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Compression damping - can someone explain?

- seb

Turbo Monkey
Apr 10, 2002
2,924
1
UK
I've never really understood the point of compression damping. In my mind you want a shock to compress as quickly as possible when you hit a bump - I understand completely the value of getting your rebound damping right, but don't get why you'd want to slow down the compression of the shock.

I always run my bikes with compression damping fully off, whether it's a fox, 5th or (in this case) RS deluxe.

Also doesn't winding the compression damping on increase the likelyhood of "blowing" the shock?

Is it purely to stop from bottoming the shock out? So if you've got it fully wound out and you don't bottom it you should leave it like that?
 

Kornphlake

Turbo Monkey
Oct 8, 2002
2,632
1
Portland, OR
Ride a shock with no compression damping and you'll understand. Some damping is good, rather you need more than the full open setting on your shock is debateable.

Supposedly on the old Fox shox you could blow them up pretty quick by turning up the compression damping, same with boxxers as I recall.

Ending stroke compression damping is pretty helpful for overcoming harsh bottoming. I've learned to be conservative with this too as you can have too much ending stroke compression.
 

RhinofromWA

Brevity R Us
Aug 16, 2001
4,622
0
Lynnwood, WA
Originally posted by - seb
I've never really understood the point of compression damping. In my mind you want a shock to compress as quickly as possible when you hit a bump - I understand completely the value of getting your rebound damping right, but don't get why you'd want to slow down the compression of the shock.

I always run my bikes with compression damping fully off, whether it's a fox, 5th or (in this case) RS deluxe.

Also doesn't winding the compression damping on increase the likelyhood of "blowing" the shock?

Is it purely to stop from bottoming the shock out? So if you've got it fully wound out and you don't bottom it you should leave it like that?
All the shock damping does is slow down and absorb the hits energy. If you had no comp damp than you wouldn't like it to much. Lack of any comp damping would be bad and youwould find you would be blowing thru the travel too fast. the oposite end is you don't want to be blowing thru your travel to slow either. :)

Comp. damping helps alow you to keep control of your bike. no different than rebound. To slow is bad (packing up...not able to return before next hit) or to fast (not taming your spring from returning to quickly). Ride a fork with no oil in the compression side at all and only in the rebound to see the difference between none and some comp damping.

Damping is to control your shock moving....the spring suspends the bike and rider and helps it to return after taking a hit. Controling the action is key.

Rhino
 
i find it cool for adjusting my fork ('00 monster t) for different types of riding. for dirt jumping or more flat to uphill trails, i turn up the compression a little to keep the bike from being so plush when i don't really need or want it. same with my rear shock (curnutt.)

then when it is more dh oriented then i open up for more plushness when it's rugged.
 

Jm_

sled dog's bollocks
Jan 14, 2002
18,855
9,560
AK
This is very circumstancial ground IMO. Certain adjustments like those found on fox rear shocks and some others are completely useless because they affect the entire range of damping, and if you try to adjust it to pedal a little better, it will work like crap at high speed because the high speed damping will be affected. In some shocks like the romic, it only affects the low-speed damping, and you can adjust it as far as you want because it will "blow off" (well, if the shock doesn't blow first :D).

Having a seperate high speed and low speed damping adjuster is really where you are going to be able to adjust in a positive respect.
 

Repack

Turbo Monkey
Nov 29, 2001
1,889
0
Boston Area
Also, compression damping works on displacement. On a rear shock (or Manitou TPC- they copied the principle), as the shaft moves into the body, the oil is displaced. This is why there is a resevoir, or Twin Tube if its a Romic. This is why the Comp clicker is located at the base of the resi. I don't know the oil velocity of a rear shock, but on a Manitou fork its 1/3 of the shaft speed. It as easy to figure out the maximum force that could ever be applied to a rebound damper, but the sky is almost the limit when it comes to how much force you can but on a comp damper.

They also help to keep you from blowing through your travel. Without a damper, the inertia would be carrying you wheel up even after the bump is gone. Think of it as the wheel catching air off of every hit, not tracking down the back side.
 

MMike

A fowl peckerwood.
Sep 5, 2001
18,207
105
just sittin' here drinkin' scotch
I've always run my Vanilla RC with the comp wide open (on the advice of some very fast racers). The point being is that it reacts to the small bumps quickly. (Damping is a speed sensitive thing).

I do the same with my boxxer. Comp wide open, rebound as slow as it will go (this is a boxxer of course).

But I've not had much of a chance to experiment too much with my Swinger yet. So I can't say if that's any different.
 

SebringMGB

Monkey
Feb 6, 2004
482
1
Washington
i always run my rc this way; i ride it with comp and rebound damping wide open. dial the comp till the compression feels right on the trail, then dail in rebound. feels perfect to me, and does not feel right with comp wide open.
 

thaflyinfatman

Turbo Monkey
Jul 20, 2002
1,577
0
Victoria
I run my high-speed compression all the way out, and the low-speed compression about halfway in for better attitude control in corners. Damn I wish I could get rid of the SPV stiction though :(
 

UiUiUiUi

Turbo Monkey
Feb 2, 2003
1,378
0
Berlin, Germany
hm for me its the other way round i prefer shocks with at least some and better some more low speed compression damping.
because of that i never found a shock which i really liked before running into avalanche.
that way i can have a shock which pedals good and still moves through the travel without feeling harsh.
 

ChrisRobin

Turbo Monkey
Jan 30, 2002
3,346
190
Vancouver
In front suspension, I've always run my forks with no or little compression. That's it, I want the fork to work as fast as possible but of course, my rebound is set about halfway (Stratos forks like to be set pretty fast anyway). For my rear shocks, again, always with no compression but with rebound set at about halfway. Right now on my Romic shock, my spring is a little soft so I have choice but to increase the compression damping (just a little mind you) just to say I don't blow through all the travel. Even then, my frame is really progressive so I've never bottomed out anyway. If I had a platform shock, I would crank up the end stroke compression and leave everything else 'off'.
 

thaflyinfatman

Turbo Monkey
Jul 20, 2002
1,577
0
Victoria
ChrisRobin said:
In front suspension, I've always run my forks with no or little compression. That's it, I want the fork to work as fast as possible but of course, my rebound is set about halfway (Stratos forks like to be set pretty fast anyway). For my rear shocks, again, always with no compression but with rebound set at about halfway. Right now on my Romic shock, my spring is a little soft so I have choice but to increase the compression damping (just a little mind you) just to say I don't blow through all the travel. Even then, my frame is really progressive so I've never bottomed out anyway. If I had a platform shock, I would crank up the end stroke compression and leave everything else 'off'.

There is no "end stroke" compression adjustment on spv shocks... there's high speed (chatter bumps/big hits) and low speed (weight shifts, cornering, smooth landings).
 

Kornphlake

Turbo Monkey
Oct 8, 2002
2,632
1
Portland, OR
thaflyinfatman said:
There is no "end stroke" compression adjustment on spv shocks... there's high speed (chatter bumps/big hits) and low speed (weight shifts, cornering, smooth landings).

I'd say you're technically wrong. Although that's what the stickers on the shock may say, really what you get is beginning stroke and ending stroke compression adjusters. Beginning stroke will make the chatter bumps and stuff feel softer or firmer while the ending stroke will keep the shock from bottoming, the air pressure will control weight shifts, cornering and such, personally I run the air pressure as low as I can, beginning stroke as low as I can and just enough end stroke compression combined with air volume to keep from bottoming.
 

Repack

Turbo Monkey
Nov 29, 2001
1,889
0
Boston Area
Kornphlake said:
I'd say you're technically wrong. Although that's what the stickers on the shock may say, really what you get is beginning stroke and ending stroke compression adjusters. Beginning stroke will make the chatter bumps and stuff feel softer or firmer while the ending stroke will keep the shock from bottoming, the air pressure will control weight shifts, cornering and such, personally I run the air pressure as low as I can, beginning stroke as low as I can and just enough end stroke compression combined with air volume to keep from bottoming.
The beginning stroke sets how far the valve can open. The air pressure tries to hold the valve shut.
 

thaflyinfatman

Turbo Monkey
Jul 20, 2002
1,577
0
Victoria
Kornphlake said:
I'd say you're technically wrong. Although that's what the stickers on the shock may say, really what you get is beginning stroke and ending stroke compression adjusters. Beginning stroke will make the chatter bumps and stuff feel softer or firmer while the ending stroke will keep the shock from bottoming, the air pressure will control weight shifts, cornering and such, personally I run the air pressure as low as I can, beginning stroke as low as I can and just enough end stroke compression combined with air volume to keep from bottoming.
Low speed compression won't stop the bike sagging when you shift your weight (which I didn't lay out clearly before), but it does stop it shifting as fast which I find beneficial, and it definitely helps with cornering attitude and g-outs. I don't find the air pressure to do much rather than make the shock feel sticky, and make it ramp up at the end of the stroke.

Aren't the compression adjusters speed sensitive? If so, how are they going to be beginning/ending stroke? My experience has been that air pressure/volume makes a much bigger difference to ending stroke compression than the high-speed compression adjuster.
 

Repack

Turbo Monkey
Nov 29, 2001
1,889
0
Boston Area
thaflyinfatman said:
Which valve are you talking about, the spv valve or the compression damping valve(s)?
I guess both. SPV act on the compression damping. Adjusting the damping os kind of like adjusting a derrailleur (there'e the kind of symily I was trying to think of before). The comp adjuster sets the rangem while the SPV tries to hold it shut. More air pressure = more resistance to pedaling inputs. But, when you hit a bump, there should be enough pressure to open the valve.
Also, because a 5e works on the same principles as a regular nitrogen-charged shock, as the shaft travels into the shock body, the size of the resi/air volume decreases, causeing the air to have more of an effect. By adjusting the initial size of the air chamber, you can effect how much the shock ramps up at the end.

Maybe this wonderful illustration will help. Air is on one side on the Internal Floating Pistom, oil is on the other. As said before, r shock comp damping works with displacement to keep the speed of the oil moving through the comp damper as low as possible. The SPV is trying to hold the comp damper closed, but has no effect on how far it can open. The charged chamber is the reason why a Fox r shock will rebound even if no spring is on it.
 

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Kornphlake

Turbo Monkey
Oct 8, 2002
2,632
1
Portland, OR
thaflyinfatman said:
Low speed compression won't stop the bike sagging when you shift your weight (which I didn't lay out clearly before), but it does stop it shifting as fast which I find beneficial, and it definitely helps with cornering attitude and g-outs. I don't find the air pressure to do much rather than make the shock feel sticky, and make it ramp up at the end of the stroke.

Aren't the compression adjusters speed sensitive? If so, how are they going to be beginning/ending stroke? My experience has been that air pressure/volume makes a much bigger difference to ending stroke compression than the high-speed compression adjuster.

I say it's really ending and beginning stroke compression rather than high/low speed because there's no real way to mechanically sense the velocity of the piston short of using an umbrella valve like the HSCV Marzocchi cartridges which have a distinct feel, definately not the same as a SPV shock. High speed hits will compress the shock more thus using the ending stroke compression damping circuit rather than the beginning stroke.

Imagine a cylinder with a step in it so that there are 2 different ID's, a pistion that is nearly the same size as the smaller step would represent the ending stroke, when the piston is in this part of the stroke all the oil has to flow through the damping circuit, in contrast in the beginning stroke where there's some clearance between the cylinder and the piston oil can flow around the piston as well as through the damping circuit. Adjusting the clearance between the pistion and the cylinder wall will control the beginning stroke damping. That's more of a TPC+ type of scenario than an SPV description but I think you get the idea.

In the end who really cares what does what rather its compression damping or air pressure or air volume, the point is that the shocks work and they're fun to use.
 

Repack

Turbo Monkey
Nov 29, 2001
1,889
0
Boston Area
Kornphlake said:
I say it's really ending and beginning stroke compression rather than high/low speed because there's no real way to mechanically sense the velocity of the piston short of using an umbrella valve like the HSCV Marzocchi cartridges which have a distinct feel, definately not the same as a SPV shock. .......
Actually, it can be either way. TPC+ is a floating piston that blocks some of the compression ports if the hit is big enough. Its to give you a little extra cushion at the end of the stroke- its usually safe to assume that if you are at the end of the stroke, you have hit something big.
Or you can have a system like what is in a Boxxer. Their compression damping sits on top of a spring. Hit something big enough, the spring moves, and more oil can flow by in an effort to save the comp damper from damage. The internally tapered legs of the older Boxxers were also used to manipulate oil flow at different points of the stroke.
I believe that Marzocchi's SSV's are built around a spring loaded shim stack.
I may not be 100% correct, but I know I am close. Basicly, all of the high-end compression damping that has been developed is intended to do the same thing, but through different means. Fox Brain is another example.
B/c of patents and stuff, pretty much every mfg is working on their own solution to the problem.