Hhhmmm about this, I have raced downhill bikes for good ten years locally, World Cup, and world champs. Also doing suspension for bikes and sleds for easy 20 years. The fox 40 is a great fork for its torsional stiffness, but definitely is not the smoothest, and I’ve raced on a lot of different forks and shocks. Pending on the track I’d be on air or coil. But this is a sled fourm not a mtb fourm.
It’s is complete logic bigger stantions or larger shock shaft is more stiction due to more surface area. The larger shaft is where all the shock fluid is in a air shock. More fluid less cavitation. Than we could get into air sleeve design ipf piston design, etc. Progressive or linear spring rates.
Air shocks have there place, light weight,and not having to swap out springs. They definitely have gotten a lot better, but still need work. A proper tuned coil shock will still feel nicer, but the spring does have a life span.
Myself I still to this date have not ridden a nice air shock that I would rave about, even custom tuned ones.
1) Come forward and name thyself! Lol. Seriously, there are VERY few guys who have raced world champs, or world cups. My full name is Jeff Brines - you'll see me as one of VitalMTBs product testers and about half way down any enduro results sheet in the pro class (lol).
2) Mountain bike suspension is worth discussing here 100% as that is the breeding ground for a lot of R&D in suspension technology. Treeboy, you will remember a certain powersports company getting into WC just for R&D...
3) Suspension on a mountain bike, at the highest level, matters a lot more than suspension on your sled (so long as your spring rate is close and weight distribution right) in the mountains. In the mountains we have the medium of snow between us and the sled. On a good day, so long as your weight transfer is kept in check, suspension matters but not nearly like it does in the DH mountain bike world day to day. (snow is the ultimate suspension!)
If guys at the top level of a sport that is so suspension intensive goes air, when they have a coil option, that is important to note and far more objective (and compelling) than the "my dad could beat up your dad" argument snowest has become. Especially when the damper in question is made by the company in the title of this thread (I'm referring to Fox product).
In DH mountain biking, you'll see a lot of riders swap back and forth depending on track, linkage and what they are looking for. They are swapping largely for the reasons I mentioned above, as well as the fact air is more progressive than coil. It has nothing to do with weight at this point. (in that sport)
You aren't wrong that larger shafts have more friction, but under load they will actually disperse this friction better and be smoother (gasp). Now, for some application this doesn't matter as side load is very minimal (skid). Others there is some side load at times (IFS). Plus you have to factor in force to the equation (how big is the lever). Regardless, I'll try and get some graphs from fox, but the whole "there is more stiction in air" arguement is so BS. They graph breakaway force using data acquisition on a shock dyno, and I know its on par with a coil.
The shape of a fox air curve *is* different, and THAT (and adjustibility with a pump) is why you pick one over the other, but the whole "coil is better I'm positive" argument is for the birds.
Your argument pertaining to cavitation isn't all that accurate at this point either. If it was, we'd always get it in mtn biking but we seldom see it (damper shaft is smaller in mountain bike than powersports). More importantly, I'd argue we NEVER get cavitation in a mountain riding environment (sled). Maybe to and from the riding spots we are in an environment that can produce it, but we aren't snowcross racers. Our suspension has to deal more with weight transfer, rider input etc (slow shaft speed where cavitation isn't at all an issue) followed by that random rock we didn't see, a log, a stump, a hole and for the really good riders - air (high shaft speed) - all of these are singular events. Either way, cavitation is likely the last thing we'll have an issue with in the mountains outside of spring conditions or the trail in/out - and even then its very debatable as I've seen small shaft shocks work just fine if tuned properly, and show zero indication of cavitating on data acquisition systems...
You are completely right that there are a ton of variables here, but don't write air off based off the old "stiction is higher" argument, it simply isn't true in 2018. Plenty of super talented riders go air, and are offered the coil choice. Personally, if I'm going Fox, I'm going air more than likely at this point. I love how much I an adjust the curve, and I love how easy it is to change the spring RATE, not just preload (which doesn't change the rate) with a shock pump and 5 minutes, they've proven durable (last season) and I guess they save weight too...