arctic & mcromo
excellent info in this thread, SUBSCRIBED
...I have a feeling I'll be needing to refer to it in the coming months
Here's more !
arctic954 wanted to know more about shock unit Damping Force Curves.
Here goes ..............
OK, arctic954 asked for some insight into what the curves mean.
Damping Force Curves that is.
So here's a bit for everyone.
Hope it helps you all.
Damping force is a resistance force.
Compression damping resists excessive compressing of the suspension unit.
Rebound damping resists the compressed suspension unit from rebounding back too quickly and too far.
Dampers for motorcycles have always been heavier on the rebound side than compression. This is why when you look at the shock damping force curves, you will see way more rebound damping force available than compression damping force. In highly simplistic terms, if you dialed in as much Compression Damping Force as Rebound, the suspension would behave as though it was solid. If you tried to dial in a reduced amount of Rebound force so that it equaled the Compression force , you would lose control of the suspension unit and it would spring back as though there was no damping at all.
The basic damping force curve shape will be basically shaped by the piston fitted.
The piston has a compression face and a rebound face. There is a wide range of piston types.If you have a Penkse Manual, look on page 23. The basic characteristics are termed as being Linear, High Flow Linear, Digressive, Velocity Dependent. Mixing is not uncommon. For example, the Penske on my 919 came from Penske with a “standard” piston that is somewhere in between a Linear / Linear and High Flow Linear Linear. So you could call it a Medium Flow Linear/Linear, which means that both the Compression and Rebound piston face porting is designed to pass oil at a medium flow rate and yield somewhat linear damping force curves. (Meanwhile, the track only Penske I have for my GSX-R750 was custom built with a true Linear/Linear piston)
Now to some curves.
First is the factory test curve for my Penske as received from, and configured by Jim Lindemann. It was selected as being a standard 919 shock with a custom spring selection. We can ignore the spring, because it has nothing to do with the Damping Force Curves.
The Horizontal Axis is shock Piston Stroke Velocity in inches / second.
The Vertical Axis is Damping Force Energy in Pounds Force.
The horizontal 0 line is what separates the Compression zone from the Rebound zone.
There is a series of curves.
The Compression Damping Force Curves are above 0.
The Rebound Damping Force Curves are below zero.
See how the magnitude of the Rebound Damping Forces on the curves are many times that of the Compression Damping Forces.
Next we’ll talk about each series of curves.
Penske will colour key the curves on the test chart you get with your shock. (You SHOULD get the test curves in the box regardless of whether the shock came from a chassis tuner, reseller, or Penske direct. I have bought customs from two chassis tuners and got the curves both times without even having to ask.)
For my 919 shock, the Compression and Rebound test curves were Orange, Blue and Green. See the attachment.
Orange is the curve you get with the unit set full soft, in other words whatever adjusters there are, are in full soft position. The full soft line will be the line closest to the horizontal 0 line about 2/3rds the way up the chart.
Blue is the line that the factory set “suggested starting point settings” result in. This will be the second closest line to the horizontal 0 line.
Green is the curve you get with the unit set full hard, in other words whatever adjusters there are, are in full hard position. The full hard line will be the line furthest from the horizontal 0 line
The second attachment is the Damping Force Curves for the Penske on my GSX-R750 dedicated track bike. Keep in mind the swing arm is linked, and the unit is fitted with a 550 pound /inch spring. See how the magnitude of the Compression and Damping forces are different . See how the shape of the curves are different. See how the 750 shock has far greater compression resistance. See how the 750 shock has far less rebound resistance. These differences tell you how complicated all of this.
(See why taking a shock from say a F3/4 and grafting it on to a 919 suddenly looks even more suspect than it did before ? And that is aside from their respective eye to eye lengths being different ! )
Hope you find this of benefit and use.