dyno series info pg 4

• Velocity.
• We dyno test each shock at several velocities on the dyno, and we always test at the same speeds.  These speeds are:
  • 1 ips
  • 2
  • 3
  • 4
  • 5
  • 10
  • 20
  • 30
  • 40
  • 50
  • 60
  • 70
• Keeping it very simple, if you think of the rear wheel on the bike, it absorbs small gradual bumps at lower velocities, and larger sharper bumps at faster velocities. 
  • (Remember, the wheel might move 12 inches, but the shock only moves 5 inches.  The linkage system and leverage ratio determine this relationship between shaft and wheel travel.)
• So we dyno test the shock at a range of velocities to give us some correlation to the different speeds the shock shaft moves while absorbing bumps.
• The dyno velocities end at 70ips simply because that is as fast as this dyno goes.  If we had a faster dyno, we would record the faster velocities.  However, it is widely accepted that tuning for harshness and ride control is done in the 0 - 50 ips range.  In other words, riders notice changes made at these velocities more readily than they notice changes made at the higher velocities.
  • Think of it like this.  To reach any velocity (low speed or high speed), the shaft starts from zero.  The initial amount of force (at the wheel) required to get the shaft moving (and the shims opening) seems to correlate with plushness. 
  • This initial amount of force can be observed at the 1 - 10ips range.   If we are saying that forces at these velocities relate to plushness, this makes these numbers very important.
    • For an example, if you made the initial force too stiff by putting a ton of preload on the stack it could be fairly harsh. 
    • Conversely, if you make the initial force very light, perhaps with only a few face shims and a small diameter separator (crossover), it would be softer but would most likely be harsh as well.
    • --> The stiffness at the lower velocities determines the ride height.  The ride height determines how much travel you have available to absorb the bump as well as where you are in the leverage ratio.  Therefore, softer does not always equal plusher.
  • Here is one example.  If you have light low speed damping, the rear tends to blow through the first part of the stroke, and then abruptly stop as it gets toward end of its travel.  It has a hard feel, even though the initial damping force numbers are light.
  • Low speed damping is necessary and good.  Being able to control the low speed damping is the key!
  • This is an important point so I'll say it again.  Being able to control the low speed damping is the key!

• Opening speed.   (part 1)
• We have observed that at velocities of around 1ips and lower, the shims haven't opened and the damping force is from the resistance of the free bleed area of the rebound needle* in the shaft.  At about 2ips, the shims start to open. 
• * Note:  With shocks, our default dyno test is with reb 10 out, and the above comment is based on that clicker setting.  If you closed the rebound clicker there would be no free bleed and the shims would have to open immediately and the initial force numbers would be much higher.

• Opening speed.   (part 2)
• We refer to 2 ips as the opening speed (os) of the shim stack.  In other words, it takes 42 lbs force to get the shims to start opening. 
  • The default rebound setting is 10 out.  We are saying that at reb-10, the free bleed area is large enough that at 1 ips, all the oil flows through the orifice.  At 2 ips, the orifice is starting to get maxed out and some of the fluid is now going past the shims.  (This is a general observation, and not intended as a definitive cut-off point).
    • If the clicker setting is changed, this number will increase or decrease.  The degree it changes depends on the initial stiffness of the stack  (i.e.  If the stack is real soft, closing the bleed will have less effect.  If the stack is very stiff, then closing the bleed has more of an effect).
• The numbers for 2ips are highlighted in yellow.  This gives us a quick reminder of where to look for the opening speed (os) range when doing our analysis.
  • Here are a few general (and approximate) observations for stock shocks: 
    • KYB 46 shocks have about 40 - 60 lbs force at 2ips.
    • KYB and Showa 50 shocks have 60 - 80 lbs force at 2ips.
    • Therefore, as a general rule, we might say the opening speed forces for most shocks that we revalve will fall between 40 and 80 lbs, depending on what opening speed (os) characteristics we are looking for.
    • Here is something else to think about.  We are saying that with whatever shim configuration you use, the compression force at 2ips is going to fall somewhere between 40 and 80 lbs.  It is reasonable to assume that a shock with 40 lbs force at 2ips is going to feel quite different than one with 80lbs force (on the same bike). 
      • THEREFORE, this can be used as a specific tuning point.  You can design your valving configuration so the opening speed is at the desired force for your specific application.
      • AND, it makes you wonder about the differences in the KYB 46 and 50 shock. If you could revalve and fit both shocks on the same bike, they would feel very different from each other.  The KYB 46 would have 40 - 60 lbs force at 2ips and the KYB 50 would have 60 - 80 lbs force at 2ips.
        

•   [dyno series tutorial pg 5]