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DSD RUNT?

slimshady

¡Mira, una ardilla!

tacubaya

Monkey
Dec 19, 2009
720
89
Mexico City
And before anyone says "yeah but Diaz thought about the concept in 2012", that dual positive air chamber concept was implemented in Fox's Talas 1 and Marzocchi's Doppio Air spring about 15 years ago.
 

toodles

ridiculously corgi proportioned
Aug 24, 2004
5,479
4,720
Australia
I don't think SD Components is trading at the moment.
No website and the Facebook page has been dead for over a year.
They're still going. Simon is just being crap I guess. Their Insta is still strong and they're in stock locally.
 

FarkinRyan

Monkey
Dec 15, 2003
611
192
Pemberton, BC
I rode one of these for a few months at least 2, maybe 3 summers ago although it wasn't the exact version available now, it was either a very late prototype or an early version of what was finally released. They've definitely taken their time getting them to mass market. Short review is that it did what it said on the tin, there was lots of adjustability in the system and it would probably be nice for stage races and changing setups on the fly with only a pump. Lot's of potential to go chasing ghosts with it and end up with a setup that isn't ideal as well, a digital pump was mandatory and small changes in pressures made big differences in behaviour.
 

mykel

closer to Periwinkle
Apr 19, 2013
5,071
3,780
sw ontario canada
I rode one of these for a few months at least 2, maybe 3 summers ago although it wasn't the exact version available now, it was either a very late prototype or an early version of what was finally released. They've definitely taken their time getting them to mass market. Short review is that it did what it said on the tin, there was lots of adjustability in the system and it would probably be nice for stage races and changing setups on the fly with only a pump. Lot's of potential to go chasing ghosts with it and end up with a setup that isn't ideal as well, a digital pump was mandatory and small changes in pressures made big differences in behaviour.
I have the IRT in a Mattoc which is basically the same thing, a second air chamber separated by a floating piston.
While it was a pain in the ass to get setup, when I did get it dialled in, it was definately worth the hassle.
After that, it was write the numbers down then set and forget.

As you say, Does what it says on the tin.

Wonder how one of these or a Diaz RUNT would play with the newer 2019 Debonair air spring. Craig at Avy is trying to get me to try the air spring before I just drop a Smashpot in. This maybe what I need to get over my reluctance to go air on this build.
 

SuboptimusPrime

Turbo Monkey
Aug 18, 2005
1,658
1,633
NorCack
I had an IRT for my Dorado before it died and thought it was great in terms of letting me run less LSC and main chamber pressure for good small bump sensitivity with excellent support for bigger hits. Cool that this is available for other forks.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
OK so help me understand why we like this over a more progressive air spring?

I get wanting to run coil- there is nothing more stiction free and reliable than a coil spring.

At the same time, most people seem to like considerable progression in the rear end of their bikes to make the bike more playful compared to a linear, "dead" feeling ride.

So is the ideal setup a linear fork with a progressive rear end? Or is linear/linear now the ideal? Or is this just another option for people to try?

I'm not a pro bro, but I like the progression that an air fork gives, and the ability to tune it with tokens. I like coils on my DH bike for set and forget reliability, but I'm confused as to what this invention solves.
 

jonKranked

Detective Dookie
Nov 10, 2005
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OK so help me understand why we like this over a more progressive air spring?

I get wanting to run coil- there is nothing more stiction free and reliable than a coil spring.

At the same time, most people seem to like considerable progression in the rear end of their bikes to make the bike more playful compared to a linear, "dead" feeling ride.

So is the ideal setup a linear fork with a progressive rear end? Or is linear/linear now the ideal? Or is this just another option for people to try?

I'm not a pro bro, but I like the progression that an air fork gives, and the ability to tune it with tokens. I like coils on my DH bike for set and forget reliability, but I'm confused as to what this invention solves.
It's essentially a dual rate air spring.
 

SuboptimusPrime

Turbo Monkey
Aug 18, 2005
1,658
1,633
NorCack
OK so help me understand why we like this over a more progressive air spring?

I get wanting to run coil- there is nothing more stiction free and reliable than a coil spring.

At the same time, most people seem to like considerable progression in the rear end of their bikes to make the bike more playful compared to a linear, "dead" feeling ride.

So is the ideal setup a linear fork with a progressive rear end? Or is linear/linear now the ideal? Or is this just another option for people to try?

I'm not a pro bro, but I like the progression that an air fork gives, and the ability to tune it with tokens. I like coils on my DH bike for set and forget reliability, but I'm confused as to what this invention solves.
I think linear and progressive are being used to describe different things here. I'm interpreting it that the air spring is progressive, but the rate at which spring rate increases is not linear if that makes sense (the curve is droopy). So spring rate stays low for a good bit of the initial travel and then ramps up a lot at the end--so you can blow through the mid-stroke which sucks. Thus, to get the right amount of mythical mid-stroke support, you have to run more air pressure, which impacts the sensitivity to small bumps or add tokens which means you can stop getting full travel. I experienced this with my Pike.

I think we want "linearly progressive" suspension where the rate of increase in spring rate is more consistent through the travel, raising the spring rate during the mid-stroke without impacting the beginning or end too much. The IRT is one way to get there.

For coil forks, I'm guessing we are leaning on the damper plus coil to get to the same place.

Also possible you understand all this and I'm talking to myself here....
 
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slyfink

Turbo Monkey
Sep 16, 2008
9,289
5,029
Ottawa, Canada
OK so help me understand why we like this over a more progressive air spring?

I get wanting to run coil- there is nothing more stiction free and reliable than a coil spring.

At the same time, most people seem to like considerable progression in the rear end of their bikes to make the bike more playful compared to a linear, "dead" feeling ride.

So is the ideal setup a linear fork with a progressive rear end? Or is linear/linear now the ideal? Or is this just another option for people to try?

I'm not a pro bro, but I like the progression that an air fork gives, and the ability to tune it with tokens. I like coils on my DH bike for set and forget reliability, but I'm confused as to what this invention solves.
I'm with sammich on this. I'm a little confused. I installed a Luftkappe in my Pike last year, to go along with the Tractive tune to my Monarch. Chassis stability from the Monarch was impressive. In fact, in my 20+ years of riding, it was the first time I'd ever felt chassis stability.

I liked the Luftkappe a lot. With it in my Pike, I was able to run just under 30% sag (maybe about 28%), and had terrific small bump sensitivity, and good mid-stroke support. But not once, all season, did the o-ring get to within an inch and a half of the crown. (when I installed the luftkappe, I removed the two tokens). Most rides finished with the o-ring at least 2 inches from the crown.

I was thinking of sending my Pike to Vorsprung for a full-service and possibly a custom re-valve. But I wonder if this solution would work better?

I'm not keen on the Smashpot for two main reasons: I don't really want all that extra weight, and the cost.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
I think linear and progressive are being used to describe different things here. I'm interpreting it that the air spring is progressive, but the rate at which spring rate increases is not linear if that makes sense (the curve is droopy). So spring rate stays low for a good bit of the initial travel and then ramps up a lot at the end--so you can blow through the mid-stroke which sucks. Thus, to get the right amount of mythical mid-stroke support, you have to run more air pressure, which impacts the sensitivity to small bumps or add tokens which means you can stop getting full travel. I experienced this with my Pike.

I think we want "linearly progressive" suspension where the rate of increase in spring rate is more consistent through the travel, raising the spring rate during the mid-stroke without impacting the beginning or end too much. The IRT is one way to get there.

For coil forks, I'm guessing we are leaning on the damper plus coil to get to the same place.

Also possible you understand all this and I'm talking to myself here....
this makes sense- linearly progressive vs rampy at the end of travel. That was part of my issue with my evil, felt like nothing then loads of ramp right before bottom out (also the shock sucked). I thought this would emulate the flatter rate of a true coil spring with no air assist. thanks for the info
 

jonKranked

Detective Dookie
Nov 10, 2005
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so i got bored and created a spreadsheet to calculate how far into the travel the fork* will be when the two pressures equalize.

Note* this is just for a Mattoc, and as of right now is done with quite a few assumptions / estimations.
 

jonKranked

Detective Dookie
Nov 10, 2005
85,571
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i typed this out in a PM with @captainspauldin but figured i'd share here anyways

so basically there's 2 air chambers
the primary and the secondary
the secondary MUST be at a higher pressure (and by a good amount, manitou recommends at least 40psi difference) for it to work properly
so basically, the pressure of the primary chamber increases as it goes through its travel
and the secondary chamber is effectively static
UNTIL the point at which the pressure of the primary chamber is equal to the pressure in the secondary chamber
and then they BOTH start compressing
so at that point it is essentially increasing the volume of the air chamber acting as the spring since they are working in unison once the pressures equalize
 

slyfink

Turbo Monkey
Sep 16, 2008
9,289
5,029
Ottawa, Canada
i typed this out in a PM with @captainspauldin but figured i'd share here anyways

so basically there's 2 air chambers
the primary and the secondary
the secondary MUST be at a higher pressure (and by a good amount, manitou recommends at least 40psi difference) for it to work properly
so basically, the pressure of the primary chamber increases as it goes through its travel
and the secondary chamber is effectively static
UNTIL the point at which the pressure of the primary chamber is equal to the pressure in the secondary chamber
and then they BOTH start compressing
so at that point it is essentially increasing the volume of the air chamber acting as the spring since they are working in unison once the pressures equalize
Yes, but what effect does this have on the fork as it goes through its travel? If I'm reading this correctly:

- initial pressure (POS 0 in the Manitou diagram) in the primary chamber would have to be higher than in a single chamber to achieve similar sag. This is benefecial for LS inputs, but not HS inputs. Does this mean it will feel like there is more stiction? Less compliant to small bumps?
- in an HS-input scenario, in POS 1, the primary chamber will ramp up earlier in the travel because it is a smaller chamber. This will make it feel like there is more mid-stroke support. But will it mean the fork rides higher in its travel?
- once the main chamber equalizes to the pressure of the secondary chamber (POS 2), they ramp up at the same rate for the remaining portion of the travel. This is what I'm having a hard time translating into the feel at the hands... Would the rider feel that transition? Is rebound affected by this? Will that end-stroke ramp up be at a lower rate over a greater portion of travel?

:confused:
 

jonKranked

Detective Dookie
Nov 10, 2005
85,571
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- initial pressure (POS 0 in the Manitou diagram) in the primary chamber would have to be higher than in a single chamber to achieve similar sag. This is benefecial for LS inputs, but not HS inputs. Does this mean it will feel like there is more stiction? Less compliant to small bumps?
yes, the initial pressure on the primary chamber is higher with the IRT than without it, but it doesn't impact performance the way you're thinking because when you add the IRT the size of the primary chamber is reduced by a pretty good amount. you can actually get better small bump compliance (depending on where you set the primary chamber pressure)

- in an HS-input scenario, in POS 1, the primary chamber will ramp up earlier in the travel because it is a smaller chamber. This will make it feel like there is more mid-stroke support. But will it mean the fork rides higher in its travel?
speed doesn't matter, its not a factor in boyles law (regarding the relationship of pressure and volume). but yes it generally gives better mid stroke support, and it will probably ride a little higher in its travel (depending on what travel and pressures you're running).

- once the main chamber equalizes to the pressure of the secondary chamber (POS 2), they ramp up at the same rate for the remaining portion of the travel. This is what I'm having a hard time translating into the feel at the hands... Would the rider feel that transition? Is rebound affected by this? Will that end-stroke ramp up be at a lower rate over a greater portion of travel?
in my experience, no, you don't feel it. you might be able to pick it up on a dyno, but when riding it isn't perceptible.

whether or not rebound is affected is, again, going to depend on what pressures you run, the pressure differential between the chambers, and your travel setting (all of which determine where in the travel this transition occurs). same goes for the end stroke ramp up. that's why i cooked up the spreadsheet (i'll share it later once i can take some better dimensional measurements, for now i had to make some guesstimates of the air chamber dimensions for volumes) - it lets you input your main chamber (primary) and IRT pressures and it calculates where in the travel that equalization / transition occurs.

the below links give Manitou's suggested air pressures:

no IRT: https://forums.mtbr.com/attachments/shocks-suspension/897293d1401457150-manitou-mattoc-manitou-mattoc-pro-expert-setup-guide.jpg

IRT: https://manitoumtb.com/wp-content/uploads/sites/2/2018/08/46-32685_Mattoc_IRT.pdf
 

jonKranked

Detective Dookie
Nov 10, 2005
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Fwiw, Manitou's recommend pressure differential is 40 psi, but when I researched across various forums a lot of people found a 50psi differential to give better performance. Personally I found this to be true as well.
 

jonKranked

Detective Dookie
Nov 10, 2005
85,571
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it definitely takes some trial and error to get right, but IMO its a worthwhile upgrade if you really like to tune your fork and are trying to maximize performance.

i remember reading back when cane creek introduced the helm, they had considered an air spring system similar to the IRT (ie effectively a dual rate air spring) but after experimenting they felt it was too complex for most riders and didn't offer enough advantage for the effort.
 

mykel

closer to Periwinkle
Apr 19, 2013
5,071
3,780
sw ontario canada
I have an IRT in a Mattoc - same thing as the RUNT, SD etc

Yes, after the IRT / RUNT the main chamber pressure is greater.
No, it does not effect small bump in any negative way.
In fact, it allows you to use a lower more supple pressure, but maintain mid-stroke and end of stroke performance.

Net change of pre vs post IRT

Better small bump absorption
Better mid-stroke support.
Similar ramp up and end of stroke.

Overall a huge win. I'm not an air-spring fan, never have been. The IRT was the only way to make the Mattoc livable for me.
I just bought a Yari takeoff for my Fugitive build. Avy damper going in, but I'm considering a RUNT instead of the Smashpot.
Craig at Avy is trying to get me to try the new 2019 Debonair before going coil. I'm wondering if the RUNT would be a good compromise based on my IRT experience as well as the better negative spring of the Debonair
 

Lelandjt

Turbo Monkey
Apr 4, 2008
2,508
822
Breckenridge, CO/Lahaina,HI
this gif does a better job

My electric dirtbike currently has a 2007 888 ATA with the exact same system. Back when I had one on my DH bike the hot mod was to remove the floating tethered piston and make the main air chamber bigger. Right now I'm running the same pressure in both chamber to make it as linear as possible and might remove the parts to increase volume.
 

kidwoo

Artisanal Tweet Curator
My electric dirtbike currently has a 2007 888 ATA with the exact same system. Back when I had one on my DH bike the hot mod was to remove the floating tethered piston and make the main air chamber bigger. Right now I'm running the same pressure in both chamber to make it as linear as possible and might remove the parts to increase volume.

Those things sucked donkey dick stock. Ramp ramp blow through and bottom......

The real way to deal with them was to remove the piston and then reduce the volume/air spring length by adding some oil after taking out the tampon string.

Fox still uses that crap under the EVOL moniker on snowmobile shocks. I do the same thing, take out air, add oil to the secondary chamber.

Are you not bottoming that thing on your sur ron? I wonder with the extra bike weight if you've just got enough pressure in there, you're getting a functional level of ramp up.
 

jonKranked

Detective Dookie
Nov 10, 2005
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that was probably when they were still using a dummy rod right up the middle of the bidness
ah yes, that's right. ten points to Gryffindor. now i remember - i think i've gone down this rabbit hole before, the newer air spring required for the runt can't be retrofitted to the earlier models, right?
 

jonKranked

Detective Dookie
Nov 10, 2005
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Get a mrp fulfill and it will be.
Then you will be the guy will win the
MoaR SchraderZ award
it would have to be the fulfill and the 2018 air spring as well, no?

edit: as 'woo indicated, the '15 era floats had an air spring with the shaft that extends all the way to the top cap.
 
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englertracing

you owe me a sandwich
Mar 5, 2012
1,573
1,069
La Verne
The fulfill comes with a plug that capped the Piston to ditch the transfer rod.
And the schrader to allow manual filling of the negative
 

jonKranked

Detective Dookie
Nov 10, 2005
85,571
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The fulfill comes with a plug that capped the Piston to ditch the transfer rod.
And the schrader to allow manual filling of the negative
interesting! i just watched the install video for the MRP ramp control and it makes more sense now. but obviously installing a runt instead of the ramp control.