Last week, we dove deep into how air volume affects your fork’s performance and how you can tune it to match you and your riding style. As we researched that, we found that MRP’s Ramp Control Cartridges offered similar tuning options, but with additional benefits.

As we learned, adding spacers reduces air volume, which makes the fork more progressive in the end stroke, helping it ramp up and prevent bottom out. The downside is that as your air volume gets smaller, you typically need to run higher air pressure, which can reduce small bump sensitivity. Here’s how MRP minimizes that tradeoff, giving you the benefit of larger volume and more end stroke control…

Noah Sears, brand manager for MRP, says “there’s some confusion this is a volume adjustment, and it’s not. It’s an independent adjustment that’s solely focused on affecting ending stroke spring curve (aka “ramp”) on high speed hits.”

Translation: You can take advantage of your full air volume for a supple ride and small bump finesse, but still control the ramp on bigger, high speed hits to prevent harsh bottom out.

“There’s a lot of downsides to (volume spacers) in our opinion,” says Sears. “With typical air volume spacers, what you typically really get is just ‘bottom out control’, not true control over the ramp. With our cartridges, there’s a valve that goes into a secondary chamber, which controls how quickly and how much air can move from the main chamber into that secondary chamber. The effect is that you have a larger air volume for low speed riding and small bumps, and a smaller chamber when you hit something really big, which will ramp harder and prevent a hard bottom out.”

Basically, a 16-position dial changes the size of a port that lets air move in and out of the cartridge. As the hole gets smaller, less air can move through. So on a big hit, it’s blocking more air than it’s letting through, effectively shutting off use of the upper section, which has the temporary effect of reducing usable air volume. So the fork ramps up more quickly for that single hit, then immediately goes back to using the full air chamber. This is what we call having your cake and eating it, too.

Technically, the only condition where the RCC doesn’t help is in a full travel low speed hit, which might possibly happen if you were to have a huge radius roll out from a fast descent, but since we’ve never actually fully compressed our forks on something like that, the chances of that being an issue are slim to none. And the everyday benefits of something like this far outweigh those unlikely outliers.

MRP offers a Ramp Control upgrade cartridge for most Rockshox and Fox forks for $140, and it’s standard equipment on their own Stage fork. Check it out at MRPbike.com.


The fun never ends. Stay tuned for a new post each week that explores one small suspension tech, tuning or product topic each week. Got a question you want answered? Email us. Want your brand or product featured? We can do that, too.

35 COMMENTS

  1. As a lighter (145lb) but still aggressive trail rider, I’m really digging the Ramp Control cartridge. As someone who likes long days, small-bump sensitivity can be hard to balance against bottom-out, which had me running really low pressures (130mm Fox 34 on a Pivot 429 Trail) with several tokens to keep me from blowing through my travel once the fork got moving. Not a great compromise.

    With the RCC I’m able to run 42psi up front without bottoming out hard on every descent like I would with one spacer. I’m still hitting full travel on every ride, but the MRP seems to keep some travel in reserve at speed.

    The only downside is that slow, big impacts (2′-plus log overs, some rolled drops) the front end does dive more than I was used to, but it’s not too bad overall.

    This and a weekend with a rented pair of Shokwizes (in the opposite order) are upgrades well worth the time and expense. I’m really happy to have done both.

  2. This is interesting information because I had exactly the misconception described (i.e. I thought it was effectively just an adjustable volume spacer). IIRC, I read somewhere that it adjusts in a range equivalent to 2-4 spacers, or something like that. Is that still more/less accurate in terms of overall range? I ask this because I run a short travel 34 (120mm) and I use 6 or 7 volume spacers, so I’d think this wouldn’t work for me. Or am I mistaken?

    Though I understand how this functions differently that volume spaces, I don’t quite get how the end effect is different. With no numbers, the right graph doesn’t look terribly different from the one from fox besides the very beginning stroke (which I would assume lies within sag for most people).See https://www.ridefox.com/help.php?m=bike&id=568. Or is that the key part? Or what would graph of speed vs. effect look like for a normal volume spacer? What am I missing?

    • Hi Feldybikes,

      The ending-stoke effect varies model to model. We actually have a model specifically for short-travel Fox 34 forks (Version B). It has a higher chamber volume and thus more effect than our standard Fox 34 (Version A).

      In a nutshell, spacers and tokens are NOT speed sensitive and Ramp Control is. So a graph of speed vs. effect of a standard spring would be meaningless – the curve is the same at different shaft speeds. Compare that to a Ramp Control-enhanced fork. It would essentially be linear at low-speeds and progressive at high-speeds. We think this is preferable, because the fork isn’t “fighting” you in situations like climbing or traversing technical terrain (rather, it’s gobbling up bumps), but it is resistant to bottoming on hard, high-speed hits.

      • Can you show this on a pressure volume curve? Way I see it is the ramp cartridge a bleed valve with that works only with a specified rate of pressure increase. This is similar to how the K2 Razor Back rear shok worked back in the late 90’s but in that case the bleed valve provided a linear damping function, whereas your bleed valve shuts off if the flow rate is too high

  3. Is this similar to the old Manitou SPV and SPV+? Seems like both offer a “platform” adjustment. I have an old SPV fork and the assembly looks similar. On those you could remove the valve spring in the SPV assembly to make it into a poor-man’s compression damping. Anyone remember those?

    • yes i remeber those.
      my experience the spd valve worked pretty well but had lacking support.
      no, it’s much different.

  4. So its essentially a Speed Sensitive Valve for the air chamber? If so, cool. In theory an SSV could be tuned to close at very low and very high rates with two linked SSV’s. So maybe they will solve the slow speed dive as well.

    • Steven, what’s your theory on this? I liken it to road bike tires versus mtb tires. If I ran 30psi in my road bike tires, with their low volume, I’d be riding on the rims. Likewise, if I ran lower pressures in my 100mm XC forks, I’d be blowing through the travel and bottoming all over the place. I’m curious what you’re doing differently.

      • If you’re running lower pressure but blowing through the travel, shrinking the volume of the air spring with a spacer allows the spring rate to increase faster as the fork moves through its travel. As your air volume gets smaller you can use lower pressure for the same amount of bottom out protection.

        There is no good tire analogy that I can think of – the closest thing is something like the Schwalbe Pro-Core dual chamber tire system.

      • You can’t directly compare suspension air springs to a tire. The biggest difference is that in a tire you do not compress the volume of the tire down to 1/2 or 1/3 of the original volume as happens in a fork or shock air spring. Its called compression ratio (Starting volume divided by ending volume).

        Compression ratio on a tire hitting a bump and bottoming on the rim isn’t high enough to compress the volume of the tire significantly or change the overall pressure much. You could check this out by taking out the valve core of your presta valve stem, pumping up the tire, leave the pump on the valve and then compress part of the tire as if you were going over a rock. The pressure won’t go up much.

        Compression ratio on a fork or shock is roughly around 3:1 at bottom out. Meaning that the pressure you start with at top out is 3 times higher at bottom out. Again, attach a pump to a fork, add some pressure, then compress the fork. The increase in pressure will be much higher than it was in the tire scenario. Though be warned because you can ruin the future accuracy of shock pump gauges by exceeding the maximum on the gauge doing this.

        And yes you can use Ryan’s ideal gas equation to figure this out also.

        And the MRP thing above is just like Arlo Englund cartridges and Cane Creek’s older air shocks the AD-10, AD-12 or Cloud Nine that used air as a damping fluid. The problem is that air being compressed and moved through valves like this is inconsistent and can be very different in 100° weather or 50° weather.

        What this cartridge is really doing is adding externally adjustable high speed compression damping. The better way to do this would be to open up the damping cartridge and adjust the shim stack, but that is difficult, you can’t tune it on the trail and most importantly, MRP couldn’t sell it to the thousands of people who own Fox forks.

        • @HDmanitoba good summary there. But the “problem” you point out isn’t really one in my experience. The performance of oil changes with temperature too, so it’s not like air is a disadvantage in this case. Go do a long, hard bike park lap and feel your air-spring stanchion vs. your damper-side stanchion and tell me which is hotter.

          Furthermore, air can be compressed but oil cannot – so you’ll never get a spike using air as a damping medium like is possible with oil. So as far as the inclusion of (or tuning of) a traditional high-speed compression adjustment in the damper being a “better” solution, that’s debatable.

          Cheers

        • The MRP “thing” is not a damper as it is not trying to control gas flow in both directions. It is only bleeding pressure spikes like riser pipes do in your home plumbing. Air bleeds back into the volume unrestricted to aid the spring’s recovery. A damper controls flow through a valve in both direcions with volume not being a factor since the fluid is constantly moving through a circuit. The MRP is still an air spring chamber in that the air sill compresses in the bleed chamber.

          PS ideal gas law is PV=nRT

          PV/T=PV/T is just a ratio for exploring the relationship between Boyles, Charles and Avogadro’s laws in a system when one of the properties is a variable

        • LOL!
          I own fox products with the RC2 damper, they work well.
          it’s almost amazing to me how the lip service of the industry manages to gloss over the fact that so many of these products are missing high speed compression adjustment.
          right you are that you can use air volume adjust in leu of hsc adj. but its stupid harder to adjust AV. obenifits of the AV adjust is it strains the damper less and that it is less likelyto cause spiking in high speed compressions with extended suspension; but more likely to cause excess stiffness during low speed compressions, generaly undesirable.

      • Tyler, you’re confusing volume with tire cross-sectional area, although people commonly use the first word to mean the second idea.

        Imagine you had a deep-section tubeless rim with insanely deep center channel. The tire would contain a very large air volume, but the tire cross-sectional area would be the same as with a conventional rim.

        Compressing the tire to the rim on a conventional rim changes the volume of the tire (a pressure vessel) significantly, and the pressure ramps up quickly. But doing the same thing to our huge-center-channel rim only changes the larger volume by a small amount, so the pressure doesn’t increase very much. As a result, in order to keep from bottoming the tire out on the rim, you’d have to run more pressure with the imaginary large-volume rim than you would with the real small-volume rim.

  5. The idea is to run a little less psi with added volume spacers cause you can get a more supple feel at the beginning stroke but still get the added ramp up. I added a spacer and reduced 5psi and definitely felt more supple but I was not digging the ride height and overall feel so I ended up adding 2-3psi back and fork feels right

    The MRP thingy looks nice tho might have to try it sometime.

  6. “The downside is that as your air volume gets smaller, you typically need to run higher air pressure, which can reduce small bump sensitivity.”

    No. As the air volume shrinks, you typically run less pressure since the smaller volume ramps up faster and resists bottom out more, so small bump compliance gets better.

    The Ramp Control Cartridge gives you a big volume for slow movements, but shrinks it for fast movements. Neither tokens or RCC _without_ a pressure change will effect the beginning stroke; but both allow lower starting pressures for a softer beginning stroke, while also providing some bottom out resistance.

    RCC helps by keeping the volume big on slow movements, so the fork will stay supple even under brake dive, ie: in the mid-stroke. Great for lighter riders so the fork stays active further into the strokel but as a a big guy that runs 95 psi and 15cc spacers for 25% sag on a Fox 36 160 (NA), I’m wondering if the ramp up from a big-hit (fast/small chamber) if the fork is already into the mid-stroke from brake-dive (slow/big chamber) would be too harsh.

    Would love to demo it, but it’s not a simple top-cap swap on my fork…

  7. I don’t know about you guys but I like my Fox 34 better with less spacers in it.
    Currently running just one and it’s far better than 3 that came stock.
    It doesn’t dive excessively or bottoms out easily at all while offering more usable travel most of the time.

    With spacers in, it would feel be way too progressive and extremely hard to use up whoel travel.
    Dropping the pressures wouldn’t fix it because it would just feel dead in the mid stroke. I find that slightly higher pressure makes the fork feel livelier while bigger volume keeps the travel smoother and more predictable.

    • @Marin, this was my feeling also with my 140mm Pike. With a volume spacer in it I had to run too low of air pressure to get it to use all the travel. Way too much ramp up at the end and dived in the initial travel too easy on steep stuff.

    • Y’all aren’t alone. For years everyone wanted “coil-like” air-shock performance, then volume spacers became popular and everyone jammed them in their forks and shocks – making them as “air-like” as possible.

      In my experience, heavily volume-reduced air-springs kill the lively and sporty initial stroke performance. I’d describe it as mushy then overly rampy.

      YMMV.

  8. The interesting bit here is that air compresses (unlike oil) so it’s a moving target in the sense of using it to control end of stroke. Cane Creek Cloud 9 shock experience here. But I am not an engineer, and have faith that MRP worked that into this. Sounds like it with a smaller exit port than the entry port.

    Clever, I would love to hear more ride reports.

    P

  9. I’ve been running the MRP Ramp Control Cartridge in my Pike for a few months and it works. Much better feel and control over tokens. It’s a little expensive but worth every penny once you understand the design.

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