tpfenning

Or in case I misunderstood your question, are you asking how the spacers work to make things more progressive? I'll try to answer that too. The air spring piston will always move ~200mm when cycling through the travel. For simplicity sake, let's say there is 250ml of air spring volume pressurized to 100psi and no spacers. The air piston is going to force that 250ml of 100psi air into a 50ml space at full compression, making the pressure far greater. Now let's add 25ml of volume spacers. You still have 100psi to start with at 0mm compression. The piston will still travel 200mm, but now that same 250ml of air has only 25ml of space to fit in at full compression so the pressure will be far greater. The different between 250ml and 225ml isn't great, but the different between 50 and 25 is a lot, so that is what makes the compression ratio higher and the fork feel more progressive with spacers.

Yes, I'm sure, someone, could, but, I'm not sure, if, it would, make sense. In short, Fox makes one air spring with a lot of tuning range. Spacers "do nothing but fill a void" but that's their entire purpose which has a significant impact on the feel of an air spring. Most people are not riding half as aggressively as Danny Hart and do not want or need that much progression in their fork, but the option is there for everyone to find what works for them. It would be prohibitively expensive to create unique air springs for different riders when cheap plastic spacers will do the trick.

@matts67: right, in my opinion you would pick the 25-26 (25.0-26.9) option, but I get your point that it's not super clear.

I read it as "31.0-32.9 pounds" and then "33.0-34.9" etc. but it is a bit odd.

Exactly the same, just completely different.