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  1. #1
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    Fox 34 vs Rock Shox stiffness, tested

    After all specualtion about the stiifness of the 34 mm stanchions vs 32 opposed to 15 mm vs 20 TA there is finally some data.
    From Bike Magazin (Germ) dec. 2011.

    The answer is... both.
    The bigger stanchions do give the Fox an edge in braking stiffness, the bigger axle on the Rock Shox nudges out the smaller one in torsion:

    Fox 34 float 140 mm travel :
    2006 g
    torsion 24.8 Nm/degr
    brake stiffness 232.2 Nm/Degr
    Revelation XX 137 mm travel
    1885 g
    torsion: 27.5 Nm/degr
    brake stiffn.: 204.7 Nm/degr.

  2. #2
    steep fast and loose :)
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    what does this actually translate to "in-the-field" however ?

    both forks are on my radar currently.......

  3. #3
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    As an engineer myself, I can't help but wonder about other variables and their effect to the end user (rider). For instance, the wheels (each part [hub, spoke, rim] and as a whole), tires, and their interface (wheel width/tire pressure/sidewall stiffness...etc), rider weight, head tube/frame stiffness..etc. All these variables could possibly have more effect on the what the rider feels over the stiffness of a fork.

    I like seeing data, but unless every variable is accounted for the data is useless. It's basic scientific rules of testing. None-the-less thanks for posting this info
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  4. #4
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    Quote Originally Posted by bquinn View Post
    As an engineer myself, I can't help but wonder about other variables and their effect to the end user (rider). For instance, the wheels (each part [hub, spoke, rim] and as a whole), tires, and their interface (wheel width/tire pressure/sidewall stiffness...etc), rider weight, head tube/frame stiffness..etc. All these variables could possibly have more effect on the what the rider feels over the stiffness of a fork.

    I like seeing data, but unless every variable is accounted for the data is useless. It's basic scientific rules of testing. None-the-less thanks for posting this info
    I am not an engineer but I don't see what you are saying. I would like to see the methodology of the test but knowing German testing, I'll bet that the forks are measured in a test jig sans wheels. It is simple to measure how much twist and fore/aft flex there is with a given force. Variables are non existent.
    The trouble with having an open mind is that people will insist on trying to put things in it.

  5. #5
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    This data is far from useless. It shows that given equal wheels and tires, the Fox will have superior fore-and-aft (braking) stiffness and the Rockshock will have better lateral stiffness.

    So the RS is about 10% stiffer in torsion (steering accuracy) and the Fox is about 15% stiffer in braking.

    Cool info, thanks for posting!
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  6. #6
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    Interesting to read, I donít think this says much about 32/34mm or 15/20mm though. The least torsionaly stiff fork i have ever owned had a 24mm axle. The stiffest for/aft fork Iíve ever owned had 32mm stanchions and Iíve owned 2 forks with 40 mm stanchions. Crown design has alot to do with these characteristics, Iíve bent crowns on a couple of forks over the years and the stanchions remained strait as new.

  7. #7
    steep fast and loose :)
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    as i said - how does this translate in use - i AM an engineer and value the data offered but wonder how much is actually felt by the end-user.......?

  8. #8
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    Quote Originally Posted by The_Lecht_Rocks View Post
    as i said - how does this translate in use - i AM an engineer and value the data offered but wonder how much is actually felt by the end-user.......?
    what "end user feeling" scale do you want the results in?

    seriously, as an engineer you should understand that how an engineered product is subjectively interpreted by individuals is neither quantifiable nor predictable in specific terms.
    Last edited by meltingfeather; 12-05-2011 at 09:47 AM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  9. #9
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    Quote Originally Posted by bquinn View Post
    As an engineer myself, I can't help but wonder about other variables and their effect to the end user (rider). For instance, the wheels (each part [hub, spoke, rim] and as a whole), tires, and their interface (wheel width/tire pressure/sidewall stiffness...etc), rider weight, head tube/frame stiffness..etc. All these variables could possibly have more effect on the what the rider feels over the stiffness of a fork.

    I like seeing data, but unless every variable is accounted for the data is useless. It's basic scientific rules of testing. None-the-less thanks for posting this info
    what you propose is impossible, and what you are saying is that all data is useless.
    every variable accounted for? is that a joke?
    how on earth would you account for the variables between individual interpretations (the "rider feel")?
    that said... you can assume all else equal for these comparisons. if you did the testing on a whole-bike basis (ignoring the "all variables" fatal shot imparted by trying to predict what individuals will feel), by your own argument the data would be useless to anyone with a different bike set-up. the testing is unitized to comopare individual compoents for a reason.
    and you're an engineer?
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  10. #10
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    Quote Originally Posted by kosmo View Post
    This data is far from useless. It shows that given equal wheels and tires, the Fox will have superior fore-and-aft (braking) stiffness and the Rockshock will have better lateral stiffness.

    So the RS is about 10% stiffer in torsion (steering accuracy) and the Fox is about 15% stiffer in braking.

    Cool info, thanks for posting!
    regarding 'equal wheels'---equal, other than the fact that one wheel would be using a hub configured for 20 mm. but I agree with your point.

    thanks Tjaard for posting. I've said it before and I'll say it again--it's sad that US magazines rarely bother making basic engr measurements such as the ones routinely made in the German bike mags.

    bquinn, re: how engineering analyses work. in my job, we routinely try to 'package' all the variables into one large predictive model, but we realize that this effort is often an endless search for the holy grail. i.e. is still worth doing long-term, but in the real world of making and testing products one has to also make use of simple, isolated tests that focus on a small set of variables and hold other variables constant.

    A grand unified 'Fork Flex' theory that takes into account headtube flex, wheel flex during cornering vs pedal strokes, wind direction, whether the rider is wearing spandex vs baggie shorts, etc etc etc, is a fun thing to think about and work toward but I hope you were joking when you said that no conclusions can be made until a grand unified theory is developed and proven.
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  11. #11
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    I assume they measure torsion in a plane perpendicular with the steering axis, but what about torsion in plane with it - what could be called "independent leg movement " - that would be a result of the stiffness of thru-axle combined with the robustness of the arch, no?

  12. #12
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    Quote Originally Posted by The_Lecht_Rocks View Post
    as i said - how does this translate in use - i AM an engineer and value the data offered but wonder how much is actually felt by the end-user.......?
    id guess they would feel pretty similar. i have a 20mm reba and a 55 and cant notice much (if any) difference other than a maxle is easier to use.

  13. #13
    steep fast and loose :)
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    b-kul : my point exactly..... so many variables equate to little noticeable difference in action.

    the lateral flex is important too - it will offer "give" during sustained cornering... less lateral flex will mean less "give" which may affect fork performance................

    perhaps................

    in real terms, neither fork is likely to be noodly in action - i'm surprised the fox lost out with 34mm stanchions in torsion, but as mentioned, perhaps axle stiffness is more important.....

    so is it worth opting for the 32mm fox in preference to the 34 for general XC / trail riding

  14. #14
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    All this begs the question: why in the heck did fox go with the 15mm qr on this fork? they obviously see the advantage of the 20mm, since they use it on their DH forks. It adds minimal weight. So why go half way Fox??

  15. #15
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    Quote Originally Posted by No Agenda View Post
    I assume they measure torsion in a plane perpendicular with the steering axis, but what about torsion in plane with it - what could be called "independent leg movement " - that would be a result of the stiffness of thru-axle combined with the robustness of the arch, no?
    I think I understand what you're saying. If the "torsion" they measured is pure torque applied to the wheel (i.e. a positive force at the rim and an equal negative force at 180 degrees from the positive, twisting around the axis of the steerer), then I believe they should have measured an additional metric; one that is related to independant leg movement. Hard cornering induces a lateral load on the tire/wheel near the contact patch, the resulting moment causing the wheel to want to rotate about an axis that's 90 deg. from the axle, nearly parallel to the ground. Did they simulate such a loading at all?
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  16. #16
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    Quote Originally Posted by bholwell View Post
    I think I understand what you're saying. If the "torsion" they measured is pure torque applied to the wheel (i.e. a positive force at the rim and an equal negative force at 180 degrees from the positive, twisting around the axis of the steerer), then I believe they should have measured an additional metric; one that is related to independant leg movement. Hard cornering induces a lateral load on the tire/wheel near the contact patch, the resulting moment causing the wheel to want to rotate about an axis that's 90 deg. from the axle, nearly parallel to the ground. Did they simulate such a loading at all?
    That. It seems that hard cornering is as common, if not more so, than riding lines that are apt to try and deflect the wheel in a left/right direction.

    Really, a ride often involves cornering while concurrently negotiating obstacles, so if they only tested torsional stiffness the easy way (fork dropouts clasped solidly and a strain gauge on the steerer) then the test is pretty limited in scope.

  17. #17
    steep fast and loose :)
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    Quote Originally Posted by wasfast View Post
    All this begs the question: why in the heck did fox go with the 15mm qr on this fork? they obviously see the advantage of the 20mm, since they use it on their DH forks. It adds minimal weight. So why go half way Fox??

    great point - it does seem erroneous to spec the 15mm on the 34mm fork...........

  18. #18
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    Quote Originally Posted by No Agenda View Post
    That. It seems that hard cornering is as common, if not more so, than riding lines that are apt to try and deflect the wheel in a left/right direction.

    Really, a ride often involves cornering while concurrently negotiating obstacles, so if they only tested torsional stiffness the easy way (fork dropouts clasped solidly and a strain gauge on the steerer) then the test is pretty limited in scope.
    Yes, we're in agreement.
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  19. #19
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    15mm is silly, just another standard marketed as being "lighter than 20mm and stronger than QR." In reality, it isn't as strong as 20mm and isn't really much lighter than a 20mm setup, especially with the Maxle Light from RS.

    Suckers bought in....and had to buy new hubs/conversion kits/wheels to keep up with their beloved new 15mm standard.

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    What this data suggests is that Fox should have designed their Float 34 around a 20mm T/A! If Rockshox is smart they'll build their next long travel 29er fork with a thicker and more rigid stanchion.

    Thicker stanchions for a 29er fork are a no brainer . If you view the fork stanchion as a giant lever arm a 29er fork will produce more leverage for any given level of travel than a comparable 26 inch fork as a result manufacturers SHOULD have made long travel 29er forks more rigid at some point: personally I think this should have happened around 140 and possibly even 120mm.

  21. #21
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    Quote Originally Posted by wasfast View Post
    All this begs the question: why in the heck did fox go with the 15mm qr on this fork? they obviously see the advantage of the 20mm, since they use it on their DH forks. It adds minimal weight. So why go half way Fox??
    shimano likes the 15mm system best and has courted most manufactures that way for trail forks.

  22. #22
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    Agreed !

    Quote Originally Posted by CharacterZero View Post
    15mm is silly


    No doubt.......however , I 'm going to give a Fox 34 Float a try anyway because I got a good deal on one ! TIG.

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    wow, I guess I thought it was obvious I was answering the question on how this effects the rider (as the final result). Guess smart people can't always pick up on the obvious
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  24. #24
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    Quote Originally Posted by BacDoc View Post
    Let me translate the German engineering data to American mountain biker parameters:

    50% say-
    "That Fox is a totally sick fork that shreds all terrain and blows the Rock Shock away!"

    The other 50% say-
    "That Rock Shock is a totally sick fork that shreds all terrain and blows the Fox away!"

    This was double blind random controlled data published in a peer reviewed journal, so you can accept this as fact.
    exactly, now lets go ride!
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  25. #25
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    Let me translate the German engineering data to American mountain biker parameters:

    50% say-
    "That Fox is a totally sick fork that shreds all terrain and blows the Rock Shock away!"

    The other 50% say-
    "That Rock Shock is a totally sick fork that shreds all terrain and blows the Fox away!"

    This was double blind random controlled data published in a peer reviewed journal, so you can accept this as fact.

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