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Is this the correct shock?

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    #46
    I won't really type pages of explanation - I think the most precise information is available in Racetech "Motorcycle suspension bible" where the typical shock layouts are described and Dixon "Shock Absorber Handbook" which goes into more detail and is more technical (a lot).

    But the main reason is that a shock without basevalve needs to run a higher pressure in order to avoid cavitation, where the basevalve helps by restricting oil flow and due to help from the restriction can get by with a lower gaspressure. A variant of this is the twintube Ohlins TTX shock where there is a restriction similar to a basevalve in both directions and it gets by with an even lower pressure.
    Normal setups have following pressures: no basevalve 18 to 20 bar (250 to 280 psi) basevalve 10 to 12 bar (140 to 170 psi) and TTX 6 bar (85 psi) - please note that shock pressure is also a variable parameter in setting up, so sometimes a little higher pressures can be seen, if going for lower pressures you risk cavitation.

    Why does a shock without basevalve need higher pressure? The flow through the main piston needs to be able to fill the volume behind the piston and at the same time the gasvolume needs to accept being decreased by the volume of the shaft - if the pressure is too low, the gas will just be compressed and not force the oil through the piston - there is now too little oil behind the piston so when the shock reverses into rebound, there is no damping - this is an extreme version of cavitation, which occurs alreday when the pressure isn't high enough to not have vacuum pockets in the rebound chamber.

    Why do you need compression damping? In short it helps putting pressure on the tire to maintain grip and it does it in a different way than the spring. Many shocks and setups have very little effective adjustment from the compression adjuster and it is often seen that the rebound adjuster has a bigger effect on compression than the compression adjuster. So when you have a good baseline it is not really relevant to adjust compression. Rebound is much more effective and important - which is why it is the first adjustment seen on shocks - no adjusters, rebound adjuster, compression adjuster, hi/lo compression adjuster, hi/lo rebound adjuster...

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      #47
      Yeah ... what he just said

      Now if you'll excuse me , my head is about to explode.

      JanM many thanks once again for passing on your knowledge to us suspension novices here.
      "Hawk Porn" http://picasaweb.google.com/11124379...eat=directlink 1990 NT650-Penske 8981, Race-tech Springs & Gold Valves, Steve Lenac six-piston caliper & EBC rotor,SS Brake lines Ft / Rear lines through SSA ,VFR brake lever, F2 front wheel, F-120/70 R-160/60 Dunlop Roadsmart, Full-Supertrapp Exhaust, Stage 1 Jet kit, K&N Filter, Corbin Seat, Pro-Tec Clip-On's/ Past Rides...1986 VFR700F2 Interceptor / 1979 Yamaha Rd400 Daytona Special

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