RPM Fork Valves

[FeralRdr]

Thanks for the info on the fork spring issue Randy, it helps me to prioritize my upgrades.

[SlowOldGuy]

Randy,
A few more technical questions.

If I install lower rate springs, then I'll have to use more preload to achieve the desired static and rider sag.  How does the RPM valve compensate for what's going to be extra sag with the softer spring rate?

I understand what you're describing when you say you need to use a spring and oil combination that will let the forks travel and push enough oil around to activate the valve shims, but under extreme riding, can this lead to excessive fork travel? 

As I comprehend suspension, the spring controls position and the valving/oil controls the velocity.  There is some overlap, if you use a thick oil, it may slow the movement down enough to influence the position.  Will I have more front end dive with the softer spring and thinner oil?  If the valve controls position, then is sounds like if I push down or pull up, the suspension will "stick" in that position until acted upon by another force or input?

Is the shim response different in compression than rebound?  Are they separately "tuneable?"  Please don't take offense to this, but I'm kind of wary of a "one size fits all" solution to something as complicated and varying as suspension.

All that said, I am planning on getting a set of the valves as soon as I can figure out a way of paying for them without the wife knowing about it.  :-)

DavidR.

[racerrad8]

Randy,
A few more technical questions.

1) If I install lower rate springs, then I'll have to use more preload to achieve the desired static and rider sag.  How does the RPM valve compensate for what's going to be extra sag with the softer spring rate?

2) I understand what you're describing when you say you need to use a spring and oil combination that will let the forks travel and push enough oil around to activate the valve shims, but under extreme riding, can this lead to excessive fork travel? 

3) As I comprehend suspension, the spring controls position and the valving/oil controls the velocity.  There is some overlap, if you use a thick oil, it may slow the movement down enough to influence the position.  Will I have more front end dive with the softer spring and thinner oil?  If the valve controls position, then is sounds like if I push down or pull up, the suspension will "stick" in that position until acted upon by another force or input?

4) Is the shim response different in compression than rebound? 

5) Are they separately "tuneable?"  Please don't take offense to this, but I'm kind of wary of a "one size fits all" solution to something as complicated and varying as suspension.

All that said, I am planning on getting a set of the valves as soon as I can figure out a way of paying for them without the wife knowing about it.  :-)

DavidR.

David, no offense throw out the questions and I will answer them or get the answer, but you have to throw away conventional suspension thinking with this product.

1) The valve does not compensate for the additional sag and that is the same with the measuring instructions included with the springs with & w/o rider. The valve has no control over sag and it should not( Unless you are running a race car and you want the shock to hold the car down and you built the rebound stack to be so stiff it cannot pass oil back through, like they did several years ago in NASCAR at the super-speedways)

I can say that it does take longer with the rider on the bike to achieve the sag measurement as the oil must pass through the shim stack. A helper to hold the bike upright is almost a requirement now.

2) No, the compression protion of the valve has two seperate valves which react to the input the fork is seeing, whether high speed or low speed travel (which I covered in the first post)

3) The spring as to allow the suspension to absorb bumps the valve is to control oil flow and spring compression & expansion rates.

4) Yes, the RPM fork valve has three different valve systems. It has the IAT (High speed; bumps) & shim stack (Low speed;cornering/sag) for compression and a shim/coil spring for rebound (Acceleration).

5) Yes, you can tune the valves with different shims and change the shim stack to suit your liking if needed. The IAT portion of the valve is not adjustable is is based off of the curb weight of the bike. The rebound portion is tunable, but it is set to allow the fastest rebound without allow the fork to employ the top out spring, that is also based off of the bike weight.

They sent me a tool when we were testing, but I have since sent it back. It is one of the things I have had thoughts of adding to inventory, but I figured it would be needed by someone who might be doing both track and road riding and the needed different valving for track.

Believe me, I played devils advocate on every aspect of the testing phase and the valve I am selling is the most complete RPM valve based on the weight of the bike. The spring rate based on the rider is the biggest adjustment required. Sure, 150 lbs rider could use a slightly different shim stack than the 300 lbs rider, but the difference in spring rate allows the shock travel to be the same based on the spring/rider weight. I tried the shim stack every way from Sunday and this is the best package for the "normal" rider. if someone is going to be tracking the bike then the shim stack might need some tuning, but the manufacture says they have a many guys using these valve in vintage events right of the shelf for the bike the purchase for and they have had great success.

Randy - RPM

[RichBaker]

David beat me to it, I'd been wondering the same things.....

[racerrad8]

David beat me to it, I'd been wondering the same things.....

Are you still wondering...?

Randy - RPM

[RichBaker]

Nope...

[miked]

I thought for a minute there Randy, you might be stocking Wondering now.....

[winddancer]

I thought for a minute there Randy, you might be stocking Wondering now.....

[Mike Ramos]

Speaking of fork valves...

Well I will leave the technical answers to the gentleman from RPM but I do have three exhibits (actually two, as one shows the speedometer & tach) that show the front fork valves in action. And I trust that you may find the answers [or at least a few] to your questions in the videos...

The first video is of a section of a rather rough road with turns and a short straight. You can see the forks exceptionally quick up & down movement, regardless of their position in the stroke. They are not just cycling up and down, but fluctuate sharply whether under deceleration (under compression) or acceleration, actually "dropping" into an imperfection in the road surface.

While the turn speeds are modest, there are moments when the forks are responding quite nicely under the added loading of the forces encountered when leaning through a turn.

The second video is of the speedometer (and I apologize for the shakiness; the mount was free standing about a foot off of the tank – I will have a better position the next time I try this). I ran the exact same stretch of road at the same speed, more or less. The speeds are of the low and intermediate range, but I can attest to the fact that at the higher speeds the results of the fork action are quite similar.

The third video (without the engine sounds) of another road I came across in an earlier video about another country road. It is hard to tell in the video, but the rear shock was limiting my enjoyment...

Easter is near. Does the Easter Bunny leave rear shocks in the basket? Here comes Peter Cottontail hopping up the bunny trail...
I sure hope I don't have to wait 'till Christmas...!

Ride safe,
Mike Ramos.

Front Fork
Approximate Speeds_Gauges
More of the Same

[Mike Ramos]

A little technical difficulty with that third video. You should be able to see it here...

More of the Same2

[Mark Olson]

Randy ,

I helped Craig install his RPM fork valves and springs this weekend and have a few follow up questions about them.

1.what is the recommended static sag ?
2.what is the recommended rider sag?
3.what is the recommended oil level with forks compressed and the valves and springs out from the top of fork, down to the oil?  130mm?
4.what is the proper placement of the washers for the fork springs ? is one needed on top of the fork valve? or just the spacer ends?

I understand the fork valves are pre adjusted and go in only one way with the long part up, but is there an adjustment necessary for a more spirited rider?  more oil? or 1 turn of the adjuster nut?

As it stands the noise from the front end sounds like a old whores bed springs.
does everything just need time to settle in?

I may have overdone the preload.  

Mark O.

[axiom-r]

I will be interested to hear others reply on these questions Mark.  For me its .25 inch static and an additional .5 inch with rider so from full "top out" of the travel it should be .75 inch with the rider on.....   can't offer any other info on the remaining questions.

Tim

[racerrad8]

1.what is the recommended static sag ?
2.what is the recommended rider sag?
3.what is the recommended oil level with forks compressed and the valves and springs out from the top of fork, down to the oil?  130mm?
4.what is the proper placement of the washers for the fork springs ? is one needed on top of the fork valve? or just the spacer ends?

I understand the fork valves are pre adjusted and go in only one way with the long part up, but is there an adjustment necessary for a more spirited rider?  more oil? or 1 turn of the adjuster nut?

As it stands the noise from the front end sounds like a old whores bed springs.
does everything just need time to settle in?

I may have overdone the preload.  

Mark O.

1) The "static sag" is as recommended in the spring installation instructions: 25-30mm
2) What is rider sag?
3) As listed in the RPM fork valve installation instructions: 6" or 152mm*
4) Washers are only required at each end of the spacer. If you have the stock washer at the top, the additional spacer included with the spring is not required.

The spring pre-load should be 15-20mm (as specified in the spring installation instructions)

I have heard that as well, but after they settle the noise is less, but there is still some noise. It comes from the spring actually being compressed and rubbing against the inner wall of the fork tube and the thin oil. That was something you could not do with the other valves...

*The oil level can and will continue be a tuning tool. There is not an adjust of the valve without complete disassembly. The nut on the top is holding it all together it is not a tuning adjustment. If you feel you need to tune the valve, I will have the tool and shims available after I get the next order so you can play with the shim stack.

Randy - RPM

[axiom-r]

Static sag is the amount the bike squishes the suspension under its own weight. Rider sag is the same thing but with the rider in full gear on the bike.....

You can measure static by pulling up and the front or rear end and measure how much it lifts before the suspension tops out.

I think the 25-30MM would be the Rider Sag amount - close to what I was saying at 3/4 inch or 19.2mm.  I am told that on a properly adjusted bike the sag is the same front and rear....

tim

[racerrad8]

Static sag is the amount the bike squishes the suspension under its own weight. Rider sag is the same thing but with the rider in full gear on the bike.....

I do not want to confuse the subject, but not according to the spring manufacture installation instructions. They list "static sag" as the "amount the bike settles, from fully extended, with the rider on board in riding position".

That is why in the RPM fork valve installation instructions it says to follow spring manufactures installation procedures.

Randy - RPM