Coil spring or air spring? Since the introduction of the air spring, this seems to be the source of constant debate. Air springs offer enhanced tuning capabilities and progressives suspension curves, yet coil springs offer that supple off the top feel through the beginning and midstroke that you can only get with a coil. For years we’ve seen more and more air spring suspension systems in search of the lightest possible system, but lately we’ve noticed a few coil systems popping back up.
Brands like PUSH have even gone as far as creating new, purpose built coil shocks for enduro bikes like their Elevensix rear shock. In an effort to match the performance of the rear to the front of the bike, PUSH turned their attention to the front of the bike with a sort of coil/air spring hybrid which looks to offer the best of both worlds…
Named the ACS-3 for Advanced Coil System, the system is a complete drop in assembly for the air side of a Fox 36 suspension fork – though Rock Shox Pike kits are on the way. Inside the kit you’ll find the Air Bump stop, Preload cap with two spacers, chosen spring, and the Lower Plunger Assembly.
Available with one of seven different spring rates, the color coded springs are made from “precision wound high tensile CrV-Si suspension spring that is shot peened, preset, and powder-coated to ensure the lightest possible spring with the most exact rate.” Combined with the lower spring bearing (above, red cylinder), the spring is allowed to rotate on its perch which is said to improve small bump compliance as it keeps the spring from binding on the mount. Each spring also comes pre-wrapped to cut down on noise.
| Part Number | Description | Fork Model | Model Year | Travel | Rider Weight Range |
| ASY-1090-110-0030 | Replacement Spring Assembly (Red) | FOX 36 | 2015-2018 | 160mm | 125-140lbs |
| ASY-1090-770-0035 | Replacement Spring Assembly (Yellow) | FOX 36 | 2015-2018 | 160mm | 140-155lbs |
| ASY-1100-800-0040 | Replacement Spring Assembly(Orange) | FOX 36 | 2015-2018 | 160mm | 155-170lbs |
| ASY-1100-800-0045 | Replacement Spring Assembly(Blue) | FOX 36 | 2015-2018 | 160mm | 170-185lbs |
| ASY-1163-800-0050 | Replacement Spring Assembly(Green) | FOX 36 | 2015-2018 | 160mm | 185-200lbs |
| ASY-1180-760-0055 | Replacement Spring Assembly(Black) | FOX 36 | 2015-2018 | 160mm | 200-215lbs |
| ASY-1180-760-0060 | Replacement Spring Assembly(Gray) | FOX 36 | 2015-2018 | 160mm | 215-230lbs |
The real magic though, comes from the Air Bump Stop – a clever integration of both coil and air springs. The pneumatic bump stop allows the spring to offer a linear curve throughout the initial and mid stroke, but once the bump stop is engaged, it controls bottom out with adjustable air pressure. Factory set at 20 psi, PUSH says that running 5-20 psi will result in a more linear feel, while running 20-50 psi (50 psi max) will provide a more progressive spring curve for the most bottom out resistance. To adjust, simply remove the cap and inflate or deflate with a standard low pressure shock pump.
The kit also includes a preload cap with two additional preload spacers. Designed to be used with or without the spacers, PUSH says the two additional spacers can be used to adjust the static sag or ride height of the fork.
Pricing and availability
On the scale, our 160mm Fox 36 27.5″ kit came in at 411g for the entire kit, and 224g for the blue spring. We’re assuming this will add a bit of weight, but will confirm once we pull out the 36 internals to verify.
PUSH is rolling out the new kits one by one, but for the initial launch kits are available for 2015 – 2017 Fox 36 Float or TALAS 160mm forks. Fox 36 140, 150, and 170mm travel kits as well as 2018 Fox 36 140-170mm kits will be available in late July. Rock Shox Pike kits will also be available, though no time is given for their availability. Finally, PUSH mentions that kits will not be available for Rock Shox Lyrik or Yari forks since the inner diameter of the stanchion is too small.
Sold for $389 for the complete kit, additional springs are available for $80, and everything is made completely in the USA.
Lower Leg Service Kit
While you have your fork apart, it’s also probably a great time to perform a lower leg service – assuming it isn’t a brand new fork. To make services easier (and less frequent), PUSH has a new lower leg service kit with almost everything needed for the initial service. The 32mm chamferless socket above is not included in the kit, but seems to be a beautifully machined alternative to the other chamferless sockets on the market. The kit does include enough Maxima Plush 10 wt lower leg fluid and PUSH SOS assembly lube for 5 services, and one set of PUSH ULF fork seals with foam rings, crush washers, and the awesome PUSH fork seal installation tube and a 60cc syringe. The Lower Leg Service Kit sells for $105, and additional seal kits will sell for $36. PUSH claims that their seals double the service interval of any fork – which, be honest, is probably closer to a more realistic service interval for most of us.
Shown here as a preproduction tool, the chamferless socket will be available as a stand alone tool for $40 each, or as a kit of five sizes (24, 26, 28, 30, and 32mm). Production tools will be hard anodized and include laser engraving for the socket size with the PUSH logo. Each socket includes a 3/8″ drive, as well as wrench flats which double as a finger hold.
