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  1. #1
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    fattie vs 29er rim lateral stiffness

    So, my intuition was right; 29er rims are weaker with lateral loads than fattie rims.

    Yesterday I rode my 29er instead of my fattie at Allaire State Park which has rooty trails with sharp corners. On a trail with a sharp corner and a root that is about 2 feet tall, I managed to bend my 29er rim when I landed the front tire... the funny part is that I've done that same corner with my fattie (which has a rigid fork) at the same speed. I like to ride fast and put a lot of stress on my bikes. Welp, my 29er rim couldn't hold the lateral load (or side load) coming off a tall root at the tight corner.

    It makes sense: 29er diameter + skinny rim = lesser lateral stiffness. 26" diameter + 80mm wide rim = stiffer rim for lateral loads.

    fattie vs 29er rim lateral stiffness-img_0421.jpg
    ^took this pic right before bending it

    fattie vs 29er rim lateral stiffness-img_0271-1-.jpg

    Have you noticed a similar thing?
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  2. #2
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    That's just a given. Wider the rim the stronger it's going to be laterally all else being equal.

    Think of it more "basic". A 2x2 board 6ft long. Standing on it that will bow and/or brake. 2x4 (laying as 2 wide, 4 tall) will bend less probably not enough to split. Go to 2x6 and and it doesn't budge.

    Then you can add light weight rims for XC racing vs AM/Trail rims. Both 29". Or cheap or wheels vs something like stans flow or spank oozy.

    Wider is stronger but build design can change that.

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  3. #3
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    Exactly. However, I did not for a second think this would happen, I thought the lateral stiffness was enough but guess not.

    ... more reason to love my fattie even more.
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  4. #4
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    Quote Originally Posted by tigris99 View Post
    Wider is stronger but build design can change that.
    Maybe cross-sectional design needs to change. That has A LOT to do with the lateral stiffness.
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  5. #5
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    Ya but that's for same width rim though. Which is why being a Clyde I chose spank oozy trail rims. Some said as good, some said better than flow ex. Different companies have different designs for stiffness and durability vs weight.

    Alloy used, build quality of the wheel also play a part.

    Then your comparing 29" vs 26". That changes loads on the rims as well. And what a 1" wide vs 3" (or more I can't tell rim width) comparison as well.

    But it's why fat rims can take a total beating and be single wall instead of double wall.

    Ive noticed the same thing plenty and I love my fatty but since my riding involves plenty of climbing. 29er is lighter and fast as well as more nimble (just vs my personal fat bike, no idea compared to others).

    Each has trade offs. Fat bike is mostly stock, my 29er I have upgraded and such to build it to handle my weight with what I ride. My 29er wheel survived something last night that I had expected to bend the hell outta it (my balls were sore for 2 hours). Creek crossing that the crossing had actually washed out a bit and I didnt realize it (rode it 50x on the past) till my man parts hit the back of my saddle keeping me from going over the bars.

    Wheels built for the purpose.

    Also 29er and fatty have 2 different cornering techniques and 29er isn't going to like turning the bars at speed near as much as a fat.

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  6. #6
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    Quote Originally Posted by tigris99 View Post
    My 29er wheel survived something last night that I had expected to bend the hell outta it (my balls were sore for 2 hours). Creek crossing that the crossing had actually washed out a bit and I didnt realize it (rode it 50x on the past) till my man parts hit the back of my saddle keeping me from going over the bars.
    Ouch... even the thought of that hurts my balls

    Quote Originally Posted by tigris99 View Post
    Also 29er and fatty have 2 different cornering techniques and 29er isn't going to like turning the bars at speed near as much as a fat.
    Completely agree. Although many people debate it, I love the beating that a fattie can take in tight corners at high speeds. The grip when turning and leaning into the inner side makes it so much easier to go faster and less braking. Never have I slipped sideways with my fattie, but common problem with my 29er.
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  7. #7
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    The amount of 'factual' information being shared here is impressive.

    Only not.

    You've shared a few anecdotes and then drawn a conclusion that has little to do with the circumstances. Of *course* it makes sense!


  8. #8
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    Being serious, not sarcastic, but please clarify. I know there is more science to wheel design but my posts are just the basic physics and engineering explaination of it. In which case none of what I stated is wrong, there is just more to the entire story. Your info is much of how I learned to build my current and first set of wheels, only set I've had that hasn't given me issues. So I'm curious to the rest behind it as some.info seems to be heavily debated.

    The cornering thing is "my experience" as to what bike I prefer for which use based on how they each handle my trails.

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  9. #9
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    Quote Originally Posted by mikesee View Post
    The amount of 'factual' information being shared here is impressive.

    Only not.

    You've shared a few anecdotes and then drawn a conclusion that has little to do with the circumstances. Of *course* it makes sense!

    He has "engineer" in his name.fattie vs 29er rim lateral stiffness-pope.jpg
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  10. #10
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    Let's not turn this into a pissing contest, be a good discussion though as I haven't seen a discussion on it yet personally (probably there somewhere I just haven't seen it)

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  11. #11
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    Quote Originally Posted by tigris99 View Post
    Let's not turn this into a pissing contest, be a good discussion though as I haven't seen a discussion on it yet personally (probably there somewhere I just haven't seen it)

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    We're comparing two rims here.

    One has a smaller diameter, is wider, and uses more material. It also uses a bigger tire.

    Thank goodness we have an engineer on the front lines to tell us that one is stronger. I don't think anyone could ever really know otherwise.

    This thread is pointless, hence the salty attitudes.

  12. #12
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    Back in the days when alloy rims were made of cheese and the option was single wall steel, you could induce considerable flex to the point of damage in a bare rim by using your bare hands.

    We used to ride offroad with those rims and bash them over rocks. Buckling wheels were such a part of life that just about every keen offroad cyclist could do a wheelbuild. One answer was to use tubulars because the rim had a box section and was much stronger/stiffer.

    My choice was a steel rim, not because it was any stiffer but because I could bang it back into shape trailside, if necessary.

    But the most important thing was to build a symmetrical wheel so each side had equal tension. It didn't stop buckles but there certainly seemed to be less instances of them.

    The growing number of gears on derailleurs has lead to hubs with huge differences in tension, and I find it hard to overcome the prejudices from my youth when looking at them. It just looks plain wrong to me, but a testament to the skills of the wheel builders these days and the quality of the rims which are now box section.

    Symmetrical wheel builds are one of the reasons I prefer singlespeed bikes or hubgear for offroad, and eschew derailleurs.

    That probably doesn't add much to the thread, but may add a bit of perspective.
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  13. #13
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    I did not think I would stir the pot lol

    I just found it interesting that my 29er rim couldn't hold up to it. I thought it would be strong enough for what I do. I did know that the fattie rims would be best, but what I am saying that the 29er rims should've been strong enough.
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  14. #14
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    Quote Originally Posted by Engineer90 View Post
    I did not think I would stir the pot lol

    I just found it interesting that my 29er rim couldn't hold up to it. I thought it would be strong enough for what I do. I did know that the fattie rims would be best, but what I am saying that the 29er rims should've been strong enough.
    That's not what you were saying, according to the thread topic and the subject line, but sounds good duuude. I hope you get some new awesome wheels.

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