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justinc5716 Added a reply to How stiff are dual crown forks?
8/10/2021 2:17pm TLDR; -The rig isn't perfect, which accounts for some of why the measured values are lower than the FEA values -The measured relative stiffness difference SC to DC RSU is ~20% -A perfectly rigid test rig would see this value increase -DC forks are better at preserving steering geometry, primarily fork offsett If you are doing the FEA the way...
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justinc5716 Added a reply to How stiff are dual crown forks?
8/10/2021 11:50am
I got around to welding up a quick test fixture today and finally got some numbers on the single crown fork. The fixture is just a piece of L-angle welded on top of two pieces of steel strap and a base to create a nice box structure. The fork steerer sits in the L-angle and then gets clamped on...
justinc5716 Added a reply to How stiff are dual crown forks?
8/4/2021 12:10pm I think you'd need to start using some more advanced constraints like RBE's. You'd create a fixed node in space and then connect nodes on the steerer tube to the fixed reference node via the RBE's (I think RBE2 would be what you want) If you split the cylindrical face of the steerer tube that'll create an edge along which...
justinc5716 Added a reply to How stiff are dual crown forks?
8/3/2021 1:04pm A fun recent finding to add to this thread: I had a pair of really hard nose-cases this winter. Part of the hazards of trail building means that you get the be the one to test things out...sometimes the bike pays the price. I had one so bad that I could actually feel the bushings bind and grind to a...
justinc5716 Added a reply to How stiff are dual crown forks?
7/14/2021 8:39am That's the same answer I've heard other places, referring to the fork lowers extending too far below the axles. I think that is totally valid, but not the entire answer since it only addresses motocross and not the rest of the motorcycle spectrum. We still have to wonder why street bikes (some Harley's excluded) with much shorter travel use USD...
justinc5716 Added a comment about photo original_20210626_EDC_Brandnertal_S1D8138.JPG
6/28/2021 12:54pm
Pretty sure that's the new Dorado under the towel. I'm kind of wondering what the point of hiding it is.
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justinc5716 Added a reply to How stiff are dual crown forks?
4/16/2021 11:29am @JamesR_2026: The purpose of this discussion is ultimately to bring experience and theory in line. One of my mentors in motorcycle racing defined this synthesis as "technology". What he meant was that experience not backed up by theory is useless. You always have to understand what you are doing and why you are doing it as a crew engineer or...
justinc5716 Added a reply to How stiff are dual crown forks?
4/15/2021 9:41am I did say that stiffness is too low, and nominally USD forks suffer from reduced torsional stiffness. This seems like a contradiction, but as the results suggest, going to a dual crown USD fork allows for stiffness-to-weight ratios that surpass those attainable with RSU forks. There is a break-even point for this to be true. Below a certain stiffness, RSU...
justinc5716 Added a reply to How stiff are dual crown forks?
4/15/2021 7:54am The idea of torsional compliance being good is strongly misguided. Sure you are providing a means of isolation for some side impacts on the tire, but remember that these impacts are now imparting a directional change to the tire rolling axis. The result is that body inputs and extra steering inputs are needed to keep the bike upright and on-course...
justinc5716 Added a reply to How stiff are dual crown forks?
4/13/2021 11:19am You did a good job putting this together. Though some of the constraints could be refined, as a piece of comparative analysis I'd say this is perfectly valid. The relative qualities of the 4 major fork categories come as no surprise really. The ensuing discussion will of course center around what qualities equate to a faster bicycle. After all, that...
justinc5716 Added a reply to Are Upside-Down forks really flexy?
3/5/2021 12:59pm I deliberately chose to separately address the last two questions in order to break things up a bit. " Or will the added compliance help by making the ride more forgivable (though you were mentioning that you'd want all the information)? And how does road vs. dirt make a difference? " It is true that compliance can be used as...
justinc5716 Added a reply to Are Upside-Down forks really flexy?
3/5/2021 12:25pm Lots of good questions there, and a lot to un-pack, so bear with me! Firstly, transmission loss is a broad measurement that results from the cumulative effects of stiffness, inertia, and damping. Damping alone tends to decrease transmission loss in the frequency region shared by a system's modal behavior. That's a complicated way of saying that damping keeps things from...
justinc5716 Added a reply to Are Upside-Down forks really flexy?
3/4/2021 2:54pm I'm so glad to see some independent engineering work going into this. Doing FEA is second-best to getting an independent lab to actually MEASURE these things. As an engi-nerd I'd really love to see that data. I used to race sportbikes and grew up riding motocross, so this has always been a quandary to me. Especially in the world of...
justinc5716 Added a comment about feature Ultra-Long, 210mm Travel Enduro Machine - Is This the Ultimate MTB?
9/16/2020 2:10pm
How was the Dorado modified to accommodate a 29" front tire and still maintain full travel?
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