To all the tech nerds out there:
I just recently picked up the SDU to replace my EXT Storia that has been making problems. I absolutely loved the HBO feature on the EXT hence picking up the SDU.
Now to my question. The HBO supposedly controls the last 20% of suspension travel on both shocks. On the EXT it ramped up the progressivity by 50% (I don’t know how much on the SDU). It gave the EXT a truly bottomless feel.
The new SDU still has a foam bumper on the shaft as the old coil shocks without HBO had to prevent harsh bottom outs. The EXT does NOT have such a foam bumper. Only a small foam ring that didn’t have any significant absorbing capabilities.
So on the SDU we have the HBO PLUS the foam bumper ramping up the final stroke. In my opinion this is noticeable and makes the ramp up harsh. Has anyone tried cutting down/out the foam bumper and only running HBO on the SDU as on the EXT? Maybe turning the HBO all the way up.
I have talked to SRAM support Germany and all my local suspension tuners, no one could give me any advice/experience.
I would love to hear your thoughts 
It feels weird with no bumper… I tried it multiple times- you’d be hard bottomed on g outs and berms etc as the HBO doesn’t do anything at slow shaft speeds. The bumper adds some spring rate at the end of stroke that was very beneficial in those situations.
you can try different size bumpers- they should be available as spare parts from RS.
I’d try bracketing the HBO setting on whatever impact feels harsh (repeat open, middle, full closed). The harshness might not be what you think.
Thanks for sharing your experience!
I wonder why the EXT doesn’t have the same problems you mention. Unfortunately I can’t get a hold of any spare bumpers. I’ve talked to multiple suspension tuners and they also can get any bumpers. The only one I found on the Internet was part of a travel kit sold in Australia…
For reference, Dave works at Rockshox R&D in Colorado Springs and I believe he's one of the main people who designed the new Super Deluxe.
Are you absolutely certain you're on the right spring rate with your new shock? If you're hitting the bottom out pretty regularly, I wonder if you might be undersprung. Even if it's the same spring rate number printed on your RS spring as your EXT spring (e.g. they're both 450 # springs), actual spring rates can vary wildly from their nominal value. Also, different shock architectures can sometimes require different springs, depending on the level of damping built into the shock or tune. I remember when Fox took out the Boost Valve in the DHX I had to go up in spring rate (on the same bike), and then later when they went twin tube for the DHX2 I had to go down in spring rate.
I second the points Dave & Robot made - The bumper acts as extra spring which is good for lower speed impacts that don't create much damping force. Trying shorter or taller bumpers is a good way to tune it though, I was pleased when I saw they were making different ones.
The Storia typically has more damping through the whole speed range so will also be reaching the end of the travel with less energy anyway. You shouldn't be using the bump stop often enough that you are noticing it, so if you are I would be looking at a stiffer spring and/or more compression damping.
What is it you feel that makes you think the ramp up is harsh?
What an honor to be able to speak to the people that create such amazing suspension (absolutely loving the new Zeb in comparison to the old one).
Makes sense that low speed impacts don’t affect the HBO that much. Didn’t take that into consideration :D. I’m currently on a 450lb spring and sit at 30% sag with a few turns of pre load. I might turn in the high speed a bit more to create a smoother transition to the hbo/bumper.
I can’t even get a hold of the normal bumpers in Germany let alone different sizes of bumpers and neither can any of the bike Shop/suspension tuners. I would definitely love to try different bumpers though!
Maybe Dave can let his colleagues in sales department know that we are dire need of some bumpers in Germany
Piggybacking (heh) with a dumb question about the 2023 SDU coil... what is the downside to using more HBO damping? I would assume the last 20% of shock stroke travel is really only on bigger hits, probably not going to use it over stutter bumps. I'm still playing around with setup on mine trying to prioritize grip. Haven't isolated just changing HBO yet, but would running it at max setting possible create harshness on square edge trail hits?
Maybe it could add harshness on huge square edge hits? But then you can just turn it wide open and the hbo basically does nothing.
I’d do the bracketing to find your preferred setup. Lots of differences between frames riders terrain etc. just twiddle the knobs and take notes.
Kind of related question, but are the SDU air HBO assemblies ever going to be available for retailers and service shops?
I've seen that basically every pro athlete running the SDU air is running the HBO version (can see the markings on stanchion). I love my SDU coil on one bike but the other one (Spec Levo) really should be running air. In the RS catalog, there's an OEM version that has the HBO and different damper tune. When I contacted SRAM support, and when my local shop contacted their B2B support, both said something to the effect of, "Yeah, you can't buy the HBO version retail. You'd have to buy the retail version and send it in to SRAM to get rebuilt with HBO. No, we can't guarantee we have the part in stock to do that."
Like many things, both extremes can feel bad in a similar way. So too little HBO (or none) will be harsh on bottom outs as the shock reaches a solid (ish) end point, but too strong of an HBO effect could feel harsh as it ramps up the damping force too suddenly.
In reality, each bike and rider is going to be different and what feels like harshness is a sudden change in force which can either be too soft of a spring + damping suddenly transitioning in to a reasonable HBO (side note - soft settings encourage faster compression speeds, compounding the effect) OR an otherwise appropriate set up running in to excessively strong HBO circuit.
An optimum set up would blend the way these forces are generated with regards to position & speed, which is why often an overall "firm" set up can be super comfortable - looking at the damping or spring rates in isolation might look stiff but because they do their job in a smooth way and "share" the load it actually feels really good in use
Short answer - try each setting at min and max, see which feels best and how they interact
Post a reply to: 2023 Rockshox SDU hydraulic bottom out