[jrewing]

Hi. I’ve got the model before the idler Aurum in XL 27.5. Really like it and getting back DH racing. Had the boxxer charger 1 custom tuned and I’m very happy with that.
Got a kage shock which isn’t the flashiest I find. Can get it modded with aftermarket piston and tuning but parts might not get here in time.
I have a rc4 small shaft I have on the way to me. It’s a CM/RM tune. CNJ8
I can build shocks forks if required but tuning direction im unsure to do.
That Aurum is pretty progressive and I run a 550lb spring, 27ish% sag. 87kg kitted up.
I think the rebound tune on rc4 will be better than the kages performance, but I’m concerned valving could be too stiff? Thought I’d ask the advice of rc4 whispers here? Cheers
Josh

 

[englertracing]

Ride it first.
If you can build em,
And you know how you like em
get restackor,
there is a learning curve but when you want a 5 10 15 or 20% change in stiffness, or rebound speed you can get very close to that. Then you can see if it was too much or not enough and get it closer on the next round.
When you want to change low mid or high speed without effecting the others you have a vastly better shot at that then you do guessing.

 

[jrewing]

Yeah thanks. I’ve heard of restackor from Moto guys. Makes sense. Have time and ability to source anything fox from a local suspension rebuild shop. Looks a straightforward shock to work on. Edit- checked it out. Might be playing with the kx450 settings too.
What’s the go to oil for fox shocks? It’s noticeable more expensive than Moto oil. Well kyb fork oil isn’t cheap granted.

 

[Happymtb.fr]

Ride it first.

exactly!

@jrewing
you can service it first, just to check that everything is ok.
you can also lower the IFP pressure as well. I got mine around 100psi from memory.
and the IFP depth as specified is more or less to ensure that the air assist has some working range, you can push the IFP almost to the bottom if you don't plan on using this feature.

 

[Redwood Mulch Chucker]

Yeah thanks. I’ve heard of restackor from Moto guys. Makes sense. Have time and ability to source anything fox from a local suspension rebuild shop. Looks a straightforward shock to work on. Edit- checked it out. Might be playing with the kx450 settings too.
What’s the go to oil for fox shocks? It’s noticeable more expensive than Moto oil. Well kyb fork oil isn’t cheap granted.

Motorex is my preferred oil. Current Fox stuff is 5wt, but the older ones were 10wt. Not sure what was stock in there.

Here is the stock tune;

Piston has some small rebound ports!
I am a big fan of crossover stacks for compression.

Looks like there may be some preload on the base valve, you'd have to measure the piston to find out. If there is, I would remove all preload if possible and add stiffness to a non-preloaded stack.

But for sure ride it stock first so you know what to go after.

 

[jrewing]

Motorex is my preferred oil. Current Fox stuff is 5wt, but the older ones were 10wt. Not sure what was stock in there.

Here is the stock tune;
View attachment 187687

Piston has some small rebound ports!
I am a big fan of crossover stacks for compression.

View attachment 187688

Looks like there may be some preload on the base valve, you'd have to measure the piston to find out. If there is, I would remove all preload if possible and add stiffness to a non-preloaded stack.

But for sure ride it stock first so you know what to go after.

Thanks. Reading Restackor theory the preload will add firmer low speed? Could work better on my high leverage- find out soon. Are all Dhx pistons the same that you’re aware of?

 

[jrewing]

exactly!

@jrewing
you can service it first, just to check that everything is ok.
you can also lower the IFP pressure as well. I got mine around 100psi from memory.
and the IFP depth as specified is more or less to ensure that the air assist has some working range, you can push the IFP almost to the bottom if you don't plan on using this feature.

Lots of end progression in frame so I’ll that’s good base line setup for ifp pressure. I take it shock works at 100psi fine?

 

[englertracing]

If you have good progession removing the boost valve may be a good thing to try.

 

[Jm_]

I took mine apart to harvest some shimz. Holy F there are so many tiny little watch parts in that thing...

 

[jrewing]

If you have good progession removing the boost valve may be a good thing to try.

I thought the boost was gone in later ones, and just a volume and air pressure adjust?

 

[englertracing]

I thought the boost was gone in later ones, and just a volume and air pressure adjust?

Could be the case. It may be that if the stickers are on it it's in there, if not it may not be.

But in fox's drawings they are in there.

 

[jrewing]

Could be the case. It may be that if the stickers are on it it's in there, if not it may not be.

But in fox's drawings they are in there.

Ok got it. It’s 1/2 inch shaft version. I think the mid-valve diagram above is a separate schematic 2011 to the base valving schematic 2014 of this Cnj8 tune..Seems odd. Reservoir has only air assist on it.
What is the oil cst used in these?? As said above differing in older rc4 v new twin tube specials. Thanks

 

[buckoW]

Ok got it. It’s 1/2 inch shaft version. I think the mid-valve diagram above is a separate schematic 2011 to the base valving schematic 2014 of this Cnj8 tune..Seems odd. Reservoir has only air assist on it.
What is the oil cst used in these?? As said above differing in older rc4 v new twin tube specials. Thanks

Yours doesn’t have the boost valve and the air assist is to assist marketing more than spring rate.

 

[Inclag]

exactly!

@jrewing
you can service it first, just to check that everything is ok.
you can also lower the IFP pressure as well. I got mine around 100psi from memory.
and the IFP depth as specified is more or less to ensure that the air assist has some working range, you can push the IFP almost to the bottom if you don't plan on using this feature.

I thought min air pressure in those was like 150psi no?

 

[Redwood Mulch Chucker]

Preloaded shims stacks are digressive and harsh (stiff) at low speeds and then softer at high speeds. It takes more force to crack them open. Generally not a good thing, the opposite of what you typically want which is supple for small events and support for big events.

If the base valve is preloaded and you make it linear, I wouldn't go too low on IFP pressure keep it 125-150 at a minimum. When the base valve has a stiff tune, it allows for lower IFP pressure without cavitating. But when you open it up and allow the shock to flow oil easier, it will cavitate if IFP pressure is too low.
EXT shocks can run 50 psi IFP pressure because there is a massive spring preloading the base valve. Also why they have a very "platformy" feeling to them.

Don't know oil in cst, but it's either 10wt (old spec) or 5wt (current spec for everything but DPS). If the rebound ports on the piston are as small as they are in the drawing, I would go 5wt. Motorex 4wt is actually 5wt in terms of true viscosity. And it's red, like blood.

 

[jrewing]

Preloaded shims stacks are digressive and harsh (stiff) at low speeds and then softer at high speeds. It takes more force to crack them open. Generally not a good thing, the opposite of what you typically want which is supple for small events and support for big events.

If the base valve is preloaded and you make it linear, I wouldn't go too low on IFP pressure keep it 125-150 at a minimum. When the base valve has a stiff tune, it allows for lower IFP pressure without cavitating. But when you open it up and allow the shock to flow oil easier, it will cavitate if IFP pressure is too low.
EXT shocks can run 50 psi IFP pressure because there is a massive spring preloading the base valve. Also why they have a very "platformy" feeling to them.

Don't know oil in cst, but it's either 10wt (old spec) or 5wt (current spec for everything but DPS). If the rebound ports on the piston are as small as they are in the drawing, I would go 5wt. Motorex 4wt is actually 5wt in terms of true viscosity. And it's red, like blood.

cool. My local moto shop has motorex, that’s easy. I actually feel this tune might be designed for the leverage of this Aurum actually. Even with a 550lb spring it’s very soft in the start and a big ramp up at the end.

With the Kage shock I have I atm, it’s the rebound that’s too loose and can’t balance with out making it harsh. Keen to see how this runs stock vs that.



Regards to mid-base-cavitation valving I did read up on that a long time ago and that’s sort of stuck with me somehow with my brain that’s not the strongest! But I did wonder how EXT got pressures that low to work when I saw a shock once.

 

[Udi]

There's a lot of incorrect information in this thread, particularly re: effects of preloaded shim stack.

If the shock is brand new and stock, run it as-is and don't change anything. If you are running a 550lb spring, it is unlikely the valving will be too stiff, in fact the more likely scenario is that the rebound damping (particularly HSR) will be a little light - however try it stock first. Solving this correctly isn't as easy as re-shimming anyway.

The stock oil in this shock is Fox Red 10wt / Silkolene Pro RSF 10wt, this is a high viscosity-index, shock specific fluid (high temperature stability). Don't use anything else unless you want to introduce a new/unknown tuning parameter. There is a datasheet here, I recommend sticking to the same viscosity (given there in cSt@40) and you want an equal or better value for VI. For reference, Silkolene has updated this fluid but only the name has changed, as per here.

Also to confirm, there is no boost valve in the stock small-shaft (12.7mm) RC4, buckoW is correct.

 

[jrewing]

There's a lot of incorrect information in this thread, particularly re: effects of preloaded shim stack.

If the shock is brand new and stock, run it as-is and don't change anything. If you are running a 550lb spring, it is unlikely the valving will be too stiff, in fact the more likely scenario is that the rebound damping (particularly HSR) will be a little light - however try it stock first. Solving this correctly isn't as easy as re-shimming anyway.

The stock oil in this shock is Fox Red 10wt / Silkolene Pro RSF 10wt, this is a high viscosity-index, shock specific fluid (high temperature stability). Don't use anything else unless you want to introduce a new/unknown tuning parameter. There is a datasheet here, I recommend sticking to the same viscosity (given there in cSt@40) and you want an equal or better value for VI. For reference, Silkolene has updated this fluid but only the name has changed, as per here.

Also to confirm, there is no boost valve in the stock small-shaft (12.7mm) RC4, buckoW is correct.

I will get the rsf oil because I found that’s the stock and quite thick cst wise. Maximas oil which I have in different grades is way lighter in weight equivalent. I looked at the Fuchs site and yes the newer formula is better Vi too, with more additives to boot. So I’ll stay with it for sure. Got to be better than a stock kage.
Are the stock fox pistons adequate ultimately ?

 

[englertracing]

There's a lot of incorrect information in this thread, particularly re: effects of preloaded shim stack.

Can you expand upon this?

 

[Happymtb.fr]

I am considering rebuilding my DHX RC4 to a different stroke length. I just want to make sure the Marzocchi Bomber CR parts will fit the DHX RC4. A lot of the part numbers are the same. I assume that Fox is not keeping old part numbers and changing dimensions... but maybe they are?

DHX RC2/RC4 | Bike Help Center | FOX

www.ridefox.com

BOMBER CR | Bike Help Center | FOX

www.ridefox.com

Edit: Bomber parts fit the DHX RC4

 

[jrewing]

How does reservoir pressure affect, if at all, the rebound valving?

 

[englertracing]

How does reservoir pressure affect, if at all, the rebound valving?

Well if changing it doesnt introduce or stop existing cavitatiion then it wont really

 

[jrewing]

Well if changing it doesnt introduce or stop existing cavitatiion then it wont really

On these shocks they have a 100psi window (100-200) of variation. If the pressure increases overall damping in Comp, wouldnt it also push back in return with some more pressure? Right….probably more so wrong haha

 

[englertracing]

Thats rod pressure which will act as spring rate.

 

[Redwood Mulch Chucker]

Avalanche Craig once said that reducing IFP pressure by about 100 psi is roughly equal to reducing spring preload by 1.5 turns.
This was for a for a Bomber CR which I think has the same IFP dimensions.