One of the unsung heroes of the modern mountain bike is the headset. As long as it is working properly, a rider rarely even thinks about the headset; however, this is a bearing that endures the forces from impacts and steering every time the bike hits the trail. It needs some periodic maintenance. Fortunately, the maintenance is really pretty simple, so long as you understand the concepts at work. This is the MBA way to perform a quick headset adjustment to ensure your steering is bang-on.
The Modern Headset
There are several variations of the headset, but this is by far the most common configuration. It includes two machined cups that are pressed into the frame’s head tube to house the bearings with races to mate the surfaces and allow the bearings to rotate as you steer.
1. Crown race: This part is pressed onto the steerer tube and sits right on top of the fork crown. It mates the fork to the lower bearing
2. Lower bearing: Rotates to allow steering.
3. Lower headset cup: Houses bearing under head tube outside of frame.
4. Upper headset cup: Houses bearing on top of head tube inside head tube.
5. Upper bearing: Rotates to allow steering.
6. Compression ring: Holds steerer tube in place and gives preload to bearings.
7. Top bearing cover: Keeps dirt and contaminants away from bearings.
8. Star-fangled nut: Hammered into the steerer tube, this gives the bolt threads to allow bearing adjustment.
9. Top cap and bolt: Installed on top of stem and allows for bearing adjustments.
1-Headsets come loose from time to time. It’s part of the reality of riding and an adjustment that every rider should be able to diagnose and fix. Here’s the quick way to see if your steering bearings are loose.
2-With the bike on the ground, apply the front brake.
3-Place your thumb and index finger on the headset as shown.
4-Now, with the front brake still applied, rock the bike fore and aft. If your headset is properly adjusted, you won’t feel any knocking or movement in the bearings. If you feel movement, your headset is loose.
5-For a loose headset, start by using an Allen wrench to loosen the stem clamp bolts.
6-Most stems use two opposing bolts. Don’t remove them; just loosen them.
7-Now, snug the bolt on the top cap. This will preload the bearings and remove the play. This bolt doesn’t need to be super tight, just tight enough to remove the play.
8-Every time you adjust the headset, you should take the time to realign the stem. We like this technique; turn the front wheel to an angle, and then use the centerline of the stem to align it with the centerline of the front tire.
9-Once the stem is aligned, snug one of the bolts to hold it in place.
10-Then, carefully torque the stem clamp bolts. These should be tightened in a 1-2-1 pattern to ensure both bolts are torqued equally. If you’re using a super-lightweight stem, you should be using a torque wrench. Most stem bolts require a torque value of about 4–6 Newton meters.
11-If this adjustment doesn’t remove the play in the headset, you may need to add a spacer. The torque on the top cap bolt is designed to pull the steerer tube up as it preloads the bearings. If the steerer tube bottoms out on the top cap, it won’t properly preload the bearings.
12-If your bike already has spacers installed, you can also use this as a way to adjust the height of your handlebars.
13-The spacers on the steerer tube can be run in nearly any combination, so long as you have enough of them. Spacers can be moved to the top of the stem to lower the bar height and vice versa.
14-If you choose to remove spacers to lower your bar height, you will be left with an exposed steerer tube like this.
15-Be sure to install enough spacers to cover the exposed steerer tube. Ideally, the steerer tube should have roughly 3–5 millimeters of space below the top of the stem or spacer stack. This is the space that’s used to preload the bearings.
16-Once you’re satisfied with the adjustment, repeat steps 8 through 13 to readjust the headset.
17-Steerer tube length is critical for safety on any mountain bike. The steerer tube should always be long enough to overlap the stem clamp nearly to the top. Our rule of thumb here is if the steerer is too short to overlap the upper bolt of the stem comfortably, the steerer tube is too short. Sadly, there is no way to only replace the steerer tube on a fork. It’s a super-precise fit to the crown. Should you run into a steerer that’s too short, the best option is to replace the fork.
If you ever have to step away from the job for a second, you can simply spin the top cap in to prevent the entire fork from falling out and hitting the garage floor. Trust us, this is an embarrassing and frustrating mistake and an easy one to avoid.
Once everything is adjusted and set, you’re ready to hit the trails. Although, it’s never a bad idea to double-check your handiwork. Loose stem bolts cause the nastiest crashes. Take the time to ensure everything is torqued properly before jumping on the bike and heading out to the trail.
THERE ARE SO MANY WAYS TO GET MOUNTAIN BIKE ACTION
Mountain Bike Action is a monthly magazine devoted to all things mountain biking (yes, that’s 12 times a year because we never take a month off of mountain biking). It has been around since 1986 and we’re still having fun. Start a subscription by clicking here or calling (800) 767-0345.