Hi, just wondering if anyone knows off hand because the SRAM service manuals don't clarify this one.
I've got a 2023 Superdeluxe ultimate air with hydraulic bottom out, set to 50mm stroke and with a 50mm damper body. The point in the stroke that the HBO activates is set by a non-removable needle inside the body.
I want to increase the stroke to 55mm, and i will replace the body when the shock needs its next service, but that is a while away and I'm bottoming the bike out a little too often. If I cut the travel reducer out right now, will I have 55mm of stroke but with my HBO activating a little early, or will there be interference within the damper that will damage the shock if I do that without having the correct body?
I don't really want to just cut it off and see if the shock cycles, because if it doesn't, the damper body is currently out of stock where I live and it will take weeks to get the shock operational again. Thanks!
you need to upgrade the hbo too:
https://wps-mtb.com/products/rockshox-super-deluxe-hbo-bolt
That is specifically for the coil and doesn't apply to the air shock I have. The needle that controls when the HBO activates is built into the damper body, i just need to know if it interferes with anything within the damper if it's the wrong length for the stroke. I'm happy with it applying early, i don't want to ram the needle into anything else because it extends too far.
I have the same issue, but I need to reduce stroke.
What I understand is that you must change the damper body, because the HBO is fixed, and with different strokes it will not work.
I don't know exactly how it works, but I assume, with a longer stroke, you may be bottoming out the HBO it self,not the shock?
Yeah if you reduce stroke then the HBO will just not engage before the shock reaches its end of stroke. it's safe to do that.
I have assumed what you are also assuming with regard to increasing stroke, I'm just trying to verify that.
How do you know that it doesn't apply to the air shock, are you sure?
Usually dampers are very similar between air and coil version of the shock. In case of coil shock I know that you should NOT only increase the stroke without also changing bottom out bolt because it would hit and damage the damper.
Coil has adjustable HBO, air has fixed HBO. So similar function, but different ways to make it work.
There is a nice little spacer that can do the trick, I also used it for my SD Coil without changing the HBO - all good so far!
https://finesse-components.com/products/travel-reduction-spacer-rocksho…
If you use just the clip, then you will lose the HBO? The HBO is stroke dependent on air shocks, so yeah, less stroke, less/no HBO?
For the air SDs, the HBO is a needle shaped thing in the base of the air shaft body, which is not removable. It's length corresponds to the stroke length so that it engages at a specific percent of travel (I want to say 20%). If you just remove the travel limit spacer without changing the shaft body, you will still have HBO but it will activate later. You can buy the complete body assembly with HBO for around $90 (also will have correct sag marks too), but that will require rebleeding the shock.
^Correct, but the opposite- if you remove the travel spacer, the needle will activate at the same stroke, but since you have more stroke (from removing the spacer), you'll have more time in the HBO zone. I can't remember if there's anything for the needle to run into or not if you increase the stroke 5mm.
You could always get a non-HBO body and run that if the HBO ones are out of stock.
Graphic:
https://cyclinic.com.au/cdn/shop/products/my23-sdlx-hbo-v4.gif?v=1676249835&width=675
So I went from 50mm to 55mm stroke on my Super deelux, So in short I'm running less HBO than I was before and if I want more HBO I need the 55mm Damper body?
Yes.
No.
The 50mm needle is actually longer than the 55mm needle. So if you run a 50mm needle with 55mm of stroke you will be activating the HBO earlier and for longer (as a % of the stroke).
Think about it:
50mm needle activates the last 20% of 50mm = last 10mm of stroke (40mm free stroke until HBO).
Same 50mm needle in a 55mm stroke shock = 55-40 = last 15mm stroke have HBO or 15/55=27% HBO
I can't remember the % it's either 15 or 20. But either way- increasing stroke without changing parts will give you more stroke in the HBO zone.
I was thinking ingen reverse.
But how does the HBO reach bottom?
The needle is cone shaped, but will it at some point completely block the hole, and case hydraulic lock if its to long?
it's a cone on top, then same diameter all the way down. But I can't remember if it will run into something else if it's too long...
best to just run it the intended way- ie correct body/needle for the stroke.
So theres a new needle for every 2.5mm of stroke? Thats a lot of needles, Im suddenly understanding the dislike of HBO from suspension designers.
I remember an identical discussion to this one two years ago, and @Dave_Camp either you or someone else who's smart said that the needle would definitely bottom out on something and break if you cut the travel reducing spacer to increase stroke length. At the time, this very smart person in the forums (I think it was you, Dave) was trying to impress on us how densely packed the inside of these shocks are to get everything to fit. Sounded like there was zero room to play with and you needed to replace the body with the correct length needle if you're going to mess around with changing travel.
Yes there’s a different needle and corresponding damper body assembly for every size stroke. It’s a lot.
I know the coil shock cannot tolerate any messing with the stroke length- as there can be metal to metal contact. I think you’re right and the air shock is same. At least I wouldn’t gamble on it.
5mm is a lot when talking about internal clearances on these things.
Thank you for giving a reply that isn't speculatory.
I'd searched the forum but wasn't able to find anything - with the tip-off I found the post you're talking about. Was in a megathread so i'd missed it. Can't remove the spacer. Ah well.
Already running the damper fully closed, more pressure than I'd like, plus progression in the spring... Such is life with something approaching an enduro bike that has 125mm of travel lol (Mullet high pivot Optic with a Lyrik and enduro/DH tires... way more capable than 125mm should ever be).
What aircan?
There are a few options and they make a big difference.
"DebonAir Progressive". Looking at the graphs etc, Linear XL one would give me a slightly more stable spring rate through the inital stroke, which would be nice, but wouldn't do much for keeping me off the bottom out bumper.
When I get a service done on the shock and replace the damper body I'll also have the damper retuned, that'll get me the performance I want and allow me to drop the ride height a bit, I was just hoping for a temporary improvement for the mean time. The Optic has no issue with 55mm of shock stroke, takes it to about 138mm of travel which is more in line with what the bike is good at doing IMO.
What you have is probably the best aircan for the application.
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