Heat is the problem.
A shock is changing Kinetic energy, motion, into Heat energy. That heat, is then transfered to the surrounding air.
Shocks with more surface area, can dissipate the heat quicker. Larger diameter or remote reservoirs and springs, helps dissipate that heat too.
They both have their Pro's and Con's.
are very light and easy to rebuild. Spring rate changes are quick (Ni gas) and can be variable to a 1/2 psi.
With an air shock, it gets hotter quicker because of the gas compression. Much like an air compressor will.
When the shock bottoms, the pressure spike could be over a 800 psi (? Get out those dusty engineering books, lets figure this out) This also causes the fast rebound we see. Heat changes the oil viscosity.
A Nitrogen gas refill set up is needed, for rebuild and adjustments. (Cheap set-up, posted soon)
have less fade and more consistent spring rates. A coil spring generates heat too, but it's not in contact with the oil, so there's less chance of fading. Less heat build up = less oil viscosity changes.
As Mick said, there is a weight penalty. A spring compressor tool is need for rebuilding. Changing spring rates, costs more, due to buying new springs each time.
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