hit a big jump or a small one the answer of the shock is really smooth.

The problem i'm getting with it is the rebound. I did the tuning to make it more faster but the problem seems that it's a LOT faster in HSC because it loose all rebound control

What can i do? That's a thing that is making me change this shock that really has an amazing compresion damping,

Nico

Npdh said:

Right now i'm really liking the damping that the 5th element provides me. It feels amazing for pedaling in downhill sections an also when you hit a big jump or a small one the answer of the shock is really smooth.

The problem i'm getting with it is the rebound. I did the tuning to make it more faster but the problem seems that it's a LOT faster in HSC because it loose all rebound control

What can i do? That's a thing that is making me change this shock that really has an amazing compresion damping,

Nico

Click to expand...

What kind of bike is this for?
What is the main rebound shim stack? Outside diameter and thickness?
What is the smaller rebound stack?

MttyTee said:

Can you imagine Robbie Gordon wheeling his trophy truck out of his million dollar trailer and hopping up and down on the bumper, then crawling under the truck to click his dampers. Amusing thought.....:biggrin::biggrin:

Click to expand...

No, but I would be happy to take it for a drive and let him know what I think of the suspension. Heck, I would even ride shotgun with him for some testing. :biggrin:

Anyway, you guys are right on with the comment that suspension can not be judged by bouncing up and down on it in a parking lot. My DH bike suspension feels stiff until your hitting rocks at high speed. My MX bike is way more stiff than the DH bike. Recreational trail riders get on my MX bike and complain that the suspension does move. However, it's nice when your skimming braking bumps or whoops and for the occational over jump to flat from 20 foot in the air.

ChrisKring said:

Anyway, you guys are right on with the comment that suspension can not be judged by bouncing up and down on it in a parking lot. My DH bike suspension feels stiff until your hitting rocks at high speed. My MX bike is way more stiff than the DH bike. Recreational trail riders get on my MX bike and complain that the suspension does move. However, it's nice when your skimming braking bumps or whoops and for the occational over jump to flat from 20 foot in the air.

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Anyone ever see the Top Gear episode where Richard Hammond drives an F1 car. It's completely undrivable for someone of his ability. He can't go fast enough to get the tires hot or heat up the carbon brakes so he can't turn or stop, and the suspension is too stiff because he can't go fast enough to get the proper downforce. he just drives off the course or totally blows all the turns.

the better a rider you become, and the faster you go the less you can rely on the parking lot test to setup you suspension. I heard that after the first WC round Gee Atherton decided he needed to go do his suspension testing on steeper tracks becasue the ones he used to determine his baseline settings weren't adequate for what he'd need for WC tracks.

MttyTee said:

What kind of bike is this for?
What is the main rebound shim stack? Outside diameter and thickness?
What is the smaller rebound stack?

Click to expand...

I have the 5th on a PDC 8to5,

I do the following valving : 1 shim small x 1 big x 1 small x 3 big

I'm running 5wt silkolene.

The shims are the ones that come with the shock.


I don't know why it happening. When I hit the shock at HSC the rebound just loose the control. but after is semi slower.

Npdh said:

I have the 5th on a PDC 8to5,

I do the following valving : 1 shim small x 1 big x 1 small x 3 big

I'm running 5wt silkolene.

The shims are the ones that come with the shock.


I don't know why it happening. When I hit the shock at HSC the rebound just loose the control. but after is semi slower.

Click to expand...

I'm assuming if you had 6 shims total that they are 0.1mm thick. I've fooled around with crossover stacks like you are running without much success. Remember, there are shims on top of the bolt that act as a low speed rebound circuit. Try this stack: 1 small against the piston, then 3 big, then 1 small.

You need to have a pretty tall stack with some more profile to it than "big" and "small" shims for a two stage stack to have any effect. It's much more useful for compression.

If the rebound side has a concave piston, use a single "small" shim on the bottom to flatten out the main face shim, then start with 3 "big" ones followed by another "small" one on top.

Honestly that issue is probably more in the shape of your rebound needle than the shimstack though...

I had a run down my local track with Udi's fork yesterday and was stoked. Possibly the best feeling fork I've ridden. While everyone has different preferences for how they like their forks to feel, this was spot on for me. Very smooth, predictable and consistent - noticeably more so than my own Boxxer WC.

Obviously it will be awhile be durability is really tested, but then I'm gonna bug udi to make me up one.

toodles said:

I had a run down my local track with Udi's fork yesterday and was stoked. Possibly the best feeling fork I've ridden. While everyone has different preferences for how they like their forks to feel, this was spot on for me. Very smooth, predictable and consistent - noticeably more so than my own Boxxer WC.

Obviously it will be awhile be durability is really tested, but then I'm gonna bug udi to make me up one.

Click to expand...

Dang, I want to make something like that even more now. Hopefully once Udi has some more time on it he might post up some tips and info for people like myself to make our own!

toodles said:

I had a run down my local track with Udi's fork yesterday and was stoked. Possibly the best feeling fork I've ridden. While everyone has different preferences for how they like their forks to feel, this was spot on for me. Very smooth, predictable and consistent - noticeably more so than my own Boxxer WC.

Obviously it will be awhile be durability is really tested, but then I'm gonna bug udi to make me up one.

Click to expand...

Don't bug, threaten!

Sounds like Udi got it right then eh. Toods drag him up here for a ride.

Udi said:

Ended up making an adjustable damper, got new pics on first page.

The new one is 35g lighter than motion control and my old damper too.

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That looks awesome!

If you have the time, could I trouble you for any construction/assembly pics and/or instructions that you could provide for this adjustable damper?

While I find the idea of a full TPC+ conversion (like Socket's) to be enticing as I could amuse myself with some TPC+ and MRD stickers on my Boxxer, your damper looks very slick, very simple, and like it would actually be a bunch easier to make/mod! I hope I'm right, because I'd love to try this out.

Udi said:

Compression:

Old damper (v1.0) pics:
1234

Click to expand...

Now that's a beauty, but how about the space between the R and the C units?

Both units are about 9 to 10 inches long, i wonder won't they come too close to one-another in full compression?

That's great, i guess i'll go for it, but i plan on mounting it on the MoCo top cap, and... i hope the TPC shims out of the Kingpin i've just ordered + the shims out of the Boxxer's shimstack will be enough for me - I plan on having the oil level take care for the progression towards the end... let's hope it works

now what does UDI stand for...Unbelievably Determined Individual?

I kinda skimmed through the posts, so don't kill me if you already answered this.


Does your New Adj. Dampner, adjust Low speed or is it a mix of Both High and Low without dampning interference?


I just made a replica dampner of your first model, the nonadjustable version, and it seems to work awesome so far. Just need to fiddle with the shims a bit more. Ill post pictures of mine if I can find batteries for my camera

Udi said:

Ended up making an adjustable damper, got new pics on first page.

The new one is 35g lighter than motion control and my old damper too.

Click to expand...

And that when I think that you have a lot of time.

Nice work maaan,

I did see it already some photos.

Continue with the photo session!

Udi said:

Well in short (probably skipping some things)

Ingredients:
- 1 boxxer spring-side topcap
- 1 kingpin rebound shaft + adjuster
- 2 kingpin TPC pistons
- 2 kingpin return valve shims
- 2 boxxer return valve springs
- 1 washer (12mm ID) cut from manitou shock reducer spacer
- Lots of shims, various OD and thickness

Method:
Put all ingredients in bowl, stir, and microwave on high for 4 minutes.

Seriously though, first you lathe down the pistons (OD = 25.20mm rebound, 25.30mm compression), and you drill the topcap to fit the threads of the rebound shaft base (this is your new compression rod), slide the 12mm ID washer over the threads before putting it through the topcap. You'll need a nut that fits the threads, either find one (almost impossible) or make one yourself from the kingpin lowers which is what I did. Careful use of teflon tape will seal the assembly. The actual damping piston end for both comp and reb should be self explanatory.

There are a few important things not to do, one is don't clamp the rebound shaft anywhere along its length (you'll crush it), I filed some flats in the very base where the port is so I could use a small shifter on it. Another is, don't overtighten your nut on the topcap/shaft assembly, the threads will break (it's manitou after all). Be very gentle with everything and you'll be okay.

Click to expand...

So, I should soon have:
-1 kingpin rebound shaft + adjuster
-2 kingpin TPC pistons (3 even!)
-2 kingpin return valve shims (I assume these will be in the fork..)

I don't have:
-1 boxxer spring-side top cap
-2 boxxer return valve springs (or do these come in my WC?)
-1 washer cut (12mm ID, how thick?) cut from manitou shock reducer spacer
-lots of shims... I will have some, but probably not enough to really play with things

Looks like I'll have to buy at least a few things, but hopefully it will all be worth it!

Hopefully I can get access to a lathe soon, once I have a top cap that should be easy to drill out. You made that nut from the lowers?? Any clue what the threads are? Teflon tape? Sounds good... The damping piston ends should be self explanatory? Haha, I sure hope so, so I don't end up...

"a small shifter" ..what is that? Gentle, that could be tough... Thanks for all the info! By the way, would you mind posting up the shim combinations that you end up using and maybe your weight/riding weight, riding style, etc. I haven't got much of a clue when it comes to tuning, and a base setting to start from would be great!

This is mainly for Kidwoo, but applies I surpose to anyone who's willing to learn about the reason why compression damping matters.

Now, I can't currently get Maple (a math program) to work like it should be doing, so I can't supply fancy graphs that would explain this really well.

Basically, I spent quite a while on an assignment last semester for Noise and Vibration on the suspended packing of an object in a box.

This like any other usual mass spring damper (aka a bike with passenger) has a motion that takes the form:

x"+(c/m)x'+(k/m)x=0

(x"=acceleration of the mass; x'=speed of the mass; x=displacement of the mass.) So the theory is all the same.

Basically, for a given displacement (fork compression), an mass decelerated with compression damping has a lower peak acceleration than one without.

In other words:

If you hit a 4" bump and you want your suspension to compress 3", a fork that has compression damping with a lower spring rate can do this with less accelerations=less force transmitted to your hands. A damperless spring can still limit the displacement to 3", but the accelerations are significantly greater.

I really will try and put some overlaid graphs up as pictures in the next day or two, because this is a concept that is fundermental in the understanding of the way suspension interacts with the ground.

If you get nothing else out of this, know that it is a mathematically provable fact that a fork with compression damping will transmit less force to a rider than one without for the same fork displacement

dilzy said:

This is mainly for Kidwoo, but applies I surpose to anyone who's willing to learn about the reason why compression damping matters.

Now, I can't currently get Maple (a math program) to work like it should be doing, so I can't supply fancy graphs that would explain this really well.

Basically, I spent quite a while on an assignment last semester for Noise and Vibration on the suspended packing of an object in a box.

This like any other usual mass spring damper (aka a bike with passenger) has a motion that takes the form:

x"+(c/m)x'+(k/m)x=0

(x"=acceleration of the mass; x'=speed of the mass; x=displacement of the mass.) So the theory is all the same.

Basically, for a given displacement (fork compression), an mass decelerated with compression damping has a lower peak acceleration than one without.

In other words:

If you hit a 4" bump and you want your suspension to compress 3", a fork that has compression damping with a lower spring rate can do this with less accelerations=less force transmitted to your hands. A damperless spring can still limit the displacement to 3", but the accelerations are significantly greater.

I really will try and put some overlaid graphs up as pictures in the next day or two, because this is a concept that is fundermental in the understanding of the way suspension interacts with the ground.

If you get nothing else out of this, know that it is a mathematically provable fact that a fork with compression damping will transmit less force to a rider than one without for the same fork displacement

Click to expand...

For most situations this is correct (assuming your step input is the same and that the compression is mathematically underdamped, which it almost always is), and probably the most succint explanation I've seen. What compression damping allows you to do, is move the point in the travel at which the peak force occurs. It's all to do with the amount of energy absorbed by the fork - compression damping provides MORE resistance force early in the stroke than a spring alone would, so that the spring is not required to compress as far. The compression damping then decreases as the fork's movement slows down and eventually reaches zero speed at maximum displacement, at which point you only have the spring force and no damping force.

Increasing compression damping means that the peak force point occurs earlier in the stroke (before max displacement is reached) and thus can be lower in order to absorb the same amount of energy. Because the compression damper is absorbing some of the energy, the spring can be run softer, and so when it reaches that maximum displacement, the spring force is lower than it would have been had you used the equivalent spring rate to achieve the same displacement response without any compression damping.

HOWEVER - note that to achieve this, the spring rate has to be lowered as you increase the compression damping. Otherwise you can increase peak force on fast hits and decrease the amount of travel used on all hits (which can be a desirable situation in itself if that's what you want).

Socket said:

For most situations this is correct (assuming your step input is the same and that the compression is mathematically underdamped, which it almost always is), and probably the most succint explanation I've seen. What compression damping allows you to do, is move the point in the travel at which the peak force occurs. It's all to do with the amount of energy absorbed by the fork - compression damping provides MORE resistance force early in the stroke than a spring alone would, so that the spring is not required to compress as far. The compression damping then decreases as the fork's movement slows down and eventually reaches zero speed at maximum displacement, at which point you only have the spring force and no damping force.

Increasing compression damping means that the peak force point occurs earlier in the stroke (before max displacement is reached) and thus can be lower in order to absorb the same amount of energy. Because the compression damper is absorbing some of the energy, the spring can be run softer, and so when it reaches that maximum displacement, the spring force is lower than it would have been had you used the equivalent spring rate to achieve the same displacement response without any compression damping.

HOWEVER - note that to achieve this, the spring rate has to be lowered as you increase the compression damping. Otherwise you can increase peak force on fast hits and decrease the amount of travel used on all hits (which can be a desirable situation in itself if that's what you want).

Click to expand...

Now thats a bloody good explanation and one of the reasons am trying to get a lot more low speed comp out of my 36, just to hold it up in the stroke more (just ordered some 0.2mm thick shims from Teknik yesterday).

Yeah all my damping was sub-critical, but when it approached critical it still had reduced peak acceleration when compared to a spring only system, it just wasn't quite as low.

I did say somewhere in there with a lower spring rate, but I didn't really highlight it. I should mention I don't do mechanical engineering, I do Ocean engineering so this stuff isn't really my forte. Ask me about wave diffraction forces on a pile array in the ocean however and you'll get a good answer.

dilzy said:

Now thats a bloody good explanation and one of the reasons am trying to get a lot more low speed comp out of my 36, just to hold it up in the stroke more (just ordered some 0.2mm thick shims from Teknik yesterday).

Yeah all my damping was sub-critical, but when it approached critical it still had reduced peak acceleration when compared to a spring only system, it just wasn't quite as low.

I did say somewhere in there with a lower spring rate, but I didn't really highlight it. I should mention I don't do mechanical engineering, I do Ocean engineering so this stuff isn't really my forte. Ask me about wave diffraction forces on a pile array in the ocean however and you'll get a good answer.

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Ocean engineering eh? Built any sweet oceans lately?

There are also situations where compression damping can increase force transmissibility (extremely high speed movements at low displacement, like hitting a fist-sized rock at 70km/h) as compared to having only a spring of higher stiffness. However, to put in perspective how fast this needs to be over say a 3" high hit, for a stock valved rear shock (DHX5) to do that with mid-range compression settings, a 450lbs/in spring and a 3:1 leverage ratio, you'd need to manage to move the wheel at approximately 6m/s. This is about the upper limit for possible vertical wheel speeds on a bike, the actual land speed you'd need for that is phenomenally high if the suspension is only moving 3" vertically.

Obviously if you run more compression damping though, the speed at which that can occur is lower...