How to: Convert your lazy SPV 5th into a shimmed damper hottie
- Thread starter Fly
- Start date
Dh kid has some shims 
honestly the best bet is to find a donor shock as buying just a few shims will be difficult. Generally they are sold in a huge assortment for moto shock tuning. Maybe try a moto tuner once you have an idea of what you need (thickness, ID, OD, quantity). The genreal ideas about shim stack damping are simple, however specific applications are very complex, and are described by advanced mathematics with parameters you will never know...thus a fair bit of guess and check.
honestly the best bet is to find a donor shock as buying just a few shims will be difficult. Generally they are sold in a huge assortment for moto shock tuning. Maybe try a moto tuner once you have an idea of what you need (thickness, ID, OD, quantity). The genreal ideas about shim stack damping are simple, however specific applications are very complex, and are described by advanced mathematics with parameters you will never know...thus a fair bit of guess and check.
that's true, the difference it makes is HUUUGE
Now I'm also thinking about leaving the spv valve in my 6way, because I don't want to disassemble my shock 10 times until I get the best results with the shims...
Does anyone know how many shims are necessary? And which diameter?
Hmm. Did you ever change the main shaft on your damper though? I'm guessing it has roughly the same effect as the o-ring swap out, because even though I messed around with my own shock to use a shim stack, my buddies shock with a chromed shaft was, as you've noted, a very competitive shock with SPV still installed.
I'd be interested to try the o-ring replacement to see just how much of a difference in feeling it achieves - I'm guessing quite a bit on the original shaft (maybe not so much on a chrome shaft because of the inherent friction loss from the better coating). When I was in contact with CR-1 engineering about 5th's (sadly I could never try out their conversion because of the prohibitive cost of shipping from aus) Craig (I think?) advised me to switch the shaft before anything else, because through their testing they'd found that to be the biggest culprit in 5th's feeling like a turd. Whichever road you wander, it still requires a rebuild either way, so it may be best if you have the resources available to switch the seals and shaft at the same time.
Really? This is definitely something I have to try then. Thanks for the info! I would have to say that like you, after getting to know these shocks a little better, I have a certain bent affection for them. They are very well engineered; its a shame a few simple shortfalls limited the performace (and thus marketability) of the SPV system. People jump on a bike with a 5th which feels cruddy, and then they jump on a similar bike with say a DHX and say "woah, that 5th compared to that Fox is hopeless". Then they distinguish that the key difference between the two dampers is SPV, and they assume (not without good reason) that the lack of performance is caused by the stable platform system. If 5th had just taken the time to replace some o-rings and use different shafts, they might have managed to stick around as one of the major competitors in the gravity scene.
There is an inherent problem with SPV on a DH bike and that's that you're essentially deliberately creating stiction and thus retarding bump absorption. You can make anything work well/better with custom tuning, but really most people don't want to have to go that far... when you pay that much for a bike/shock you want it to be good out of the box.
I can also recommend you trying the o-ring tuning, it makes BIG difference!
I have a swinger 6way, so it has a chrome shaft, but after changing the o-ring to a softer one, it became as smooth as my vanilla rc
so try it, you won't be disappointed
the only problem is that the softer o-ring won't be so durable as the original one, so you'll have to change it oftener
but it's not a big problem imho
Fly- even with a 5th that has been worked on, some people dont like it as much because of the simple parking lot test. only riders who feel that their bikes are too 'soggy' so to say understand how well the 5th works when it uses its travel wisely.
are you saying there is an inherit problem with the design or is it just the o rings?
SPV in general. I don't know what the o-ring deal is, but deliberately creating stiction (which is essentially what SPV is, low-threshold zero-speed friction) helps nothing on a DH bike, especially if the thing pedals fairly well to begin with. Maybe it has its place on a trailbike, but I don't ride much XC these days so I'm not up with the latest and greatest in going-uphill technology.
IT IS NOT STICKTION! I've heard this time and time again. Sticktion, or breakaway friction is higher than dynamic friction. Pressure (force, really) builds and then "breaks away" to a reduced dynamic friction. Stiction effects both rebound AND compression.
BM
i am not sure about deliberately creating stiction, but you should really give a 5th with proper o rings in it a try. the stock o ring is rock solid, like a plastic washer really. the replacement one is much softer. the durometers are 100 and 70 respectively.
on the 5th element i have, there is not a point in the travel where i feel there is a threshold to overcome, you can feel that there is alot of damping, but nothing like a threshold. even if you do the push down test in the parking lot.
i cant say that the 5th is the best shox i have every tried, and i dont have it at a point where it has taken over the role of my main shox. but its getting there, still a few mods here and there. i agree as a stock shox its crap. but doesn't mean it should be over looked.
the way that the 5th works which no other shox works is what keeps me interested in it. and right now i am working toward making my dhx more like the 5th. and if i can take that slight edge off the 5th on the smaller bumps, it would me my main shox for sure. the main problem i have with the 5th is that i am a light rider on a low leverage bike. most other riders would have no problems with it.
just my very long .02
dhkid
You probably already know this, lower the air pressure to reduce the damping on smaller bumps. You can adjust the damping on big hits with the volume adjuster. What PSI are you running?
Another tip on 5ths is to calibrate the pressure everyday after the shock has warmed up. a really cold day with a cold shock is different than a hot day with a warmed up shock. Also, keep in mind that you lose air when you put the pump on so you can not measure the air pressure other than when the pump is initially on.
You probably already know this, lower the air pressure to reduce the damping on smaller bumps. You can adjust the damping on big hits with the volume adjuster. What PSI are you running?
Another tip on 5ths is to calibrate the pressure everyday after the shock has warmed up. a really cold day with a cold shock is different than a hot day with a warmed up shock. Also, keep in mind that you lose air when you put the pump on so you can not measure the air pressure other than when the pump is initially on.
haha I'm well aware of what stiction is, and while you're right that SPV doesn't affect rebound, in compression it's still got the same characteristic as stiction - you require a certain threshold force for it to move at all (which can be significant, especially if you use it as a pedalling platform, or if you've worked on the shock extensively like dhkid then maybe it's not), then the force required to keep it moving (dynamic friction) is lower. This is the very purpose of CV/T, or SPV, or whatever you want to call it. It's just more controlled than normal mechanical stiction.IT IS NOT STICKTION! I've heard this time and time again. Sticktion, or breakaway friction is higher than dynamic friction. Pressure (force, really) builds and then "breaks away" to a reduced dynamic friction. Stiction effects both rebound AND compression.
BM
High force (relatively) at zero shock speed = equivalent to stiction. Sorry, but no two ways about it.
It's funny to hear someone who hasn't worked for them say that. You couldn't be more right. Just shortly after Progressive got sold to an investment group the MTB engineering effort began to decrease. The last version of the 5th coil sold really wasn't much different from the first version. Hence the harder shaft seal which, at the time, coupled well with bikes that needed help with pedaling efficiency and was more durable. Bottom line is, management (who couldn't see past the end of their own nose) chose not to invest a small amount of money to maintain a large market share of a small industry. Instead the chose to invest/waste HUGE sums of money to try and get a small market share of a large market.....and we all know how the story ends. The knowledge and potential was there.
As far as the shaft and shaft seal go...even though the 5th shaft looks haggered it's relatively smooth, a chrome plated shaft would be smoother though. The shaft seal makes a world of difference either way.
I'm more than sure I've spent more time working on 5th's than dhkid. I know the purpose of CV/t and you have it wrong. It takes X amount of force to get the shock moving (basic control valve, no bleed), and it takes a force initially = to X to keep it moving, but that force very soon after it starts moving gradually rises. The force is never (at least should never be) lower to keep it moving than it is to make it start moving. It is very controlled, deliberate, AND adjustable!
The oring sticktion is brutal. It's more dramatic, and to have also affect rebound is a performance killer. The difference is night and day.
BM
A large portion of the 5th's stiction is from the stock shaft seal, it's as hard as chinese algebra. But your right, at zero shaft speed the CV is held shut tighter than a corresponding shim stack would be. But that is what gives it it's positive LSC characteristics. The rise in pressure on the piston face for any type of input that could potentially be called "spiky" or "harsh" almost completely mutes out the zero shaft speed stiction, nobody is going to hit a bump and generate 1"/sec shaft speed and say it feels harsh.
Time in front of a dyno has proved this. In the range of what could be called HSC the CV displays a much rounder "nose" on a position vs force graph than a similarly tuned shim damper, and in the range of LSC it has a slightly squarer "nose" than it's shimmed counterpart.
I'm sure your well aware of this but I think the Control Valve's strongest application is long travel off road vehicles.
Hmm, see this is what I originally thought as well. I thought there was no way SPV could be a good idea. But as the other guys have noted, you really have to try a 5th with at least a new shaft seal (and optimally a new shaft as well) before you can truly judge the merits of the system. You literally would not believe the difference. I'm not being unrealistic here - its obviously not that good that you'd go sell your DHX to buy a 5th, but it'd definitely stop you selling your 5th to buy something else.
Yeah, but you know the problem with that is keeping them cool so that the air pressure remains somewhat consistant. It may be possible to overcome with large cooling surfaces. However, I think G.L. already spent a lot of effort trying that.
All this got me convinced that I was not crazy when I really like the Swinger on my Sunday I used as back up when the DHX is in for service (its a custom Sunday tuned Swinger).
I was speaking more in theoretical terms but you are correct. Though there has been work done on systems that balance out the pressure increase.
yes, theoretically, they would be awesome for long travel desert trucks and buggies since the platform could act in the same manner as an anti-sway bar on a car without having the negative effects that cause it to be left off of long travel trucks. Anyone that has seen a trophy truck make a high speed turn on pavement would understand the need.
min pressure 50 psi, shox oil weight, 50% 5wt, 50% 2.5 wt. air chamber size maximum. like i said, other riders wont have trouble with it. i aint complaining, just know that most shoxs are designed for the lower end of the weight scale. just trying my best to get them to work the way i want.
Though I've not had the chance yet to prove it, I don't think temperature/pressure rise would be that much of an issue for a long duration endurance race. You would just set the pressure hot. The cold performace wouldn't be as good, but they'd only take a few minutes to heat up and then be good for the rest of the event. The temperature problems would be a far greater issue for short events, like SX and rally, though I still wonder how long they really would take to get up to operating temps. 1/2 a lap? A whole lap? More?
BM
Wow, hard to believe you can even feel the platform when riding with those settings. You need to get on a winter training plan of ice cream and watching TV.
Seriously though, if the port size on the main piston was increased it should lower the threshold with the same air pressure. Never had a need to do it so I never discussed it with the guys at progressive. Maybe MttyTee can verify.
i have no problem with the amount of damping it self. i just need it to be a bit plusher on the smaller bumps. on everything else its a dream.
my winter training involves some work outs and riding, of course the 'occasional' alcoholic beverage.
i am actually going racing in sunny indonesia in two weeks time. 
i cant wait, racing here in england doesn't start till april-may.
my winter training involves some work outs and riding, of course the 'occasional' alcoholic beverage.
i am actually going racing in sunny indonesia in two weeks time. i cant wait, racing here in england doesn't start till april-may.Yes, but the relevant part is that there is, for the third time, force at zero shaft speed (in compression). This is an unnecessary hindrance to bump absorption on a DH bike. If that force is going to be significant enough to compensate for a bike pedalling badly, it's got to be reasonably high, and if your bike pedals fairly well then it's not needed anyway. There are other, flat-out better ways of implementing position sensitivity, adjustability, good compression curves etc. I'm not saying shocks with SPV are unrideable or even outright bad or anything like that (I've owned a few btw), but the idea is flawed from the beginning. Sure, you can reduce its effect a lot (with external and internal tuning and mods) but at the end of the day it doesn't really provide benefits that can't be provided without the tradeoff of stickiness.
Yeah, but how's that prove SPV is a good idea? There is more to a 5th than the control valve...
BTW, I've come across two 5ths that didn't have any noticeable stiction when there was no air pressure in them and I was compressing the shock by hand. One of those I later rode on and it still felt sticky and uncompliant (and I'm no lightweight I assure you).
I guess my experiences have differed from yours... I've found one 5th that felt fairly smooth in rough chunder and braking bumps (that was on an M1 that was way undersprung for me, with minimum damping in all directions), but some of them I've ridden just give the impression that the shock is a split second too slow to react. It's hard to explain in words... kind of like your rear wheel is really heavy and has so much inertia that you can really feel it getting kicked around.
I agree about the long travel off-roaders thing... cars/buggies in particular really need the lateral stability thing. You've probably seen Dust to Glory? Where those trophy trucks have the inside front wheel off the ground when cornering on the asphalt corner right off the start line. Definitely helpful there.
Unfortunately one of the Control Valves positive features can be a negative one...adjustability. A 5psi difference is def. noticeable. Which means even if you fully understand what you are doing with set up even if you are anal and check your psi everytime you ride, something as silly as a worn out shock pump can throw things off.
Ok, first of pressure does effect sticktion. Under pressure the oring is forced to one side of the grove, and to try and extrude out past the shaft, but that's how it's supposed to work. The more pressure you apply, the harder it tries to seal, until it fails. But shocks are relatively low pressure hydraulic devices so you don't often see extrusion failures except when the oring groove was improperly designed.
2nd, here's an internal mod you can't argue with. There's a small button head screw that holds the low speed rebound check shim stack on the end of the bolt (on later model 5ths). Drill a small hole, make several .030, .040, .050 and so on... Then you have a bypass that allows oil to move even it the CV doesn't open. No more platform. The size of the orifice will determine at what speed the CV will kick in.
BM
I'm fairly well aware of how seals work, however if the o-ring really is as hard as you guys say, it's going to be affected very little by the pressure, and like you say, it's a pretty low pressure to begin with. Even 140psi is only 10 bar, as far as pressure sealing goes that's nothing. I'm currently working on brake systems where we have moving pistons with o-ring (though square profile) sealing at 200+ bar (2800psi) with no problems. Can't say I've measured the stiction increase there, but you get the point
Like I said, if we're going to talk internal mods then it's a totally different ball game... then you're comparing custom valved stuff to stock hardware. And then you're still trying to work around the effect of the control valve, which just proves my point that it's not an ideal method in the first place!
Like I said, if we're going to talk internal mods then it's a totally different ball game... then you're comparing custom valved stuff to stock hardware. And then you're still trying to work around the effect of the control valve, which just proves my point that it's not an ideal method in the first place!
I can't get over how much internet forum posters focus so much on one tiny aspect of CV/t, such as platform. Geez... Get over it! Seriously, how long ago was the 5th element shock released? Forever ago! It's an old product! What Progressive (should I say, regressive) failed on over and over again was keeping up with the times! When it came out is' only competition were Romic, vanilla, and a few obscure others. You can't really call that competition!! If you turned your compression adjuster all the way in on the vanilla (remote resi model) you could make your shock lock out and explode! tiny body, 3/8" shaft, piss poor damping. Then came the 5th, with real damping, and bikes didn't pedal the best back then so it's was a heaven sent. Other shock manufacturers got the hint and went to work and came out with new stuff. And as far as the public is concerned, new is good, even if it's not. They like new, shiny, bling components. Then the word "platform" got put right up there with the "F" word, and then PSI didn't do anything new so it went by the wayside. PSI's experience has always been with cruiser bike shocks, they sell the same technology over and over again, year after year, and you just can't do that in a performance oriented market.I'm fairly well aware of how seals work, however if the o-ring really is as hard as you guys say, it's going to be affected very little by the pressure, and like you say, it's a pretty low pressure to begin with. Even 140psi is only 10 bar, as far as pressure sealing goes that's nothing. I'm currently working on brake systems where we have moving pistons with o-ring (though square profile) sealing at 200+ bar (2800psi) with no problems. Can't say I've measured the stiction increase there, but you get the point
Like I said, if we're going to talk internal mods then it's a totally different ball game... then you're comparing custom valved stuff to stock hardware. And then you're still trying to work around the effect of the control valve, which just proves my point that it's not an ideal method in the first place!
The control valve in the 5th shocks is a very basic, simple, no brainer application of the technology. Consider it a model T, compared to the potential the control valve could have with proper time and research to develop it. No other technology can give you the kind of bump absorption and position sensitivity, that can all be externally adjusted, than the control valve. Fox new this, so they put one in the DHX. It's the same technology, just a different application of it. So when you say your DHX rocks, keep in mind it has a control valve in it.
Saying using a bleed screw is working around the effect of the control valve, than that's the same as saying ohlins having a compression bleed orifice in one of their shocks is like trying to work around the effects of the shim stack. It's not a valid argument.
BM
If you need any pointers talk to Shaneo with the blue DH team, Jezza my mate, or even Snow from up the coast.
They've all modded SPV Dorados into TPC+ Dorados. They do tend to blow up catastrophically every few months though. You'll need a few cartridges, they tend to be destroyed when they blow. Imagine sucking all air out of a Coke can. Thats what one of Shaneo's did at Brookfield when it hydraulic locked on a rock.
Have fun, they end being pretty nice forks.
Yeah I'm not gonna replace my Boxxers except maybe for some drunk runs. They're not a real good chassis and not in perfect nick. Just thought I'd have a go at building a shimstack to replace the SPV unit.If you need any pointers talk to Shaneo with the blue DH team, Jezza my mate, or even Snow from up the coast.
They've all modded SPV Dorados into TPC+ Dorados. They do tend to blow up catastrophically every few months though. You'll need a few cartridges, they tend to be destroyed when they blow. Imagine sucking all air out of a Coke can. Thats what one of Shaneo's did at Brookfield when it hydraulic locked on a rock.
Have fun, they end being pretty nice forks.
It's a pity Manitou fell for the whole SPV thing. The old Dorado had a brilliant damper.
One tiny aspect of CVT? Pretty sure that was the primary purpose when it was introduced actually - pedalling stability, just like roll stability in the off-road trucks that Curnutt designed it for. It only has one other characteristic, progressive damping, and that happened to be a by-product that Fox later made much better use of.
I know Fox have something equivalent to a CV in it (MttyTee said it technically infringes the patent), however they use it in a different way because it is in essence a "normally open" valve (when combined with the Propedal reverse-preload thing) which tries to close as you get close to bottom out, as opposed to something that needs to open first THEN do that. In this way, you don't have the stiction effect, it's simply an end-stroke/bottom out control. Beginning stroke compression damping is handled primarily by the shim stack. Unless I'm very much mistaken, the original purpose of the CV/T was to provide stability ("platform") because long travel bikes pedalled like arse with the old generation of pogoshocks, with the secondary benefit being that you could control bottom out. Nobody ever cared that much about bottom out resistance before someone gave us a knob to twiddle with it, and there are other ways of doing it anyway.
And again dude, for like the fortieth time, YOU CANNOT COMPARE CUSTOM TUNED SHOCKS TO STOCK UNITS. If it needed that kind of modification then its execution was fairly poor to begin with, or it was flawed, or both. You can make anything work well enough, even RS Pro Deluxes, if you're prepared to tune it internally.
So, my point that SPV/CVT, in the incarnation that 5th and Manitou use, has no place on a DH bike stands.
Anyway I'm just going to leave it at that... I think we're just arguing semantics by now. You can go and happily ride your 5th/whatever, I'll go and bounce uncontrollably down the trail on my uncontrolled-valve suspension
Have you met Charles Curnutt? Ever shaken his hand? Did you have the chance to discuss the CV theory with him? If not, then I don't think you have any place to make any statements regarding the primary purpose of the control valve. I have, btw, and if that was the only purpose of the CV then there are much easier ways to go about it. More reliable and cheaper ways. All you need is a spring pushing against a washer. Which by the way is what the RP3 has in it!One tiny aspect of CVT? Pretty sure that was the primary purpose when it was introduced actually - pedalling stability, just like roll stability in the off-road trucks that Curnutt designed it for. It only has one other characteristic, progressive damping, and that happened to be a by-product that Fox later made much better use of.
I know Fox have something equivalent to a CV in it (MttyTee said it technically infringes the patent), however they use it in a different way because it is in essence a "normally open" valve (when combined with the Propedal reverse-preload thing) which tries to close as you get close to bottom out, as opposed to something that needs to open first THEN do that. In this way, you don't have the stiction effect, it's simply an end-stroke/bottom out control. Beginning stroke compression damping is handled primarily by the shim stack. Unless I'm very much mistaken, the original purpose of the CV/T was to provide stability ("platform") because long travel bikes pedalled like arse with the old generation of pogoshocks, with the secondary benefit being that you could control bottom out. Nobody ever cared that much about bottom out resistance before someone gave us a knob to twiddle with it, and there are other ways of doing it anyway.
And again dude, for like the fortieth time, YOU CANNOT COMPARE CUSTOM TUNED SHOCKS TO STOCK UNITS. If it needed that kind of modification then its execution was fairly poor to begin with, or it was flawed, or both. You can make anything work well enough, even RS Pro Deluxes, if you're prepared to tune it internally.
So, my point that SPV/CVT, in the incarnation that 5th and Manitou use, has no place on a DH bike stands.
Anyway I'm just going to leave it at that... I think we're just arguing semantics by now. You can go and happily ride your 5th/whatever, I'll go and bounce uncontrollably down the trail on my uncontrolled-valve suspension
Have you ever ran a DHX on the dyno? Have you ever compared the curves to a 5th? Because let me tell you, metering the shaft displacement oil with the control valve is a poor way to do it. It makes the effectiveness of the CV far, far less. I do give Fox credit for making the opening/closing point of the CV adjustable via the preload on that spring. I actually had an idea like that way back, but like I said, Progressive fell behind the times and had no interest in developing new technologies.
BM
Right, well since I've been comprehensively smacked down on that front, I'm going to fall back on my original point and say I still think "conventional" SPV shocks, where the CV is a "normally closed" valve, are fundamentally flawed for DH purposes, because the CV as it stands creates unnecessary extra "stiction" (there's your favourite word again )
And again, maybe you can make the shock work well with mods, but if it doesn't do it out of the box then I'm just not that interested.
One thing I am interested in though, is why you think the shaft displacement fluid is less well controlled through fox's boost valve than that passing through a main piston CV?
)And again, maybe you can make the shock work well with mods, but if it doesn't do it out of the box then I'm just not that interested.
One thing I am interested in though, is why you think the shaft displacement fluid is less well controlled through fox's boost valve than that passing through a main piston CV?
Do I want to do this to my 5th on my bullit? I use it as an AM/SC/FR/DH bike - I need to pedal - A LOT -- will this make it super DH active? I recall Vaniklla RC's on bullits being crazy active and great for DH, but horrid for pedaling.
Anyone?
this looks fun. weeee...
Anyone?
this looks fun. weeee...