Installing 7.875x2.25 (200x56mm) Shock on RockyMountain Instinct ???- Mtbr.com
Results 1 to 15 of 15
  1. #1
    Cactus Cuddler
    Reputation: tehllama's Avatar
    Join Date
    Jul 2013
    Posts
    1,797

    Installing 7.875x2.25 (200x56mm) Shock on RockyMountain Instinct ???

    I'm on a Fox CTD Evo (stock shock with the RM tune), and considering how expensive it is to get the full 200 hour refresh on this thing done, I was looking at just buying a Manitou McLeod or Monarch DebonAir RT3 for the bike and calling it good.

    The thought recently occurred to me that with the Ride9 settings I run (forward) I could conceivably run a slightly longer shock and get a slight increase in travel.
    Nudging up to the next longest travel shock (and included 3/8" increase in eye to eye OAL) would basically set the bike up at the Ride-9 XC flavored static geometry (less BB drop, 74.3 effective STA where my seat is, and depending on sag put my effective pedaling BB height about half an inch higher after my taller A2C fork).
    The increased shock travel would net an approximately 145mm rear travel.

    I realize I'd be pretty much completely on my own with regard to figuring out the best shock tune, and be operating outside ideal/warranty parameters on the frame, but despite loving how this bike rides so much already - I'm totally willing to screw that up if there's an outside chance of making it 'more baller' at minimal cost.

    Am I an idiot for even considering this? Is there some really obvious reason that they kept the Instinct as a 130mm travel bike (and didn't push it towards 145mm travel) other than bottom bracket height?

  2. #2
    ups and downs
    Reputation: rockyuphill's Avatar
    Join Date
    Nov 2004
    Posts
    15,530
    I think you'd want to check what happens with 15mm more wheel travel from the extra 0.25" stroke at the seat tube before going to much further with the idea. You might have to run a small rear tire to get clearance at full travel. I don't have an Instinct handy to eyeball what the implications are.
    I'm a member of NSMBA and IMBA Canada

  3. #3
    Cactus Cuddler
    Reputation: tehllama's Avatar
    Join Date
    Jul 2013
    Posts
    1,797
    Hmmm... I definitely wouldn't want to run anything smaller than a 2.35 Ikon out back.

    I'm just trying to think through what the I2I at compression would be for a 7.5x2" and 7.875x2.25" shock, and I'm still thinking that the longer shock would actually yield more distance between the seat tube and the tire a bottom-out than the stock one... but me thinking through that 2-D problem is still no match for real validation of it.

    The other interference issue I'm concerned might be real is with the control link - if that would swing down and hit the body of a larger and longer shock.

  4. #4
    ups and downs
    Reputation: rockyuphill's Avatar
    Join Date
    Nov 2004
    Posts
    15,530
    In that forward Ride9 position, if you fully deflate the 2" stroke shock and measure the tire clearance to the seat tube, that will tell you if you have that extra 1/8" of clearance
    I'm a member of NSMBA and IMBA Canada

  5. #5
    Cactus Cuddler
    Reputation: tehllama's Avatar
    Join Date
    Jul 2013
    Posts
    1,797
    I'll give that a look - the difference is that the longer shock even at maximum compression should be 1/8" LONGER than the current one; that said there's no way to tell without actually giving it a look to see what else might crop up.

  6. #6
    mtbr member
    Reputation:
    Join Date
    Feb 2014
    Posts
    16
    Curious to see the result but not sure if there is a point in going bigger, the instinct will rarely bottom out unless your in some really burly terrain. I upgraded to a monarch rt3 debonair, running 1 band and it completely changed the feel of the bike to me, especially climbing. With the shock empty I was was surprised how little clearance I have against the seat tube with a hans damf on the rear.

  7. #7
    Cactus Cuddler
    Reputation: tehllama's Avatar
    Join Date
    Jul 2013
    Posts
    1,797
    Quote Originally Posted by Bluenose View Post
    Curious to see the result but not sure if there is a point in going bigger, the instinct will rarely bottom out unless your in some really burly terrain.
    This nails it, as I haven't really bottomed it hard despite riding some stuff stupidly and being 235lb with the shock set at 200psi. I just seem to use 85-90% of the travel, and then it just ramps so hard that I swear I'm getting compliance out of the tires and rear triangle instead of using that last bit of shock travel.
    I guess what I'm after with that longer stroke and less OEM-budget shock is to be able to run less pressure on the air spring so I have a longer plush mid-stroke, but lean on the LSC to make it pedal reasonably well on boring climbs (it's already great on technical climbs). The Monarch RT3 Debonair could probably do exactly that for me, I just would struggle to resist the urge to tinker with the whole setup to get a 150/145mm travel bike with the only penalty being .7" added BB height (348mm - 13.7"), and the cost of suspension changes to get it there.

  8. #8
    Cactus Cuddler
    Reputation: tehllama's Avatar
    Join Date
    Jul 2013
    Posts
    1,797
    Well, I just finished installing it (Monarch RT3 DebonAir 200x57mm shock) - also moved to the front-most Ride9 setting while I was at it.

    At bottom-out there's a touch over half an inch to spare, the only two tight spots are the air port (had to use the SRAM long-nosed shock pump to fill it), and between the debonair part of the can and where the top pivot for the control linkage goes in the frame - it winds up with a literally paperthin gap at top out. That's it, it's installed and working nicely.
    Sag is currently set to body weight - which seems to come in a tick above the 35% I was shooting for - so I'll nudge it up to 250psi and start working from there. Just hopping around snow, it already feels as good as the unit it replaced, and I was nowhere near the right setup.

    It's too snowy right now to make any meaningful performance observations, so those will be forthcoming.

  9. #9
    Cactus Cuddler
    Reputation: tehllama's Avatar
    Join Date
    Jul 2013
    Posts
    1,797
    Deliberate double post. Still too snowy to say anything that definitive on getting it tuned properly, but going to the RT3-DBA Monarch is a step forward even with limited experience - in Pedal mode it's about as plush over the rougher stuff as the old CTD-Evo was in Descend mode. My cockpit setup is still a bit off (moved to a 150mm dropper at the same time as jacking up the geometry a fair bit), so climbing was awkward for me, the bike however kept up. Downhill was where fewer changes were at play, and even on a challenging mix of snow/ice/mud/hardpack, I was pretty impressed.

    Pictures:



  10. #10
    mtbr member
    Reputation:
    Join Date
    Oct 2015
    Posts
    1,270
    Wouldn't the head angle decrease effectively negate the extra rear shock performance in the rough stuff? I much prefer a bit slacker head angle in the gnarly steep downs to get the fork working better than a fraction more rear travel. The Fox CTD evo stuff is utterly rubbish so I'd assume you would be just as happy with the normal length Monarch debonair upgrade.

  11. #11
    mtbr member
    Reputation:
    Join Date
    Oct 2015
    Posts
    47
    I believe he has a 150mm fork so his HA was already slacker than stock anyways. Stock fork is 130mm and in the most forward Ride9 position with the 130mm HA is 67.7, at 150mm his HA would have been probably 66.5 or less actually considering the BC Edition with a 140mm fork in forward ride 9 is 66.7, so going with the longer travel rear shock wouldn't change the geo all that much for the HA. BB would be where the most noticeable change would occur. Bike looks pretty sweet.

  12. #12
    Cactus Cuddler
    Reputation: tehllama's Avatar
    Join Date
    Jul 2013
    Posts
    1,797
    Affirmative - 150mm Pike on there, so I'm still actually within the advertised range for HTA/STA, just at 5/8" higher bottom bracket (13.8" static). I'm still getting pedal strikes due to lack of technique, and some combination of being asthmatic, climbing steep technical singletrack, and being at 7000', so the drawbacks of that aren't particularly major uphill; I just haven't been able to fully pin it on any rough or interesting descents to see how much that has been affected.

    The standard length MonarchDBA is really going to be the gorilla in the room, especially since the lower settings (heavier rider) seem like they'd really favor the Debonair setup for my style of riding, but I'd probably really want the 'correct' tune on the shock to get that sort of performance (which means acquiring one off a BC Edition Instinct or Thunderbolt)... the cost on this option was so attractive, I couldn't help it. Worst case, the bike I'm saving up for runs that shock size anyway.

  13. #13
    Cactus Cuddler
    Reputation: tehllama's Avatar
    Join Date
    Jul 2013
    Posts
    1,797
    Gotten a grand total of two really significant rides, but for both of them I've just been hunting down ideal air spring pressure on the shock, and contending with lingering rear tire survivability issues (bringing 245+ lb of stupid off stuff to flat on a 2.35" Ikon seems to expose existing sidewall damage I've done from blowing the tire off the rim at high speed and pinch flatting on granite). I've been all over the place on air pressure, but now settling closer to 35% seated sag (255psi) and getting 90% of travel - any more than that and I need a better tire.
    I'm starting to feel like there's a bit too much HSC on the base shock tune - the higher pedaling threshold setting is working great, and I just adore the small bump performance with the Debonair negative spring. I think moving to the Monarch RT3/DBA is probably most of the performance delta, though I'm surprised that I haven't found myself wanting a more progressive shock setup.

    Since it looks like drivetrain options for cost-effective 1x conversions are becoming a thing (11-46T XT or 9-42T eTRS), and I'm really thinking a 160mm air spring for the fork and offset shock hardware (~3mm possible) would make this a plenty capable sled, I think I'll keep going down this rabbit hole and get up to speed on making my own adjustments on the shim stack to get a slightly plusher mid-range and use some other tools to get the end-stroke ramp-up and pedaling performance I want out of it. The offset bushings are really just to bring the BB lower, and accommodate the silly-long fork. Realistically I don't need a 6" travel bike 90% of the time... but it is so fun to use 90% of the capability all of the time, and the times I do burn through all the travel I'm thankful for it.

    [ETA] - More tinkering on it today (3.4.16). I definitely could use with a little less compression across the board (around sag, it's really efficient yet active for technical climbing when set wide open), but small undulations that don't create tons of shaft speed just sit on the LSC threshold, and make it feel like an ungainly hardtail. As soon as terrain gets interesting, it's performing great, but on buff XC trails littered with small chunder I could do with a lot better small bump performance.
    With sag out to 35%, getting 95% of the travel is happening on 18" drops, so I suspect the air spring is close enough to where I want it. I realize it would be somewhat easy to put a spacer band on the negative spring to make the shock a touch more sensitive on small stuff, but I really want a slightly plusher wide open setting, so it looks like the DIY M/L tune (pulling the first of the 0.15 shims on the compression side of the stack), which will put it more or less in between, and hopefully let me use more of the travel as well. I realize this is still a non-standard tune (not all they way to the RS OEM M/L on reducing the compression, but I did still want a bit extra because I'm so heavy, and can no longer take advantage of the lower Ride9 settings), and the heavier pedaling platform will help with the same (I prefer a nice sharp knee if possible on compression, once I'm using travel from sag point I want plushness over support, especially since my starting point is fairly deep into the travel to begin with, and starts to ramp pretty noticeably within 1" of wheel travel anyway).

    What I have to tinker with now is whether or not to pick up a used 970MSL frame that is my size, and make my 950AL the wife's bike.
    Last edited by tehllama; 03-04-2016 at 01:46 PM.

  14. #14
    mtbr member
    Reputation:
    Join Date
    Nov 2019
    Posts
    1
    Reviving an old thread here... do you still have the instinct you did this on OP? I have a 2016 Instinct 950MSL and am toying with doing the same. Do you have any pictures?

  15. #15
    Cactus Cuddler
    Reputation: tehllama's Avatar
    Join Date
    Jul 2013
    Posts
    1,797
    So, turns out this actually went to plan quite well.

    The 'Large' size based on 2014 geometry, with a 40mm stem, 780mm DH bar, and dropper post actually fits my 5'7" wife brilliantly. Slam the seat forward to get a steep effective STA, short stem brings the bars back to brilliant, and the geometry is actually great for a long-legged all-mountain bike.
    This made me feel good about moving to the XXL size myself (50mm stem, 810mm bars).

    I did get two seasons of riding out of that bike, one of them in this configuration. I did like the extra travel and plushness in the chundery and big (well, less small) hit trails I enjoy - everywhere else the BB height increase made it feel less dialed in for handling. The Ride9 full-slack setting made this usable, but not being 'in' the bike at the right settings did make it feel like a slight drawback, especially with how capable the front end can be on a 160mm fork 29er.

    Fast forward to converting that into the wife bike - I found that I can run it closer to 50% sag (yeah, that's some Damien Oton level silliness), and put the BB right where it actually belongs. Handling comes right back, and the stock spacer configuration actually means the travel is usable. What was previously slightly excessive LSC/HSC response, with less air spring pressure (relative to rider weight) actually turns into a well-damped system with great control on small and medium-sized hits. What it gives up are the big hits (i.e. it can bottom now, and does not do so as gracefully), but in that application she isn't bottoming it, but instead having piles of traction everywhere.
    I found this article actually quite informative - https://nsmb.com/articles/steve-math...spension-guru/

    Only practical downside here is that the pedaling performance (effective anti-squat) on the leverage curve for the bike is a bit off, meaning the suspension is neutral in all but the lowest few pedaling gears. Great for traction, but the efficiency loss is noticeable, especially putting a <150lb rider on a >30lb bike. It really does feel backwards, having me weigh 100lb more and on the 29# version of the bike, but it is what it is.
    I have tried to make up that difference with a MinionSS out back - great desert tire for efficiency while pedaling, and the massive amounts of plushness and negative travel actually cover up its lack of knobbiness great in the dry - and on wet roots/rocks the laws of physics come back with a vengeance, but living in the desert that's a trade I'll make every day, especially for a bike she seldom rides in the wet.

    The other version I had been contemplating was getting a Metric Trunnion 55mm travel shock (I think it's the 185x55 size), custom bushing connection, and rocking that. Would make it a solid 140mm travel bike, and the only immediate drawback is bushing performance in initial stroke, but that's less of a sever problem. If I ever decide I 'need' more performance out of my current setup, that's a direction I'd look at.
    The alternative would be moving to an Avalanche coil shock - a bit pricy even for the basic/simplest one, but they do have drop-in sizes that are long-shock, and if you're looking to really pick up performance, I think that's actually the direction to go, unless you want something mildly exotic, or find a deal on that oddball trunnion size.

    On my setup (XXL, Pike150mm 46mm offset w/ Vorsrprung Luftkappe), the shock is a DVO Topaz in the nominally correct size (technically 50mm travel, making it a 152/127mm bike, or 6"/5" travel setup).
    This shock is impressive on damping performance, and tunability, even at my limited level of experience on this. The external reservoir and bladder-driven compression adjustment range works great out of the box, and plushness matches my sillier >45% sag setup on the long-shocked Monarch. The rampup is a bit aggressive stock, but for my clyde size it's actually quite a practical trade.
    To me the limitation remains pedaling support, but that's more of a result of me going to a 30T oval ring (and eTRS 9-46t cassette) losing some of the kinematic anti-squat, then trying to bodge that with the LSC platform, but I have a really wide sweet spot if I want extreme ground-hugging performance at speed.

    Grip performance, even with low-grip rear tires, is enough that I'm PR'ing downhill trails out of the box, and knocking on KOMs for trails that suit me... There's a lot of other variables at play here (carbon wheels/frame/crankset, fresh tires, better sizing and cockpit fitment, freshly rebuilt fork, fresher drivetrain), but the part of that I'm personally able to attribute to shock performance also says there's a real improvement on a piggyback shock with that much adjustability.

    As far as pictures, unless you know it's a long-shock setup, most people don't realize it is. Even studying the BB drop closely, it sits right where most 650B bikes are relative to the axle-axle line static, and running more sag it just looks right.
    I'll dig for pictures, but they exist on here already.

Similar Threads

  1. Replies: 0
    Last Post: 04-20-2015, 08:36 AM
  2. New rear shock for Camber 29r? will a 7.875x2.0 fit?
    By questlove967 in forum Specialized
    Replies: 6
    Last Post: 11-25-2013, 10:27 AM
  3. Replies: 19
    Last Post: 10-14-2013, 07:22 AM
  4. SC Nickel - Installing Rear Shock
    By bloodninja in forum Santa Cruz
    Replies: 4
    Last Post: 04-04-2013, 11:18 AM
  5. 7.875x2.25 shock on DW Sultan
    By gmk in forum Turner
    Replies: 5
    Last Post: 03-07-2011, 04:54 PM

Members who have read this thread: 22

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

THE SITE

ABOUT MTBR

VISIT US AT

© Copyright 2019 VerticalScope Inc. All rights reserved.