After reading this question and answer, I was surprised to learn that most shock pumps use a Schrader valve. My mountain biking days are a distant memory, so I'm not well acquainted with the type of shocks that require a pump. But given that high end bikes (the type of bikes that probably feature this kind of shock) almost certainly come equipped with Presta tubes, why would the shocks require a Schrader?
Schrader valves are stronger, for one. Breaking a weaker, smaller valve that has a (perhaps just in my experience) frustrating attachment mechanism for pumps on a $1,000+ fork would be unacceptable.
Schrader valves have at least one valid disadvantage on a road bicycle: their larger diameter is a deterrent for use because it reduces the strength of the rim significantly on a narrow-rimmed bicycle wheel (the main point), they use a spring that can wear out to hold their own pressure where Presta valves hold their own (ancillary point, if one at all) and are slightly heavier (retroactive justification from the Presta preachers). None of these matter for a shock.
High-end road bikes were designed for one thing: going fast. Their rim material takes an enormous amount of additional stress from the smaller width, higher inflation rates of the tires, and simultaneously have as much weight, material, and spokes taken away as possible to leave a somewhat durable wheel. In this setup, the hole diameter DOES make a sizable chunk out of the material and strength of the rim, and the smaller diameter allows for more performance and smaller width, lighter weight rims, and so is 'the thing' in the higher end models. Only a 6mm diameter hole is drilled vs an 8mm hole for a schrader.
Don't confuse 'costs more' with 'better'. In the mountain bicycle / BMX / downhill / trials / non-road bike world, the high end bikes are not all presta. Most utility bicycles (even expensive ones) are schrader for the convenience. They're more of an irrelevant (performance-wise) selection of what the rider wants on these types of bicycles. This isn't because they're skimping in other areas, but the Schrader vs Presta debate doesn't really matter when the rim is wide enough to compensate for the larger hole that must be drilled.
Also note that Schrader valves are much, much, much more common. They're used in refrigerant systems (both on your fridge in your home and in your vehicle's A/C system), plumbing test ports, pneumatic systems, hydraulic systems, and in many other industrial applications as well. I have never seen a presta valve that is not on a bicycle (so if industry is using them, they're cleverly hiding them everywhere I look). This makes the cost of design, tooling, and testing a much less costly proposition for the manufacturer (and, in the end, the consumer) - by not having to break the trail for using a less common valve in an application it's not been used before.
A fringe benefit of Schraders that may or may not apply in this context is the removable core. When I was a Diesel mechanic the trucks would get ice and dirt lodged in the valve stems, and a simple tool would extract the core, leaving a decent size diameter to expel air, or shove a small screwdriver into to clear debris. Further, if the spring was ever worn, or the seal mechanism not sealing, this core could be replaced without replacing the entire valve stem, and it made depressurizing tires much more tolerable (take the cores out, walk away for five minutes). I couldn't imagine how irritating Presta valves would be. If the seal seat of a presta valve 'wore out', got chipped or otherwise failed on a shock, the whole valve would have to be replaced - which depending on the design, might be a permanent fixture in the shock tubing.
The valve on a shock should be easily replaceable though. Since it's metal, which screws into another metal piece, with an O-ring to make a seal. While I agree that Presta valves are more prone to breakage (with modern tires, it's the main reason I have to replace tubes, since I almost never get flats anymore), it wouldn't really be an expensive or difficult repair. This is completely different to bicycle tubes, in which fixing a presta valve is pretty much never done, because it's difficult, and the tubes are so cheap.– KibbeeFeb 28, 2013 at 13:52
In principle, yes - if the valve is easily replaceable, presta and schrader aren't any different. Designs are already in existence for o-ring sealing schrader inserts, where as far as I'm aware there are no o-ring sealing presta designs, that'd have to be custom made. Should is another key word - because nothing says they must be replaceable. They are also replaceable, but not without tire removal/breaking the bead on vehicle wheels, which would make them a pain on many other applications. Feb 28, 2013 at 17:35
While this certainly does a good job of illustrating the differences between Presta and Schrader valves, the only bit that is relevant to the question of why Schraders are better for shocks is that they are stronger. This is kind of a moot point if the valve is easily replaceable, as @Kibbee indicates they should be. The universality of Schraders outside of cycling is also moot since the pressure is so high that a special pump is required. Also, Prestas with removable cores have become common place and the cores can be changed with a pair of needle-nose pliers.– jimchristie ♦Mar 2, 2013 at 20:19
Strength is not moot, people would prefer to not replace breaking parts to the alternative. The valve may or not be replaceable (you may need to replace additional parts as well, or it could be formed into the metal as one piece), so until I see evidence that ALL air shock models have replaceable valves, that point is not moot either. The use of Schraders outside this market is very relevant to the reduced cost to the manufacturer in design, tooling, mating equipment, and other factors that are important when they select which valve to use. Mar 3, 2013 at 11:37
After doing some more reading after my initial question I suspect it's precisely because a lot of those bikes have a presta type valve. Shocks have a much lower volume of air so they require a lot more precise amounts of air, and therefore leakage generally needs to be avoided. They also normally appear to want a higher pressure than you would normally put into a tire. This means that you generally can not use the same pump you would on your fork.
The modern shock pumps tend to have dials for pressure readings, special fittings to prevent any leakage, and can go up to a higher pressure.
Many of them do use regular ol' Schrader valves, so the point isn't to ram home that 'You can't fit your normal pump up' - especially since prestas don't dominate the downhill/extreme travel fork market. If it was, they wouldn't use either valve. The valve is usually a regular schrader with nothing remarkable about it, though the pump heads can use a proper threading instead of the crush-some-rubber-in-there of sloppier pump heads. Feb 28, 2013 at 9:09
However, it should be noted that this is the proper Schrader fitment - if you look at refrigerant/industrial/non-consumer usage. The sloppiness of car/bicycle tire pumps was not the way they were designed to be used, just a convenient afterthought. Feb 28, 2013 at 9:11
shock pumps also pump a much smaller volume of air per pump as you'd expect with the lower volume of air you mention. I've tried to pump up a tube on a tire with a shock pump and it takes forever and the pump gets hot in the process.– jxramosJun 28, 2017 at 17:48