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Are Upside-Down forks really flexy?

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1/7/2021 9:53 AM

I was told by someone who raced MX in the 90s that the main advantage of the USD forks were that the RSU forks were too long- to get 300mm of travel the lowers extended far below the front axle- think 2005 Manitou travis, but worse:
Photo


This would make your fork a trench digger when you leaned over in the ruts. USD forks, since they telescope into the uppers, don't have this issue. I was persuaded that this was the main reason why MX switched to inverted.

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1/7/2021 10:12 AM
Edited Date/Time: 1/7/2021 10:12 AM

Ooooooh, of course, good point. With USDs the stanchions can go past the lower crown, I think I mentioned this in the first post, but connected to bushing spacing.

And with MX forks this issue is present even with 200 mm travel due to the smaller wheel.

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1/7/2021 11:54 AM

FWIW, having ridden a Shiver for about a decade, I would make the following statements:

you could notice the torsional flex in the parking lot, but it never felt like a disadvantage on the trail. if anything, the bike felt like it stayed on-line better, rather than hitting a rock with the front wheel causing the whole bike to jar and change direction. obviously a lot else going on there, bikes were much heavier too, which is going to have an effect as well.

maintenance was easier. faaar easier. even taking into account how much more complex dampers and springs are today, just the process of doing a basic service on a USD is easier due to how things are mounted in the legs, and how much easier it is to seal things with an inverted design.

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1/7/2021 12:54 PM

Why is it easier to do service and sealing? It's more or less the same... Or am I missing something?

Dammit, all these comments regarding staying on the line and the like are really intriguing smile

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1/7/2021 5:25 PM

Primoz wrote:

Why is it easier to do service and sealing? It's more or less the same... Or am I missing something?

Dammit, all these comments regarding staying on the line and the like are really intriguing smile

It's been probably fifteen years since I last serviced my Dorado, but I recall it being very easy, drop in place kind of stuff. Just choose your oil weights and tune. The shim stacks were delightfully exposed and easy to play with.

I'm guilty of not reading the entire contents... But did Manitou's Hex axle design play in at all? It seems the right solution to moderate the torsional rigidity.

And Primoz... Try a double crown USD fork, ASAP. That bit of torsional flex allows the front end to flow better through ruts and roots than a RSU fork. So while the wheel is active and flowing, the rider is centered and carving their line. The effect has saved my ass many times.

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1/7/2021 10:38 PM

What about trying zero offset on the lowers of a USD fork, where the axle is directly below the stanchions? Or a USD fork brace like the DVO Emerald, on the back like a RSU Manitou fork, or even on both sides? Those might help a bit with the torsional rigidity.

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1/7/2021 10:46 PM
Edited Date/Time: 1/7/2021 10:51 PM

Hi Primoz. I'm attaching picture of very interesting laboratory test that I found when studying Cannondale Ocho fork. That test was performed by Mountain Bike Germany magazine, I don't know when, but according to tested fork models, it must have been long time ago :-) in order to compare stiffness levels of one of the firts Lefty versions with its competitors.
Of course, today you're not going to publicly find similiar test of Ocho with modern RSU forks but I think the results would be similiar eventhough maybe not that much different.

So, eventhough I applaud the amaount of work you did with your study, I think you oversimplified the conclusions regarding the torsionall flex of UST forks because of the fork model you did choose.
Another point I dare to say is, in my opinion the entire idea/concept of positive effects of telescopic fork flex (and bad effects of fork stifness) on the ride quality is just a self-justification of poor fork design with biggest problem being in a fact it's a telescopic fork with cylindrical stanchions.

See the picture. Oldish Lefty is 2x torsionally stiffer than RS Judy XC LT and 4x !!! than MZ 21. Sideload stiffness is interesting, as well.

Personally, if I was to design myself a front suspesion telescopic fork it would definetely be singlesided USD. Even if dual-crown, but USD and single-sided.

Photo

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1/8/2021 2:20 AM
Edited Date/Time: 1/8/2021 2:21 AM

Primoz, thanks for the stress pictures - makes it really clear why the brace helps the RSU fork in torsion so much - much lower bending stresses in the stantions as they meet the crown. 👍

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1/8/2021 3:25 AM

The images show displacement of particular model points (in mm). Not actuall stresses (MPa).

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1/8/2021 3:50 AM

The pictures in the first post are displacement from the original model /therefore the top being blue and the axle being red). I linked markmedown a set of 6 images (front and back of each variant, including the bridgeless RSU) showing stresses in one of my answers. So it is MPa, not mm, but in that particular case. It's in my looooong answer somewhere, an imgur link.

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1/8/2021 3:57 AM
Edited Date/Time: 1/8/2021 6:41 AM

Fluider you are right about the lefties being super stiff torsionally - in fact I think most Cannondale designed forks achieved that - I remember my Headshok from 1997 was much stiffer torsionally than anything else. The key is that the lefty, like the headshok before it, used a square sliding interface between upper and lower with needle roller bearings between them to reduce friction.

This meant the the leg itself could be used to react torsion through the square interface with wide rollers. Either side of the sliding interface the large diameter tube is the most structurally efficient way to resist torsion. Net result assuming you have beefy enough axle and crown interfaces is a fork that is very stiff in torsion.

With a normal fork that uses cylindrical stanchions and bushes etc there is no way for the fork legs to individually resist torsion so the torque applied through the axle must be reacted by bending in each fork leg. This is very obvious from the images Primoz showed and puts the stresses back into crown similar to the fore-aft bending case.
In torsion the brace in the RSU reacts some of opposing bending in each leg so the stresses in the crown are reduced and the overall deflection improves massively.
I think Cannondale actually did a Freeride fork with needle rollers in each leg - the Moto FR. I never rode one but I imagine it felt incredibly stiff in torsion.


Aside - when riding a lefty I had a weird sensation sometimes that when braking it would steer a little. Structurally this makes sense but I think it should be too small for me to feel so was probably based on subconcious expectation not reality.

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1/8/2021 6:28 AM

I am surprised that no-one mentioned it but the bushing arrangement in the USD fork is wrong. At least on my MX fork, one bushing is on the stanchion and the other one on the outer. This results in an increase in distance as you go through your travel which should stiffen the fork as the impact goes and when you need stiffness the most. I am not sure what impact it would have on torsional rigidity (since frontal is already superior, who cares ?) but it might be worth experimenting with a proper USD bushing setup to give that style a chance. And since dynamic bushing spacing could have an impact, doing the test at 30% SAG could also show more realistic results.

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1/8/2021 6:41 AM

Never thought about Leftys steering, but it makes total sense as the wheel is mounted single sided - the bike should always steer a bit to the right then (with a righty it would steer to the left). This is relatively normal.

Anywho, I don't really see a reason why an upside down fork would be easier to service. Having the shimstacks exposed is a matter of damper layout and I'm guessing could be achieved on an RSU fork as well? Doesn't DVO market their stuff as having easily tuneable damping circuit through quickly removable shimstacks?

The hex design does help, but not here. I explained this, the axle is bonded to the lowers and it's not representative of the real world. One of the simplifications as you could complicate your life with hex axles, knurled axles (Intend), pinch bolts, inserting a hub and varying the axial preload (which should also play a role in the end), have a standard maxle that's just inserted into the holes, where you could then play with clearance between the axle and the dropouts, etc.

So, if anything, the real world axle situation should be worse if anything than what I simulated here with a Hex axle bringing it closer to these results.

Like I said, the dual crown stuff is coming, not sure when though, I'm NOT giving any dates as they are usually moments to wave at as they pass by smile

Zero offset I think won't make much of a difference (doesn't really have any grounds to do so), maybe marginal results, but there are two real life factors against it - you need some offset to not have a trail value that's too high and it's good to have the bottom of the fork clear to assemble it. The construction would become more complicated with no offset. It has been done, but it's one of the things I mentioned in the second (long) post where things need to be made such that they are easy and cheap to manufacture, otherwise they are just good ideas.
The fork brace I'm afraid wouldn't actually do much as well. It would do something, but not much, as it's a relatively thin, but most importantly, an open section. Tube and box sections are by far the best thing for torsional stiffness length wise and the bigger the box the better (the highest loads are seen on the part of the box section that is furthest away from the central axis). Once you slit that box section length wise (cut it along the seam kind of situation), you lost TONS of torsional rigidity. Plus it would still be a relatively long structure. If that brace could be affixed and slid along the outers it would be a different story, but then you're just going towards the RSU fork anyway smile

How was the USD fork model wrong? The lefty is a completely different animal, as has been mentioned, it runs on flat surfaces on needle bearings. Previously they had 4 flat surfaces (every 90 degrees around the stanchion) with 22 needle bearings on each of them (88 in total, there's even a specialised lefty servicing program called Eighty-Aid) with the Ocho moving to three flat surfaces (don't know the details about the number of needle bearings here). This, as markmedown mentioned, changes the torsional situation greatly and is in no way similar to any RSU or USD fork, except for the Moto FR. Sure, doing a needle bearinged USD fork would help, but it would simply be too expensive (and probably quite a bit heavier too).

Good for you that you would go single sided. But the market shows that this is in fact not the better solution and the reason for this is very simple, but multifold. For single strut forks you need to prevent rotation. You can do that with keys, like we have it done in suspension posts, but those usually have high clearances, making them wobbly side to side (very bad torsional stiffness in effect). The way Cannondale does it makes sense, but in order to make the flat surface you need a thicker stanchion (since you're removing material) and you probably need a much harder surface due to smaller contact surface areas between the small needle bearings compared to relatively large surfaces of bushings used in two-legged forks. Plus you need a companion surface of similar smoothness and hardness characteristics inside the outer, while you can just drill away the outer of a two-legged fork and push in the bushings, you just need to take care of the diameter tolerances to achieve the correct fit and the correct inner diameter of the bushing for the fork to work. Then there's the damper and spring construction, with two legs you put one in each, simple. How do you do it in a lefty? Sequentially? Sure, you do have the space with two crowns (and you do need them...), but still, it's a bit more complicated. With current offerings the flat surfaces on the stanchions are much higher up, enabling cannondale to use normal lip seals, but they used to use booties because sealing the flat surface stanchions isn't as easy as it is for round surfaces.

Everybody that has tried one, said the Lefty is THE most smooth fork ever. Because of the needle bearings. Which makes complete sense as rolling element bearings will never have the breakaway stiction that sliding bushes have. But given how many of them are out in the wild and given how they are constructed, it seems two-legged forks are simply too good and too cheap to manufacture for Leftys to make a serious dent... Not to mention that it's a PITA (less so with the Ocho) to get the front wheel of due to the rotor being there smile

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1/8/2021 6:52 AM
Edited Date/Time: 1/8/2021 7:02 AM

Erwan_Ghesquiere wrote:

I am surprised that no-one mentioned it but the bushing arrangement in the USD fork is wrong. At least on my MX fork, one bushing is on the stanchion and the other one on the outer. This results in an increase in distance as you go through your travel which should stiffen the fork as the impact goes and when you need stiffness the most. I am not sure what impact it would have on torsional rigidity (since frontal is already superior, who cares ?) but it might be worth experimenting with a proper USD bushing setup to give that style a chance. And since dynamic bushing spacing could have an impact, doing the test at 30% SAG could also show more realistic results.

I specifically said I compared like to like. Without any changes in bushing location.

Plus, how many USD MTB forks use an outer bushing? Intend uses two standard bushings.

The stiffness effect of this would be more noticeable as you went further into the travel, at smaller travel numbers (this was performed at only 25 % of travel) there wouldn't be such a big difference.

As for the wrong/correct bushing arrangement, I'm fairly certain outer, sliding bushings are an utter PITA. They can get deformed during installation (the Reverb bushing is easily opened up when you are opening it up to mount it in its place), they are I'd say more prone to any exposed edges, possibly damaging the sliding surface than internal bushings and are harder to dimension. In the Reverb I know for a fact that an O-ring is mounted behind it to add some additional pressure and dimensional compensation to it.

The kicker? You would need a very thick backing strip to make it stiff to be solidly mounted or a VERY tightly controlled tolerance of a closed ring to keep it in place. Internal bushings are squeezed together, adding to the rigidity when mounted, so they are easier to mount. Then, when you have the bushings mounted, you can't assemble the fork the way you do now, you would have to insert, with an USD fork, the stanchion from the top for it to come out at the bottom. Thus, if I understand correctly, you need to remove the whole dropout assembly. Or do it like the Reverb does it, by removing the sealhead from the outer, pulling both of them from the outer and dealing with the seals and bushings in that state. This is of course doable, the Float X2 shock for example has a similar arrangement, but servicing that as opposed to a Super Deluxe or a DPX2 is more complicated.

In any case, like I said, doable, but also a bit expensive. The main issue? You have to take care of the quality of the inner surface of the outer tube as well, as it becomes a sliding surface too, just like the stanchion. I'd hazard a guess that this kind of surface grinding and/or polishing is relatively expensive, more so, when it's on the inside. So it makes all the sense in the world to keep the bushings of the internal variant and be done with it. I'm fairly certain that with the travels we see in mountain bikes it's not worth the hassle and costs for that gain in stiffness.

Plus, who said that this kind of bushing arrangement works only in an USD fork? It can just as well be used in an RSU fork.

As for the sag value, I'm confident in saying you didn't read the original post. The analysis was performed at 25 % of sag of a 160 mm fork in all cases, except where the travel was evaluated, which was done at 0, 40, 80 and 120 mm of travel.

Also, thinking about it a bit more, I'm not so sure it would help stiffness that much (it would, the question is how much) as it would help with bushing binding deeper in the travel, making the fork smoother. And all of this stuff is something that wasn't touched on as stiffness, besides the fork being more stiff, can also influence smoothness since the stanchions can run in the bushings more smoothly. Spacing the bushings apart more aids in the smoothness regardless of the stiffness.

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1/8/2021 7:01 AM
Edited Date/Time: 1/8/2021 7:07 AM

I am not sure what you understood but one bushing is fixed at the top of the inner, the other one at the bottom of the outer. On a MX usd fork it makes changing bushing a breeze since those are 2 "big C-clips" that you put on by hand, check a MX fork bushing service maybe. Never tried it on a Mtb fork since it is pressfit and can get missaligned indeed. Watch at 2min20sec to see bushing removal:



You are right that there is another surface that needs to be precisely machined but is it not the case too for air forks for instance ? Yet those are not more expensive than spring forks. Moreover when considering MX forks' price, which is in the price range of medium to high range MTB forks, yet being much bigger chicks of materials I think the suspension industrie is already forking us enough and can precision machine few more inches for what they charge us lol.

I actually read your initial post, probably 80% but those 25% SAG have slipped through sorry for that. Either way SAG is vastly irrelevant with fixed spacing bushing isn't it ?

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1/8/2021 7:40 AM
Edited Date/Time: 1/8/2021 7:46 AM

It's quite possible the industry is forking us, more so Fox than Rock Shox (going to a hand build Intend costs just a little more compared to a Fox fork...).

No, it's not, as the total length of the fork changes and thus the stiffness changes a lot. Moving bushings are a different story and would add to stiffness, but less length to deform over will mean less deformation overall. It's the last graph wink

Ah, so it's this kind of process... I mean I never said it's not possible to do it, just that it's more complicated than what we have now. And more expensive. And you mentioned the bike industry shafting us already, imagine the price of a fork with a moving bushing smile

As for air springs, no, the lowers are relatively raw, it's the inside of the stanchion that is also ground, so both the inside and the outside are finely finished for the air spring to work. Using a coil spring or a cartridge air spring would mean there is no need to finely finish the inside of the stanchion and that could be made cheaper, but a cartridge air spring would be heavier. Plus with the bladder, cartridge damper units we don't need that surface, but the cheaper ones, like the Motion Control damper from Rock Shox, still use the inner surface of the stanchion for the damper side as well. I don't know the details outside the RS universe, but I'm guessing there's a supply chain for outer and inner ground/polished stanchions set up in Taiwan and those parts are relatively cheap so they get used like that if they are needed or not.

One thing to note, the WP fork from your video appears to have a hard chrome surface of the inner stanchion, indicating it might be steel, not aluminium... Which could help with stiffness too, depending on the thickness though. The outer appears to be cut on a lathe too as it has a relatively large collar and a tapering diameter going from the bottom of the stanchion up towards the lower crown. And then thinning out towards the top crown.

The outer though might be thicker there just to deal with the clamping load itself, to prevent deformation (squeezing or pinching) and thus preventing binding of the bushing. I remember Boxxers had a problem with the piston of the air spring passing past the lower crown and torquing the bolts of the lower crown too high caused the air piston to get stuck. They then changed the air spring to not go past the lower crown.


Also, do I see correctly in the vide that the bushing on the inner stanchion is something along the lines of a polymer bushing infused with lubricant (Igus like)?

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1/8/2021 7:55 AM

BTW; regarding upside down forks, I googled for the Fox USD fork (to see if there was maybe any info regarding bushings) from 8 years ago and found the https://www.pinkbike.com/news/fox-dh-fork-inverted-prototype-2012.html with the following conclusion:

The outcome? After much testing it was decided to discontinue development of the inverted fork, simply because Fox couldn't attain the torsional stiffness that they were looking for without it becoming much too heavy for their liking. Word is that both Gee and Aaron were big fans of how the prototype fork handled fast, rough sections of trail head on - thanks to the increased fore/aft stiffness of the inverted design - but felt that the standard right side up arrangement of the current Fox 40 had the inverted fork soundly beaten in the corners. Fox admitted that they could likely remedy this by added more material, but the fact of the matter is that the majority of competitive downhillers would likely balk at purchasing a new fork that weighs substantially more than what they are currently using, even if it did offer advancements in damper technology or other areas.

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1/8/2021 8:30 AM

Primoz wrote:

Why is it easier to do service and sealing? It's more or less the same... Or am I missing something?

Dammit, all these comments regarding staying on the line and the like are really intriguing smile

the seals work better due to always being lubricated. the seals on my shiver needed replacement once in 10 years.

as for the other stuff, Primoz rightly noted that a lot of the damper stuff is just a matter of design. what is unique to USD forks:

on a Dual crown fork, you can remove the legs individually, still fully sealed, and work on them on a bench. The closest you get to that in a conventional fork is dropping the entire lower half.

even on a fixed crown fork, when doing a USD design, it's fairly easy to design it so that you can drain the fork from the top cap, then remove an upper retainer, and drop the entire rest of the assembly out of the bottom. Never have to yank a footnut for a basic service, and never have to do the dance of squirting oil between the footstud and the hole in the lowers to get the bath oil in. heck, no reason you couldn't even do a full oil replacement on the damper without removing it from the lower leg.

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1/8/2021 1:49 PM

I rode several Lefties over the years, and I still think its the best chassis design for mountain bikes. They feel smooth in the parking lot, but on the trail they are unreal. So much less hand fatigue. No binding with side loads and torsional loads. This video demonstrates:



The Lefty suffered from 3 problems:

1. Its Cannondale. They already suffer from a reputation, to say the least. Plus a proprietary part that needs proprietary interfaces will aways remain proprietary. If the lefty was its own thing and not tied to a bike brand (and could use traditional headsets and hubs) then it would have been more successful in the market.

2. Damping. Every Lefty until the Ocho had garbage damping. They used pass-through thru-shaft designs I believe, like what Trek is doing with rear shocks. This sounds good, but in practice makes it very difficult to tune anything other than the low speed rebound. Its also hard to put a damper and air spring in the same leg. Cannondale also just sucked at engineering good damping (something incredibly hard to do).

3. Quality Control. One of my Lefties was never serviced, never taken care of, leaked out of the cracked boot, but still was buttery smooth after years of abuse. I've felt others that out of the factory were trash, harsh, sticky, and never got better. I think a huge percentage of Lefties were lemons.

I want to try and (re)build my own lefty, 160mm travel 29er, with modern offset and stuff a boxxer or lyrik damper in it with a coil-over and see how that performs.
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1/8/2021 2:01 PM

So are we all forgetting about this?

https://www.xfusionshox.com/products_detail/76.htm

It used brass keys like a dropper to increase torsional stiffness. It was never released outside of Taiwan. I got some rep from x fusion to admit that the brass keys would bind pretty badly over even moderate torsional loads, and while they were designed to snap and break under extreme loads to prevent damage to the rest of the fork, they always broke too easily.

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1/8/2021 2:33 PM

Wanted to mention Pinkbike comment section on the Intend dual crown DH fork about the Revel and I see now you were in the thick of it at the time :D

Regarding your comments about the lefty, kinda seems like tolerancing was an issue (part of QC, like you mentioned). If you think about it, it's REALLY important to have the flat-to-flat distance of the bearing surfaces under a relatively fine tolerance, otherwise the needle bearings will flop around on their own (and the bearings also have some tolerance on them as well). If you have too much clearance and floppy bearings, the whole fork will move around, depending on whether it's only one axis that has an issue or both. With forks binding the issue might be opposite, not enough clearance or even a tight fit.

I'm wondering how the Ocho with only three surfaces changed this, it might have some leeway on this, as X radial distance affects the effective spacing perpendicular to the other surface by 'only' 86 %...

With standard bushings you need clearance anyway. Too much clearance? Yeah it's gonna flop around too and many forks these days have this issue. But people seem to have learned to live with it. And torsionally it's less of an issue with two legs.

That's part of the cost and manufacturing issue I was mentioning regarding leftys a bit higher up, it's much easier to grind down a smooth, round tube than it is to make flats into it afterwards...

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1/10/2021 10:36 AM

Erwan_Ghesquiere wrote:

I am surprised that no-one mentioned it but the bushing arrangement in the USD fork is wrong. At least on my MX fork, one bushing is on the stanchion and the other one on the outer. This results in an increase in distance as you go through your travel which should stiffen the fork as the impact goes and when you need stiffness the most. I am not sure what impact it would have on torsional rigidity (since frontal is already superior, who cares ?) but it might be worth experimenting with a proper USD bushing setup to give that style a chance. And since dynamic bushing spacing could have an impact, doing the test at 30% SAG could also show more realistic results.

Well, there are as far as I know two companies using MX fork bushing arrangement, CRconception and BOS Obsys (not sure about this 100% but let´s say 99 lol). Neither of those forks are significantly more expensive then FOX equivalents that are produced in numbers 100x higher or more thn either of the two, CRconception is one man show just like Kornelius from Intend as far as I know..

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1/10/2021 11:15 AM
Edited Date/Time: 1/10/2021 11:18 AM

Looks like it for the Obsys yeah, it appears you remove the collar on the outers containing the seal to remove the stanchions with both bushings when disassembling the fork.

But yeah, a moving bushing is still something that isn't limited to an upside down fork, as I've mentioned. It is easier to do with a dual crown fork and have relatively large bushing overlap even at zero travel as you can send the top of the stanchion past the lower crown, but that's not a benefit with a single crown fork.

What surprised me the most about CRconception is the price, doesn't really seem that high for a onemanband product when looking at the singlecrown version (I'm not up to speed with prices for dual crown forks).

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1/10/2021 11:50 AM

The price of crc forks is indeed reasonable. One obvious limitation of RSU forks is that they all use magnesium lowers (except for latest intend forks) which is too soft for sliding bushings to work. When I saw prototype of intend forks I was really hoping to see sliding bushings in there and I was honestly surprised when they aren´t, seems like wasted potential for big improvement and with gain in unsprung mass for no good reason. .

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1/10/2021 1:40 PM

Well, of course they're going to use magnesium lowers as they are light, castable and cheap smile

But if you wanted a sliding bushing in magnesium lowers, you could still insert a thin bushing along the whole length with different surface properties - aluminium with hard ano, brass (good sliding properties) or even polished/chromed steel. But we're at the price problem again, as always.

And when I say price, it's not only the cost of these components. The cost that is the problem lies in the toleracing of said components, in the reliability of their manufacture, in the assembly process, etc. etc. The bushing arrangement we have is very simple and easy to make work, you drill out the lowers and finish them off with a reamer to achieve the correct diameter, with the lowers clamped in a fixture and an appropriate (CNC) machine you will achieve fairly good parallelism and centre to centre distance of the two holes to prevent excessive binding, press in the bushings (that are bought for the price of a few 10 cents) and be done with it. And then you just insert the CSU with the stanchions and the fork is assembled.

With the sliding bushing I mentioned servicing, but servicing is so expensive and manual that it's not really an issue there, but assembly on a production line is a different animal.

Geezus my job really killed my creativity and openness to wild ideas :D

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1/12/2021 9:15 PM

Why do you consider making the properly toleranced hollow space for sliding bushings a problematic, when manufacturers have no problem with making the properly toleranced hollow space for damper piston? It's not about possibilities, but about their design and production quality control.
I have seen a picture of some modern day FOX 36 fork with MISALIGNED dropout holes, clearly visible with eyes !!! Why do you think they introduced floating axles? IMO in order to compensate for low casting quality of lowers. In Rockshox forks technical drawings some dimensions are toleranced with +-5mm.

Anyway, an interesting video of fore-aft noodleness of Boxxer and FOX40:
https://imgur.com/a/LwLDhkA

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1/12/2021 9:24 PM

Or Pinkbike's huck-to-suck video compilation here:

?t=115

At 1:55 starts Cannondale Ocho fork that has probably to lowest fore-aft flex from the entire video despite being XC fork and only single-leg. Directly after Ocho goes FOX 38 that have notibly greater flex.
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1/12/2021 10:00 PM
Edited Date/Time: 1/12/2021 10:03 PM

URL for the RS tolerances.

I never said it's not possible to make the inner surface of the outer tube appropriate to have a bushing slide on it. I said it's more expensive, as, opposed to castings, it requires finer control over the surface quality and hardness. And that it adds another component that requires this besides the stanchion. And it requires it on the inner tube surface, which logic dictates is harder to work on than the outer surface.

And I specifically said that even such a good idea (even a Lefty with keyed stanchions) isn't worth much if it's really hard to make it quickly, cheaply and with good reliability. We are bemoaning bike prices in the current state, would you be happy to pay 2000+ USD/EUR/etc. for a 150 mm singlecrown fork from the major manufacturers?

Regarding the Ocho vs. 38, the Ocho was on a 29er, the 38 was on a 27,5" bike. The same movement will appear larger on a 27,5" bike because of the difference in size of the reference geometry (wheel size). Plus the 38 has a longer travel, which, if you look at the last graph in my first post, plays a huge role as well. And the rider does appear to handle the huck a bit worse on the Nomad than on the Cannondale, insinuating a higher jump height on the Nomad compared to the Cannondale. Which would of course mean higher forces...

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1/13/2021 6:16 AM

Primoz wrote:

URL for the RS tolerances.

I never said it's not possible to make the inner surface of the outer tube appropriate to have a bushing slide on it. I said it's more expensive, as, opposed to castings, it requires finer control over the surface quality and hardness. And that it adds another component that requires this besides the stanchion. And it requires it on the inner tube surface, which logic dictates is harder to work on than the outer surface.

And I specifically said that even such a good idea (even a Lefty with keyed stanchions) isn't worth much if it's really hard to make it quickly, cheaply and with good reliability. We are bemoaning bike prices in the current state, would you be happy to pay 2000+ USD/EUR/etc. for a 150 mm singlecrown fork from the major manufacturers?

Regarding the Ocho vs. 38, the Ocho was on a 29er, the 38 was on a 27,5" bike. The same movement will appear larger on a 27,5" bike because of the difference in size of the reference geometry (wheel size). Plus the 38 has a longer travel, which, if you look at the last graph in my first post, plays a huge role as well. And the rider does appear to handle the huck a bit worse on the Nomad than on the Cannondale, insinuating a higher jump height on the Nomad compared to the Cannondale. Which would of course mean higher forces...

I still wish they had some RSU dual crowns and an inverted dual crown in there for us to see....

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1/13/2021 6:56 AM

So that CRConception fork looks incredibly interesting. I've heard about him before but forgot. Does anyone have experience with this or speak french? Google Translate isn't perfect, but from what I can tell its 2.2kg , which is the same as a 38, but its an effing coil shock! The €1349.00 works out to be about $1600 USD.

http://www.crconception.com/ONLINE-STORE/fore297-fore-297-2020-precommande/%23wbs1&gid=1&pid=1

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