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frame design-an effort

Discussion in 'Downhill & Freeride' started by freeriding, Sep 25, 2012.

  1. freeriding

    freeriding Monkey

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    hallo everybody!

    lots of work done.

    what do you think?

    Untitled-2.jpg

    6.5 cm of rearward axle disposition (this is why i have a cs length of 396mm)

    pedal kickback can be lowered at 16 degrees with a chain cog.

    feedback appreciated.
     
    #1 -   Sep 25, 2012
    Last edited: Sep 26, 2012

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  2. Pslide

    Pslide Turbo Monkey

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    Looks good to me.

    Everyone seems to love their Zerodes, seems like your design works on the same principles.

    Is this just a fun exercise for you, or do you have grander plans?
     
  3. norbar

    norbar Turbo Monkey

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    10.5'' shock? Isn't it too progressive?
     
  4. freeriding

    freeriding Monkey

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    it is 267 x 90mm (10.5” x 3.5”) as most dh bike companies use nowadays. it offers more adjustability and higher shock longevity.

    it is progressive as it should be, cause of the linear nature of the springs.

    in the end the lr regresses to ensure that the shock won't bottom out harshly.

    i had many issues to overcome in the design, such as chainstay length, shock-wheel clearance, bb height, rocker arm low pivot-bb clearance, centralized and low centre of gravity.

    i have some detailed cad drawings and started also to work on solidworks.

    don't know if i can move forward producing it myself, maybe giving it to a company and sell it.

    or am i too naive??? :weee: :rofl:
     
    #4 -   Sep 25, 2012
    Last edited: Sep 25, 2012
  5. freeriding

    freeriding Monkey

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    look at the rear axle path.

    it is higly rearward giving unsurpassed square bump compliance, it 'eats' everything on its way.

    and look how balanced the rear and front axle path is, leading in stability, in balanced geometry all the way of the travel, as the suspension works and wheelbase that is constantly balanced.

    high pivot magic!!

    sxsx.jpg
     
    #5 -   Sep 25, 2012
    Last edited: Sep 25, 2012
  6. UiUiUiUi

    UiUiUiUi Turbo Monkey

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    this...
    but maybe go ahead and build one for yourself and then see whether it is all you thought it should be... and then go from there...
     
  7. freeriding

    freeriding Monkey

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    could i maybe come in contact with some factory in far east to build one for me?

    it that possible? how expensive would it be?
     
  8. demo 9

    demo 9 Turbo Monkey

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    with that much rearward, you WILL need some sort of pulley or other type of system to avoid ripping the derailleur off. (jedi, zerode, brooklyn)

    Look sweet to me, but (and i could be wrong) i think zerode wanted to do a design similar to that, but couldnt because of chain growth, which is why they added the gearbox.
     
  9. wiscodh

    wiscodh Monkey

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    i dont know if you will be able to find a manufacture that will do a one off proto with the possiblity of no production. Might look for a smaller custom builder or somone like zen. If you do find somone, it will be expensive probally around 8-10k for the frame, if you have everything speced out for the builder. Engineering drawings, cad files for the machined parts, tube profiles, ect. If you dont have any of that, your cost will go up. If you got the cash and the want go for it, ride it, learn from it, and have another go at it.
     
  10. norbar

    norbar Turbo Monkey

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    1. It doesn't have to be progressive. I know it's preference but looking at many designs it is very progressive (and they use springs too) Also why it is progressive right after sag point to get linear only later? Unless you want it to run more than 33% sag.

    2. It's not regressive at the end. It's progressive.

    3. 10.5'' isn't the most common. 9.5'' is the most common. Light riders will have trouble finding springs for the bike. Especially with something like an rc4
     
  11. freeriding

    freeriding Monkey

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    with the pulley as shown, i have a very low pedal kick back, and a chain growth of only 12mm.

    so no problem and no gearbox needed.

    rvevbe.jpg
     
  12. freeriding

    freeriding Monkey

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    1. as you said it is preference. linearity for me suits better with progressivity. mostly dh bikes now choose progressive lr.

    2. yeap, english is not my native language, especially technical terms. :p

    3. i know, but i believe that 10.5'' is the best suited here. i can adjust it though for an 9.5 spring. preference thingy again.

    thank you for the feedback! jeep it up!!! :thumb:
     
    #12 -   Sep 25, 2012
    Last edited: Sep 25, 2012
  13. demo 9

    demo 9 Turbo Monkey

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    :D didnt see the pulley
     
  14. StyledAirtime

    StyledAirtime Monkey

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    where'd ya hear that tidbit? Dodzy and rob had Been building gearbox bikes seperatly for a while then got together on a job and decided to pool together creating the first proto after deciding to use the Alfine. Dodgys first gbox bike had a inboard brake and carbon rear end. And rob has had a few gear box trail bikes before Zerode came about. Always gear boxs tho
     
  15. norbar

    norbar Turbo Monkey

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    1. It is not true that most dh bikes are progressive. Not that progressive. Some went a bit more progressive but for example Trek made the carbon session a bit less progressive for it to behave better on the rough tracks. Demo is very linear even if it got a bit progressive in the last iteration. Most plowy bikes are more linear than progressive. My legend is even a bit regressive at the end.

    Linear leverage rate is better for the rough but it is also better for shock setup imho. You can easily make the design much much more linear and still have a bike that bottoms out very rarely. Also a linear shock + a fairly linear bike(very few are a total flat line that doesn't change) doesn't mean the bike will be easy to bottom out.

    2. 10.5'' is a fad. The benefits in terms of damping control and shock longivety are minimal and basicly you make it a PITA for riders under 160lbs to get a spring. Especially if they decide to go with an rc4 but with that shock you also have a problem with the frame being very progressive (that shock also is quite progressive).



    As for selling the project -I doubt the companies would be willing to test it. Especially without a working prototype and after a proper FEA.
     
    #15 -   Sep 25, 2012
    Last edited: Sep 25, 2012
  16. freeriding

    freeriding Monkey

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    1. take a look:














    NOW look at mine:

    wt4gt35t.jpg

    i guess that's enough...:weee:


    2. 10.5 is used by wilson and the new gambler. more to come i guess! preference though as i said before.


    i am an engineer, i'll make a finite element analysis, although i am not sure i'll go that far.
     
    #16 -   Sep 26, 2012
    Last edited: Sep 26, 2012
  17. norbar

    norbar Turbo Monkey

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    What was enough? Most of the shown bikes are less progressive than your design. Yours of course it's not boarderline but if you want something that goes well through the rough I'd go more linear. You leverage ratio is similar to the Willson so that is an argument. Never rode the bike. Other ones are less progressive than yours. Also not the differance between the 88 and 99 sessions. I may be nitpicking because the wilson supposedly rides really nice but a bike doesn't have to be that progressive to not bottom out.

    As for 10.5 catching on - it was the same a few years back. A few frames had it and people thought it was a new standard but nothing happened. Again try to find a 150lbs spring.
     
  18. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

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    That's actually not true, a higher leverage ratio in a given part of the travel will allow the wheel to move more easily (eg. out of the way of a bump) in that part of travel - thus a more progressive early stroke will generally give better bump absorption characteristics. This is actually quite handy, as you can build lower pivot bikes that have better bump absorption characteristics than their pivot location would otherwise allow.

    The downside of increased progression is that you also use up a lot of travel very easily, and this can result in a somewhat wallowy and unstable ride. But there are clever ways around this, as linkages allow the L/R curve to change shape at different positions in the travel. Shock setup can be a bit more difficult but it hasn't really been an issue in my experience. However with that said, I don't see the need to go very progressive on a high pivot bike, as bump absorption characteristics are already excellent.
     
  19. freeriding

    freeriding Monkey

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    look at the canfield, the phoenix and the makulu...isn't that progressive?

    i made the design with a 240 x 76mm (9.5” x 3.0”) shock and 211mm of travel.

    LR more linear!

    i guess we're all happy now! :rofl::thumb:

    Untitled-3.jpg

    cheers bros, keep it up!!
     
  20. norbar

    norbar Turbo Monkey

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    Less progressive than your designs. All of them. Don't look at the overall steepness. Gradient and how the ratio changes after sag are important. Progression before sag is good imho but I am a bit sleep deprived at the moment. Also due to the fact that the leverage gradient lowers with travel they will not feel progressive. It will be more like my legend feels.
     
  21. freeriding

    freeriding Monkey

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    you mean regression. when the lr is progressive, in a certain amount of travel, the leverage is lower than that in a regressive, which means that less force is exerted to the shock and thus, less compression.
     
  22. norbar

    norbar Turbo Monkey

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    I'm stupid, you are right. should have remembered that. Still the frame has some progression after sag. I'm not really a believer that dh frames should be very progressive in the latter part of the travel.
     
  23. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

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    Nah, I meant progression. I believe if you have a straight LR curve where the LR number is high at 0mm of travel (say 4:1) and is low at 200mm of travel (say 2:1) then that bike would be defined as progressive - even though the LR is getting lower as travel is used.

    That's because at 4:1 the wheel moves more for a given amount of shock travel, and thus moves more easily, whereas by 2:1 the wheel moves less for a given amount of shock travel, and thus is harder to move - or 'ramps up'.

    I thought this was the universally accepted definition of progression but correct me if I am wrong - I believe our understanding is the same, perhaps you are just defining it differently.
     
  24. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

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    Don't really agree with that either, as you end up with a frame that is heavily dependent on a progressively valved damper to work correctly (unless you want to run an air shock, which comes with its own set of drawbacks). The Legend for example would struggle to function well without an RC4, same story on the Sunday.

    Take that shock away from either of those frames, and you end up having to compromise between maintaining bump performance and maintaining acceptable travel usage.

    But even with the appropriate shock, I think there are other concerns, for example damper progression is unidirectional (for lack of a better descriptor) so you don't get the 'pop' on the return stroke that you would from a bike with mechanical (LR) progression - because in that case the spring would return the stored energy as opposed to the damper dissipating it. I think that's part of the reason these particular bikes (when sprung and damped correctly) are less poppy than more progressive alternatives - and personal preferences for pop/plow aside, this results in the bike requiring more rider input and energy to clear obstacles.
     
  25. norbar

    norbar Turbo Monkey

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    I agree with you but I think we also need a decent compromise between staying up in travel and stability/plow ability. I haven't ridden a bike like the wilson so I can't comment on the sweet spot between something with a progression wall like the 951 and something that is progressive yet stable.
     
  26. freeriding

    freeriding Monkey

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    my mistake, ****ing english terminology...

    however you wrote:
    this is a characteristic of the regressive lr, not the progressive. (for about the same starting leverage value-that is in 0mm wheel travel)

    in the progressive you have a more strict use of travel, cause for a certain amount of travel you have less leverage, than on a linear or a regressive lr.
     
    #26 -   Sep 26, 2012
    Last edited: Sep 26, 2012
  27. freeriding

    freeriding Monkey

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    let's see this chart for example:



    the santa cruz (regressive) can reach eg 50mm of travel, quite more easily for the same bump, compared to the rocky mountain (progressive).

    this means that the regressive lr uses easily a lot of travel...
     
    #27 -   Sep 26, 2012
    Last edited: Sep 26, 2012
  28. norbar

    norbar Turbo Monkey

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    Nope. Udi is right on that right. Don't think of it in terms of - progresive/regressive but in leverage ratio alone. A progressive bike at the end is hard to bottom out because the ratio goes to low numbers and you need more force to compress the shock but with progressive begining you get a high leverate ratio in the fist part of travel.


    Udi I'd rep you but must spread moar.
     
    #28 -   Sep 26, 2012
    Last edited: Sep 26, 2012
  29. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

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    A progressive bike will start soft and end firm. A degressive bike will start firm and end soft.

    With all else equal (which is not the case on the graph you linked, so I won't refer to it), the progressive bike will have the tendency to use the initial travel more easily than the regressive bike, as the LR is higher at that point. The degressive bike will be firmer initially, however use travel more easily later in the stroke, and thus bottom out more easily.
     
  30. no skid marks

    no skid marks Monkey

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    Longer shocks have slower moving pistons and push the oil slower. Good to a point(and for keeping cooler), but then tuning becomes harder when to big.
     
  31. mtg

    mtg Green with Envy

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    I think the confusion of terminology of progressive/regressive is because:

    The leverage rate curve is an inverse of what people normally find intuitive. Ie, when people say "progressive", it is commonly accepted that they are referring to the characteristics of the spring rate curve at the rear wheel, which produces a regressive leverage rate curve at the shock.

    It would make more sense if the leverage rate number was inverted, so a progressive spring curve at the wheel also made for a progressive "leverage" curve, but then instead of talking about 2:1 or 3:1, we'd be talking about less convenient ratios such as 0.5:1 or 0.3:1.

    This same thing used to screw me up when I was working on car suspensions, and to get it straight, I put the definition on my desktop background for a few months to forever burn it into my brain.
     
  32. freeriding

    freeriding Monkey

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    unfortunately i think you are wrong.

    the regressive lr uses more travel for the same bump. the mechanical advantage gets higher through the travel, this is why.

    in a progressive lr the mechanical advantage reduces...

    and for ****s sake, we are talking about leverage rate, NOT bike rate (shock rate related to wheel travel) which is the inverse (opposite relationship) of leverage. (in bike rate we use the terms rising rate and falling rate)

    the diagrams that i put show the Leverage Rate.
     
    #32 -   Sep 26, 2012
    Last edited: Sep 26, 2012
  33. freeriding

    freeriding Monkey

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    long story short:

    Wheel Travel divided by Shock Stroke = average Leverage Rate (eg, a 5 inch travel bike with a 2.5" travel shock has an average leverage ratio of 2.0).

    Shock rate is the inverse (opposite relationship) of leverage. Shock Stroke divided by Wheel Travel = average Shock Rate.

    this means that a progressive LR, has a rising rate (in the bike rate diagram) and a regressive LR has a falling rate.

    *bike rate diagram (shock rate related to wheel travel)

    now let's talk. :rofl: :thumb:
     
    #33 -   Sep 26, 2012
    Last edited: Sep 26, 2012
  34. norbar

    norbar Turbo Monkey

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    That is untrue.

    A degressive bike as it was pointed out starts hard and ends up blowing through travel at the end. Progressive is the other way around.


    Though can't we get back on topic. Udi have you tried devinci? I really wonder how progressive is too progressive for linear shocks like ccdb? I'm not a fan of super progressive bikes but yeah, legend is too linear (it is regressive at the end too) but unbottomable bikes are silly.
     
    #34 -   Sep 26, 2012
    Last edited: Sep 26, 2012
  35. freeriding

    freeriding Monkey

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    THIS IS WHY regressive LR use the initial travel more easily than progressive, FOR A CERTAIN BUMP/. :rofl:

    it's simple!
     
    #35 -   Sep 26, 2012
    Last edited: Sep 26, 2012
  36. freeriding

    freeriding Monkey

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    to make it more simple:

    the blue lr is progressive.

    the red is regressive.

    for the same bump, which do you think will reach easier 150mm of wheel travel???

    red of course...

    the same for 50mm wheel travel (since the starting LR is the same value for both)

    sfdfvdwv.jpg
     
    #36 -   Sep 26, 2012
    Last edited: Sep 26, 2012
  37. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

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    Nope.

    You are making an error in your comparison graphs. For the sake of this comparison you cannot use two curves with different average leverage ratios - of course in the scenario you are drawing, what you say is true - but it is not a fair comparison.

    Now think about the simple pair of LR lines below, they have the SAME average LR. Which one will use its initial travel more easily?

     
  38. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

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    Agreed, but I think it's understood now.

    I haven't really apart from a brief carpark test, but I think the LR curve on that bike looks very reasonable. If we believe the linkage file, heavy ramp-up only starts after the 200mm mark. I'd ride the Devinci quite happily, I think it would be an excellent bike. The 951 you mentioned on the other hand has a ridiculously progressive curve (it apparently drops below 1.5:1 in 8" mode, insane given a 3" shock).

    I think it's worth noting at this stage (you'd obviously know this) that the linkage graphs are never going to be perfectly accurate, but furthermore results tend to be more inaccurate for bikes with short links, as pivot placement can cause greater variations from reality in these cases.
     
  39. norbar

    norbar Turbo Monkey

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    1.5??? Always thought it was just a tad below 2.0. That explains a lot. That is also crazy.

    One thing that has me wonder is is the a bigger flattening of the curve after sag noticeable (as in dw dhr vs devinci). Is it even worth the effort or slightly progressive after sag is not really a noticeable issue (outside of maybe being anal about details). I need to try to bum a test ride from the local turner shop.


    EDIT: Looking at reviews a lot of people complain about turner being a bit too eager to go through its travel in mid travel.
     
    #39 -   Sep 26, 2012
    Last edited: Sep 27, 2012
  40. tacubaya

    tacubaya Monkey

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    Udi is right