Push Industries is a US manufacturer that specialises in producing high-end suspension components and upgrades for existing forks and shocks. The ACS3 Fork Coil Conversion kit is one of its newest products, and as the name implies, it’s designed to turn your air-sprung fork into a coil-sprung fork. But is that a good thing? We got Tom Nash on the coil upgrade program to find out. Over to Tom!
Coil springs have been on something of a comeback in recent years, and we’re not just talking about those found on heavy duty freeride and downhill bikes.
In the search of ultimate plushness and small-bump sensitivity, more everyday trail riders have been sucking up the small weight penalty to seek out the benefits of coil-sprung suspension for use on their all mountain bikes and enduro race rigs.
There’s good reason for this too. According to Push Industries, there is nothing that beats a coil when it comes to outright suppleness, traction, and mid-stroke performance. That’s because a coil spring inherently suffers from less friction than an air spring, and the linear rate provides a more consistent feel throughout the entirety of the travel. Because of this linearity however, coil springs can lack big-hit performance when compared to an air spring, since there’s less adjustability when it comes to dialling in bottom-out control.
Turn Air Into Coil
Aiming to harness the benefits of a coil spring while also addressing the shortcomings, Push developed the ACS3 Fork Coil Conversion Kit. Designed to replace the air-spring assembly in select RockShox Pike, Lyrik or Fox 36 forks, the ACS3 kit is a complete system made up of a steel coil spring (for small-bump sensitivity) along with an adjustable Air Bump Stop cartridge (for big-hit control).
At the very least it’s an impressive piece of engineering, and if it means anything to you, the whole kit is manufactured and assembled in Colorado.
Push boldly states that the ACS3 kit is “the most advanced MTB spring ever created”, and really it should be given it costs just shy of 400 quid. Prior to testing though, I was somewhat skeptical of those bold claims. Could the ACS3’s performance live up to the price tag? And could a single spring system really provide all of those purported benefits in a single fork?
What Will It Fit?
Before we get carried away though, it’s important to note that the ACS3 isn’t designed to suit every single fork on the market. With the primary demographic being aggro trail riders and enduro racers, the ACS3 kit is designed for forks within the 140-170mm travel bracket. More crucially, it only comes in three different models. There’s one for 2014-2019 RockShox Pike forks, one for 2015-2019 RockShox Lyrik forks, and one for 2015-2019 Fox 36 Float/Talas forks. If you’ve got a Cane Creek, MRP or X-Fusion fork, you’re out of luck.
When selecting the ACS3 kit on the Push website, you’re presented with numerous drop-down options that allow you to select your wheelsize, fork travel and riding style, so that you can get the right spring for your fork. The ACS3 kit offers no fewer than seven springs in 5lb/in increments across each travel length, with a fair overlap between each. Gone are the days when a spring could be be bought in soft, medium or hard rates only.
I have the ACS3 fitted to a 160mm travel Fox 36 on my Santa Cruz Hightower 29er. Factoring in my weight of 80kg (with gear) I was sent the blue spring, which sits right in the middle of the seven spring range. If you’re on the boundary between two different springs, Push recommends you to consider your riding style – if you are hitting a lot of big drops and jumps, then go for the heavier option. As someone who keeps their wheels on the ground for the majority of their riding I opted for the lighter option.
A word of caution for those interested in taking the plunge: because you’re fitting a spring into the stanchion it is likely to cause some light scratching to the inner surface over time, which is entirely normal and non-detrimental to performance or longevity. However, if you tried refitting the original air spring, those scratches aren’t likely to play well with the O-ring that slides up and down the inside of the stanchion.
That means once you go coil, you can’t really go back to air. Then again, I highly doubt you’ll want to.
If you’re happy taking the lower legs off your fork to do an oil change then fitting the ACS3 is very simple, especially using the video that is provided on Push’s website as a guide. The only specialist tool required is a dental pick or similar to help gently remove the retaining ring from the inside of the left side fork tube. I also opted to change the fork seals at the same time given the fork was apart and fresh oil gets added at the end of the process.
On The Trail
Fitting the ACS3 added just over 200g to my fork, most of that being due to the spring itself, and this weight will vary slightly depending on the travel of the fork. Once fitted, all that needs to be done is to add some air to the Air Bump Stop cartridge in the same way you would add air to a standard air fork. This can be set between 5 and 50 psi, depending on the amount of progression you want to the end stroke.
Intrigued as to the effectiveness, I initially set the Air Bump Stop cartridge to 5psi. Unsurprisingly this meant that the fork remained very linear throughout and I blew through the travel on my first test run. But, boy was the fork super plush. This created its own issue in that the sag was just over 30%, which is a little too much for my liking. By adding the two provided plastic spring preload spacers though, I was able to reduce the sag to 25%, lifting the ride height of the bike in the process.
To help counteract the super-plushness I also increased the low speed compression damping by two clicks and reduced the rebound damping by a click. The fork was now starting to feel really good, but I was still going through its travel to a point where I would be looking to fit a heavier spring. I was a bit reluctant to do that though, since I’d give up some of the beautiful suppleness.
Instead, I tried increasing the pressure in the Air Bump Stop cartridge to its maximum recommended setting of 50psi.
This absolutely transformed the fork’s performance.
Because the Air Bump Stop only kicks in for the last 35% of the travel, the first 65% will feel the same regardless of what pressure is in the Air Bump Stop cartridge. That meant I still had the super-plush feeling I was enjoying from the ACS3’s coil spring, but now the final third was protected from the bottoming I had previously experienced. The added progression was also much more what I had been used to from the fork prior to the conversion.
Taking the fork onto a wide variety of trails in the Tweed Valley, the ACS3 kit excels. The plushness in the start of the stroke is amazing, and is exactly what you’d expect from a coil spring. The added traction and comfort was apparent from the off, most noticeably on climbs where the wheel just rolled smoothly over roots and rocks that may have knocked me off line previously.
Once rolling downhill though, it’s the increased sensitivity in the mid-stroke that helps to take away all chatter and medium-sized hits that a rough bit of trail can throw at you. And when those hits and drops open up, you’ve still got that bottom-out progressiveness of an air fork to keep you from slamming through the travel. It really is the best of both worlds.
In my experience, the ACS3 Fork Coil Conversion Kit delivers on Push’s bold claims. Put simply, you get the sensitivity and consistency of a coil spring, with the end-stroke adjustability of an air spring.
Yes, it adds a decent chunk of weight, and it is a hugely expensive upgrade – especially if you’re adding that cost on top of an already expensive top-end fork. For those with a compatible fork that’s a couple of years old though, this upgrade could be a great alternative to shelling out for an entirely new one.
Personally, I love what the Push ACS3 conversion kit has done to my fork’s performance, and I will definitely be moving this fork to my next bike. Apart from the dropper post, this is the single most ride-changing bit of kit I have put on a bike – it is that good.
|Product:||ACS3 Fork Coil Conversion Kit|
|From:||tftuned.com (UK), or pushindustries.com (US)|
|Price:||£399 / $389 USD|
|Tested:||by Tom Nash for 4 months|
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Glad you agree, just an awesome bit of kit.
Since when did the exchange rate go the other way?
Sounds great, and a year or two ago I might have been tempted.
But the new Debonair air spring for RS forks is so supple (and reasonably priced at £42), the “want” just isn’t there any more.
This isn’t a new idea.
The Marzocchi 66 RCV that I have still kicking around my garage used this same design.
It would be interesting to see the comparison with Luftkappe or DebonAir. My Lyrik with Vorsprung upgrade is at par with DHX2 at the back, but maybe it could be even better…amazing how technology goes forward!
I’m a tweed valley resident & I’ve just ordered an elevensix for my YT capra 29er. (£800 sale price)
Would you recommend I bite the cash bullet & pair it with this upgrade for my 170mm fox 36?