The 9point8 Slack-R head kit is a very specific piece of kit, that if it fits, will slacken your head angle. It’s well made and cheaper than a new frame, but it’ll only fit certain frames, and on top of that you’ll need to make sure you have enough fork steerer for it to fit.
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9 Point 8 Slack-R – how it works
The 9point8 Slack-R headset kit changes the head tube angle on bikes with IS headsets. (IS41/28.6 upper bearing and IS52/40 lower bearing only.) Using three parts of well-machined aluminium, it consists of two cups that fit into the frame and are held by a sleeve that it is tightened up against. There is a specially machined tool that you’ll need for fitting, so don’t lose it. There are 16 different length kits, ensuring the best fit for your head tube length.
The Slack-R works by changing the angle of the steerer in the head tube, effectively changing the head angle of your frame set-up. It’s a simple idea, and the Slack-R is a well machined and finished component.
Installing is straightforward, but it’s important to follow the instructions carefully, especially making sure the cups are lined up with each other and down the centre line of the frame. Once installed, tightened and set, you pop your bearings back in and install the fork. This ensures the headset keeps the bearings aligned and that the steerer still rotates correctly.
Two things to bear in mind: the angle changes by 1.2 to 1.8-degrees, and there will also be a slight change to the bottom bracket height, a stack increase and a decrease in reach. The biggest change is to the wheelbase. For a full in-depth on all these changes, take a look at the 9point8 website.
9point8 Slack-R – How it rides
Once installed and checked over, my immediate observation was the addition to the head tube length. The Slack-R adds around 20mm, as you are effectively installing headset cups to the frame. It’s this additional height that allows the cups to accommodate the angle change. As a result, you may find you need a new fork or that you lose a few spacers, which is definitely worth calculating before purchasing.
Out on the trail, my bike felt more stable at higher speeds and in fast corners, thanks to the longer wheelbase, and the bottom bracket seemed to strike fewer rocks. The slacker angle was noticeable, but not drastically; it’s a subtler feel. It certainly adds confidence to steep terrain; with a reduced feel, you might be going over the bars.
9Point8 Slack-R – Verdict
The Slack-R is well made, and although it achieves enough change to a bike’s geometry to improve its handling, the fact that it’s fairly niche and may sometimes require new forks to install makes it a carefully considered purchase. It’s also as expensive as a high-end headset, so may be worthwhile if all the numbers add up for you and your bike.
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