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Discussion Starter · #1 ·
This is for those guys out there with SPV forks who don't like the platform feel.

I've taken the rebound check valve out of my SPV blacks and so far I like it. The fork is left without a platform but still has a useful amount of low speed damping which is tuned by the air pressure.
My fork still doesn't have enough high speed damping, but I think this is a factor related to my machined down piston not displacing as much oil through the ports as a factory one would. I've got a few ideas I'm working on.

This mod is easy if you know how to pull the lowers off your fork and it is completely reversable if you don't like the results.

First depressurise the damper, then turn it upside down, remove the lowers (careful of any spilling lube oil) and remove the damper by removing the damper side endcap. Stroking the damper a few times with the fork inverted will reduce the amount of oil you lose when you withdraw it.

The damper will look a lot like the one below. The rebound check valve and spring are inside the silver topcap, it simply unscrews and the valve with spring can be removed and put somewhere safe if you wish to reinstall it at a later date. Replace the cap, reassemble the fork and test ride.
 

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Black Lion
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Dougal said:
This is for those guys out there with SPV forks who don't like the platform feel.

I've taken the rebound check valve out of my SPV blacks and so far I like it. The fork is left without a platform but still has a useful amount of low speed damping which is tuned by the air pressure.
My fork still doesn't have enough high speed damping, but I think this is a factor related to my machined down piston not displacing as much oil through the ports as a factory one would. I've got a few ideas I'm working on.

This mod is easy if you know how to pull the lowers off your fork and it is completely reversable if you don't like the results.

First depressurise the damper, then turn it upside down, remove the lowers (careful of any spilling lube oil) and remove the damper by removing the damper side endcap. Stroking the damper a few times with the fork inverted will reduce the amount of oil you lose when you withdraw it.

The damper will look a lot like the one below. The rebound check valve and spring are inside the silver topcap, it simply unscrews and the valve with spring can be removed and put somewhere safe if you wish to reinstall it at a later date. Replace the cap, reassemble the fork and test ride.
i am interested in the ride report with this mod. i do like the feel of my SPV Minute but am always interested in hot-rodding my fork.
 

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air pressures

Dougal said:
but still has a useful amount of low speed damping which is tuned by the air pressure.
Are you still running air pressures in the same range as your stock SPV setup?

Haven't done this to my fork yet, but I did the mod on my old SPV assembly (recently upgraded to evolve) to better understand your description. Was really easy and completely reversible as advertised.
 

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Discussion Starter · #4 ·
AOK said:
Are you still running air pressures in the same range as your stock SPV setup?

Haven't done this to my fork yet, but I did the mod on my old SPV assembly (recently upgraded to evolve) to better understand your description. Was really easy and completely reversible as advertised.
I'm liking the result much better than before hand. I've also modded the damper to give more high speed compression damping (this could be solely due to me machining it down in diameter earlier) and the result is almost pleasing. My last ride was at 50psi, I've dropped the damper pressure back to 40psi but haven't had a decent ride since.
 

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What happens if you run <30psi SPV air pressure? I see that Manitou recommends >30psi I think, just curious if it's an option to use less air to reduce the platform.

(I currently have an active rear shock, but considering an SPV fork on sale, so I want to balance the bike until I go platform rear)
 

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fsrxc said:
What happens if you run <30psi SPV air pressure? I see that Manitou recommends >30psi I think, just curious if it's an option to use less air to reduce the platform.

(I currently have an active rear shock, but considering an SPV fork on sale, so I want to balance the bike until I go platform rear)
No SPV pressure ==> no damping ==> damage.
 

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Discussion Starter · #8 ·
fsrxc said:
What happens if you run <30psi SPV air pressure? I see that Manitou recommends >30psi I think, just curious if it's an option to use less air to reduce the platform.

(I currently have an active rear shock, but considering an SPV fork on sale, so I want to balance the bike until I go platform rear)
If you run no pressure, the compression circuit can't close itself. This means you've got no rebound damping either as the oil takes the easy way home.

SPV without the platform still isn't as good as TPC+, but it's still good.
 

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TPC+ is opposite SPV

Dougal said:
If you run no pressure, the compression circuit can't close itself. This means you've got no rebound damping either as the oil takes the easy way home.

SPV without the platform still isn't as good as TPC+, but it's still good.
I haven't seen more than the Manitou diagrams and only demoed TPC+ and SPV. Manitou's web site may still have diagrams of TPC+

From the diagrams it appears that TPC is about a 10mm range of no compression damping, or very fast/soft compression damping as the shock shaft begins movement before a normal slower shaft speed main circuit compression damping begins. The main circuit has shimmed blow-off valving for high shaft speed compliance for sharp hits. The initially freely fast/soft TPC+ damping range compensates for seal and bushing stiction that produces friction damping at the very start of shaft speed.

In contrast, SPV restricts low shaft speed damping to rather slow/firm compression until shaft speed and hydraulic pressure blows open the main hydraulic port circuit. There is no shimmed high speed blowoff valving for sharp hits in the current SPV designs that I'm aware of.

I have not ridden an SPV, Propedal, 5th Element shock that I liked for handling except with nearly 6 or more inches of travel. Others may like the firm handling for shorter travel.

- ray
 

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Discussion Starter · #10 ·
derby said:
I haven't seen more than the Manitou diagrams and only demoed TPC+ and SPV. Manitou's web site may still have diagrams of TPC+

From the diagrams it appears that TPC is about a 10mm range of no compression damping, or very fast/soft compression damping as the shock shaft begins movement before a normal slower shaft speed main circuit compression damping begins. The main circuit has shimmed blow-off valving for high shaft speed compliance for sharp hits. The initially freely fast/soft TPC+ damping range compensates for seal and bushing stiction that produces friction damping at the very start of shaft speed.

In contrast, SPV restricts low shaft speed damping to rather slow/firm compression until shaft speed and hydraulic pressure blows open the main hydraulic port circuit. There is no shimmed high speed blowoff valving for sharp hits in the current SPV designs that I'm aware of.

I have not ridden an SPV, Propedal, 5th Element shock that I liked for handling except with nearly 6 or more inches of travel. Others may like the firm handling for shorter travel.

- ray
Not quite right.
The TPC compression damper works on displacement, because of this it isn't as sensitive to small impacts as a conventional monotube damper (think of a fox vanilla shock) due to needing a certain size impact to flow enough oil to physically open the shims.

So manitou added a second floating compression piston (TPC+) which in my 00 year Xverts have 14mm of float. Because it's a displacement system, that 14mm of piston travel equates to 40mm of wheel travel. This gives a two stage compression damper with much better senstivity where each piston can be tuned individually throughout the speed range.

On small impacts (less than 40mm from sag), the first piston floats with the moving oil and only the second (top) piston and shims are giving you damping. This is a far cry from no compression damping.
After that 40mm, the lower piston hits it's stops, from this point the oil must flow throught both compression pistons and their shim stacks.

The low speed compression adjuster on the top of a TPC fork controls the free flow of oil through the compression pistons. On a TPC+ fork it initally controls the oil flow between the pistons. Winding this up slows down the reaction of the floating piston, giving you more inital compression damping in addition to giving you more low speed compression damping.

The shim stacks are not a high speed blow off (or blow open). They're actually proportional valves that open further depending on the velocity of the oil flow through them. The shape and size of the stack determines their behaviour to different oil flows (impacts).

SPV is simply a pneumatic valve to hold a compression circuit closed. More pressure in the damper provides a firmer platform by placing more preload on the valve. SPV does blow open all the way to it's stop on fast hits, becoming yet another orifice damper.
 

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Dougal said:
SPV is simply a pneumatic valve to hold a compression circuit closed. More pressure in the damper provides a firmer platform by placing more preload on the valve. SPV does blow open all the way to it's stop on fast hits, becoming yet another orifice damper.
Does it mean that when the SPV valve opens, it operates like a FFD which has a shim-stacked rebound and orifice compression circuit? If that is true, doesn't that make it inferior to TPC?
 

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Yea, what he said

Dougal said:
Not quite right.
The TPC compression damper works on displacement, because of this it isn't as sensitive to small impacts as a conventional monotube damper (think of a fox vanilla shock) due to needing a certain size impact to flow enough oil to physically open the shims.

So manitou added a second floating compression piston (TPC+) which in my 00 year Xverts have 14mm of float. Because it's a displacement system, that 14mm of piston travel equates to 40mm of wheel travel. This gives a two stage compression damper with much better senstivity where each piston can be tuned individually throughout the speed range.

On small impacts (less than 40mm from sag), the first piston floats with the moving oil and only the second (top) piston and shims are giving you damping. This is a far cry from no compression damping.
After that 40mm, the lower piston hits it's stops, from this point the oil must flow throught both compression pistons and their shim stacks.

The low speed compression adjuster on the top of a TPC fork controls the free flow of oil through the compression pistons. On a TPC+ fork it initally controls the oil flow between the pistons. Winding this up slows down the reaction of the floating piston, giving you more initial compression damping in addition to giving you more low speed compression damping.

The shim stacks are not a high speed blow off (or blow open). They're actually proportional valves that open further depending on the velocity of the oil flow through them. The shape and size of the stack determines their behavior to different oil flows (impacts).

SPV is simply a pneumatic valve to hold a compression circuit closed. More pressure in the damper provides a firmer platform by placing more preload on the valve. SPV does blow open all the way to it's stop on fast hits, becoming yet another orifice damper.
I was over generalizing.

On a related topic, while researching better motorcycle suspension for my '02 ZX-6R I've run across what is termed "Gold-Valve Emulators" which are add-on valves for simple single port rod and shaft damping common in OEM oil bath forks (probably in mine, not sure). The add on valves are very much like SPV without using air pressure, actually more like Romic platform damping design, using an adjustable spring loaded ball check valve that opens more an more flow and less damping resistance as shaft speed increases. They apparently closely emulate shimmed valve port damper design for digressive resistance to compression travel speed, and are even more externally adjustable.

Seems like Romic used "Gold Valve Emulator" type damping for platform combined with a type of shimmed valve for main compression damping.

- ray
 

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Discussion Starter · #13 ·
eastpeak said:
Does it mean that when the SPV valve opens, it operates like a FFD which has a shim-stacked rebound and orifice compression circuit? If that is true, doesn't that make it inferior to TPC?
Yes I believe SPV is inferior to TPC.

Bear in mind that the piggy back rear shocks with SPV have additional compression circuits which may be shimmed (I don't own one to pull apart).
 

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Shim Stack

i ride light and hate the feel of SPV over loose pebbles shale and rocks:eek: . I have been offered the option of removing the SPV and replacing with shim stack any thoughts,:confused:
Love the single crown shermans and would hate to replace them:eek:
 

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Discussion Starter · #15 ·
Mr Smith said:
i ride light and hate the feel of SPV over loose pebbles shale and rocks:eek: . I have been offered the option of removing the SPV and replacing with shim stack any thoughts,:confused:
Love the single crown shermans and would hate to replace them:eek:
If you get TPC assemblies (compression and rebound) for a good price, then do it. If you keep your SPV assembly you can go back any time you choose.
 

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It does not act like a FFD, ever. The control valve will regulate oil flow as a function of the internal pressure inside the damper. With a velocity increase, the effictive "orfice" increases allowing more flow, like a shim stack would, the difference is that it's not as sensitive to speed as a shim stack. The idea is to make up for it with position sensitivity. It can be tuned to have less damping at 60in/sec at the beginning of the stroke than a shim stack, but have mroe damping at the end of the stroke at even a lower velocity.

Let me try to explain it better. When we try to tune a set of CV/t shocks for a new application, we will take the OE shocks and dyno them, through the whole range of damping adjustments and speeds to find a baseline setting. Then we will tune our CV/t shocks to have less damping at the beginning of the stroke, about the same in the middle, and more damping at the end. The idea is, for the small bumps and ruts in the track where you are riding in your suspension, the compression damping is lighter, making the wheel be able to move out of the way of the small bumps more quickly and letting the wheel track the terrain more smoothly, but have the higher end travel damping to help absorb the larger impacts and landings.

I can't comment on which is better, SPV or TPC+. I haven't ridden TPC+ very much. I will comment that I'm not satified with the performance of my Minute 2 fork. I can also comment that what has been done in MTB with CV/t technology is very crude and there's far more that can be done to improve its performance. It's very sad that I haven't been allowed to incorporate any new technology into the MTB shocks.

BM
 

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bmadau said:
I can't comment on which is better, SPV or TPC+. I haven't ridden TPC+ very much. I will comment that I'm not satified with the performance of my Minute 2 fork. I can also comment that what has been done in MTB with CV/t technology is very crude and there's far more that can be done to improve its performance. It's very sad that I haven't been allowed to incorporate any new technology into the MTB shocks.

BM
What are your complaints about the minute 2? I rode a minute 1 and loved it. The only complaint I had was that it rode a little too high in the travel and was sketchy on jumps and drops.
 

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I really didn't have any for the longest time. I rode in tight techy stuff where it's big bump absorbtion shined, and I didn't care about the small bump ride. The fast sections were pretty short and abrupt, less than one minute each. Then I went and started riding this fireroad climb, and on the way down the small chattery bumps are too harsh, where I could go as fast as I dared for 15minutes. It'd create a vibration in the bars that made holding on too hard, my hands would start to burn. On trails that have somewhat smooth sections in between rocks, step downs, waterbars and such, it works great. It definately pedals well. I think it suffers because the forks are 1:1 with the wheel, and directly in line with the handlebars, unlike a rear shock that levered 2~3:1 and the saddle/BB is in between the rear wheel and front wheel, to some degree.

BM
 

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Spv, Good And Bad ...

Both my bikes have SPV front and rear and I can say that Im pretty happy with how well Swinger air shocks work on both back suspension systems. Interestingly, despite a big difference in suspension systems between my Giant Reign and my Vt ( shocks are identical and interchangeable ) Swinger shock does very well at letting these 6-ish inch travel bikes peddle well and soak up the bumps. On my Vt I have lots of sag (35%) and a high SPV setting while on my Reign I have 25% sag and a low SPV setting. After heaps of mucking about these settings seem to suit the suspension systems. This says a lot for the adaptability of the shock.

Cant say the same for my forks, Nixon Platinum and Minute one. Bouncy on roots and rocks and quite unreliable. My Nixon packs down over multiple big hits. The SPV system has got a couple of of advantages on forks though ...

1) anti-dive : under down hill hard braking both my forks seem to work quite well.

2) The peddling efficiency ; five years ago who would of thought that we could trail ride a 6 inch fork.

It would be great to be able to turn off SPV on the fly!!! (Like Rock shock pop-lock)
 
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