We view our tech polls as a useful yet limited source of information. But even with a shovelful of salt and the knowledge that there's a ton of participation bias (you're more likely to respond to a poll about creaky CSUs if you've had a creaky CSU), we were surprised at the large number of people
who said they'd owned at least one fork that started creaking at the CSU. So we ran a follow up poll
which provided more context by asking how many forks PB users have owned in total, and from which brands.
It's worth bearing in mind that the Pinkbike audience in general doesn't necessarily represent the wider MTB market - if you're checking the homepage everyday you're probably more into mountain biking than the average rider. Also, as was pointed-out in the comments several times, it is possible that in many cases creaking headset, stem or axles have been misdiagnosed as creaking crown.
Digging into the data from both polls, my big-picture takeaway is that the number of reported creaking CSUs for each brand was very strongly correlated with their popularity among our audience. There weren't any especially notable outliers from the trend; no one brand has a wildly high number of creaking forks relative to the number of forks they sell, and no brand seems immune to creaking either. Nevertheless, it seems clear that a significant number of Pinkbike users have had creaking fork issues. So, to investigate further I reached out to representatives from the major suspension manufacturers and tuning companies. I asked them all the following set of questions:
• What causes forks to creak at the crown? Is it more often at the junction of the stanchions or the steerer, in your experience?
• Can you give us any idea of how common this problem is?
• What could be done to minimize the risk of creaking?
Sean Estes - Fox
Due to the nature of their design, single crown forks experience the highest loads at the CSU region (crown/steer tube/upper tubes assembly). This is especially true on modern enduro-style bikes with long-travel and slack head tube angles – both of which increase leverage and loads. CSU assemblies are press-fit, meaning the steer tube and the stanchion tubes are pressed into the crown. Over time, due to repeated forces generated while riding, under some circumstances creaking of the press-fit interfaces can begin to develop. The greater and more frequent the forces, the sooner creaking can develop. Dust and water migration from harsh climates and direct pressure washing have shown to accelerate this phenomena.
We realize this can be a frustrating issue for riders, and we want you to know that we share in that frustration. Taking care of riders is our top priority and we proudly stand behind our products – on the service side, we will gladly take care of anyone experiencing creaking crowns as quickly as we possibly can. On the product side, we’ve recently implemented some running changes to help address this and we’re close to introducing additional updates that we feel confident will provide an extremely robust long-term solution. We will have more to share on that soon.
Chris Mandell - RockShox
This is not something that we see occurring in our forks that often. But to be perfectly frank, it is something that can happen to any fork. We spend a considerable amount of time and resources in the product design process and our product assembly practices to eliminate the chance of this happening. If a rider should experience this issue they should take it to their RockShox retailer and we will work with them to correct it.
Steve Mathews - Vorsprung Suspension
Fork creaking is the result of micro slippage between parts of the press-fit interface surfaces (crown to steerer and crown to stanchions) due to the differences in surface displacement under bending loads - to visualise this, bend a paperback book and watch the pages slide over each other as it bends. It is not immediately clear why creaking does or does not happen on any given fork, nor can I give you good info on whether it's usually the steerer or the stanchions, but the fact that virtually all forks start silent and only some develop noise indicates that fretting wear
and/or plastic [permanent] deformation of the press fit surfaces are the likely culprits.
Some service centres around the world press out the steerers/stanchions from the crowns, apply retaining compounds and press them back together to quiet them down.
However due to the tight tolerances involved in thin wall aluminium press fits, we decline to do that, as we do not have sufficient data on the manufacturers' tolerances and surface finish requirements for the press fit interfaces, and given the visible wear on press-fit parts that have been taken apart, it is a risk we do not wish to assume. However, anecdotally this procedure seems to have had good results for some people, at least in the short term, though I don't have any meaningful information on whether that type of fix is consistent or durable - try it at your own risk.
I don't know how common CSU creaking is as a percentage of forks out there all told, but we do see it quite frequently on long travel singlecrown forks from all the major manufacturers (some forks more commonly than others), but then again we're located in an area where people manage to destroy every single bike part ever made. There's close to a metre of leverage between the crown and the contact patch of the tyre, and any load placed on the wheel exhibits a significant bending load that is borne by a relatively small interface on a SC fork. There isn't much that a rider can do to prevent their CSU creaking, it's not a maintenance problem - the problem comes from an inanimate structural part. What's the solution? I don't have a good answer for that - I've seen many proposed "obvious" solutions online, such as anodized crowns, tighter press fits, retaining compounds etc, but my opinion is that if it was as simple as any of those, we wouldn't be having to discuss this, because it clearly isn't an easy thing to get right since so far nobody has nailed it 100% of the time. The only surefire solution I have seen is longer stanchions and a second crown, which has its own obvious drawbacks!
Cornelius Kapfinger - Intend
The reason for creaking crowns is micro movement between the two parts crown/steerer or crown/stanchion. Both joints are heavily affected for creaking noises, just because of the dimension of the joint compared to the huge leverage of modern bikes.
If you sum up all length, fork length at full travel and 29" wheel radius, you have around 1 meter of lever with a huge force down at the tire if you brake hard and hit bumps and so on. This loads come together at a 0.04m diameter steerer tube with around 25mm height. It is obvious that the joint is too small for this load. Same for the stanchions, but at least you have 2 of them, but the problem still will occur.
But this problem can be solved to 100% using a little chemical help, which connects the two partners not only by a certain pressing force, but also with chemicals. The magic thing is Loctite. Loctite has the property to connect two metals by hardening without air in between. Although it can be that there is a little micro movement somewhere, the Loctite avoids ANY creaking noise there like a grease.
At picture one you can see how a normal aluminum crown without using Loctite looks like after 1 year of riding + 1 solid run on a test bench ( 100000 cycles normal load + 12000 cycles braking load). It looks like a battlefield. This one creaked afterwards.
Four years ago I started using Loctite for all Intend forks to strengthen both the steerer/crown joint as well as the stanchion/crown joint and since then there was not a single creaking case out of 300 forks.
Cornelius claims that good old Loctite solves the creaking and damage shown in the first image.
So for me and my Intend forks I solved this problem to 100% and my customers can be really sure not to have trouble here.
Franco Fratton - EXT
EXT's crown extends up the steerer tube, increasing overlap in a bid to minimize creaking.
Our experience is very limited on fork and CSU critical dimension and assembly technique, but we are trying to learn and improve our technique. Our understanding is quite simple: both steerer and stanchion get a press fit into the crown; this is the industry standard on a single crown fork.
We believe that both the steerer and stanchion can contribute to the creaking problem and we think it’s mainly the steerer that's the most suspected as it’s the most stressed area as it’s far away from the wheel axle.
Also the ratio between the steerer diameter and the press fit zone on the crown is very high and this induces a massive pressure gradient on the contact surface coupling. We also believe the problem stems from choices made to reduce weight and height. It is very difficult to maintain consistent coupling surface dimension and surface finish on the press fit area if dimensions are down to minimum wall thickness to maximize weight saving.
For this reason at EXT we have decided to introduce an innovative (patent pending) design that doubles the contact surface between the steerer and the crown in the “press fit” zone. In this way we achieve a much greater press quality and characteristic in the coupling area preventing possible creaking noise. We use very dedicated tools and press fit technique as well as dedicated glue/lube to facilitate the press fit, reducing friction and improving adhesion between the stressed surface on the CSU.
Phil Ott - Manitou
Creaking in a suspension fork can come from any number of interference fit parts, most of the time it is the joint between the steerer and crown, or crown and legs. We do not see (or is it hear?) many creaking CSUs from the field due to a proprietary manufacturing method we’ve developed over the years. Of the very few we do see the joint between the crown and legs is typically the culprit. Generally, the higher the press fit force the lower the risk of creaking. As the mountain bike world pursues lighter weight components the reduction in material of a press fit joint will create a trade off with the amount of force that can be applied to the press-fit joint.
The natural flex imparted by riding stresses these joints and imparts microscopic deformation of the leg and/or steerer tube. Creaking is caused by the friction between the two components of the press fit joint expanding and contracting at a microscopic level. All Manitou interference fit parts use a proprietary technique during the assembly process to virtually eliminate movement in a press fit joint.
Thomas Westfeldt - Öhlins
The CSU is a critical part of the fork both from a safety and performance perspective. The main challenge may look simple on paper; the bonding of three aluminum tubes into a crown made of the same material. When riding a lot of stress is being put on these parts and you want the stanchions to keep their alignment into the lowers for best possible performance - In this bond (stanchion to crown) we have not seen any issues even in our toughest tests.
If there is creaking sound from the fork, which is very uncommon in ours, it tends to originate from the other bond in the CSU, between the crown and the steer tube. We have put a lot of developed into our solutions to the steer/crown bond; our first fork the RXF34 did not even have a bond but a one-piece creek free design. Is was good for not creaking but complicated to manufacture / use with different headsets so we have progressed from that and developed a better design and manufacturing process. In the assembly process each step is controlled and recorded for every individual fork.
For customers that experience issues with noise from the front end of the bike it is important to check the stem, headset and axle are installed correctly. If there is still a creaking noise the rider should turn to a service center for a check.
Chris Porter - Mojo Rising
Seb, I've been an expert making forks creak but...I'm not the one that was able to make it stop!
The reason they creak is a kind of corrosion, the technical term is fretting corrosion which describes the constant tiny movements between the surfaces of the stanchion and the crown, generally one anodised and one non-anodised pressed part. Usually the two parts are pressed in with some kind of grease or assembly paste but that tends to simply move around in use and leaves sections of dry parts to create this fretting corrosion in time.
We've seen bushes binding so much they overcome the press fit when the fork twists! I can't be sure 'cos you can only see the before and after, not the during [but] we noticed shadows of the corrosion outlining the cutaway in the crown going round the stanchion in steps like corroded ghosts of former alignments, suggesting the stanchion had rotated in the crown.
Noah Sears - MRP
Crown creaking is an issue we legitimately rarely experience with our forks, but we’ve certainly dealt with it before. Our local terrain (and Moab, nearby) and environment do a great job of eliciting the types of forces that cause creaking to appear, which has been a benefit to our R&D. Locally we have a lot of square-edged hits, hucks-to-flat, and heavy-braking-required spots, coupled with pernicious moon dust that permeates every nook and cranny on your bike. Should any customer have creaking, once we establish the fork is the culprit (often it’s the headset), we take care of them 100%.
Along with just about every part interface in a fork assembly, the CSU interfaces provide opportunities for noise when you get parts moving relative to each other. The stanchion-crown and steerer-crown press-fit interfaces bear particularly high loads. By design we stiffen those interfaces with strategically located material via part shaping, maximize interface areas strategically, optimize interface interference magnitudes, utilize anodized bores in all areas, and include the use of bonding agents in the press-fit regions.
Noteworthy here is that the dual-crown configuration of the Bartlett fork substantially alters the dynamic of the interfaces at play, distributing loads across a broader configuration of contact points and surface areas, leveraging the stiffness of all parts of the system to increase overall system rigidity and allowing for the tailoring of localized loads. Riders who’ve experienced creaking frequently on other long-travel forks may want to give it a gander.
What have we learned?
Why do forks crowns still creak after nearly three decades of development? It could be that more people are riding harder than ever on single crowns. The growing popularity of long-travel 29" forks doesn't help either, because these longer forks put more leverage and stress on the crown. All this means that building forks that never creak is no easy task, and possibly harder than ever.
Perhaps unsurprisingly, no brand was willing to tell us the exact percentage of forks that come back with creaking crowns, but reading between the lines they give the impression that the warranty rate is far lower than the polls suggest. That's not surprising given the inevitable biases associated with opt-in polls discussed above.
One of the most interesting comments in my view was the assertion from Fox that fine dirt and water ingress from pressure-washing can accelerate corrosion and increase the chances of creaking. Perhaps this helps explain why some riders report many creaking crowns and others none - the dirt where you ride and how you wash the bike could have an impact on longevity. It's also very interesting to hear that they acknowledge the problem and are working on a solution.
So are dual crown downcountry forks the only way to stop creaking in the future? We hope not...