Threadless headsets are one of the single biggest improvements to bicycle design, they're elegant and simple to use and adjust for perfectly smooth steering.
Our guide below shows you what we believe is the best method to adjust a threadless headset. We've included a list of the tools and materials that you will need to complete the job and in some cases where you can buy them. If there are others that you prefer then feel free to let everybody know in the comments.
Tools & Materials
The day the ubiquitous threadless headset was conceived and developed by American, John Rader in 1990 was a good day for all cyclists. Freeing bikes (and cyclists) from troublesome threaded steerer tubes, threaded cups, lock rings and spanners to effect bearing preload was a stroke of forehead slapping genius. Road.cc first met Rader and saw the prototype threadless headset at the world mountain bike championships in Italy back in 1991. We couldn’t have expected this simple method of pre-loading headset bearings to change the way we attach forks to frames forever, but it did.
1. Loosen the stem bolts
The trick with threadless headsets is not to forget the to loosen the stem pinch bolts first. Without doing that first you’ll get nowhere swinging on the top cap bolt for main bearing adjustment. Just back the pinch bolts off enough that the stem can be moved from side to side with light hand pressure. The beauty of the threadless headset is that we only need a 5mm Allen key to preload our headset bearings. You might also need a 4mm Allen key if your stem pinch bolts require it. There are no threads on the steerer tube to worry about, spanners or counter tightening.
2. Check the clearance
We've undone the top cap and removed it, so you can see the star nut (in this particular case an expansion wedge). As you apply torque to the top cap bolt the bearing is loaded, effectively pulling the fork steerer upwards. You need to make sure that the top edge of your stem, or steerer spacer, is around 3mm proud of the top of the steerer tube.
If you have an aluminium steerer then it's fine for the stem to be proud of the steerer. If the steerer is made from carbon fibre then we very strongly recommend you have a 5mm spacer above the stem so that the stem is entirely clamped round steerer and can't crush the top.
3. Adjust the bearing preload
Depending on how loose your headset bearing feels you can make adjustments to the bearing tension with the 5mm Allen bolt located in the top cap. Adding tension to the bolt will pull the threaded star nut (which is found wedged inside the steerer tube) upwards, moving the fork crown race bearing more tightly into the lower headset cup. Alternatively, reducing the tension on the bolt will back off the bearing preload, effectively loosening the bearing.
4. Check for looseness
When you’re happy that you have the bearing set to the correct level or preload, apply the front brake only. While holding the front brake on, rock the bike gently back and fore. If you feel any looseness - it’ll often feel like a feint knocking feeling - then add more preload tension to the bolt until the looseness stops.
5. Make sure it's not too tight
Cranking on too much preload tension can harm the steering sensitivity of your bike. You’ll feel this as a sensation of stiffness in the steering, and when ridden a bike with an over tight thread less headset will have a tendency to auto-steer off line. To check that you haven’t over preloaded the bearing, raise the front wheel off the ground, by lifting the front of the top tube, then gently rotate the handlebar through its normal range of movement from lock-to-lock. The bars should move freely with no sticking, binding or resistance on any kind. If the bar doesn’t rotate freely (as here where the steering is catching), then back off the preload tension until it moves freely without bearing play.
6. Straighten the bar and tighten the stem bolts
It only takes a seconds to make adjustments and check them, so you’ll zero in on the perfect adjustment in minutes. When you’re happy with the new headset bearing tension, align the stem and bar and do up the stem pinch bolts to the recommended torque.
7. Keep it greased
While it’s not strictly an adjustment, it just helps make adjustments easier if you periodically give the component parts of the threadless headset a light greasing, to ensure they snug down nicely and help keep water ingress at bay. The crown race bearing, the one which sits on the crown of the fork inside the lower end of the head tube is particularly prone to sitting in moisture and rusting or drying out. If you do grease your headset components, be sure not to get any on the steerer tube itself, as the stem needs to grip it tightly. Grease on the steerer will only mean you’re over tightening the stem bolts to gain suitable grip, potentially causing damage to the stem and the steerer tube.