Manitou SPV - so what does it actually do?

The Rookie

Have Manitou Skareb elite forks on the MTB, and while I'm generaly happy, I've been struggling to get my head round the SPV, so I reserviced the forks at the weekend in an effort to try and understand it.

The way the manual reads the compression damping is controlled by the air pressure and you can change the ramp in rate by turning the red inner section (which lowers it into the leg chaning the volume of the 'air can' equivalent.

However with it apart, I'm less sure, the compression damper is on the rebound damper leg as a seperate assembly on the top, all the change in pressure seems to achieve is giving you a smaller volume air sprng to the main one, I can't see how it affects the damping

Also the fill tolerance (10mm in height) is significantly larger than the few mm you can get by winding in the volume adjuster on the SPV assembly while the volume change in bump is small anyway as its only the 10mm diameter damper rod that's decreasing the air volume.

Have I got it right, or have I missed something?

nicklouse

the SPV is the Manitou Pro pedal it is there to help reduce the large low frequency inputs.

never actually bothered with any of their forks but on the shocks it does work about the same as the Fox Pro pedal and the 5th Element shocks.

The Rookie

That's as maybe Nick, but on the fork I can't see how the air pressure changed the damping at all.....it just looks like a second smaller can air spring

supersonic

Is there a valve on the SPV?

The Rookie

Yes...
Looks almost the same as this
http://www.chainreactioncycles.com/Mode ... elID=21199
Manual gives a min pressure for that side, although I can't recall it off the top of my head!

Air valve in the middle and the red section screws down into the stanchion to change the air volume (slightly).

supersonic

It is an older system: the pressure on the damper in the chamber affects the comp damper. The adjuster/oil volumes are a bit clumsy, but are something you can at least experiment with. The ramp up not only affects a small air spring, but the damper too, so you can adjust end stage damping (position).

30-100 psi ;-)

The Rookie

OK thanks SS, what I couldn't/can't figure is how the pressure changes the damping - I could see no way for it to do that.

What further concerned me was that the oil fill volume variance is 10mm while the red adjuster can only be wound in about 5mm, add to that that the volume change due to damper rod intrusion amounts to only 1/7 of the air volume (at min fill level) at full travel which suggests the alleged adjustability is more illusiary than actual!

I have a non SPV air cap off another Manitou I may try to see if I notice a difference that justifies the extra weight of the SPV cap!

nicklouse

The Beginner wrote:

the few mm you can get by winding in the volume adjuster on the SPV assembly

this concerns me. IIRC there was more than 10mm of adjustment.

The Rookie

OK It may wind down further, the trouble is my 16mm socket binds on the outer and you can't get the valve cap off or the shock pump on with it more than about 5mm in, either way the adjuster can't do any more than compensate for the fluid level varaince specified by Manitou.

nicklouse

it should do a lot more than that.

I sugest moding a socket to adjust it.

I made a big difference on the shocks.

mrmonkfinger

The Beginner wrote:

how the pressure changes the damping - I could see no way for it to do that

I don't know the exact layout in the forks. But, on the rear shocks, SPV is an on/off valve placed in the compression side of the oil circuit.

The pressure in the SPV chamber is essentially just there to push against a spring loaded valve, keeping it closed. When it opens you get normal compression damping. When it is closed, it gives very high damping. ie as Nicklouse says, a lot like Fox PP.

The pressure is only suppose to control the point at which the valve opens. More pressure = faster shock movement needed for valve to open.

The volume adjust is only to adjust the bottom-out compression of the shock.



The manitou shock I have doesn't have SPV, just a regular shim stack. For me, the "SPV" air pressure for the non-spv shock adjusts the overall shock progressiveness. Its a nice bit of kit IMO.

I did read internet rumours that the implementation on the forks was less effective than the rear shocks.

The Rookie

Forks totally different, they are failry classic assembled forks.

The rebound damper is screwed into the bottom of the stanchion in the normal way but contains and extra compression valving system on its tip above what looks like the same rebound damper on the Sliver forks I have in bits, there is no floating piston (but doesn't really need to be as that looks like it's just keeping fluid and air from mixing in your diagram.

I understand your description, not sure if it does work like that as I can't see how the air pressure (or rate of rise) affects the damping (not to say it doesn't, I just can't see it!), maybe I'll dump the air spring pressure out and try some 'bump' tests, the problem in a fork is the ratio of air 'above' the fluid to the displacement due to the intrusion of the damper rod is quite high (lots of air to little intrusion) compared to the rear shock, maybe I should try overfilling with fork oil to make the ratio more aggresive! Its not claimed to give a pro pedal effect, more to allow the forks to be run 'soft' with additional compressive damping to 'save it' or otherwise (from the decsription anyway)

mrmonkfinger

The Beginner wrote:

Forks totally different, they are failry classic assembled forks.

had a funny feeling this would be the case

The Beginner wrote:

floating piston (but doesn't really need to be as that looks like it's just keeping fluid and air from mixing in your diagram.

yes, that's its entire function

The Beginner wrote:

I can't see how the air pressure (or rate of rise) affects the damping

I presume you get what the SPV does, yes? The SPV is held shut, normal. That is done just by the air pressure in the chamber. Once your fork is moving fast enough to overcome that air spring, SPV pops open, and suddenly you have normal (ie not much) compression damping. That's how it affects compression damping - the exact pressure dictates when the SPV opens. Just like an on/off switch. Crude, but effective enough.

The Rookie

MrMF, thanks for all that!

Ok that's slightly different to how Manitou sell it in their description on the forks but close enough, the description implies more a 'rising rate' than the on off you describe.

It's still not clear to me HOW it (mechanically) actually does that, but I'll loose the fork spring air pressure tonight (forks aren't yet back on the bike) and try some tests with different air pressures in the SPV as a starter to see if it does anything obvious! Just doing a manual 'bump' test with min (30) and max (100) pressures I should feel something different!

The Rookie

Well, air spring depressurised and cap removed for good measures, SPV tested with everything from min to max pressure, fully adjusted out to fully adjusted in, all at nominal oil fill (120mm from top) within 1mm and I couldn't detect any change in compression damper performance at all! SPV cap removed and replaced with the spare plain one to save 16g! After a normal compression damper now!

mrmonkfinger

The Beginner wrote:

MrMF, thanks for all that!

Ok that's slightly different to how Manitou sell it in their description on the forks but close enough, the description implies more a 'rising rate' than the on off you describe.

No problem. I think the forks are slightly different to the shocks, so take my description with a pinch of salt. The SPV might not cover all the oil ports, so could be tweaked to have a more subtle effect.

The Beginner wrote:

It's still not clear to me HOW it (mechanically) actually does that

On the shocks, it is just the air pressure statically pushing against the body of oil. The pressure from the oil keeps the valve closed when shock/fork is at rest. There's no direct mechanical linkage from the air pressure to the SPV valve.

When you compress the shock/fork, the flow of oil pushes in the other direction against the SPV valve. Once it rebounds, the SPV closes again and the one way oil flow keeps a higher pressure on the correct side of the SPV.


The SPV chamber does affect the whole damping curve as well as just platform.


Better half has an SPV shock on her bike which is pretty effective, we dialled out all the pedal bob in the space of a few minutes. The platform doesn't seem to get in the way of normal riding. Made a great fix for a bike which had quite a lot of bob, OH always thought it needed a lockout switch but the SPV does a good enough job.

The Rookie

OK thanks for that, I think the problem with the forks is that the rate of change of pressure is much lower than in a shock, I may try overfilling the damper leg to get that ratio up to somewhere closer to the shock to test. The shock looks like at full bump the shock air space gets close to zero, on the fork it reduces the air volume from circa 105mm tall to 90mm tall by internal diameter of stanchion.

mrmonkfinger

The Beginner wrote:

The shock looks like at full bump the shock air space gets close to zero, on the fork it reduces the air volume from circa 105mm tall to 90mm tall by internal diameter of stanchion.

The volume difference affects progression - shouldn't affect whether the SPV works or not.

The Rookie

Got you, but is it pressure or rate of change of pressure that activates it....if the latter then volume is crucial, if the latter then the volume adjuster is pretty meaningless on a fork where it's effect is pretty minimal at best

mrmonkfinger

The Beginner wrote:

Got you, but is it pressure or rate of change of pressure that activates it....if the latter then volume is crucial, if the latter then the volume adjuster is pretty meaningless on a fork where it's effect is pretty minimal at best

If you mean SPV when you say activates, then it is just pressure. There's a bit of a picture about half way down:

http://www.krankin.co.nz/design%20dd.htm

Pressure from oil flow is speed dependant - move fast enough, the pressures match, SPV opens... . When the SPV is open, the whole SPV valve has an increased volume - its the oil displacement coming from the increased volume, that's the mechanism by which the air pressure keeps it closed.

The volume adjuster is there purely to increase the spring rate at the bottom out position. As a tiny extra air spring. That acts against the oil displacement.

The Rookie

Thanks that sort of makes sense for the rear, For the front it would sound more like a floodgate that 'Stable pedal platform' although the manitou manual describes it as working the other way round:-

DAMPING ADJUSTMENT – SPV EVOLVE
With SPV Evolve damping, your suspension’s compression damping
characteristics and position sensitivity can be set with an SPV pump (Manitou part
#85-4161). For proper function of your SPV damping system follow this
procedure:
1. Start by removing the red SPV air cap located on the top of the right fork
leg, as you are looking at the fork from the rider’s position. (DORADO
MRD X-Works forks have this adjustment at the bottom of the right fork leg).
Using a dedicated SPV pump (Manitou part #85-4161), inflate the fork to the
pressure recommended in Table 7.
2. Check sag per procedure above.
3. Adjust SPV pressure. More pressure will create more compression damping,
hold the bike up more and pedal better. Less pressure will create less
compression damping, allow more sag, and be more responsive and supple.
Do not run SPV pressure below 30 psi.
4. Adjust SPV volume. With a 16 mm socket wrench or the SPV 16 mm volume
adjust socket (part #85-3007), you can adjust the air volume in your SPV
Evolve suspension. The volume adjust hex is colored red and is located on
top of the right leg. Turning the volume adjuster inwards will create a more
progressive damping effect and make the suspension firmer from mid-stroke
to bottom-out. Turning the volume adjuster outwards will make the
suspension more linear in compression damping and have a softer finish.
Refer to the Answer Products website for specific tuning information about your
SPV suspension.

That is damping increasing as pressure goes up, rather that the damping decreasing as you overcome the pressure.

The trouble is the variation in volume of air, and thence pressure due to damper rod intrusion is low, the adjustment verses the permitted variation in oil fill volume is low (i.e. the same amount, so the air volume you end up with is fairly random), so tuning it to give a consistent result is somewhat impossible and you're effectively just turning the static pressure, so may as well use a conventional damper!

Example, say the damping switch point is at 108psi, so if I have the minimum air volume (to book) and max pressure (100psi) it will come in circa half way through the travel, if I have the air pressure below 90psi it will never come in ever!, say it comes in at 65psi (half way between max and min stativ pressure) any pressure over 65psi and it will always be in - its starting to sound like a marketing gimic on the front is it not? UNLESS at the front the responce is linear (ish) to pressure rather than on/off, but as I've shown the volume change effect on pressure is so hit and miss as to render the adjustable volume meaningless!

mrmonkfinger

SPV is definitely a floodgate type thing. Get the damper moving fast enough and the compression damping drops sharply.

The Rookie

Which is not what "Turning the volume adjuster inwards will create a more progressive damping effect and make the suspension firmer from mid-stroke to bottom-out" says!

Turning the volume adjuster (ignoring it's effect is pitiful) inwards will increase air pressure later in the stroke (relative to static pressure) and allegedly increase compression damping, which is nothing like floodgate!

mrmonkfinger

The Beginner wrote:

Which is not what "Turning the volume adjuster inwards will create a more progressive damping effect and make the suspension firmer from mid-stroke to bottom-out" says!

Turning the volume adjuster (ignoring it's effect is pitiful) inwards will increase air pressure later in the stroke (relative to static pressure) and allegedly increase compression damping, which is nothing like floodgate!

The manitou user manuals I've read were a bit crap when it came to explaining the finer points of setup & operation, I think they lost something in translation. I always thought the SPV volume was confusingly named. Should have been called 'bottom out adjust' or similar.

You've nailed what the volume adjust does (or should do), but I think you're missing something about how the spv "floodgate" is set or works, the volume adjust doesn't really affect the 'floodgate' side of the fork

minimum (30psi) in the spv chamber (ignore the volume) - spv is always open, little or no platform effect
maximum (100psi? 150psi?) in the spv chamber (ignore the volume) - spv is always closed, extremely firm platform

All you do with these things is just gradually increase the pressure in the spv until any pedal bob vanishes. and then leave it alone.

If you've set the correct sag on the forks, but you get the odd bottom out on a big drop, then fiddle with the volume adjust, otherwise don't bother with it, it is literally just to help stop the travel topping out

The Rookie

OK, It's possible the manual is misleading (either by accident or for marketing reasons), I'll try as you suggest and see how it goes.