In the PB comments section there have been rumblings recently of forks creaking at the crown-steerer unit (CSU).
The CSU is made up of the steerer tube, crown and stanchion tubes in a single-crown fork. These components are all machined separately before being pressed together
in the production process. But sometimes, this happy union can go the way of Brad Pitt and Angelina Jolie when either the stanchion tubes work loose inside the crown, or the crown starts to wobble free of the steerer tube, resulting in creaking and a phone call to the warranty department.
This is not so surprising when you think about it. Now that 29" forks with up to 180mm travel are common, the axle to crown measurement can be very long - around 595mm. The forces that act on the crown when braking come from the contact patch, which in such a fork is around 90cm from the crown, so the forces act over a very long lever, and these aren't small forces. If you pull the front brake hard on tarmac, you could generate close to 1g of deceleration. That means the rearward force at the contact patch could be equal to the weight of the bike and rider.
Because the crown is furthest away from the contact patch, it experiences the most torque of any part of the fork. Yet the distance over which the stanchions connect to the crown is only around four centimeters, while the connection between the crown and the steerer is even shorter. In contrast, with a dual-crown fork the torque is transmitted from the stanchions to the headset over the distance between the crowns.
As you ride through rough sections of trail, the crown is subjected to stress in different directions very frequently. Landing to flat (as in the industry-standard Huck To Flat Test), causes the fork to flex forwards; braking or riding into large bumps causes it to flex rearward. It's easy to think how years of this repeated stress could lead to failure. When watching the Huck to Flat Test in all it's gratititous slow motion, it doesn't take much imagination to see how ever-slackening head angles can increase the load put through our CSUs.
Despite this, I've never experienced a creaking crown, and most Pinkbike staff members either never have, or haven't for a while. But the trouble with testing bikes for a living is that we rarely get to put as much ride time on one bike as a consumer would.
So it's over to you. Let us know if this is a problem you've faced. We're keen to gauge how common this is.