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What's up with the Fox RC4?

bdamschen

bdamschen

Turbo Monkey
Nov 28, 2005
3,378
157
Spreckels, CA
Slater said:
It could also be that one shock is actually better than another. I'm pretty sure Ohlins, the winningest damper manufacturer in motorsports history, might be able to build a better, more consistent shock than Fox. Its not like Fox is known for bandaid-free MTB shocks.
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And it's not like Ohlins is known for any MTB Shocks prior to the Cane Creek. But build quality was never really my point in the first place.

A fox dhx or RC4 or marzocchi roco or manitou revox properly tuned are great shocks and perform great. I'll bet in a blind test, most of the people who are tooting cane creek or avalanche or elka or BOS as the only shocks worth riding wouldn't be able to pick the lesser expensive shocks out of the mix.

And what do all those rabid cane creek or elka riders do for a fork? Are they just miserable with what they have because their fork can't deliver the same amazing performance as their shock?
 
Sandwich

Sandwich

Pig my fish!
Staff member
May 23, 2002
22,160
7,435
borcester rhymes
Slater said:
It could also be that one shock is actually better than another. I'm pretty sure Ohlins, the winningest damper manufacturer in motorsports history, might be able to build a better, more consistent shock than Fox. Its not like Fox is known for bandaid-free MTB shocks.
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not to get into a whirlwind of stupid, but fox also makes moto and offroad shocks, among others, and have oodles of other experience I'm sure. Their shocks are also on at least half the bikes out there.

I'm sure ohlins is capable of making the best mtb damper available...do they is another question.

Few people would argue that the MTN-3 shock from avalanche wasn't supremely capable...it just cost a fortune and weighed a ton.

Point is, can and do are separate and while the CCDB IS probably a great shock, I doubt that nothing else even comes close, especially if it's appropriately tuned to the rider.
 
Acadian

Acadian

Born Again Newbie
Sep 5, 2001
714
2
Blah Blah and Blah
kidwoo said:
Nah that frame's goin up for sale soon. I got a sick troy lee kit so I have to update my frame every year to match the colorwayz yo.


That proto rfx is sick. Fox is making a fork though!!???:eek:
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dude your intraneat will never be fast enough to keep up with me. you're kit just doesn't match the broad Band Colorwayz - total faux pas.

dude - with Fox's new suspension you can run over people and sh|t! :thumb:
 
dhkid

dhkid

Turbo Monkey
Mar 10, 2005
3,358
0
Malaysia
Handy Man said:
for ****s and giggles:

The damping ratio (z) is the ratio of damping (c) to two times the root of the mass (m) multiplied by the spring rate (k).

Over damped: the system returns to equilibrium without oscillation (z>1)
Under damped: the system oscillates before settling at equilibrium (z<1)
Crit Damped: The system returns to equilibrium as quickly as possible without oscillating (z=1)

On a bike, and on vehicle suspension in general, critical damping is optimal
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you wont be able to ride a bike that is critically damped, it will be way to stiff. dh bikes are roughly around 0.3 for the really fast guys.
 
H

Handy Man

Chimp
Oct 21, 2009
36
0
Good to know. Also, damping ratio doesn't really apply to modern suspension systems because the damping is nowhere near constant... unless you want to talk about individual damping ratios for rebound, compression, hi speed, low speed, etc...
 
S

Slater

Monkey
Oct 10, 2007
378
0
Pat Tellier said:
I love it when forum specialists explain how shocks such as the RC4, BOS, Double Barrel and Elka are either progressive or linear when they are all speed-sensitive dampers.
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Care to explain how the bottom out adjustments on some of these dampers are speed sensitive and not position sensitive?
 
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time-bomb

time-bomb

Monkey
May 2, 2008
957
21
right here -> .
Slater said:
Care to explain how the bottom out adjustments on some of these dampers are speed sensitive and not position sensitive?
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ok, i am going to put on my specialist hat for a moment. the bottom adjusters are neither speed sensitive or position sensitive. they work the same on either type of shock. it just allows you to adjust the spring curve from linear to progressive by dialing in the knob and making the chamber smaller causing the shock to ramp up more in its stroke. speed sensitive and position sensitive are referring to the type of damping on the shock, that can be compression and rebound. the bottom out has nothing to do w/the damping.

that is my understanding anyway. someone please correct me if i am wrong.
 
S

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
Pat Tellier said:
I love it when forum specialists explain how shocks such as the RC4, BOS, Double Barrel and Elka are either progressive or linear when they are all speed-sensitive dampers.
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Well the RC4 actually IS a progressive damper - its compression curve should really be plotted in 3D since it's both position and speed sensitive.

IH8Rice said:
isnt it just adjusting the chamber size??
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Yep, but that affects the compression damping on the RC4. The "boost valve" is a pressure relief valve that's held closed by oil pressure (oil pressure in the resi = air pressure in the resi), with a spring that's preloaded to hold it open early in the travel. On the original DHX, the propedal knob adjusted the preload on that spring via a reverse thread - in other words, turning up the propedal backed off the spring preload, so there was less spring force trying to hold the valve open against the oil pressure. This spring preload is not adjustable on the RC4 (pretty sure it's still in there though - they might have just put a bypass circuit in there instead, in either case the result is more or less the same).

As the shock compresses, the shaft displaces oil into the reservoir, which in turn compresses the air/gas in the chamber, resulting in higher air pressure which as I said before means higher oil pressure. This higher oil pressure means a higher force holding the boost valve closed, ie higher level of compression damping further into the stroke. This is why the RC4 is a legitimately progressive design - it's exactly the same principle the 5th Elephant and Manitou Gangbang shocks work on, except the pressure relief valve (boost valve/CVT valve) on those was on the main piston rather than in the reservoir. Dyno plotting any of these shocks using a CVP results in a large degree of hysteresis because of this - the compression curve can be significantly different in two difference positions in the travel even at the same speed.

FWIW, I own a CCDB, an RC4 and spent months riding an Elka. I'd happily rock any of them really, though I'll sum up the pros and cons of each briefly:

RC4:
Pros
- Independent HSC/LSC controls that work fairly well
- Smoother than the DHX5
- Adjustable progression via bottom out resistance
- Generally worked well, wasn't hypersensitive to setup

Cons:
- the air spring effect in the RC4 makes getting the right spring a bit confusing. Not a big deal once you've got the right spring (I needed a 300 to get the same sag as the CCDB with a 350!), it rode fine in the Sunday and the Legend.
- Rebound was more linear than the Elka or the way the CCDB can be set up, needed to be set a bit slower to prevent kicking. Not a big deal though, especially if you like your rebound on the slower side.
- Even with LS/HS settings maxed out, the level of compression damping wasn't that huge - I typically ran both LSC and HSC near maximum. A heavier rider or someone on a higher leverage ratio bike might find that they couldn't get enough though, but keep in mind I like a fairly firm compression setup compared to most people.

Elka:
Pros:
- Super controlled
- Very effective HSC/LSC adjusters
- Very easy to set up because most of the tuning is done for you in the factory
- Rebound curve worked really well for me, was poppy and lively without ever kicking, made it easier to find the sweet spot in the range
- Best user's manual ever for sure, the setup advice is absolutely spot on.
- Stable and planted.

Cons:
- Largish shaft diameter creates some of the air-spring effect the RC4 has, not to the same extent though and like the RC4 it wasn't a huge issue on the Legend or the Sunday I was on - affected sag and spring rate a bit but not a real cause for concern.
- Had some mechanical issues with stuff coming loose inside the shock, Elka say they've since sorted it with redesigned parts. No real surprises there, first-generation products almost always have those kinds of hiccups. If they've fixed that properly then I can't come up with any serious criticisms of the shock. Make it even smoother somehow? haha

CCDB:
Pros:
- Highly adjustable. Duh.
- Adjustable LSR/HSR as well as LSC/HSC mean you can be very very picky about aspects of the ride and tune it to suit
- Very stable, compression damping is very effective and you can really control the bike's behaviour well.
- Lower stiction than anything except the BOS Stoy
- Every click makes a small but distinct difference to the ride
- Huge range of adjustment... though this can be a bad thing too.

Cons:
- As I had the old tune, it seemed like the damping at very low speeds was a bit excessive, making the shock feel pretty dead, but then I had to crank the HSC a bit more than I would have liked to get the low-mid speed support I wanted. I suspect this was due to the poppet valve shims being too soft and opening too easily, meaning the LS circuits (both compression and rebound) had to be closed more than I would have liked. I think basically this created very linear, perhaps even digressive LS curves whereas I would have preferred that it was a bit more progressive in order to increase suppleness at the very low end of the speed range. The BOS Stoy definitely delivered that characteristic - at pushing-on-the-seat speeds it felt like there was almost zero damping, yet the low-mid range damping was very strong. Hopefully the new tune has fixed that - I've heard the damping can be set up a lot lighter. I'll most likely get my shock reworked with the new tune prior to this season so I'll update my opinion then.
- Let's not kid ourselves, this shock takes a while to set up. Each adjustment makes the difference it says it does, but it does take a while to figure out the relationship between riding characteristics and which adjuster you need to turn. It is very possible to set one of these up like utter crap - especially if you don't know what you're doing.
- Actually pretty easy to bottom out on bikes that aren't inherently progressive, especially in g-outs and whatnot, unless you want to really crank the compression and deal with the resulting deadness.


Goddammit I spend too much time on this ****.
 
S

stinky6

Monkey
Dec 24, 2004
517
0
Monroe
Socket please delete that post: it was logical, factual and based on really riding experience and therefor has no place on a forum. Seriously that was helpful. I don't know much about suspension tuning but I've been sifting through the threads on here lately and picking the right peoples brains when I go riding and I'm starting to notice difference in my setup.
 
Transcend

Transcend

My Nuts Are Flat
Apr 18, 2002
18,040
3
Towing the party line.
Socket, great post. So far, the elka is the greatest feeling shock I have ever run. I am super impressed and Pat offered amazing customer service when i was in a pretty good spot (ie: no one had the ginormous shock my 225 proto needed, and he jumped at the chance to help - Merci Pat.)

I will be trying out an RC4 in the next couple of weeks just to see how it feels on that bike. The progressive rebound on the Elka is pretty amazing, and it will be really hard to beat I think!
 
S

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
Transcend said:
Socket, great post. So far, the elka is the greatest feeling shock I have ever run. I am super impressed and Pat offered amazing customer service when i was in a pretty good spot (ie: no one had the ginormous shock my 225 proto needed, and he jumped at the chance to help - Merci Pat.)

I will be trying out an RC4 in the next couple of weeks just to see how it feels on that bike. The progressive rebound on the Elka is pretty amazing, and it will be really hard to beat I think!
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Yep, I'm a big fan of the Elka too - it's like a mass produced BOS Stoy in my opinion. The damping feels quite similar in many respects, especially that daddy-just-caught-me feeling when you land a jump or whatever, but the BOS is just that little bit more refined and amazingly stictionless (not that the Elka is bad with stiction, but the BOS really is the market leader in that regard). The rebound curves on the two feel pretty similar on the trail too. If I had any money I'd have one of those too, but as it stands I've already got a CCDB and an RC4 so it's a little hard to justify buying a 3rd top-end shock. I think the RC4 is a very capable shock, but its quirks with the air spring and strong end-stroke compression might mean it's not ideally suited to frames that already have a lot of progression in the linkage. Oh also the bottom-out bumper on the RC4 is quite small and crappy compared to most other shocks. Not exactly the end of the world, just makes bottom outs a bit harsher than they might otherwise be.

I think it's pretty cool that MTB suspension has come this far - we now have a lot of legitimately high-performance options. You can always get a bit more out of it, and as always the devil is in the details, but I think it's pretty hard to write any of the RC4, Elka, CCDB or BOS off as crappy, maybe a particular shock is not suited to your bike but in their element all of them work very well, all of them IMO noticeable improvements over a DHX5 or a Vivid. No recent experience with a Roco or anything from Manitou so can't really comment on those.
 
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C

Commencal-guy

Monkey
Nov 25, 2007
341
0
Massachusetts, US of A
Transcend said:
Socket, great post. So far, the elka is the greatest feeling shock I have ever run. I am super impressed and Pat offered amazing customer service when i was in a pretty good spot (ie: no one had the ginormous shock my 225 proto needed, and he jumped at the chance to help - Merci Pat.)

I will be trying out an RC4 in the next couple of weeks just to see how it feels on that bike. The progressive rebound on the Elka is pretty amazing, and it will be really hard to beat I think!
Click to expand...

Would the Progressive Rebound on the Elka work better for some frame designs? Progressive rate, Falling rate, Linear ect...

Just curious... I have the Elka on my Commencal Supreme DH, and the Progressive Rebound seems to suit the Progressive nature of the Contact System.
 
S

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
Commencal-guy said:
Would the Progressive Rebound on the Elka work better for some frame designs? Progressive rate, Falling rate, Linear ect...

Just curious... I have the Elka on my Commencal Supreme DH, and the Progressive Rebound seems to suit the Progressive nature of the Contact System.
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You can't really make that generalisation. "Progression" needs to be measured at the wheel, and on any frame without an approximately linear rate, there will be position sensitivity of the damping as well as speed sensitivity - this applies in both compression and rebound. They have different tunes (in rebound as well as compression) for different leverage rates, I don't know exactly what the tunes are but I'd speculate they're all aimed at getting a similar effect at the wheel (insofar as it's possible given the variation between linkage designs).
 
C

Commencal-guy

Monkey
Nov 25, 2007
341
0
Massachusetts, US of A
Socket said:
You can't really make that generalisation. "Progression" needs to be measured at the wheel, and on any frame without an approximately linear rate, there will be position sensitivity of the damping as well as speed sensitivity - this applies in both compression and rebound. They have different tunes (in rebound as well as compression) for different leverage rates, I don't know exactly what the tunes are but I'd speculate they're all aimed at getting a similar effect at the wheel (insofar as it's possible given the variation between linkage designs).
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I understand, I wasn't trying to make that generalization. I was just curious to see if the Nature of Elka's Progressive Rebound had beneficial and negative effects on any frame design with a Progressive, Linear, Falling suspension rate in design.
 
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S

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
Commencal-guy said:
I understand, I wasn't trying to make that generalization. I was just curious to see if the Nature of Elka's Progressive Rebound had beneficial and negative effects on any frame design with a Progressive, Linear, Falling suspension rate in design.
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Well it's not my place to speak for Elka since I don't *know* what their tunes are as such, but what I meant was basically that they're (presumably!) trying to get a certain damping rate at the wheel (which is the relatively progressive rebound damping, in the speed-sensitive sense) in order to achieve a certain ride characteristic (good tracking and traction without bucking/kicking or instability). To understand how those are affected by the linkage rate, you need to understand the relationships between spring, mass, and damping coefficient, and the way these are manipulated by the linkage rate. If anyone wants the full explanation I can go into the mathematical details, but basically if you're willing to take my word for it, a progressive linkage gives you a higher damping ratio (ie ratio of damping coefficient vs critical damping coefficient) further into the travel, because the relationship between spring rate and critical damping coefficient isn't linear.

Basically, the linkage increases the spring rate and damping coefficient (when measured at the wheel) linearly compared to each other, but the mass of the system isn't altered, so the damping ratio increases. This basically means your damped natural frequency decreases - that means the suspension returns slower, relative to the spring force, at points further into the travel (this is a technically vague explanation but I'm trying to put it into plain English to get the idea across). Given that higher rebound speeds are expected at points further into the travel than near the top of the stroke, this to some degree may help achieve similar ride characteristics (in terms of not kicking/bucking or being unstable) as having a shock with a more progressive rebound curve (in the speed sensitive sense).

As a result, I expect that if you dyno'd all the different rebound tunes Elka use, they wouldn't all be the same shape (even when normalised for different rider weights or leverage ratios). Some would be more progressive than others, some may even be digressive.

Overdoing it with a progressive rebound curve at the shock as well as a highly progressive linkage might result in something that can't open up enough to allow the shaft speeds you need for good tracking, yet still bounces around a lot early in the travel. However, as always, the concepts are nice to understand but it's the numbers that count - if you can't quantify it then it's not really useful knowledge. For what it's worth, I think it's pretty interesting that there is so much focus on the compression stroke when it comes to linkage progression, yet I've never heard anyone mention the relationship between linkage rate and rebound characteristic before. I suppose that besides the possibility that few if any people have considered it at all, that kind of thing is far far harder to educate the general public on enough that you can use it as a marketing plug. It might also be comparatively easy to tune around given that unlike the compression stroke, there is at least a vague relationship between shaft speed and position during the rebound stroke.

Anyone out there want to give me a job working with suspension? Will travel, won't fart on your computer chairs :)
 
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P

Pat Tellier

Chimp
Sep 8, 2004
62
0
Montreal, QC, Canada
Usual leverage ratios have traditionally been in the range of 3.2:1 down to 2.4:1 for most designs. Nowadays, we are seeing more and more designs with a ratio closer to 2:1, which is the most efficient ratio for a damper.

To complete Socket's already good explanations, Elka has several rebound valvings. Each one is mostly progressive and intended for a range of leverage ratio. Some variations have been developed for specific bike designs that have unusual leverage ratio curves, such as the Intense 951, the Santa Cruz V-10, the Evil Revolt and many others. These bikes have been designed to achieve specific ride characteristics that go around what most shocks are designed for, so we have to alter the damping to get the most out of those frames.

I know most will be curious to know how/what is changed, but that's where the Elka magic begins. We spent quite some time to figure that stuff out!
 
Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
4,918
1,213
Hey Pat,
Got a couple of questions for you.

1. Just wondering if you can elaborate on the issue below and whether it's fixed? I've heard a few different stories about squeaks and something coming loose in the shock (two different issues I presume) and it'd be good to hear what was fixed and how.

Socket said:
- Had some mechanical issues with stuff coming loose inside the shock, Elka say they've since sorted it with redesigned parts.
Click to expand...
2. Can you explain what factors you take into account when choosing a tune for a customer, and how they impact the tune? Also, is there a certain number of tunes you choose from based on those parameters?

3. What actually changes between tunes, is it just the shim configuration on the main piston, or are other things also changed - like HS adjuster spring rate, port sizes, etc?

I ask because I've had average experiences in the past when given a shock "tuned for my application" because of manufacturer/tuner oversights - simple things like not considering rider weight, or not having enough tunes to choose from. I opted for a CCDB which put all the tuning range back in my hands, and that's been a nice change - but it's always good to try new things.
 
P

Pslide

Turbo Monkey
Jan 14, 2002
1,373
0
Feet on the ground, head in the clouds.
Pat Tellier said:
Nowadays, we are seeing more and more designs with a ratio closer to 2:1, which is the most efficient ratio for a damper.
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I didn't know that. So there is an advantage to going to lower leverage ratios (according to Pat).

Is that based on fluid dynamics (oil viscocity/flow/etc)? Why 2:1?

For a while I was beginning to think the lower leverage ratios were just a perceived benefit rather than a real benefit. I think this was compounded by the fact that shock makers were catching up with frame designers when low leverage frames first came out.

I'm not sure I can see many frame designers going all the way to 2:1, considering packaging and weight trade-offs. Plus, I think anyone would struggle to show that a 4" shock would work any better than a 3" shock for any given bike. At least Foes hasn't convinced me!
 
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