The thought of sawing into your newly bought carbon fork can seem like a scary prospect but with some straight forward tips you’ll be well equipped to make the cut.
Measuring and cutting your fork steerer tube has two parts, dry assembling of the headset, and deciding where to cut, we're here to demystify headset parts, measuring (twice) and cutting carbon. Fitting the expanding plug and adjusting the headset is covered HERE
First of all, the headsets we provide with all of our aluminium frames are integrated headsets, this means the bearings sit directly in the frame rather than a pressed in cup, the bearings themselves are held in place by their chamfered outer edges mating with the machined chamfers in the frame's headtube and being held under compression. Fitting an integrated headset doesn't require any special tools.
The first time you assemble the headset it's best not to use any grease or anti seize and dry fit the components. This dry-run is just to find where you need to cut the fork and is a much cleaner job if everything isn’t covered in grease.
Depending on the year and model of your frame, the fork will have either an integrated carbon crown race or will require the use of the supplied split crown race. If the fork crown is flat you'll need to slide on a split ring crown race.
The larger lower bearing slides onto the steerer tube with the external chamfered edge facing upward.
Place the smaller upper bearing into the frame with the external chamfered edge facing downwards to match the chamfer in the frame. Now slide the fork's steerer tube through the frame and top bearing.
Slide the compression ring, washer and dust cover onto the steerer tube one at a time and push down until flush with the top of the frame.
Determining how many headset spacers you need can be done in a number of ways: from bike fit data, replicating an existing bike or from a trial and error method after a few test rides. The important thing to remember is that you can always remove spacers later on, but you cannot add more once you have cut the steerer tube down.
We recommend no more than 40mm of spacers underneath the stem and to add one 5mm spacer above the stem to allow it to clamp properly and prevent damaging clamp forces. Once you have decided on how many spacers you want underneath the stem, add them to the steerer tube, push the fork upward with one hand and slide the stem down onto the steerer tube with the other.
Gently tighten the stem bolts to stop the fork dropping out and mark the steerer tube with permanent marker at the top edge of the stem. Stand back and make sure this setup looks sensible, is the fork inside the frame properly? Are your preferred number of spacers below the stem?
remove the stem, spacers, dust cover, washer and compression ring, then drop the fork out of the frame.
To double check your cut line, find your headtube length on your frame's geometry table, add 9mm for the headset dust cover, add the height of spacers you're using under the stem and add the stack height of the stem. For example:
A 56cm Palace R with 20mm of spacers and a Fizik R1 stem has:
160mm headtube + 9mm for headset dust cover + 20mm spacers + 40mm stem stack height = cut line 229mm away from the crown
Clamp the fork using a pipe cutting guide or V blocks (an old stem clamped in a vice will also work) and using a carbon fibre cutting blade cut the steerer square along the line you marked earlier. Park tools carbon cutting blade: https://www.parktool.com/product/carbon-saw-blade-csb-1
When cutting carbon we recommend wearing a particulate mask as carbon dust can be harmful to your health, use a vacuum cleaner to catch any dust, do not sweep it up. (yes, the stuff is that nasty)
The fork should now be the correct length for your frame, repeat steps 1 to 4 making sure to grease the chamfered edges of the frame, the bearings and the compression ring. For info on fitting the expanding plug and tensioning your headset CLICK HERE.