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Thread: Ask the experts

  1. #9026
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    Traditionally, the main failure mode for breaking spokes from fatigue was when the tension was too low. The spokes would drop to zero tension when they're opposite of the wheel load, and then snap back to tension once the wheel rotated and that spoke wasn't opposite the load anymore.

    Purely based on speculation, that doesn't seem like what's happening with carbon wheels. At least with my wheels, lack of spoke tension wasn't the issue. Or more accurately, the wheel was properly tensioned, so if spoke tension dropping to zero was the issue it means there's something about carbon rims that's causing spokes to drop to zero tension even when they're properly tensioned. That doesn't seem right - if anything, the stiffer carbon rim should keep loads more uniform across the spokes.

    I'm also fairly sure I'm not abusing these wheels any more than I have wheels in the past. Although admittedly, older aluminum wheels that I abused generally had thicker spokes and more of them. And the the wheels didn't last that long because the rims died long before spokes started snapping. But still, I'd rebuild those wheels with a new rim and the same spokes, and rarely had spokes break (except from trauma).

    So I dunno. My bunch is just that aluminum rims were flexier and transmitted a bit less stress into the spokes.

  2. #9027
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    Fatigue doesn't require that the spokes' tension go to zero. If that happens the fraction of a full stress cycle is larger than if it does not, but a spoke that falls to 1 lb of tension sees basically the same fatigue unless there's enough deflection at the rim to actually buckle the fully unloaded spoke, which should be rare.

    Maximizing the tension in the spokes keeps the lowest tension higher, which reduces the fraction of a fully reversed cycle it sees each time it's (partially) unloaded. This (and the fact that tension only goes up when you put a stick in there) is why Brandt argued that tension should be as high as possible up to the rim's buckling point, nipple failure, etc.

    Dunno how applicable that is, but if you've got less weight in spokes than you once had you probably need to be running the tension higher and taking advantage of the higher buckling point of the rim. Conversely, a wheel that's too stiff when the spokes are tight enough to live is going to kill spokes.

  3. #9028
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    Quote Originally Posted by jono View Post
    Fatigue doesn't require that the spokes' tension go to zero. If that happens the fraction of a full stress cycle is larger than if it does not, but a spoke that falls to 1 lb of tension sees basically the same fatigue unless there's enough deflection at the rim to actually buckle the fully unloaded spoke, which should be rare.

    Maximizing the tension in the spokes keeps the lowest tension higher, which reduces the fraction of a fully reversed cycle it sees each time it's (partially) unloaded. This (and the fact that tension only goes up when you put a stick in there) is why Brandt argued that tension should be as high as possible up to the rim's buckling point, nipple failure, etc.

    Dunno how applicable that is, but if you've got less weight in spokes than you once had you probably need to be running the tension higher and taking advantage of the higher buckling point of the rim. Conversely, a wheel that's too stiff when the spokes are tight enough to live is going to kill spokes.
    Agreed with that.

    Mostly what I was getting at is that low spoke tension isn't the issue. Tension on my carbon rims is as high (or higher) than on my aluminum rims. So... [shrug]

  4. #9029
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    And the spoke count? It'd be awfully convenient if setting spokes x tension the same between two wheels gave the same results. Probably too convenient.

  5. #9030
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    Experts, riddle me this one.

    I've been running a Hydra rear hub for about `1000 miles now, first on my trail bike and now on my enduro pig. It's a 32H centerlock microspline version if that matters. I've serviced it (cleaned and regreased spring/pawls) a couple times and overall have no complaints with it.

    Couple weeks ago I had the bike in the stand and noticed a lot of drag on the wheel. When I spin the wheel slowly by hand the hub feels ever so slightly notchy. It's also visible when the wheel slows down and stops, it seems to overcome a "sticky spot" then get stuck into the next one and backspin a couple degrees before stopping. As if there was a notch somewhere in the bearings and not enough momentum to overcome that.

    Initially I thought the rear axle torque was too high (GG recommends 25 Nm) and somehow squeezed something wrong. Things looked better at 15 Nm but I tested it again yesterday and the behavior doesn't go away completely at low torque. I cleaned/regreased everything and inspected the hub thoroughly, nothing's fucked. The bearings aren't ultra smooth but nowhere near as bad as the behavior of the wheel suggests. Off the bike the wheel spins freely on the axle without any notchy behavior so I still think there's something about the dropouts pushing on the endcaps too hard while torqued to spec. I asked GG, they told me their torque spec is correct but I can back it down as much as I want as long as I have enough thread engagement. GG owners are all over the place on this, some claim 25 Nm on the rear axle is barely enough, some run it down to 13 Nm with no issues, some have the rear axle come loose all the time...

    Thoughts on how to deal with it? I really don't understand how torque can be an issue here unless one of the bearings is not pressed in fully. Or maybe the bearings feels OK by hands but are completely shot and that becomes obvious when tensioned? I'm tempted to replace them and just see but I figure I'd ask.
    "Your wife being mad is temporary, but pow turns do not get unmade" - mallwalker the wise

  6. #9031
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    I certainly don't torque my rear GG axle to 25NM. I'd guess I run more like 10NM or so. Like they said, I tighten it enough to snug up and not back out, and nothing more. I've been running a Hydra hub for a couple thousand miles and replaced the bearings once. I'd just replace the bearings if I were you. It's super easy on Hydras.

    The only other thing I can think of is that I9 Hydra needs different endcaps for Microspline vs. XD. I think it's mostly a difference in where the lip seals on the endcaps goes (if you use the wrong ones on MS, you get less seal) but it may have an effect on the overall width. I don't know if your wheelset started out XD and got converted, or something like that.

  7. #9032
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    I had something like this happen on a Chris King. Replaced the bearings and problem solved. I think under the side load, the rough spot torqued a little different creating the resistance.

  8. #9033
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    Quote Originally Posted by Andeh View Post
    I certainly don't torque my rear GG axle to 25NM. I'd guess I run more like 10NM or so. Like they said, I tighten it enough to snug up and not back out, and nothing more. I've been running a Hydra hub for a couple thousand miles and replaced the bearings once. I'd just replace the bearings if I were you. It's super easy on Hydras.

    The only other thing I can think of is that I9 Hydra needs different endcaps for Microspline vs. XD. I think it's mostly a difference in where the lip seals on the endcaps goes (if you use the wrong ones on MS, you get less seal) but it may have an effect on the overall width. I don't know if your wheelset started out XD and got converted, or something like that.
    Thanks, 10 Nm is what I run on my trail bike and previous 2 bikes. I couldn't believe the 25 Nm spec on GG, seems insane, that's the kind of stuff I'd hate to have to loosen trailside with a small multitool...
    The hub was brand new as a MS so I never messed with the end caps.

    Looks like 2 votes for replacing the bearings, I ordered a set. Gives me a reason to pull out the bearing press which isn't seeing all that much use.
    "Your wife being mad is temporary, but pow turns do not get unmade" - mallwalker the wise

  9. #9034
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    My enduro bike is excellent, but obviously I'm pondering if it's possible to throw some money towards slight improvements. Tell me if my theory is sound.

    It's a 170mm forked 29er, 652mm stack, 77,5 seat angle, 64 head angle, 34mm BB drop and 170mm cranks. Reach and all that is where I want it more or less.

    I have a slightly negative ape index, so I like a bit of stack. I "need" 170mm cranks for my legs, but wouldn't mind slightly more clearance, should probably have more rear sag - currently at 24-ish%, manufacturer recco is closer to 30%. Don't really need that slack of a head angle, wouldn't mind slightly slacker seat angle.

    And no, I won't buy another / a different bike.

    My plan/theory is putting a 180 fork on. According to one of those calculators that will give me 3-4mm more stack, 3mm less BB drop, take the seat angle down to 77,1 degrees and the head angle down to 63,6 degrees.

    Then, if I put in a +1 degree headset I'll end up at a total of +6mm stack, -5mm drop, seat angle of 76,8 degrees (why does that happen?) and a head angle of 64,3 degrees.

    So, more squish, and all geo numbers moved slightly towards where I think I would like them. And I could probably move down 25lbs on the spring and get closer to 30% sag.

    The question is; will this be noticable at all? Thinking maybe the BB drop and seat angle changes are most noticable? And the rear sag if I get a softer spring.

  10. #9035
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    I think the higher BB would be slightly noticeable, but if you went to a softer spring and sagged more, that'd probably more or less cancel that out. The seat angle probably isn't super noticeable, but if it is, you could scootch your saddle forward on the rails a little to cancel it out. Also keep in mind that the calculated numbers you have are probably unsagged, so while a 180mm fork is taller than a 170, you also will probably run a little more sag, so the difference is less than the calculated numbers imply.

    Personally, I'd probably just put the 180 fork on it and not bother with the angleset. A 63.5-ish HA seems about right for a bike with a 180 fork, and none of the other numbers look out of line.

  11. #9036
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    Quote Originally Posted by sf View Post
    My enduro bike is excellent .
    no you won't notice it

    I think god is telling you that you have too much money,

    save the coin for when something actulay breaks
    Lee Lau - xxx-er is the laziest Asian canuck I know

  12. #9037
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    What is the trait you're trying to get? And why are you at ~24% sag?

    The reason the + angleset slackens seat angle is because it pulls the front wheel closer to the headtube. The fork is a fixed length so it raises the HT (and BB) up. The rear tire stays on the ground so you effectively rotate the frame slightly counter clockwise. Conversely, using a - angleset pushes the front wheel out, lowers the BB, and steepens the ST.

  13. #9038
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    So, a bit of background. My main riding terrain varies a lot in steepness, but not a lot of sustained pitch either way. A lot of technical flats (yes, really) and climbs. It's pretty rough and not very fast, but the roughness lends itself to having a fair bit of travel. Actually my old 29 Strive had pretty good geo for riding it, just a tiny bit steep in the front and slack in the rear.

    Because of this slightly softer set-ups, not too low BBs, and not to extreme geo is preferable. Modern enduros work well, but are geo-wise a tiny bit more than needed. In addition I regularly ride more enduro-appropriate terrain.

    Quote Originally Posted by toast2266 View Post
    I think the higher BB would be slightly noticeable, but if you went to a softer spring and sagged more, that'd probably more or less cancel that out. The seat angle probably isn't super noticeable, but if it is, you could scootch your saddle forward on the rails a little to cancel it out. Also keep in mind that the calculated numbers you have are probably unsagged, so while a 180mm fork is taller than a 170, you also will probably run a little more sag, so the difference is less than the calculated numbers imply.

    Personally, I'd probably just put the 180 fork on it and not bother with the angleset. A 63.5-ish HA seems about right for a bike with a 180 fork, and none of the other numbers look out of line.
    Yeah, I wasn't super clear on the fact that trying to get more sag without more rock strikes is a rather big part of my plan. So your first sentence pretty much matches my intention.

    Agree with trying the new fork first, but since the angleset seem to approx double the positive geo effect it's tempting.

    Quote Originally Posted by XXX-er View Post
    no you won't notice it

    I think god is telling you that you have too much money,

    save the coin for when something actulay breaks
    I got my Lyrik at a very good price, and currently MY23 Zebs are very nicely priced at certain sites. All of that matters not if changes are not noticable, obviously

    Quote Originally Posted by Andeh View Post
    What is the trait you're trying to get? And why are you at ~24% sag?

    The reason the + angleset slackens seat angle is because it pulls the front wheel closer to the headtube. The fork is a fixed length so it raises the HT (and BB) up. The rear tire stays on the ground so you effectively rotate the frame slightly counter clockwise. Conversely, using a - angleset pushes the front wheel out, lowers the BB, and steepens the ST.
    Thanks

    See above, wasn't too clear about my motivation. 400lbs spring, was between that and a 375. And really, at 24% it climbs so well, and it's more than decent downhill, but still - a bit rough at times. Thinking that if I get closer to 30% without even more marks on my cranks, and in addition got slight positive changes on other geo numbers, it might be worth it.

    Basically; slightly more enduro-ish suspension feel, slightly more towards trail bike geo. Slightly

  14. #9039
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    IMO drop a spring rate and add a click or 2 of LSC to your taste for climbing. I could see 24% rear sag in 2 cases: you're only riding flow trails, or you're hitting massive hucks all the time. The bike's balance will feel better if you get closer to the intended 30% rear sag. This will let it sit a little deeper in rear travel descending, slacking things out a bit. You'll probably use less front travel of what you've got as well.

  15. #9040
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    Quote Originally Posted by sf View Post
    I got my Lyrik at a very good price, and currently MY23 Zebs are very nicely priced at certain sites. All of that matters not if changes are not noticable, obviously
    You might already know this, but keep in mind that the Zeb's axle to crown is longer than the Lyriks. So going from a 170 Lyrik to a 180 Zeb will increase your axle to crown about 15mm.

    The Zeb is also a much stiffer fork, which may or may not be what you want.

    (also, agreed with Andeh's take on the rear suspension).

  16. #9041
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    Quote Originally Posted by Andeh View Post
    IMO drop a spring rate and add a click or 2 of LSC to your taste for climbing. I could see 24% rear sag in 2 cases: you're only riding flow trails, or you're hitting massive hucks all the time. The bike's balance will feel better if you get closer to the intended 30% rear sag. This will let it sit a little deeper in rear travel descending, slacking things out a bit. You'll probably use less front travel of what you've got as well.
    Yeah, I'm neither of those. Thanks

    Quote Originally Posted by toast2266 View Post
    You might already know this, but keep in mind that the Zeb's axle to crown is longer than the Lyriks. So going from a 170 Lyrik to a 180 Zeb will increase your axle to crown about 15mm.

    The Zeb is also a much stiffer fork, which may or may not be what you want.

    (also, agreed with Andeh's take on the rear suspension).
    No, I didn't know that. Thought it was 10mm, but theoretically that should give me even more of what I think I want.

    Yeah, I've heard/read that the Zeb is a stiffer fork. But that's the chassis right? I don't need a stiffer fork, but if that fork also allows me to run a little more sag - cause the midstroke support is supposedly very good on the MY23 - it could be very interesting. Have considered a Runt in the Lyrik for the same reason.

    I've ridden a double crown a few times, and it never struck me as too stiff as such. And it should be stiffer than a Zeb, right?


    Anyhow; I guess the following should be done;
    - drop down a spring rate. And really, 5% sag is 3,5mm on a 65mm stroke shock
    - see how it feels
    - consider a 180mm fork, theoreticaly it should be good
    - and sometime in the future - when current headset is due for a change - consider a angleset

    Sounds logical; guess we'll see happens when bored in tweener season

  17. #9042
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    I had a Fox 36 on a 5.5, now I got a zeb on my Bullit, I smack a lot of stuff with the EP8 motor but also with the pedals.

    My Zeb cames with 1 donut in the air chamber so at the proper air pressure ( me=165 lbs ) I only used about 5" of travel so i would agree with the mid stroke support assertion

    shop bro suggested taking out the donut which increased the amount of fork travel by about an inch

    even with no donut at the correct airpressure i don't normaly use all the travel

    i liked the fox 36 and now I like the ZEB
    Lee Lau - xxx-er is the laziest Asian canuck I know

  18. #9043
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    Quote Originally Posted by sf View Post
    Yeah, I've heard/read that the Zeb is a stiffer fork. But that's the chassis right? I don't need a stiffer fork, but if that fork also allows me to run a little more sag - cause the midstroke support is supposedly very good on the MY23 - it could be very interesting. Have considered a Runt in the Lyrik for the same reason.

    I've ridden a double crown a few times, and it never struck me as too stiff as such. And it should be stiffer than a Zeb, right?
    Yeah, stiffer chassis than the Lyrik. On the upside, it feels very precise, and when you're hammering through rough stuff, the fork flexes a lot less so it stays smoother because your bushings aren't binding. On the downside, that stiffness can sometimes make it feel like the fork pings off of stuff that a flexier fork would've just kinda noodled through. But yeah, double crowns should be stiffer than the Zeb, unless it was an ancient double crown with small stanchions (or an inverted double crown).

    Deals can be had on those Zebs right now. I think your worst case scenario is that you buy it, ride it a bit, hate it, and either 1) keep the Zeb but reduce it's travel to 170, or 2) sell it for a loss (but probably not a huge loss). Much more likely is that you'll like it and keep it on there.

  19. #9044
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    Ask the experts

    I’m kinda anti-upgrade-itis right now. So what I hear is, “my bike is great, but I’m itching to drop a grand on it to make a very subtle change that I probably wouldn’t notice in a blinded test. But since we’re creatures of bias, I’ll perceive it as a religious experience worthy of endless praise”
    Ride your bike. All bikes today are moar awesomer than all bikes a few years ago. Enjoy it. Spend money when shit breaks. Spend money on trips.


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  20. #9045
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    Yeah, urge to purchase comes and goes.

    Will go for the spring swap first, then see about the rest.

    Thanks all

  21. #9046
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    Quote Originally Posted by Boissal View Post
    Experts, riddle me this one.

    I've been running a Hydra rear hub for about `1000 miles now, first on my trail bike and now on my enduro pig. It's a 32H centerlock microspline version if that matters. I've serviced it (cleaned and regreased spring/pawls) a couple times and overall have no complaints with it.

    Couple weeks ago I had the bike in the stand and noticed a lot of drag on the wheel. When I spin the wheel slowly by hand the hub feels ever so slightly notchy. It's also visible when the wheel slows down and stops, it seems to overcome a "sticky spot" then get stuck into the next one and backspin a couple degrees before stopping. As if there was a notch somewhere in the bearings and not enough momentum to overcome that.

    Initially I thought the rear axle torque was too high (GG recommends 25 Nm) and somehow squeezed something…
    I had to replace my rear hydra hub bearings way earlier than expected with similar symptoms. Appeared it was only one bearing that was actually shot though. Bearing replacement fixed the issue.

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