Ask Pinkbike: Tight Shock Bushings, Top-End or Tuned Shock, Spring Rate vs Force
Here at Pinkbike, we get inundated with all kinds of questions, ranging from the basic "Can I have stickers?" to more in-depth, soul-searching types of queries like if you should pop the question or what to name your first child. Ask Pinkbike is an occasional column where we'll be hand-picking and answering questions that have been keeping readers up at night, although we'll likely steer clear of those last two and keep it more tech-oriented.
Tight shock bushings?
Question: Sam asks (in real life): I have a 2015 Mondraker Foxy with a Fox DPS shock. Recently the shock was serviced and it came back with new shock bushings. Unfortunately, I noticed the sensitivity of the rear suspension wasn't great. When I took things apart to investigate, the frame bearings are running smoothly and the shock slides easily with the air removed, but the new bushings seem really tight. If I clamp one eyelet in the frame or vice, the force needed to rotate the shock on the bushing is really high. Is this normal? Is there anything that can be done?
 | The Foxy's suspension design means the shock eyelets have to rotate a lot on the two short links at either end. That means any friction in the bushings will have an outsized effect on the suspension sensitivity. By removing the shock and feeling how tight the bushings are to rotate, I've noticed that different shocks and different bushings have very different amounts of friction. The bushing is a plane bearing that relies on a precise fit to work properly, so small manufacturing tolerances could create a noticeable difference. One option would just be to wait it out. Riding will gradually wear down the bushing and this should reduce friction eventually. Just make sure the eyelet bolts are done up tight so the sliding surface is between the metal pin and the plastic bushing, and not between the pin and the frame. My local suspension workshop told me they could ream the plastic part so it's ever so slightly looser-fitting. If that's not an option, you could try sanding down the pin with fine wet and dry paper to reduce its diameter slightly. I did this successfully once by putting the pin in the chuck of a drill and gently sanding as it spun to keep it even. Be warned though: I did this as an experiment on a particularly tight bushing, it will likely reduce the lifespan of the bushing and pin. If you do go down this route, make sure to remove material little by little, regularly checking the tightness in the plastic bushing. It needs to be a snug fit and should take some force to install; otherwise, it will soon develop play. |
The bushing, which these days are usually plastic as on the right, will eventually wear down and loosen up.
Spring rate vs spring force
Question: @dreamlink87 asks in a previous Ask Pinkbike comments section: Preload doesn’t change spring rate [of a coil spring], right? It just changes where in the spring your starting point is. Which I guess changes your starting spring rate, but not the actual spring rate?
| You're partly right. The spring rate, also known as the spring stiffness, is the amount of additional force required to compress the spring an additional incremental distance. So, the number of pounds-force for every additional inch of travel, or in the correct metric system, Newtons per additional millimetre. In a graph of force against travel (like the one opposite), the spring force is the height of the line; the spring rate is the gradient of the line. |
This graph represents the force (vertical axis) against travel for a 100 lb/in spring (blue line); a 100 lb/in spring with 100 lb of preload (red), and a stiffer 150 lb/in spring (orange). The red and orange curves provide the same force at 2" travel (so the same sag) but the springs they represent would feel very different to ride.
Just because you can preload a coil spring, doesn't mean you should.
| The spring rate is a function of the spring itself, so as you say, you can't change that by preloading it. Preloading the spring creates a force offset so if you had a 100 lb/in spring and you preloaded it by one inch (which would be crazy), it would require 100 lb of force to get it to move at all. So long as there's more than 100 lb of force on the spring, the spring rate/stiffness/gradient would be the same, but the fork would ride one inch higher in the travel for a given force. But when there's less than 100 lb of force acting on the spring, its stiffness is essentially infinite because (within that limit) the fork won't move at all with increasing load. This isn't such a problem for road-going vehicles where the wheels are usually loaded more than the amount required to overcome the preload. In that case, preload can be a useful way of adjusting ride height without affecting the stiffness of the suspension. But on a mountain bike, the suspension is coming in and out of the first part of the travel regularly. In this case, the infinite spring rate is less than ideal because the preload force has to be overcome before the suspension can start to move at all. This causes the suspension to feel harsh, top-out and provide less traction. On a mountain bike, "preload adjusters" are really about allowing for different spring lengths without play. If you want your fork to ride higher but don't want a stiffer spring rate, try bumping up the travel or just raising the bar height. If you want the bike to sit higher at the rear, you could try fitting offset bushings to effectively lengthen your shock, or use the flip-chip if you have one. |
High-End Shock or Custom-Tune?
Question: Craig asks on Instagram: I'm thinking of getting coil shock for my enduro bike. Do I get one with all the adjustments like a Fox DHX2 or should I get a cheaper shock and get it custom-tuned for my bike, weight and riding style?
| Keeping in the Fox/Marzocchi catalogue for the sake of comparison, you could get a Marzocchi Bomber CR for $330 / £349, a Fox DHX for $549 / £629 or a DHX2 for $649 / £719. In all three cases, springs are sold separately. These cost £47 for a standard steel spring and $130 / £155 for the lighter SLS spring, which saves around 300g. The first thing to note is that the Bomber doesn't have a climb switch. That may bother some, but plenty of people never use their lockout anyway. The DHX also gets detents on the preload collar and numbered dials, which the Bomber lacks, but these are nice-to-haves rather than essentials. The valving and bottom-out bumper are arguably more refined on the DHX too, but I can't say if this is a tangible benefit. That aside, the Bomber and DHX both offer low-speed compression and rebound damping. I haven't ridden the DHX, but the Bomber is pretty much the same as the old Fox Vanilla RC, which was very impressive when fitted to the Saracen Ariel 80. Pinkbike's Mike Kazimer and Matt Wragg have both ridden the Bomber CR and came away impressed. "For 90% of folk it’ll be good without tuning," Wragg tells me. "When I took it to a DH track I could find situations where I wanted more HSC to handle the hits [this is on a YT Decoy ebike], but around the house, it just works. Very impressive wee bit of kit." Meanwhile, the DHX2 adds high-speed compression and rebound adjustment, using Fox's clever VVC high-speed rebound system for more proportionate high-speed rebound adjustment. Does that matter? It depends on how much time you're willing to spend setting it up. Suspension tuning is all about tradeoffs, so more adjustment doesn't automatically mean more performance, it just means there's more scope to fine-tune if you're willing to go down the rabbit hole. But in my view, it can take a lot of work to get a four-way adjustable shock in the right ballpark if there isn't a good starting point from the frame manufacturer, let alone making it work better for your needs than a two-way adjustable shock could. I often get asked to help set up friends' bikes and those with four-way adjustable shocks are most often overdamped or imbalanced relative to the fork. That said, most shocks fitted to bikes from the factory are chosen and tuned to provide an appropriate range of adjustment for the bike, so buying one off the shelf is a bit more of a gamble especially if there's less adjustability to work with. This is particularly true if your bike has an unusual leverage ratio, so check with the frame manufacturer or a good suspension tuner first. As you say in the question, that's where custom tuning can come in. The change from buying a Bomber instead of a DHX2 will pay for a custom tune (if you need it) plus a spare SLS spring or two. That means the two low-speed adjusters should be all you need for fine-tuning the damping and the spare springs will encourage you to focus on the most important parameter: the spring rate. |
A relatively basic shock is probably fine for most people. So long as the tune is in the right ballpark, putting in the work to find the ideal spring rate and (low-speed) damping settings is 90% of the battle.
151 Comments
Makes sense due to tolerance/fit with shock eyelets.
I dont know why this posted twice? I was replying to two comments at the same time, so maybe I made it bug out?
I'm assuming the pin/bolt isn't wearing, so will try to source the tighter ones. Think that might help?
Funny however that the low end shock and the high end shock both end up making Fox more money!!
This is the way
Look at RWC needle bearings. They are very pricey, but make a big difference on suspension designs which require lots of shock eyelet bushing rotation.
www.enduroforkseals.com/products/rear-suspension/shock-eyelet-bearing-kits/6mm-8mm-thru-bolts/NEEDLE-BEARING-22.20.html
Maybe I just got lucky with a combination of good QC on mine and frames that are gentle on eyelet bushings.
Just goes to show you, don't trust random strangers on the internet. Unless they have candy...
www.pinkbike.com/news/fox-announces-new-fit-fork-dampers-and-a-roller-bearing-kit-for-shocks.html
Have used RWC needle bearings with great results on several shocks and frames. If a frame has a design that benefits from one it is a good way to go in my experience.
The other path would be something like the TFTuned that might be built to a higher standard than what the OP may be using.
Unfortunately, I have the same experience with RWC - they felt good, but were short lived. Same with the RS and fox outboard eyelet bearings. Not worth the cost, relative to just replacing igus bushings more often, cheap and effective.
I ran the bearings for at least a year, only had to clean the bearings (twice?), and the bike was so smooth when I sold it. Only issue was the breakaway force was so low I felt the rebound damping needed a retune.
Spherical bearings would be a better solution.
If you use a good bushing like fox or huber, you absolutely feel no difference in friction versus a bearing.
And of course, if a system worked perfectly once, and then a part was changed and the system no longer works perfectly, it is the new part that is the source of the problem 99% of them time whether it be mechanics, computers, or even teams of people.
www.sram.com/globalassets/document-hierarchy/tuning-manuals/rockshox-rear-shock-piston-tuning-guide.pdf
You can also buy the additional shims required to take the medium tune to any of the tunes listed .
Tuned is always the way to go and the way that shock is built, is sufficient for Craig to do his work on it the way he likes, and this the performance is absolute top notch
It’s been years since I opened up and played with shim stacks. I appreciate the link, and it’s saved for future reference on my new Spire!
You'll then have quite possibly the single best coil shock available, at a great price.
I found a new second hand CR here on PB for my Scott Ransom... it's magical
I feel (and have seen using telemetry) that most people have their spring rate wrong, meaning they set their spring curve wrong and that has an impact on the damper settings. I'd say around 90% of bikes I've helped set up with telemetry their rear is under sprung and rebound is way to slow because of this. If it's this hard to get the spring rate balance correct imagine throwing in a 4 way adjustable damper on top?!
I also feel if bike/suspension companies are going to supply this much adjustment they should do more testing and development with their shock set up in particular instead of giving the end user a huge amount of tuning potential and very little in the way of information for even a starting point.
Just a few of my thoughts.
Having this fixed he said gives the end user a simpler damper to setup that will still offer great results.
Keep the mystery alive PB
Be safe be well,
Incognito Robin
Honestly, I believe Vanilla R/Bomber are the best after custom tuning for the particular frame and rider
DO NOT DO THIS!
I don't mean to be a dick, but I am genuinely stunned that PB are dishing out advice like this. This is terrible advice for a number of reasons.
The advice re: basic/high end shocks is also wide of the mark. PB is normally really good. But I honestly think you should just take this article down. It is not good
Those might be cheaper with a good enough damper out of the box compared to a tuned Bomber.
The shock came stock with a firm rebound tune, tired a medium, and now I'm onto a light tune. Really affordable and have proven great results so far.
www.mtbr.com/threads/tight-bushings-harshness.1129699/page-23
I once bought a mid level Fox shock for my old Tallboy and had it tuned by PUSH before I installed it. It worked just as requested- good work by PUSH.
Then I saw a Cane Creek DB Inline Air for half price, bolted that on and never looked back. The difference was indescribable, and the tuning options of the CC meant I could set up that bike for anything.
I spent $800 on an Ohlins shock for my new Tallboy because I will never go back to a single tube shock again. That’s the difference.
So far on a Tallboy V4 absolutely zero coils don’t fit in the tunnel. They all do. But some are too close for comfort like Rockshock and EXT. Ohlins, Marz Bomber CR, DHX2, Any Cane Creek, Fast, all fit with no rub issues
What type of bearing is it actually? A spherical plain bearing - ball that rotates in a race? Or a plain bearing/ journal / bushing. - straight bore that you can put a pin through?
Is it totally plastic or metal backed with a self lubricating liner (th?
If it's plastic, i think the author has sound advice. Make it fit.
If it is a self lubricating liner there could be two things causing the tightness. Poor quality or swelling.
Swelling
Many of these bearings are shipped in oil simply because the race or ball is Iow carbon steel and the oil prevents corrosion. However, the oil can actually swell the liner and create quite a bit or torque increase.
Wipe the oil off. Orient the ball 90 degrees and flush with solvent. Allow to dry (it should equilibrium in about 72 hours)
And the torque should come down significantly.
Poor quality.
I'm sure whatever is specified into the bike will suit the need fine. However, manufacturers are looking to find the best price point. Quality and consistency are often sacrificed. Replace it with another bearing. The torque may be just fine. Or you can find aerospace grande parts that will be a huge overkill, but I guarantee the torque will be good( expect to pay 10x to 20x for a part as well).
Hope this helps. If you have the specific bearing I would be more than willing to more about it.
Fail
www.pinkbike.com/contest/advent
Maybe they are doing a little bit more due diligence to weed out bots this year and it is taking longer to confirm legitimate winners.