High speed compression

[MTRIDER]

Could someone give me some info on high speed compression damping ? Like, where does it kick in ? I cant tell much of a difference, can you revavle just that circuit ? How does it know when to switch circuits? Just by how fast the wheel is moving ?

Thanks
Mike T

01 YZ 250 (if that makes any diff)

 

[marcusgunby]

We need some more info?is this forks or shocks?
When you say you cant tell much difference do you mean using the high speed adjuster?You can revalve just the high speed circuit.It is how fast the wheel travels that decides what circuit works.

 

[JTT]

Also remember that the separation between HSC, MSC and LSC is almost theoretical...what I mean is there is not an actual a physically separate "circuit", so it doesn't really "switch". I hope this makes some sense :)

 

[afm_722]

Sounds like MTRider is referring to his adjustable high speed compression damping on his shock. MT, I have found that a number of my buddies were adjusting this adjuster wrong. Assuming you've adjusted correctly (closing it clockwise, then opening between 1.5-2 1/4 turns counterclockwise), then you should feel a definite difference between a half a turn of adjustment. If not, you probably need your shock serviced.

Normally, when there a lot of closely spaced choppy bumps, the bike likes a little less high speed compression. Lean more towards the 2 turns out setting. You should notice that the rear end squats a bit more on acceleration and it should be more responsive to the small choppy bumps in the initial part of the travel. Turning will suffer a little bit, but there are ways to address that. Generally, the high speed setting is better left at or near factory or your suspension tuner's recommendations. You can adjust a half a tunr one way or the other, but 1.5-2 1/4 is the sweetspot. (not coincidentally the low speed and rebound adjuster are usually at their best settings in the middle of their range, too. factories and suspension tuners generally valve their suspension this way.)

As far as where the circuits take over or how, there is a bit of a gray area in the middle of the stroke where they overlap. Generally, the low speed compression adjuster will aid the shock toward the last half of its travel. It aids bottoming control and when the bike is under a g-load (like a fast section going into a cavity where g forces are forcing the supension to compress and use most of it's travel, low speed compression can help keep the bike under control in this situation. Also whoops are another obstacle where a large portion of the travel is used.)

For example, just the other day I was going through a similar section like a describe (cavity) and the bike under g-forces was a bit loose or moved side to side, because at the bottom to top of this cavity were some bumps. Since my rebound was already a bit light, I added a couple clicks (clockwise) of low speed compression and the bike tracked straight and true and I was able to not burn up as much energy holding onto the bike.

Rebound is important too, but I believe rebound compliments the compression settings. I'll usually focus on getting my compression settings correct, then fine tune with rebound.

Good luck!!

 

[JTT]

Remember too, that rebound will also effect compression ;)

 

[marcusgunby]

afm makes some good points-the high speed adjuster is badly named as it really doesnt affect the high speeds much at all, think of it as a midspeed adjuster.I tend to use it to alter the ride height of the rear.Some shocks High speed adjuster work better than others-the poor design ones i believe just preload the stack on the low speed adjuster.
I think the Showa ones work well, the KYBs not so well.The techno flex shock has separate Low speed and high speed adjuster which should work better than the other type.

 

[James]

I can't figure out if Honda prints their manuals wrong, makes the high/low speed compression different than anybody else, or if their is a general misconception about high and low speed damping.

The Honda manuals say that High speed compression adjustment affects bottoming as in landing from big jumps (not low speed as AFM suggests)

It also says that low speed affects the initial travel such as skimming over choppy bumps (again...opposite of what AFM and others have said)

Finally, It was my impression that they are named high and low speed damping due to the speed of the compression of the suspension and not the speed of the bike so they appear to be appropriately named to me. The piston in the should would most likely be moving at a higher speed when landing a big jump (high speed compression damping according to honda) than when accelerating out of a corner over some bumps (low speed damping according to honda).

I'm not saying anybody is wrong exactly...I just get confused every time I read one of these threads.

 

[afm_722]

Hey James, this is often a misconception with my riding buddies too. As another member suggests, high speed also has a large affect on ride height in the rear (especially under acceleration). Because of this fact, doesn't it make sense that high speed affects the first part of the travel more?

Oh yeah, this is really going to confuse you!! When I back out of my high speed compression clicker...yes, I do bottom more, but it's not because of that adjuster alone. Because you've softened up the intial part of the travel, it blows through this portion quicker and often "overtakes" the last part of the travel. So, often times, when I back out of the high speed, I'll add a few clicks of low speed!!

Have you ever watched the Nationals on ESPN? Carmichael's mechanic last year, at every race it seemed, always said "because of the choppy bumps, we're going to reduce the high speed compression a bit". Seems like they kept backing off his high speed compression clicker. No wonder his bike looked like a chopper (that and the linkage....)

Also, it's a known fact that shaft speeds on the shock and fork are much higher (although less travel is used) while traversing choppy exit bumps or enter shallow hard terrain braking bumps. High speed can be equated to shock speeds. Landing from big jumps, the shaft speeds are much much slower. Sand is another subject!

So, in a nutshell, it doesn't surprise me that the 2003 Kawasaki's dropped the high speed compression adjuster as there has been a lot of confusion out there. Don't feel bad because the manuals often time don't help the situation.

Bottomline, is feel the effects for yourself. What we tell you in print, won't make sense until you feel it. Suspension tuning sometimes is a black art it seems. First you need something good to work with (springs and valving), then you need to correctly analyze what clickers need to be adjusted and/or if the fork oil height needs to be altered. It's very very easy to go off on a tangent and never find a good setting. It's very important to start with a baseline (the owner's manual or your suspension tuner's recommendation) and work from there.

Much of what I discuss is stuff I have "felt" and after all these years it seems I finally know what clickers need to be adjusted the first time out. I used to fall in the trap of saying "I want my suspension to be plush, so I'm going to back off on the clickers". This might have worked for fire roads, but it sure didn't in motocross!!

We're here to help, but a lot of it is trial and error. Of course, when your trialing and erroring be careful!!

 

[James]

My comment on the SHOCK piston speed (not the piston in the "should") was referring to the actual movement of the piston. Considering the linkage, going over the small choppy bumps might make the wheel move quicker, but in a limited range of movement, resulting in little movement of the piston in the shock. On a large jump with the suspension fully used, the linkage causes the shock to compress at a faster rate and the piston itself moves through the shock much faster than it would if the suspension were not fully compressed. SO the actual movement of the piston through the travel of the shock would be faster landing a big jump than it would over small bumps out of a corner.

An obvious difference I can feel is if I soften the low speed compression, the suspension isn't as harsh on roots and rocks. This would seem to affect the initial third of the travel as I don't go fast enough over roots and rocks to bottom the suspension. This would also substantiate Honda's instructions.
Going over the jumps, it does feel more suscpetable to bottoming this way, and this probably is related to having less low speed so the entire load is carried by the high speed valving, as you described.

Another item that adds confusion is the valving itself. The low speed valving is what is used by the initial travel of the suspension. The mid-valve is next, then the high speed valving. So obviously, if the low speed is for initial travel, it is what would be used over small bumps and such and the high speed valving would definitely come into play when you are using all of your suspension landing a jump. Why would the name it one way on valving but yet do it opposite on the adjusters?

Maybe they should call it initail travel, mid travel, and full travel valving/adjustment and drop the speed confusion altogether.

 

[afm_722]

Hey, James have you verified this with a suspension tester??? Theoretically, when you're talking about rising rate linkages, it sounds good. In the real world it doesn't. This isn't voodoo. Just ask any of the suspension tuner's (MX-Tech, Race Tech, Pro Action....). Let me know what they say.

 

[marcusgunby]

James i think you are confusing yourself, if a shock has a single stage stack every shock movement is affected by the stack design including the high speed part.The talk of different parts of compression stacks ie low speed, mid speed etc is really that -just talk-in reality every alteration has some effect on all speed ranges-just some more than others.

Think of shaft speed only, once you throw in pistons and shim deflections it can get really confusing.The high speed adjuster on most shocks is one of those things they designed to help sell a new model-its use is very limited and hard to use correctly.

The small choppy bumps will cause the shim stack to be moved alot is a very small time frame, a hard landing on a smooth downside of a jump may open up the shim stack less.

 

[James]

The topic is right here in front of them...I guess they can let us all know what they say. I don't think you'd argue that there isn't a ratio effect from the linkage. Actually, which part should I be verifying with the suspension tuner besides what the high speed compression adjustment does?

I haven't been impressed with any of our local "suspension tuners" and I do have a call in to Race Tech on another issue so I'll run this by them as well.

Again, I'm not saying you are wrong...just clarifying my confusion with what you are saying.

 

[afm_722]

James, good idea about having a suspension guru chime in!! FYI, here's a snip from factory connection that addresses shock and fork piston speeds:

Supercross tracks usually produce slower piston speeds from the shock and forks than an outdoor track, with a much greater G-out load. This means less damping produced by the shock and forks in a situation that causes more or a bottoming load. Note: to be competitive on a true SX track, a SX only type fork and shock setting is needed to handle todays obstacles. Remember that SX only setting will not be suitable for an outdoor MX.

 

[JTT]

Originally posted by James
Maybe they should call it initail travel, mid travel, and full travel valving/adjustment and drop the speed confusion altogether.

The problem with that idea is that valving is speed sensitive, not position sensitive. The valve has no way of knowing where it is in the stroke, only how fast the fluid is moving through it.

James, have you actually had a shock apart and looked at how it works? (not intending to be demeaning in any way). I know for me, it made a big difference in understanding what is going on in there and why.

The terminology also makes it more confusing, as Marcus said, the HSC adjuster does not truely adjust the HSC, IMO anyways. It is more like a mid to mid-low adjuster. afm_722 is right, it is better that it simply "go away" for most people, as it simply adds confusion.

 

[James]

JTT,

I have seen pictures. And this makes the most sense, that the shim stack affects the damping based on speed, not position...especially since the entire compression shim stack appears to be less than an inch in length.

So if this is the case, then is the advantage to having 2 and three stage valving simply fine tuning it since the shim sections have space in between them allowing them to work a litlle independently.

More specifically, I guess I won't be losing a whole lot by using Race Tech's two stage valving as opposed to try and have somebody tune the existing 3 stage valving on my Honda (considering that I am not a pro or even a decent amatuer)?

 

[marcusgunby]

James you have it correct-fine tuning is the key-with a single stage stack, if you alter only one shim it will have to affect the whole stack.When you separate the stacks it makes it a little easier to deal with.However if we alter the LSC part of a 2 stage stack it will still alter the HSC as high speed is the total of low speed and high speed combined.So you lower LSC stiffness and you will lower total stack stiffness.I havnt found a rule for working out total stack stiffness and doubt i ever will.Its done on eperience and i often mess up.I tried to design my own 3 stage stack using only the shims from a 01Cr125-it didnt work as the crossover(bend over or sperator shims)were too big in dia and caused the total stack strength to be too stiff.

Generally single stage stacks are used in SX where you want max bottoming resistance.It also holds the suspension higher in the stroke.

A 2 stage stack is used most and comes on most bikes std.This is a nice compromise.

A triple stage stack is used by Proaction mostly or by other tuners for woods riders.

IMO the 3 stage stack is the hardest to get right.

The KTM125sx comes with a sinlge stage stack to help it control bottoming as it has little rising rate-this makes them harsh to say the least-they would be better off using a 2 stage stack and accepting some bottoming.

Dont overestimate the linkage rising rate on most bikes-it does little until deep into the stroke.RT has a graph showing the rising rates on a few bikes including the KTM and its suprising.