Spherical bearings
08-11-2015, 01:27 PM
#41
Joe's OP was in reference to spherical bearing mounts, not so much coaxial perches. The two are related though so I chimed in.
I don't have any handy infographics and can't articulate all the math. I've seen spring rate plots taken by indycar teams back in the 80's with and without coaxial perches. Can't find them on my machine. The difference in linearity is surprising. Any coil spring when compressed in a straight line has a small amount of nonlinearity. Coil springs also twist a bit, thus the reason for our Torrington bearings. If one or both perches are allowed to tilt off axis a smidge, rate linearity is improved a bit. Further when a coil spring is compressed between two planes not parallel with each other (all non-coaxial perch "pillow ball" miata mounts), rate deviations are increased as well as thrust loads being imparted on the shock shaft. All these ancillary forces adversely affect the suspension action. Imagine the shock compression smoothly at say 400in/lb then it hits a spike where extraneous loads cause the rate to jump to say 440 in/lbs, then 3/4" further into travel ease off to 380 in/lbs. Even our Club Sport setup is affected by this, despite having very low friction dampers. Our bushing, collar and hat assembly are engineered to allow as much tilt as possible with a minimum of vertical compliance to reduce side loads on the shock shaft. IOW, we try to make our bushing setup act like a bearing. It's as good as you'll get with NB mounts but the billet coaxials go the next two steps beyond in reducing or eliminating unwanted forces acting on the shock.
Google search comes up with some good results
http://webcache.googleusercontent.co...&ct=clnk&gl=us
We worked to bring the price down on the billet coaxial perches on and off for the last 4 years. Finally got everything nailed down. Very happy with the result. The idea is for everybody to be able to afford them for their project Miata.
I don't have numbers for you. Less friction and binding is better. Can I feel the difference? Yes, but I'm the guy that designed the shocks. Will you be able to? Maybe.
I don't have any handy infographics and can't articulate all the math. I've seen spring rate plots taken by indycar teams back in the 80's with and without coaxial perches. Can't find them on my machine. The difference in linearity is surprising. Any coil spring when compressed in a straight line has a small amount of nonlinearity. Coil springs also twist a bit, thus the reason for our Torrington bearings. If one or both perches are allowed to tilt off axis a smidge, rate linearity is improved a bit. Further when a coil spring is compressed between two planes not parallel with each other (all non-coaxial perch "pillow ball" miata mounts), rate deviations are increased as well as thrust loads being imparted on the shock shaft. All these ancillary forces adversely affect the suspension action. Imagine the shock compression smoothly at say 400in/lb then it hits a spike where extraneous loads cause the rate to jump to say 440 in/lbs, then 3/4" further into travel ease off to 380 in/lbs. Even our Club Sport setup is affected by this, despite having very low friction dampers. Our bushing, collar and hat assembly are engineered to allow as much tilt as possible with a minimum of vertical compliance to reduce side loads on the shock shaft. IOW, we try to make our bushing setup act like a bearing. It's as good as you'll get with NB mounts but the billet coaxials go the next two steps beyond in reducing or eliminating unwanted forces acting on the shock.
Google search comes up with some good results
http://webcache.googleusercontent.co...&ct=clnk&gl=us
We worked to bring the price down on the billet coaxial perches on and off for the last 4 years. Finally got everything nailed down. Very happy with the result. The idea is for everybody to be able to afford them for their project Miata.
I don't have numbers for you. Less friction and binding is better. Can I feel the difference? Yes, but I'm the guy that designed the shocks. Will you be able to? Maybe.
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08-11-2015, 01:28 PM
#42
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