9Point8 Slack-R Headset Review

by 20

What if you want a slacker head angle, but your bike won’t accept slackset-style headset cups? Enter the 9Point8 Slack-R!

  • Brand: 9point8
  • Product: Slack-R Headset
  • Price: £119.99
  • FromShorelines Distribution
  • Tested by: Chipps for 10 months

Not everyone is after a point and shoot, racy bike, right? The marketing blurb for my Yeti ARC hardtail reads something like “Far beyond a juiced up thorough-bred XC race bike, the ARC is built around a 130mm fork for a massively capable trail bike.”

The ‘before’ shot when shiny new – and 67°

“It’s your instant-feedback steed for any trail” – but what if I don’t really want instant feedback? It’s true that the Yeti ARC is a great trail bike, but after probably two years of ownership, I’d decided that it could probably do with chilling out a little. The Yeti, with recommended 130mm fork features with 67°/76° angles. Which is great for that instant-feedback feel of XC racing, or slinky, sinuous trails of the South Downs, but it can be a little much for loose, dry, rocky trails that I now find myself riding most of the time. It was a bike that I felt I needed to be fully-caffeinated in order to keep in line. At speed, it would still get knocked off line and any thoughts of ‘You could ride this and sell the full-susser’ went out the window. Indeed, my Singletrack World colleagues in the ‘rad’ office joked that the 2000s would like their geometry back…

Three size-specific parts and one tool

I decided to get one of those slack-headset jobs, but reading the fine print on the Yeti FAQ, it seems that Yeti didn’t recommend it – and then from a practical point of view, the Yeti, like many bikes, features headset races moulded into the actual carbon of the head tube of the bike. Headset bearings simply drop in, so popping the headset out and pressing a new, slacker one, in was out of the question. It looked like I’d have to learn to love the twitchy beast.

Then, I discovered the Slack-R headset from Canadian company 9Point8 (makers of nice dropper posts too). The Slack-R is a three-piece replacement headset. The upper and lower parts feature the same chamfered edges as a cartridge headset bearing does, only instead of a bearing, it’s a machined sleeve that offers a new, slacker position for that bearing to sit – turning your integrated headset into a kind of external cup headset. The third part of the Slack-R is a sleeve that threads into both upper and lower new external cups and (using a special splined tool and socket set) pulls both headset parts tight together. You’ve essentially built a new head tube inside your existing one. It’s a complicated premise, but it’s simple enough once you see the parts, which themselves are neatly machined and smartly black anodised with 9Point8 graphics and notched so that you know how to orientate the two cups in your head tube.

The Yeti as stock, with integrated headset cups. Stem spacers still to add (I ran about 15-20mm under the stem in the end)

There are a few requirements needed before you get ordering, though. You’ll need to measure your head tube and decide on one of (normally) two options for the new angle available. This will be affected by your head tube length: a shorter headtube has more potential for bigger angle adjustment. For my medium Yeti ARC, I had a choice between –1.4° and –1.7°. Benji would argue that everyone needs slacker and no one needs any half measures. Luckily, 9Point8 were nice enough to send me both kits to decide which I preferred.

The three parts and the tool after a few months’ use. (No rub marks anywhere, though note the two bits still together…)

Not every bike needs this level of intervention to get a slacker effective head angle, but 9Point8 lists compatible bikes that, among others, includes Cannondale, Norco, Marin, Orbea, GT, Revel, Scott and even some Specialized bikes. Basically, if your bike has ‘moulded-in’ headset bearing cups and you can’t press in a new cup, then this is probably what you need…

The other caveat with installation, is that you need around 20mm of ‘spare’ steerer tube. If you’ve already slammed the stem and scalped the steerer, you won’t get the Slack-R to work, as it’s effectively making your internal headset an external one. Luckily, I always chop my steerers conservatively in case I need to move the fork on to a different bike.


The kit comes as three boxes, containing the different upper and lower cups, along with the central sleeve (which uses a clever combo of regular and reverse thread to get the two halves to tighten together) as well as the sturdy splined installation tool.

What followed was then: remove fork, remove bearings (and around 20mm of stem spacers), clean everything up and get ready to install the two cups. 9Point8 recommends carbon paste to get the two cups to ‘bite’ and not rotate as you tighten. This is where you need a third hand or handy friend, as you need to place the upper cup in place – with its notch aligned with the centre line of the bike, and the lower cup along with the central sleeve. I added the recommended blue Loctite to the threads, to keep them from moving (more of that later) and then threaded the sleeve on a few threads to the lower cup before offering the lot to the upper cup and threading that on too. Then it got complicated, as you need to use the 9Point8 socket tool in the head tube to tighten the two cups together. While doing this, you need to make sure that neither cup twists (its slot from the centreline of the bike) or you’ll end up with a slack headset on the wonk. As the tool is only an interference fit on the central sleeve (and it needs a 19mm socket and an extension bar, so it’s constantly falling off the tool) I kept dropping the socket while trying to keep the two cups from moving while I tightened.

After a lot of fishing around on the floor for the tool again, I got it all installed in about half an hour and was ready to reinstall and ride! The old cartridge headset bearings drop straight in and the fork and stem bolt on as normal, only with a few spacers fewer.

The new Slack-R top cup with Hope headset reinstalled. You can see the slot in the back of the Slack-R to mark centre position.

First and second impressions

Using my not very accurate method of angle measuring using my phone, my head tube angle had changed from a ‘before’ of 67° to an ‘after’ of around 65°, which was good enough for me. The front axle was now around 10mm further away from the bars, due to its new ‘external’ headset, which helps with that new angle measurement. Meanwhile, the handlebar position hadn’t changed due to the addition of the top cup, but the removal of 15mm of spacers.

On the trail, the feeling wasn’t dramatic, but it was noticeable. After a single on-trail tighten of the headset bearings, I got on to riding all my favourite spots. The bike felt calmer and more composed on the front end and I noticed the babyhead rocks of my regular descents had way more effect on my rear wheel now, rather than the whole bike bouncing around.

After a week or so, I felt I needed to tighten the headset again, but when I did, I felt some binding when rotating the bars. This turned out to be due to the lower cup having rotated around 30° in place. I’d obviously not tightened it properly, so I went back to the workshop, re-Loctited the threads and re-carbon greased the cups. Most importantly, I paid particular attention to tightening the cups correctly and making sure there was no creep while cranking the three parts together. There’s no real way of manually stabilising the cups (like with a spanner, pin-spanner or whatever – it’s just hands and carbon grease), so you need to make sure they’re in line, and stay there, while you tighten the central sleeve. After my first re-do, the headset hasn’t budged at all. I’d still suggest throwing the splined tool in your bike bag if you’re off racing or travelling, as no other tool from a regular bike shop can replace it if you need to tighten things up, mid-holiday…

Don’t overdo the Loctite!

I initially installed the –1.4° kit, but later on went back in put the –1.7° kit in. To be honest, the 0.3° change between those two was hard to notice, compared to the noticeable calming that the –1.4° kit had from stock. I suggest to be like Benji and just go full-on first time.


There have been a few issues. Mostly when I went to swap over between the two angled sets, I discovered that I’d completely overdone it on the Loctite and only one cup budged from the centre sleeve. In the end, I had to drill a hole in the central sleeve to put a screwdriver through, so I could brace it and use the tool on the other part. Lesson learned.
One other reported issue is of a slight creaking in use. I hadn’t noticed this initially, but watching GoPro footage confirmed that there was a creak on bigger hits. Opening up the system, you see how the carbon grease dries out over time, leaving just a dry white paste. I’m about to lightly grease things all over as well and see if that cures things.

And, to aid installation, it would be great to have a way of stopping the cups from spinning as you tighten the central section with the tool. Spanner flats might be a little too old school, but a pair of pin spanner holes might be a subtle addition. And if 9Point8 can find a way to re-engineer the tool socket to accept a more commonplace workshop tool, that would save a lot of travel worry for riders.


Needless to say, installing this 9Point8 Slack-R headset kit will usually void your frame warranty. I waited a year and decided I’d take the chance anyway and I’m delighted with the performance. I’m certainly not a ‘slack-sled’ disciple, given that I’m not a rad downhiller and way more of a trail rider, but I’ve been really impressed with how this kit has made my bike less nervous and my descending more confident. And on climbs, I can still get round those tricky switchbacks on the climbs… In terms of value, it’s a really nicely machined bit of kit and the instructions and advice on the website on what fits which bike is invaluable. It’s not cheap, but it’s made my bike more enjoyable to ride, more confidence-inspiring and shelved any ‘Ooh, should I swap the frame for something radder’ thoughts. And from that point of view, it’s a bargain. Way cheaper than shopping for a new frame.

Signing up to our mailing list is not only a great way to keep up-to-date on all things Singletrack but it is also a great, free way to support us.

Sign up to receive awesome editorial content from Hannah every week.

We appreciate how handing over your email address is a mark of your trust in us. Check your inbox for our confirmation email and click the link to activate your newsletter.
We don’t spam! Read our privacy policy for more info.

Check out a previous newsletter here

Review Info

Brand: 9Point8
Product: Slack-R Headset
From: Shorelines Distribution
Price: £119.99
Tested: by Chipps for 10 months
Chipps Chippendale

Singletrackworld's Editor At Large

With 23 years as Editor of Singletrack World Magazine, Chipps is the longest-running mountain bike magazine editor in the world. He started in the bike trade in 1990 and became a full time mountain bike journalist at the start of 1994. Over the last 30 years as a bike writer and photographer, he has seen mountain bike culture flourish, strengthen and diversify and bike technology go from rigid steel frames to fully suspended carbon fibre (and sometimes back to rigid steel as well.)

More posts from Chipps

Viewing 20 posts - 1 through 20 (of 20 total)
  • 9Point8 Slack-R Headset Review
  • 2
    Full Member

    This is where you need a third hand or handy friend

    It was a moment of comedy confusion when I cam to the installation of my Slack-R. – How do I hold all this together and the extension and the socket, and the tool… Eventually I purposefully over rotated one cup past the centreline so that on tightening it would come back to central, I had to eye it up and couple of times and it still took a bit of faff-on but (more through luck than judgement I suspect) got it lined up and tight. I also had a bit of binding at full handlebar rotation, but that eased off after a while. I periodically check it, and its remained solid.

    Impressed, its a good bit of kit, does what it says, can be installed pretty easily at home, is well finished, and looks the part.


    Free Member

    Haven’t these been around for years though? I’m sure i considered one of these for my old santa cruz abour 4 years ago.


    Full Member

    Scary maaaaan – invented this in my head only last week and it’s already manifested in earthly form

    Full Member

    ^ username checks out 🤣

    Agree with many of the points raised and mine currently looks like the one Chips removed with the centre part still fitted to one cup. That frame ended up an unrelated warranty so I haven’t found the need to refit but might do so at a later date. I’ll likely 3d print something to try stoping the cups rotating during fitting. Wonder if they could extend the tool’s length a little and fit an o ring to get around the tool dropping out all the time? That might make fitting easier too.

    Full Member

    I’ve realised that if I’d turned the frame upsidedown, that would have at least stopped the tool falling out. It’s something that would be way easier to do from new, with a blank frame, rather than with the forks hanging off the front brake hose, trying to feel or see where the grooves were on the cups with a head torch…

    Full Member

    I think I fitted mine using both hands AND my mouth!

    THERE’S your extra hand!


    Full Member

    Great review. Thanks for all the installation insights; it’s always helpful to know these things up front.

    It’s not often a bloke my age wants to be a bit slacker up front, but in this case, this is just the kiddy.

    Full Member

    @chipps did you ever consider the potential alternative of going up to a 140 or 150mm fork?  Yeti are now saying that (even the older ’21) Arcs can run up +20mm forks from the stock 130.

    Full Member

    @danieljohnreynolds – I briefly did. However, I only had 130mm forks to hand. Also, while jacking up the front end with an extra 20mm of fork will slacken the head angle by (only) about a degree, it’ll do the same to the seat angle, which was already on the edge of a little too slack for modern times..

    Full Member

    Am I right in thinking you need to buy a conventional type headset that fits in the Slack-R ?

    Full Member

    Am I right in thinking you need to buy a conventional type headset that fits in the Slack-R ?

    Good question. My assumption had been that your existing bearings would slot right in to the Slack-R but perhaps the Slack-R needs a specific bearing that may or may not be what you already have?

    Full Member

    Am I right in thinking you need to buy a conventional type headset that fits in the Slack-R ?

    The bearings I took out of the Yeti headset just dropped into the slack-R cups. This type of design is intended to provide a solution for bikes with integrated headsets, it does that by effectively making it a conventional design, but the cups still use the same bearing sizes.

    Full Member

    Oh nice. I thought Chipps had needed to buy a Hope to fit the Slack-R cups, but that must just be the top bearing cover he had on pre-SlackR. cheers!

    Full Member

    I fitted one of these kits a few weeks ago and did what nickc did when fitting. Couple of attempts were needed but got it spot in the end. Thing is I’ve not been out on the mtb bike since so I’ve not tried it out yet.

    Full Member

    I had one fitted one to my Arc too and am very happy with how it rides, still climbs very well too

    No issues at all with it, fitted by my LBS though, no creaks or slipping

    Looks super neat, almost looks part of the frame

    My frame is an XL and I went for a 1.7° kit (Mike)

    Actual measurements were about 2° slacker and about 25mm longer wheelbase

    Full Member

    Very cool. Any idea on how it affect other Geo numbers.? Namely BB hight and SA.?

    Full Member


    I took quite a lot of measurements before and after with the bike in exactly the same position.

    Seat angle – no measurable difference (within 0.5°)
    BB height – 2mm higher

    Obviously my measurement methods are not super accurate (e g. lying on the floor squinting with a tape measure) but “not much” is the answer

    Full Member


    it is basically two adjustments:

    ‘first is that it creates an external cup on the bottom of your head tube/top of fork crown. So, like going to a longer travel fork, this will raise the front, which also slightly raises the BB, and slackens the head angle and the seat tube angle.  The rule of thumb is 0.5 degrees per 10mm, all though his does depend a lot on wheel base.

    But, it also changes the angle of the steerer inside the head tube, which will slightly drop the front end again, so the net result will be very little raise to the front end, and even less to the BB. Similarly, the seat tube angle won’t change as much as just adding the externa cup would have.

    Full Member

    My wife had an older, but nice, Stumpjumper a few years ago. We passed  it to our 11 year old daughter, knowing she would grow. But, she was already riding some quite challenging trails, and racing local enduros, so the 65 degree head angle was quite steep, especially as it had older forks with 51mm offset (even with a mullet set up).

    Adding this gave the bike the extra degree to get it inline with modern geometry. Worked great and she rode, raced (and won!) on it for 2 years. Now she has out grown it, but for 2 years, this buying kit was much better than a whole new bike.

    Full Member

    I used one of these on my 2018 hightower lt – now wondering exactly why I decided to take it off again. One reason was the bike really didn’t want a slacker seat tube, even 0.5 deg, I think the other is just that although it felt more stable when fast, the overall balance of the original geo was pretty good for my local twisty trails.

    Removal wasn’t entirely straightforward and the slackr cups have some marks left by my stilson wrench

Viewing 20 posts - 1 through 20 (of 20 total)

You must be logged in to reply to this topic.