Bearings or bushings for pivots? VPP-style vs DW link-style?- Mtbr.com
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  1. #1
    Belltown Brazer
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    Bearings or bushings for pivots? VPP-style vs DW link-style?

    Xpost from framebuilding

    Hey - by way of introduction over here in shocks and suspension: I'm a hobby framebuilder with 75-ish frames under my belt and I have just recently started farting around with FS bikes. I'm a long time rigid and hardtail rider - with only some time on an AMP B-1 in the early 90s and a FSR enduro in the early 20's as my FS riding experience. But, my kids are going faster and higher and seemed to need FS. I built my boy a single pivot bike and he is just ripping on it. So I build myself a single pivot. The FS is fast - it doesn't really even feel like I'm going that fast and then I look at the Strava segments and I see new PRs. Hmm.

    Well, the bike I'm riding was my second crack at a FS bike and it has some issues that I want to fix on the next one. And I've been doing some thinking:

    It seems to me that a bushing would be better suited for the high frequency back and forth load that a pivot sees. It would be better at supporting the side to side loads. But the bearings sure are touted as an upgrade on the popular production bikes. I have heard of bushings wearing too quickly. I ordered some nice oil-impregnated bronze bushings and they are smooth on my Al shaft - about as smooth as the bearings I just used. I also ordered up some plasitc igus bushings (specifically noted on some manufacturer's PR) and they are nice too. And light, and cheap.

    Without trying to start and argument here - what is the general thinking here re: bushings/bearings.

    Now - I'm thinking a multi link suspension next. I don't see it as too much harder than the single pivot, really. There is the links to fabricate - but I can get some AL bar stock and go crazy with the drill and maybe even mill. Don't think that it would work for a fella trying to make a living at this, but that is not my point.

    I like the designs with the one piece swingarm: VPP, DW link, CVA, maestro, etc and would like to do a variation of one of those - as opposed to a four bar or something with pivots at the dropout.

    But my question here is which style works better? According to what I've read the main difference is the orientation of the upper link. The one has the upper link pivot on top and swings CCW, the other upper link has the pivot on the bottom and swings CW. I think the CCW upper link would be easier to fabricate because the shock pivot is on the same shaft as the lower pivot on the upper link - and it's already "inside" the front triangle. The CWupp er link is "outside" of the front triangle and some arrangement has to be made to attach the shock to the swingarm. Could be that upper link is also a rocker - but that might be getting beyond what I can fab in the basement.

    But I've heard (remember I'm a reformed rigid guy here) that the CW upper link is "better" than the CCW upper link. What's some thoughts on this...

    Anyway, thanks for any input you might have! Good day - B
    Departing from East Hampton, CT

  2. #2
    Shortcutting Hikabiker
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    If executed properly bushings work well but bearings will probably be a little more forgiving.

  3. #3
    mtbr member
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    When bearings wear out, it's not a big deal to replace. When I lived in the Pacific Northwest, I popped new bearings into the pivots every year. Not sure how easy replacing worn out bushings is...

  4. #4
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    Interesting thread. Usually, a bushing or bearing is irrelevant because 2 frames generally wont be similar enough that the only difference between them comes down to that.

    Theres just not that much movement in the links. Im not sure the performance difference is significant. A bearing sure does seem easier to replace.

  5. #5
    Track Junkie
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    Turners have used a bushing system for awhile now.

    I'm riding a Turner Burner with bushings. I'm impressed with the rigidity/lack of play in the system. However, there is a bit of resistance/"stiction" in the busings. It also seems like a very difficult setup to get perfect, because there is more emphasis on alignment of the pivots and the horizontal plane of the actual pivot. But, when it works, it's great.

    Turner's system is comprised of several different pieces for each pivot bushing, and also has a lube-port for each one. It's a good (not great) system, and with a few small modifications, I've found it to be much more reliable and serviceable than bearings, with a longer service-interval time.

    BTW - I'm over 250lbs, and don't stick to easy trails. I'm hard on pivots & suspension.

    Hopefully you can disassemble a Turner pivot to get some ideas for your next frame.
    I get paid to ride shotgun.

  6. #6
    fuggansonofahowa
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    I'll contribute - I'm older than dirt. This is something to think about and may not be as applicable today:

    I like bushings, I rode a Proflex 856 when full suspensions were considered taboo. Those bushings worked well.....until I had to replace them. The bushings were impossible to find. After that I purchased an Ibex Atlas (aka Azonic Revenge). When it was time to rebuild the suspension, despite the frame being discontinued, the bearings were standard sized and my aftermarket options were plentiful.

  7. #7
    Elitest thrill junkie
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    Ok...that didn't work...

    Shoot, had a whole nice thing typed up.

    Anyways, go looking through the archives for Dave Turner's post on why he chose IGUS bushings with grease ports. Some great info there.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

    You're turning black metallic.

  8. #8
    Fat-tired Roadie
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    I was just going to say "stiction" too.

    But funny Jayem should mention IGUS. My coworker has a bunch of IGUS dryline stuff sitting on his desk right now. It certainly doesn't feel like it has a stiction problem.

    I could also see using bearings where there's a lot of movement and bushings where there's not.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  9. #9
    mtbr member
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    It is more difficult to do a bushing system well and that is why almost all mass manufacturers are using bearings.

    Bearings performance can start to degrade after 6 months and the only cure is replacement. Bushings can start to need maintenance about the same point and a simple regrease will keep them going.

    My 2001 Turner 5-spot prototype runs IGUS bushings with seals and grease ports. They are still smooth and tight. All bushings are still original. Turner use hard anodised aluminium pins for the bushings to run on, stainless steel is an excellent option and easier to work with but heavier.

    I have stripped and cleaned/regreased the pivots on my Turner about every 12-18 months in the 11 years I've owned it.
    Owner of www.shockcraft.co.nz, Mech Engineer, Tuner, Manitou, Motorex, Vorsprung EPTC, SKF, Enduro
    www.dougal.co.nz

  10. #10
    Elitest thrill junkie
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    I had a nice long reply before, but I'll include some highlights:

    In most bearing systems, the suspension may rest of 2-3 bearings, with the limited rotation that the link sees, this causes pitting and groves, which over time causes play, which means metal slams into metal on every impact, which eventually can ovalize the bearing mount, which is usually not fixable. Now, most people replace the bearing before that happens, but it just goes to show you how poor a bearing system intended for low load-high rotation applications is. Unless it's an angular contact bearing, it's also usually p*** poor for dealing with sideloads, but another way to get around this is to double up the bearings, like Ventana does.

    When Dave Turner designed his first bikes, he got with a mechanical engineer and worked out that a tapered bearing system would be the best at dealing with the various directions of forces and providing the required contact area, but this is extremely expensive to do, because you have to seal them, have to get ones small enough, but high enough quality, and so on. So Dave asked what the next best thing was, and the IGUS bushings with greaseports were the answer. These aren't your garden variety bronze impregnated throw-away bushings that came on bikes like my Diamondback and Rocky Mountain, these were a hard composite material with great rigidity and resistance to lateral loads that didn't wear fast and with the greaseports, lasted a long long time. These required high tolerances for fit, but since Turner made everything in-house, it all worked out. These helped give turner their reputation for bikes that lasted year after year, rather than being all clapped out and used up after a season or two, like my specialized E29.

    Bearings are cheap though, so it's somewhat easy for manufacturers to slap bearings in there and not really care whether or not they hold up after a year. Another disadvantage is the blind-puller that's required to install/remove many bearings.

    Interestingly, the new carbon turners have angular contact full-compliment bearings packed full of grease (if you've ever opened many bike bearings, there's often only a smidge of grease in there and mostly just empty space). I hope these hold up well, but I'm definitely partial to their IGUS bushings, those were excellent IME and my Turners held up year after year, unlike most bikes I've had with bearings. I think bearings CAN be done correctly, but most manufacturers don't really care to do what's necessary to design a good bearing system, or even a bike that's intended to last year after year for that matter. Turner's new system will probably be ok, but I'm going to test it out to see

    If you're going to make a bike with bearings, make them with grease ports, or at least make it so you can EASILY remove and replace them, rather than needing a blind puller because there's no lip for other tools. Make sure you have enough ball bearings so it doesn't pit right away, but also make sure the pivots are large enough to give proper rigidity to the bike.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

    You're turning black metallic.

  11. #11
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    FYI: you guys may want to check out pretty much the same discussion going on over in Frame Building.
    don't tell me, "Show Me " !

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