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Thread: Ask the experts

  1. #5601
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    Quote Originally Posted by toast2266 View Post
    Yeah, I've read that before. I think they're wrong.

    Here's a video of a carbon rim impact test. The impact doesn't bottom out on the rim, so it's not a particularly hard hit. If I'm riding a rough downhill, I'd guess I encounter an impact like this every 100 feet or so. And that rim is flexing quite a bit. Certainly more than the tiny fraction of an inch that Nox is saying happens. And this video is for an older rim, which I'd bet is stiffer than some of the newer rims that have more vertical compliance built into them.



    I've ridden a lot of different carbon rims. Same bikes, same tires, same tire pressures. Differences in flex (both vertical and lateral) are most definitely noticeable.
    What? That ram is absolutely compressing the tire completely and hitting the rim. If you're doing that every 100 feet or so you are running too little tire pressure, and you're buying a lot of new rims. Obviously if the rim is being directly hit by something it will flex/break. My argument assumes that you have enough tire pressure to keep the rims themselves from hitting stuff. Anyway, I won't continue to argue with your anecdata. Science is useless against that.
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    ride bikes, climb, ski, travel, cook, work to fund former, repeat.

  2. #5602
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    Quote Originally Posted by climberevan View Post
    What? That ram is absolutely compressing the tire completely and hitting the rim. If you're doing that every 100 feet or so you are running too little tire pressure, and you're buying a lot of new rims. Obviously if the rim is being directly hit by something it will flex/break. My argument assumes that you have enough tire pressure to keep the rims themselves from hitting stuff. Anyway, I won't continue to argue with your anecdata. Science is useless against that.
    What rim impact?




    There are two kinds of engineers. There are those that do a bunch of calculations and then try to tell everyone that they're not feeling what they're feeling because it doesn't agree with the calculations. And there are those engineers that take what everyone is feeling and try to engineer their products around it. Which is why almost every successful carbon rim manufacturer has pushed to add more vertical compliance into their rims, because it was pretty much universally agreed that most of the early carbon rims were too stiff. And then there's Nox, who I haven't really heard anything about in a few years.

  3. #5603
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    So, I don't expect the weight to be super accurate on BTLOS's or Light Bicycle's websites, but similar wheel builds (30mm internal, 28 straight-pull bladed spokes, dt swiss hubs, brass nipples) are different by 100g.
    So, at least 1 of these is wrong.
    Or maybe I was doing the shallow one. Those seem fragile. Seriously, if I am on a full suspension with 150mm and 130mm travel, do I really need that much compliance? Pike and Deluxe Ultimates.
    Edit: nope, not shallow. Standard 30mm internal, matte, UD. Not premium, not enduro.
    No longer stuck.

    Quote Originally Posted by stuckathuntermtn View Post
    Just an uneducated guess.

  4. #5604
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    Nevermind. They do actually have different listed rim weights.

    The BTLOS are a little heavier and cheaper.
    Which would you get?
    No longer stuck.

    Quote Originally Posted by stuckathuntermtn View Post
    Just an uneducated guess.

  5. #5605
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    Thats how Nino Schurter sets his tire pressure. He presses his thumb as hard as possible in the middle of his tread, if he feels the rim with his thumb, he adds a little bit or air.
    16.6 PSI in the front and 17.4 PSI in the rear. A 30mm ID rim with 29 x 2.4WT Maxxis Aspen (720g) or Recon Race (740g).

    Oh ya, ID refers to the inside dimensions of an object.

  6. #5606
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    I didnt like the feel of my carbon wheels. LB's but i bet theyre all similar to some degree. Wasnt just vertical compliance either. They were harsh side to side. Definitely noticed them pinging off stuff. I can see where theyd be beneficisl if youre xc racing. Stand on the pedals and the bike goes forward instead of flexing. That stiffness is at the expense of ride compliance . I didnt have a reliability problem but i can see where a carbon rim might have a shorter life span for some people. I look at my purchase as a waste of money for minimal weight savings. Maybe 28spokes or less and together with the newer shallow wall height has added enough compliance but ill be f'd if im going to spend that much $ to be disappointed again. 32 hole j bend spokes lacing up hope wheels or hope hubs go a dt rim ftw

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  7. #5607
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    Click image for larger version. 

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    yea or nae? And does anyone have a coupon code? (I don't Facebook, so I can't get the coupon code by sharing the link).
    (also, IDK if I can buy this right now.)
    No longer stuck.

    Quote Originally Posted by stuckathuntermtn View Post
    Just an uneducated guess.

  8. #5608
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    [QUOTE=toast2266;6367934]What rim impact?
    /QUOTE]

    The first impact tore a spoke out of the rim. Posting a video of a destructive rim test and then claiming that you hit your wheels that hard every 100 feet is...and interesting strategy.

    Since I'm waiting for some chickpeas to cook, I'll cunt up the thread further by disagreeing with the assertion that describing the width of something by using the term "inner dimension" somehow makes more sense than just using the abbreviation for "Inner/Internal Width". Last time this came up we went in circles for a while and I believe it was ultimately determined that "ID" as an abbreviation for "inner dimension" is used in the cardboard box industry, which would seem to have minimal crossover to wheels.... The commonly understood meaning of "ID" when referring to tubing etc is "Inner Diameter".

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    Last edited by climberevan; 07-31-2021 at 04:17 PM.

  9. #5609
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    There is also this:
    Name:  wheel build 2.jpg
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    More solid with 32 hole, but shallow rims. Weight isn't very high. Price is much better.
    No longer stuck.

    Quote Originally Posted by stuckathuntermtn View Post
    Just an uneducated guess.

  10. #5610
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    When I changed to carbon from some Stan’s wheels it was night and day. Same tires, same pressures. The biggest difference was lateral stiffness. The bike (an older turner sultan) was completely transformed on corners. No wobble, no flex. Like on rails.

    I did not notice any vertical change.

    However, when I finish building a new alloy wheel or a new carbon wheel and roll it out with out a tire the spikes ping the same and in load/wind. Makes me think the vertical elasticity is similar


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  11. #5611
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    [QUOTE=climberevan;6367979]
    Quote Originally Posted by toast2266 View Post
    What rim impact?
    /QUOTE]

    The first impact tore a spoke out of the rim. Posting a video of a destructive rim test and then claiming that you hit your wheels that hard every 100 feet is...and interesting strategy.
    meh. It was the first video that popped up, and as I said above, they were testing a prototype with extra spoke tension. Sure, a nipple ripped through. But the point is the rim flexed quite a bit.

    But since you want to be picky, here's another video if a Stan's rim that was specifically designed to have vertical compliance.




    If someone says anything about literally any other part of a bike being noticeably stiff / noticeably flexy, no one bats an eye. Handlebars too stiff? Sure. Frame too flexy? Sure. Cranks too flexy? Sure.

    But the second anyone says a rim is too stiff or too flexy, some internet pseudo engineer will inevitably pipe up with [nerd voice] "actually, if you refer to page 47 of Jobst Brandt's The Bicycle Wheel, you'll find that it's physically impossible for you to notice the flex in a wheel."

    Bike wheels aren't magic. They flex, just like every other part of the bike. It's noticeable, and it has a tangible effect on ride quality. Anyone who says otherwise is completely oblivious to what their bike is doing under them.

  12. #5612
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    Every world cup dh team that is sponsored by a carbon rim manufacturer is running 28 spokes or less and their mechanic has the spokes with substantially less tension than most anyone would run for a reason.
    Nico was undertensioning aluminium wheels and trying to find added compliance in frames, forks and bars all through the early 2000's. That continues today. Whats that carbon rim isabeau rides? I think sram bought them and theyre under the sram banner now. Super low profile and single wall trying to get compliance

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  13. #5613
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    Quote Originally Posted by grinch View Post
    Whats that carbon rim isabeau rides? I think sram bought them and theyre under the sram banner now. Super low profile and single wall trying to get compliance
    I think she's on those crazy Zipp rims. Those things look pretty interesting - curious to try them.
    Last edited by toast2266; 07-31-2021 at 06:43 PM.

  14. #5614
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    Quote Originally Posted by stuckathuntermtn View Post
    There is also this:
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    More solid with 32 hole, but shallow rims. Weight isn't very high. Price is much better.
    I like that build.
    Quote Originally Posted by powder11 View Post
    if you have to resort to taking advice from the nitwits on this forum, then you're doomed.

  15. #5615
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    My comparison was pretty apples to apples. Same tires, same pressures, same handlebars and frame and suspension settings. The only difference was that the new wheels are 30mm wide vs the 27mm stock ones, which, yes is a touch more volume, but I started out on the low end of my usual pressure. And then seriously thought there was something wrong with my fork. But there's a weight and natural frequency difference there too so like rebound for example might now be too high. Anyway I turned it down a click, run my fork in full open more, and am sticking to the lower range of pressure I like, and did a lower service, and have been on a few rides, so it seems fine/normal now. Eventually I'll swap on the other wheelset which has real tires so that'll be something of a contrast.

    Like sure yes the suspension is moving the most, and then the tires, and then the wheel and frame flex are small in comparison, but you still notice a little bit.

  16. #5616
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    Quote Originally Posted by stuckathuntermtn View Post
    There is also this:
    Name:  wheel build 2.jpg
Views: 166
Size:  87.2 KB

    More solid with 32 hole, but shallow rims. Weight isn't very high. Price is much better.
    If it were me, I'd do 28h. 32h on aluminum rims for sure. But on carbon rims, I think you're fine with 28h. If you break a carbon rim, it's usually not because there aren't enough spokes. And, per the argument above, 32 spokes make the wheel a bit stiffer vertically, which isn't usually what you want.

    I'd also do a 240 hub. But that's just paying for gram savings. 350 is functionally fine.

  17. #5617
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    I'd also send them an email before clicking "buy" and ask them if they actually have all those hub options in stock or if there's an option that has a shorter lead time or is in stock / has the parts in stock in north america.

    I tried to order some tubular rims from LB the other day to build some cx wheels and apparently my bank rejected the transaction and turned off my card without sending me any sort of a notification so that was fun when I tried to pay for my beers earlier. I'd been emailing a guy and he sent me a custom invoice but said it only worked for a limited period of time so I wasn't sure if it was just no good any more or what.

  18. #5618
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    Quote Originally Posted by jamal View Post

    Like sure yes the suspension is moving the most, and then the tires, and then the wheel and frame flex are small in comparison, but you still notice a little bit.
    I stand by my offer. Let's set up 2 wheelsets with rims that are within a couple of mm IW and a few dozen grams, put on identical tires and pump them up the same. Then we can put some kind of cardboard shroud on the rims so they can't be seen. Double blind the test and I'll buy a set of BTLOS wheels for anyone who can reliably pick out which is which.

    Oh, and I also don't vertical frame flex is meaningful, even on a road bike. Lateral, definitely. On a MTB with low pressure tires and suspension there is just no way a mm or two of frame flex could possibly translate.
    ride bikes, climb, ski, travel, cook, work to fund former, repeat.

  19. #5619
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    Quote Originally Posted by toast2266 View Post
    I think she's on those crazy Zipp rims. Those things look pretty interesting - curious to try them.
    Thats them. They might be good.

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  20. #5620
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    Quote Originally Posted by grinch View Post
    Every world cup dh team that is sponsored by a carbon rim manufacturer is running 28 spokes or less and their mechanic has the spokes with substantially less tension than most anyone would run for a reason.
    Nico was undertensioning aluminium wheels and trying to find added compliance in frames, forks and bars all through the early 2000's. That continues today. Whats that carbon rim isabeau rides? I think sram bought them and theyre under the sram banner now. Super low profile and single wall trying to get compliance

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    These

    https://www.sram.com/en/zipp/models/ri-moto-30-a1

  21. #5621
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    I'm no expert so I'll ask: how can a ridiculously fast pro rider, XC or otherwise, run a PSI lower than 20 and not destroy their rims, flat, or roll their tires on fast corners, even if they weigh something like One Twinkie Five?

    It can't be simply finesse, we all get exhausted and/or make mistakes. Only time I got away with under 20 was with Maxxis DD's and it wasn't on purpose. Some serious 'bonggggsss' on my rear rim woke me up to my flacid PSI. Edit: with a Cane Creek coil rear shock.

  22. #5622
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    Quote Originally Posted by Bushwacka View Post
    Thats them. Still not sold on them. Not sure i want my tire and tread twisting. Thinking it might feel like a flexy bead on a tire. It does indicate that people are recognizing carbon rims, or rims in genersl, should have a degree of compliance though. I think carbon as it is now is just a poor material for rims

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  23. #5623
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    Quote Originally Posted by toast2266 View Post
    If it were me, I'd do 28h. 32h on aluminum rims for sure. But on carbon rims, I think you're fine with 28h. If you break a carbon rim, it's usually not because there aren't enough spokes. And, per the argument above, 32 spokes make the wheel a bit stiffer vertically, which isn't usually what you want.

    I'd also do a 240 hub. But that's just paying for gram savings. 350 is functionally fine.
    Quote Originally Posted by jamal View Post
    I'd also send them an email before clicking "buy" and ask them if they actually have all those hub options in stock or if there's an option that has a shorter lead time or is in stock / has the parts in stock in north america.

    I tried to order some tubular rims from LB the other day to build some cx wheels and apparently my bank rejected the transaction and turned off my card without sending me any sort of a notification so that was fun when I tried to pay for my beers earlier. I'd been emailing a guy and he sent me a custom invoice but said it only worked for a limited period of time so I wasn't sure if it was just no good any more or what.
    Thanks
    Can't do J bend 28h unless I do I9 1/1 from LB.
    So, again, straight pull CX-ray ok?
    Might also prefer 240s, but whatever.
    BTLOS build comes out a little too good to be true price/weight wise, so that makes me leery of durability because of the standard tri matrix.
    No longer stuck.

    Quote Originally Posted by stuckathuntermtn View Post
    Just an uneducated guess.

  24. #5624
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    Someone should buy a couple of these. Loosen the wheel tension on one and compare for compliance

    https://www.bikeradar.com/features/h...ike-prototype/

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  25. #5625
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    I dunno, I was a hard core anti carbon wheels guy for a long time, I'm light, pretty smooth since I come from fully rigid/hardtail for decades background, but rally pretty decent...I didn't wreck alloy wheels but I certainly spent a bunch of time truing them, and they certainly had flat spots and wobbles. I picked up some Reserve 30's last spring and I haven't had to touch them once, and they're still deadly straight. They like to be pushed and handle some gnarly hits, they feel way more solid that my alloy wheels without being harsh at all.

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