Looking to make your trail or enduro mountain bike just a bit slacker? And do so without any major mods and for only $20? The Niner Slacker Puck lower headset bearing cup lets you do just that, and it ships with their RIP9 and JET9 models but can be ordered separately for other bikes.

Niner introduced the current generation RIP9 and JET9 in summer 2016 as their first 29/27.5+ bikes able to run both wheel and tire sizes. The bikes were designed around 51mm offset 29er forks, which were still the norm at that time. If you opted for the 27.5+ wheels and tires, they simply spec’d a fork with 10mm more travel to match the 29er’s geometry.

Along with mid-term updates to those bikes’ cable routing, Niner also started shipping the bikes with a 15mm lower headset bearing spacer they called the “slacker puck”, which was designed to let you adjust the geo yourself if you wanted to swap in 27.5+ wheels and tires without having to buy a new, longer travel fork.

niner slacker puck lower headset bearing cup spacer lets you slacken your head angle on any mountain bike

Now, with more 29ers coming stock with 44mm offset forks (Niner included, thanks to a rolling spec change this past summer) and more bikes pushing the front end slacker, the slacker puck can also be used to update your RIP9 or JET9 geo as needed.

The effect is that it’ll make the head angle about 0.5º slacker. For the RIP9, it goes from 67º to 66.5º, and ships with the bikes (but not pre-installed, even though their geometry charts show the numbers with it). By itself, it’ll increase trail slightly, and it’s meant to be paired with a shorter offset fork, which will also increase trail. But, the combo will help limit wheelbase growth, and the overall effect should be more stability on the descents and high speeds.

The tradeoff? As with any slack bike with lots of trail, handling might be a bit slower in the tight, twisty stuff or want to wander on the climbs. It also raises the BB about 3.5mm, too. Do you need it? Depends on the type of riding you’re doing. If you’re doing more down than up, it might be a nice upgrade.

The Slacker Puck is a lower headset cup that pushes the bearings out by 15mm and works with their ZS56/40 lower bearing. Those numbers mean a headtube with a 56mm internal diameter, and a standard 1.5″ tapered lower fork steerer tube. If those numbers match your bike, chances are it’ll work. Link below goes straight to the product page.



  1. If I recall correctly, Niner needed to file bankruptcy and seek new owners partly because they lacked money to be used for R&D. Now, just a few months later, they have done it! Behold the creation of a taller lower headset cup!! Standing ovation and round of applause.

    • That is all a matter of opinion, riding style, terrain, etc. When I first started riding two years ago the front end instability and lack of feel freaked me out quite a bit. I was a pro motorcycle roadracer and did a lot of training between races on MX and dirt track bikes. My brain is looking for something from the front end that until recently you couldn’t get with a MTB frame. I have a Jet9 RDO with an angle set raking it out 1deg more and I run very little sag in the front end (18mm vs the recommended 32.5mm) which rakes the front out even more. My measured head tube angle is just about 65deg. In addition to that I changed out the fork crown for one with 9mm less offset to get more trail out of it. That all sounds like the bike wouldn’t steer at all right? For me it’s a non issue. I ride with some super fast racer types and they have no detectable advantage in the tight stuff. Do I have to use more bar effort? Probably. On the flip side the front end has a ton of feel and because there is a ton of trail I can push the front end through corners forever before it want’s to tuck. And while it’s pushing I can feel ever little thing. Let’s be realistic here. A MTB that steers like a “truck” still steers lightning fast with very little effort compared to a motorcycle. Nothing a set of 780mm bars and some upper body strength can’t solve. You’re not wrong in your statement……for you. But you are wrong by including “we”. There are a lot of people that don’t like the fast steering, low trail, low effort, low stability geometry that is found on most bikes.

    • I completely agree! I sold my Stumpjumper in order to get the latest one and it was a very poor decision on my part. Unfortunately I was unable to ride it before I bought it, so now while I have one of the prettiest mountain bikes ever I ride my hardtail because it is so slack I can’t take my hands off the bars and I’ve had to nickname the bike Bobbi….. I with there was a solution to change the angle with an offset headset buuuttt Specialized mountain frames are integrated bearing types so for now there is nothing I can do except for reducing the fork travel way down! #werenotalldownhillbros

    • My 2005 Prophet MX came with exactly this kind of lower headset cup. One of the first things I did was removed it and fit a Works -2 angle headset, which improved the bike enormously. If this is Niner’s idea of abig release it’s no wonder they went belly up.

  2. The purpose of the part is to keep the geometry the same when going from 29 to 27.5+. Its NOT to make the handling slacker. The niner product page is clear on this.

    It would be (deleted) to install this with 29 wheels. The extra instability of the higher bb more than negates the .5 degree HTA change. If you want slacker, use an angleset. NOT this.

  3. All – FWIW, Niner didn’t make any announcement about this product, we found it and thought it was interesting and worth a post. There are a lot of bikes that use adjustable chips, switches and far more complicated systems to achieve a similar effect. It’s all about options, and we love the idea that you can tune your bike’s handling and geometry to suit your needs with a quick, cheap and easy to install part. What’s not to like?

    As for the product page’s intended use, that was the original plan (maintaining the geo when switching from 29er to 27.5), however it can still be used with 29ers to achieve the changes mentioned in the article.

    (some comments on this post have been removed because they were either irrelevant or violated our comment policy)

    • It’s curious that you would respond twice to defend such a non news worthy product that has been available from Niner (and other brands) for quite some time. Pure speculation, but I’m guessing there is more to this. Have you been recently compensated with a new Niner or maybe some extra advertising money in exchange for this?

      • No advertising money was exchanged for writing this, and to be honest Niner originally didn’t think this was worth posting, but I thought it was a cool little add-on. The reason I’m defending it is because:
        A) I think it’s important that we maintain a positive comment environment on Bikerumor, and comments that poo-poo something just because it’s a small innovation have no place here. Small innovations and ideas lead to big ones, and we celebrate them all.
        B) Trashing a brand or person because they make something that might only appeal to a select few people or situations makes no sense. It’s like calling someone stupid because their opinions differ from yours.
        C) If we ignored little things like this, then you’d only see the same “big news” items here that you see on every other site. This is the type of niche, boutique, hard-to-find and easy-to-miss product that makes our coverage special and sets Bikerumor apart. If you only like seeing mainstream stuff, you can find that anywhere.

  4. Hey BR Staff. I think you have some bad math…

    “The effect is that it’ll make the head angle about 0.5º slacker. For the RIP9, it goes from 70º to 66.5º”

    it is either 70 to 69.5 or 67 to 66.5 – or that cup manages a 5.5 degree change

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