4. Click the Fork Pressure tab to view the breakdown of compression forces.
For example, we can determine:
-- how much is bv force
-- how much is mv force
-- how much is gas force (from inner chamber spring [icspr])
-- how much is drag force
This is where it gets interesting. Column B (from above) shows the bv force and column C shows the mv force. This shows the relationship between the bv and mv, and can see how much work each is doing at the different velocities. In other words, for any given velocity, we want to consider how much force is coming from the bv and how much is coming from the mv. Knowing these forces are the key to balancing/optimizing the pressures.
Once you pressure test and compare enough bikes, you begin to see a pattern. For example, one thing we noticed for amateur MX is that all forks produce about the same compression and rebound damping forces. Whether it's a 125, 250 or 450, the dyno numbers are all very close and fit within a tight range. This allows us to define a scale for the fork compression forces. We started by simply calling them soft, average or stiff. Of course we want more than just average MX, so we expanded the scale to include soft woods to pro SX. Now the scale looks like this.
---> This is the 'fork compression target number' scale [fkc target nu].
Using the scale above, we can rank the 2014 YZF 250 mv and bv numbers. Rounding and comparing the numbers at 70ips.
-- mv force = 24 lbs = stiff
-- bv force = 38 lbs = stiff+5
This tells us exactly how this fork fits in the scheme of things. Proportionately, the bv force is much higher than the mv force. At this point we won't say if this is good or bad. We just have a way to see how they relate.
The beauty is that this scale works for all forks from all manufacturers. It doesn't make any difference if they have different piston diameters, different bv or mv stems, different needle tapers, different cartridge rod diameters or any of the multitude of different parts that are found in forks. We have found that once any fork is set up and feels decent on the track, the numbers are going to fit the scale.
You can see how this simplifies the tuning process. You simply pressure test any fork setting, see where the bv and mv forces fit in the scale, and adjust accordingly. Through extensive testing we have found what we consider to be ideal 'target numbers' for the bv and mv force, depending on the application. When a new bike comes in, we valve the fork accord to our current recommended 'target numbers' and let the rider test. If changes are needed, it is easy to adjust the bv or mv stack, depending on the rider feedback.
This is an ongoing process. Each time we make an adjustment, our target number scale improves. Because we have a definitive way to compare the valving configurations, the valving process is easier and more precise. This would be hard to achieve with seat-of-the-pants shim swapping, not knowing how stiff the bv and mv are, and not being able to see the relationship between the two.
We will conclude with an example of one extreme difference between bv and mv force. We received a SX fork that lost all its compression damping. Upon inspection, we noticed the bv icrod was bent. After replacing the rod and pressure testing the configuration we saw the bv force was very stiff.
-- mv force = stiff+2
-- bv force = stiff+14 (off the scale)
Very unbalanced. We revalved and opted for:
-- mv force = stiff+7
-- bv force = stiff+8
The rider rode the forks and said they worked very well.
7. We have a similar method for analyzing and comparing shocks.