How do we feel about trunnion and clevis mounted shocks?

I've got a yoke mounted shock on my Stumpjumper Evo, looking on the forums, getting through shocks does seem to be problem. So far so good for me. My plan is to service it regularly, keep on top of the frame bearings, and when/if it does go, I'll replace with a spherical mounted shock of some sort.

I've heard about trunnion shocks having the same problems. I think it depends on how hard you're going to ride it. If you're going to cane it, then I'd go with the conventional shock.

My emtb has a yoke thing and it’s done over 4000 miles so far on the same shock without any issues I think they’ve made shocks stronger to cope with this.

Specialised are a bit different as they tend to have a higher leverage ratio and longer yoke than most.

It's a double whammy with the permanent yokes and suchlike because you've also not got the free choice of shocks. I just won't buy one- never ridden a bike that seemed to really enough by it if anything compared to similar conventional ones (in fact a bunch of bikes with really specific shock mounts seem to actively lose out from their eccentric designs), and the downsides are obvious.

Sure, some bikes do it well and it's not a problem but enough bikes do have problems with it and you generally only find out a couple of years down the line... Some like Ibis frinstance don't even really seem to understand that it's wrong- it's like "oh yeah our bikes can eat shocks and the shock we sold to you with the frame doesn't work well with it, anyway, the solution is to replace it with a coil shock that you didn't want, at your expense"... But it doesn't even have to go wrong, it can work fine and just be bad, like some specialized shock/yoke combos. "Here is the new Specialized, it has a Fox Triad and you can't change it with anything else... wait... come back! It's 3% stiffer!" Being able to change shocks is massive, it can transform a frame.

The thing about packaging is, sure, it might let you build the frame exactly how you want it. But really, is that worth it? What frames out there can you honestly say are so much better? You have these really tightly packaged, clever designs sometimes and from an engineering point of view you can admire it but equally you can have bikes that are so much simpler, have space for whatever shock you like with standard mounts and even a bottle and do they ride badly? Generally, I don't see any meaningful correlation between the two and a bunch of companies seem to spend more time on suspension ****ery than they do on geometry. The approach seems to be "this is a great suspension design that only works with a funky shock" but that mostly sounds like a bad suspension design. So many of those packaging decisions don't even seem to be especially functional- oh you need a daft shock so you can have a tiny front triangle and a massive seatmast? Have you considered just not doing that? (see also: shocks that end up in really stupid places)

It's sometimes not a solution, it's the admission of failure. I'm doing a simple, boring engine swap in a car, you see people making all these compromises and bodges or living with total impracticality or spending 5 years in the garage and sying "look what it took to make this work at all" when the smart thing to do was probably to use an engine that fitted. For something sufficiently mad, yeah that's cool, I'm impressed with your tank engine or whatever but when it's your track car or your daily driver, it's usually just doing it wrong, but doing it wrong really well and being smug about how hard it was and revelling in the annoying compromises.

And the suspension design you choose is still as much about brand identity and marketing and IP as it always was. Oh yeah all our bikes use this design. What are the odds that the same suspension design works great for your XC race bike and your park bike? But we own the design of this 7-link dual-shock contra-rotating low pivot design and we named it after our dog so we're using it even though it needs a banana shaped shock that sits in front of the stem.

OTOH... after all that rant my longest lived full suss is a trek remedy 29, just retired it at 9 years old- it has a frame-specific, pre-trunnion trunnion shock and it was fantastic- they built the frame and shock to work together so there's no sideloading effects, and they did it so they could put a clever shock in it that works with the frame. I've had some of the best shocks in the world but never had a trailbike shock/frame setup that worked better, Dirt Mag said the same. So it <can> work but I suspect you've pretty much got to be Trek, and able to phone up Fox and say "make us a specific chassis exactly like this" and phone up Penske and say "make us magic internals" and get your 5000 inhouse engineers to design for that exact shock so you can build it in your own factories to those exact specs and then get Tracy Moseley and Justin Leov to test the crap out of it and overall just aim your ridiciulous resources at the project. Most manufacturers just can't do that and I think most that could, don't. It doesn't fit the model either, they sold that frame essentially unchanged for at least 5 years in this world of churn and novelty. (and for about a grand more than its closest competitors at RRP...)

Basically, tldr, put a proper shock in it unless it's really, really going to be worth it, and it's almost certainly not.

How much would the trunnion feature in your decision making?

It wouldn't.

2 trunnion shocks in the house. Zero issues.

Oh yeah, unless I missed it I was surprised that he didn't mention shock length- he talks about packaging, overlap, getting more bits into the shocks but for me just having more shock for the same amount of travel is a good thing, it's obviously just easier to get good control if the shock moves more. Used to be pretty much standard to have 50 or 57mm shocks for 160mm of travel.

We run Trunion on the Fury, works fine.

My Trek ex9.8 had one too, it worked fine.

No issues here

Packaging is a big issue when everyone wants space in the frame for a bottle mount and/or storage locker.

Packaging is a big issue when everyone wants space in the frame for a bottle mount and/or storage locker

Both of which are excellent things IMO.

But as he points out in the video, a lot of companies are using trunnion mounts, but not making any use of the extra space afforded above the shock.

It can't hurt to fit donething like either a spherical bearing on the eyelet end if you've got enough material to open it out to 16mm, or one of the DHSign Shockfix units instead.

Running a trunnion shock on a very long, slack, long travel steel frame (as I had the shock already so designed round it) with a spherical bearing on the eyelet, zero problems at all.

Onzadog
Free Member

But as he points out in the video, a lot of companies are using trunnion mounts, but not making any use of the extra space afforded above the shock.

True, but that's not the only benefit, trunion effectively creates more space around "below" the shock mount for the shock. Just because there's space above it doens't mean it was usefully usable with all the other constraints of pivot and lever and such.

Had one once on a specialised, will never again. Eventually the shock blew up and needed replaced and there were no aftermarket options available.

Onzadog
Free Member
But as he points out in the video, a lot of companies are using trunnion mounts, but not making any use of the extra space afforded above the shock.

Quite a few using the space to fit a motor under the shock

I would prefer standard as there are lots of options for cheap replacement shocks, spare parts are normally good, and generally more reliable.

I would avoid yoke, seen way to many issues on customers shocks with destroyed shafts and damper bodies. Also if they are the stupid end bolt damper bodies they can be difficult to get hold off. Long term proprietary parts are dropped relatively quickly.

Trunnion is generally ok as long as the frame alignment is ok, and frame bearings are maintained. If something is out it will chew the shock up in short order.

I would chose frames that have enough lateral stiffness through the linkage design the shock should not be side loaded.

Both trunnion and clevis mounts are the work of the devil. Trunnion would be fine but the amount of misalignment in some frames is shocking. Clevis has improved with the greater bushing overlap on metric shocks but that isn't afforded to all shocks, some brands ignored the advantage and just made the eyelets longer.

I personally would not own a bike with either of them.

VS will have a trunnion shock option when the shock hits the market. In videos they have been using prototypes with bridges that can fit both standard and trunnion mount frames. To not realise a trunnion mount shock would remove a vast portion of the market.

My Sentinel’s X2 died a couple of times, but suspect that’s because it’s an X2 rather than because it uses a trunnion mount. Alignment is evidently good when removing/fitting shock. Expect the Ohlins coil replacement will be far more reliable.

Fox currently have some big upgrades/changes for the 2021+ X2, especially for the trunnion version.

Can someone explain why mountain bikes have gone down the route of bearings and metal bushings in the shock mounts? Most other applications use rubber bushings to allow for that flex/missalignment.

I'd assumed that it would feel worse (c.f. track cars being rose jointed rather than bushings) but then RS came out with "buttercups" which ammounts to the same thing. How long before we swap solid bushings for polyurethane?

Can someone explain why mountain bikes have gone down the route of bearings and metal bushings in the shock mounts?

Lower friction in theory, weight is a lot lower on mtb compared to a car.

Would rose joints be the best?  allow for misalignment but solid

The most insightful part of the video is where he say's something like "if shock manufacturers designed bikes"

The fundamental issue seems to be more that frame manufacturers can blame the shock manufacturers for poor design that leads to shock failure and that trunnions and yokes exasperate this.

I think the shock manufacturers have to take some responsibility here.

It seems to me that trunion shocks are built exactly the same as traditional shocks, even though they’re obviously going to have higher lateral forces going through them.

It’s the same issue with coil shocks on yoke mounted bikes. It’s only when they started to go wrong that the manufacturers started to review things and change the design and recommendations for their shocks.

Thank god Northwind's latter comments weren't as long as the first, Jeezus! 😀, I'll have to read it when I've got more time, personally I just don't like the look of trunnion or even saying the word and I hate the look and idea of yokes even more, perfectly aligned bikes are few and far between, bearing mount one end and some kind of self alignment mount on the other is the way to go.

This lokks like one of those no brainer upgrades next time you need a new DU bush on a trunnion, clevis or any other shock:

https://dhsign.it/en/14-fixshox

Would rose joints be the best?  allow for misalignment but solid

If a trunnion frame is not aligned well then a rose joint won't help things because the frame will still be trying to bend the shock to the side as it goes through the travel.

It seems to me that trunion shocks are built exactly the same as traditional shocks, even though they’re obviously going to have higher lateral forces going through them.

A shock manufacturer will struggle to build a shock that can work with the forces of a poorly aligned frame. If a trunnion frame is out of alignment at full extension it will only get worse as the shock compresses. Also they cannot take into account riders riding frames with knackered bearings.

He doesn’t really explain with the clevis mounts, why turning the shock mount 90deg is a bad thing. As a moron, it looks to me like that would allow more sideways movement, rather than less…? Or is just the clevis/trunnion combo that upsets him?

it looks to me like that would allow more sideways movement, rather than less…?

There's no bush in there for it to pivot around. Just a spacer that clamps the end of the shock eyelet.

It does allow more movement. The concern is that the movement then becomes the bending point allowing the shock to move further away from the neutral centre line of the bike and therefore experience greater side loading.

It does allow more movement.

So why is there no bush in the shock eyelet? *
If there was movement in that joint it'd wear the eyelet out pretty quick.

*there was no bush in any of the clevis mounted shock bikes I've ever had.

It allows more movement that clamping around the shaft, but it's not supposed to. If everything stays perfectly on that centerline it's not a problem. If there is the slightest deviation from that centreline then more it deviates, the more it wants to push off that line.

From my experiences there's no movement in the clevis/shock joint.
Rather it transfers the movement in to the shaft and that's what causes the damage.
Hence there being no wear on the eyelet but damage to the shaft it's self.

It's not free movement that's being considered here as it's not a bushing. It only takes the slightest bit of flex/movement to then increase the side loading through the shock.

Trunnions in vertical shock frames - yes it gets you a bigger shock in a smaller space, but that’s only really of benefit to the smallest frame size available.
we’ve had size specific chain stays, maybe we need size specific shocks.
if the small had a 190x50 and the large a 210x50. Or a trunnion on the small frame and regular fit ent on the larger.

I have had a bike with a clevis mount which didn’t have any issues, but it seemed to be a solution to a problem which doesn’t exist really.

Trunnion I don’t have an issue with, the concept of it is fine - the problem is bike companies who cheap out & can’t make a straight frame, out of whatever material (yes Transition, looking at you).

If it’s straight, it’s fine & almost immediately obvious as it should never be a fight to get a shock in.