NC stock shock dyno
Jazzman,
I'm enjoying the conversation! I agree with you on your point that in
an OEM case, one can go with a longer body to make up for the volume
of the shock shaft, strictly for economic reasons. My point was only that
this isn't always the case (my fifth grade teacher drilled us to watch out
for the use of the word "always"
).
Again I agree with you that (and watch out for always!) many monotubes
can have a higher internal friction due to the need for the seal on the
separating piston. But (here's the almost part), some shocks (and oddly
sometimes twin tubes) use a gas bladder instead of a separating piston.
Though I've never measured one, it appears that the internal friction
would be about the same in either case (twin or mono) in the absence of
a second piston. In fact with a remote reservoir and a gas bladder one
could probably make a monotube with less internal friction (from seals)
than a twin tube design, because you could eliminate the shaft seal and
only have the one piston seal. I've seen at least a motorcycle shock
built this way.
It just came to mind that I had a set of Boge shocks on my enduro back
in the early 70's that were of twin tube construction using a nitrogen gas
bladder stuffed into the outer casing. I know because I converted them
myself from emulsion to non-emulsion. Man we had to do a bunch of
crazy things back then in an attempt to make a suspension work. Fitting
heat sinks, monkeying with oils, drilling out valving, playing with all those
disc washers. Much easier just to buy stuff and bolt it on! And so much
cleaner, too.
Can we move to a discussion of active suspensions where things get real
interesting?!?! (just kidding!)
So are you a II-V-I guy?
I'm enjoying the conversation! I agree with you on your point that in
an OEM case, one can go with a longer body to make up for the volume
of the shock shaft, strictly for economic reasons. My point was only that
this isn't always the case (my fifth grade teacher drilled us to watch out
for the use of the word "always"
).Again I agree with you that (and watch out for always!) many monotubes
can have a higher internal friction due to the need for the seal on the
separating piston. But (here's the almost part), some shocks (and oddly
sometimes twin tubes) use a gas bladder instead of a separating piston.
Though I've never measured one, it appears that the internal friction
would be about the same in either case (twin or mono) in the absence of
a second piston. In fact with a remote reservoir and a gas bladder one
could probably make a monotube with less internal friction (from seals)
than a twin tube design, because you could eliminate the shaft seal and
only have the one piston seal. I've seen at least a motorcycle shock
built this way.
It just came to mind that I had a set of Boge shocks on my enduro back
in the early 70's that were of twin tube construction using a nitrogen gas
bladder stuffed into the outer casing. I know because I converted them
myself from emulsion to non-emulsion. Man we had to do a bunch of
crazy things back then in an attempt to make a suspension work. Fitting
heat sinks, monkeying with oils, drilling out valving, playing with all those
disc washers. Much easier just to buy stuff and bolt it on! And so much
cleaner, too.
Can we move to a discussion of active suspensions where things get real
interesting?!?!
(just kidding!)So are you a II-V-I guy?
The difference in length between twin vs. mono isn't due to having to account for the rod volume, because both types have to do that, and typically rod volume doesn't change significantly between the two on the same application. BUT, each accounts for it differently. The twin tube places the extra volume OUTSIDE the inner tube, concentric with the rod. The monotube places the extra volume BELOW the oil chamber. The only way a monotube won't be longer than a twin tube is if there is enough dead length built into the twin tube (which depends soley on the location of the upper and lower shock mounts on the chassis) to account for this extra volume requirement WITHOUT extending the damper. In some cases it is possible, in many it isn't. There would be no other reason to make such a change to length and travel. I think we may be making different points, or maybe I'm misunderstanding you.
Generally, I agree with your points about speacial cases where a monotube may have very good fricition characterisitics. I think we both agree though that for the vast majority of OEM applications and even many aftermarket/race dampers, twin tubes will be much better in this regard than monotubes.
Not sure what you mean by II-V-I (program code for a certain OEM?). . . so I'm probably not one of them. I'm just an engineer who has a bit of experience with shock design and tuning.
Generally, I agree with your points about speacial cases where a monotube may have very good fricition characterisitics. I think we both agree though that for the vast majority of OEM applications and even many aftermarket/race dampers, twin tubes will be much better in this regard than monotubes.
Not sure what you mean by II-V-I (program code for a certain OEM?). . . so I'm probably not one of them. I'm just an engineer who has a bit of experience with shock design and tuning.
I was wondering where you had gone
I'm not a shock designer, but in looking at a few different designs, it
appears that the only reason for having the separate chamber in a mono
tube is to account for the shaft volume, as oil is essentially
incompressible, unless it is in the form of an emulsion. If you tried
to build a shock without something to compress inside, it would be
hydraulic locked.
Yes, it sounds like we do agree on this topic more than we disagree.
II-V-I is a jazz chord progression. I'm just an amateur tenor sax dude.
I threw that out there given your net name...
I'm not a shock designer, but in looking at a few different designs, it
appears that the only reason for having the separate chamber in a mono
tube is to account for the shaft volume, as oil is essentially
incompressible, unless it is in the form of an emulsion. If you tried
to build a shock without something to compress inside, it would be
hydraulic locked.
Yes, it sounds like we do agree on this topic more than we disagree.
II-V-I is a jazz chord progression. I'm just an amateur tenor sax dude.
I threw that out there given your net name...