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Originally Posted by fe1rx
I was referring to the implicit factor of 2 "correction" in my formula based on the incorrect moment of inertia calculation I made.
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I don't think that was how the statement I quoted read, but OK.
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In other words, my estimates for other hypothetical bar stiffnesses, based on similar geometry but different diameters, is invalid.
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Right. But to repeat what I quoted:
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Originally Posted by fe1rx:
.... Testing is definitive. I did the math to be able to estimate the stiffness for a hypothetical different bar. That is certainly suspect now. A factor of 2 correction for arm bending and bushing deflection isn't appropriate for a wide range of bar diameters, because bushing deflection will become more significant for stiffer bars.
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I had mentioned that for the Mazdaspeed6 24mm front bar Phate tested, it turned out the measured rate was about 1/2 the Puhn calculated rate ( no bushing flex ). From that very limited data, I made a simple, emprical formula to adjust the calculated rate for oem bushing flex, where ratio "R" I explained earlier: Corr = 1/R^1.35 . To some degree, bushing size will increase with the bar dia, but stiffness is strongly related to the bar area moment of inertia, ie (D1/D2)^4 for solid bars, and bushing stiffness is likely proportional to the D^2. Could you check if it applies to your measured vs calculated stiffness? I know you tuned the oem bar parameters to get full agreement with the measured, including the factor of 2 for corner rate by mistake. Perhaps you have another way to adjust the Puhn calculated stiffness to include the ridgid body bar end displacement due to oem bushing flex, and urethane bushing flex?
There is also the possibility that at higher cornering G's, the load could be beyond the loads we tested, and the bushing will stiffen up.
Most important, I think you did a great piece of engineering on this thread, on topic with the Ohlins install.
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