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1) Most air springs are more progressive than their coil spring counterparts. This actually can make tuning tricky (can make the last 1/3 of the travel feel harsh). One way WP is trying to mitigate this is by using larger air volumes (this makes things more linear) coupled with larger negative volumes (helps things "off the top" a bit).
You can tune the progressiveness of an air spring in ways you really could never do with a coil spring. Oh, and don't forget, you've still got the oil levels to further tune things. (secondary air spring)
2) Suggesting the fork won't settle in and does not perform well through square edged impacts because its air is a hypothesis that shouldn't be taken at face value (but I'll give you a few reasons in a minute - weight, geometry & the adiabatic process).
First you have no idea what kind of high speed compression Dean is running here. Too much HSC does not bode well for these kind of impacts. The problem is Dean needs HSC when he goes gas to flat (this is where cone valves can really help - but I digress). A good tuner could (maybe) find differentiation in shaft speed & position with respect to casing/going flat and square edged impacts, but this can be one of the hardest parts of suspension tuning. Most importantly, it has nothing to do with the spring (well, almost nothing, again more on that in a minute).
Second, one thing that does seem clear with some of the air forks is they do tend to ride a little higher in the travel. When you add this to a front end that is 3 pounds lighter what do you get? An "unsettled" front end. This has more to do with weight and geometry though, not spring design.
Third, the biggest point one can make around air spring design & "feel" would be pertaining to the adiabatic process. The adiabatic process is the relationship between pressure & temperature. I won't go into the math (I already feel like I'm writing a dissertation) but the adiabatic effect is the speed sensitivity an air spring will showcase (remember, a coil spring is only position sensitive). This can lead to a different feel at high shaft speed, and again something that needs to be taken into account on the damping side of the equation too. Again, if this was hugely problimatic, we'd be venting our forks to atmosphere through some kind of check valve. Instead we use the space between the damper and the outer legs as a secondary spring, so yeah, every fork is technically an air/coil hybrid!
Ultimately, you'll learn you can't take valving from a coil fork and successfully move it to an air fork, especially with a good rider. However, if you use the uniqueness to your advantage, valve it around these properties, you can have a very high performing fork that is a lot lighter and a lot more versatile (in theory anyway).
In closing, I don't think WP is all the way there with exploiting all the strengths of an air spring, but over the next 2-3 years I do believe they'll get there, and the only ones who will hate on them are the ones who have some sort of pre conditioned bias against the technology.
I didn't say that anywhere; inferred or otherwise.
The questions at hand is a mix between "why does WP insist on air springs" and "suspension won't get any better".
I'm suggesting air springs can actually be made to perform very well and suspension will indeed get much better (unlike "a swingarm" (which I also would bet gets better). I feel I've backed both points up adequately. As far as your 17s go, yeah, an air sprung fork can also be very bad, just like a coil sprung fork can also be very bad. Devil is in the details.
I appreciate the technical insight and hope WP does eventually get it right. I’d love to stop paying $1500 for suspension parts on top of a $10k bike that is awesome in every other way.
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(I know, my analogies need work)
I don't understand why KTM doesn't ditch the air fork and just copy the SSS fork. It would kill on the shootouts and also customer satisfaction. After riding my sons bike I have seriously just considered buying a set of forks off a yz250f and adapting them to the KTM (if that's possible). They're that good.
I have been working with (paying) the premier WP suspension technician on improving my WP AER 48 since I got the bike last September. He is a former WP factory suspension technician.
I have tried all combinations of oil height, fork pressure, valve stack changes, compression and rebound settings.
I even tried several different sag, spring weight, link and knuckle options in the rear, because I really do think the air fork is the way to go in the future, and I didn't really want to be forced to convert to a Cone and Trax combo over the stock components.
I really want to like the air fork, I have four pars of them, and the latest re valve is pretty good as compared to what they were.
But in the end I relented, bit the bullet and purchased pairs of Cone and Trax components after test riding a Husky equipped with them at Glen Helen.
Every rider has a different feel, but FOR ME, the WP 7548 fork doesn't jar me in a rut filled with square edges like the AER 48 did, I can also turn in much easier in with a more planted feeling.
Like I may have said before, on some sections of a track, like flat landing or whoops, I think the AER fork is superior to the spring fork in giving confidence and stability - but for the small bumps and chop, It is just too jarring for me at race speed to try and get some comfort.
But yeah, CVs are awesome.
One other thing I do want to point out, I'm an off road rider and can sacrifice some bottoming resistence to open up the fork's damping through square edged impacts (I'm using oil heights and the spring to prevent bottoming more than HSC).
Have either air springs or spring valve oil dampers (cone valves) succeeded in any of them? I think coil springs and shim valving have faced all challengers over suspension history and still come out on top. I find it hard to believe that there is some remaining secret to be unlocked, some idea KTM is going to have that hasn't already been tried in other racing.
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They are better than anything I had on my 06 CRF. BY A LOT. I've ridden new YZs, and after riding them stock to stock, back to back, I honestly don't know what the fuck people are talking about when they talk down about the AERs. Granted, I'm a big dude, and maybe if you're a 160 lb mini man then the YZ is perfect or whatever, but the KTM does everything I want it to do better than any bike I've ever had.
And regarding your claim about coil springs being the best ever and taking on all-comers, here's a photo of Mercedes-Benz F1 suspension circa 2019. Show me the coil spring.
Lots of KTM pro racers are on air springs.
I spent under $500 with Enzo and that included revalving the rear shock as well, for suspension that I liked better than my previous YZ. It didn't feel perfect but no suspension I've ever ridden felt perfect. Lastly, I've ridden Austrian bikes with Ohlins, WP cone valves and a few bikes with Showa & KYB A-kit setups.
But the takeaway there is both the Yamaha and KTM suspension are very capable for everyone, even guys as fast as him.
Alot of teams use Air in SX because it has the characteristics that suit it better, such as ramp up and a more dead feeling. Small bump compliance is low down the list so they can run higher pressures and cyclic heat increasing the 'spring' pressure is less prevalent than outdoors. Still a fair few riders running Air forks outdoors as well. Once the air is set it's just shims and pistons like a Spring fork, it just requires different stacks due to the difference in 'spring' properties.
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