Review: EXT Arma Downhill Coil Shock

Once you’ve filled out the order form that requires not only the shock size and rider weight you’ll have to specify which bike the Arma will be bolted onto as well, because each shock is custom built with a 4-week lead time. EXT also understands that a rider’s needs may change depending on the tracks, so the choice of two lightweight steel springs is built into the $1,100 price tag.



Details

Bottom out control might not be all that you’re after when it comes to choosing a rear shock, nor should it be. The Arma V3 also has high and low speed compression with one rebound knob to cover all bases without too much complication. Reaching the dead end of the travel can still be done, but thanks to that HBC circuit, it comes with more of a love tap than a punch. To make sure riders are using the full travel efficiently, the elastomer bottom out bumper has been reduced in size from the previous version of the Arma.

To simplify the process of swapping springs, the rebound adjuster has been reworked to allow the coil to slide off without needing to remove the dial. Changing the spring requires you to remove the C-clip retainer and then slide the heavily machined shock collar over the rebound knob, like one of those interlocking brain teaser puzzles - it just clears at the right angle. A closer inspection will reveal a tiny plastic set screw that rests in reliefs to prevent the shock collar from unwinding as the spring oscillates. EXT’s Superlight springs can be up to 30% less mass than a standard steel coil and the 500 lb/in spring weighed 435 grams.

On the inside of the high-tech looking Arma, a 14mm shock shaft drives a 29mm diameter main piston. A spring-energized main seal is used to reduce friction and the shock shaft is treated with a slippery coating to keep things sliding like butter. To avoid cavitation, which is the phenomenon of bubbles forming under rapid pressure changes, a 24mm valve piston produces high turbulent flow. That also reduces hysteresis, or lag in the damping. Further adding to the consistency of EXT’s damper design, the rebound circuit can separate bump and oil flow.

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Performance

To reiterate the exclusivity of EXT’s shocks, this Arma was custom tuned for a Commencal Supreme 29/27 and my weight. I started on a 475 spring for the slower, steeper North Shore trails, but quickly moved up to a 500. On fast, flat out bike park speeds, jumping up to a 525 certainly wouldn’t be out of the question. I started with one turn of preload and left the clickers exactly how they were set from the factory.

To add some context between the shock and the bike, Dan Roberts dug into the details of the Commencal Supreme 29/27 in his review last summer and found that his particular bike had more travel than advertised. The overall progression is low and linear towards the end of the travel; something that would test the limits of the Arma's HBC.

Diving straight into familliar upper Cypress DH tracks, I was comfortable with the nature of the Arma right away. Maybe it’s the commitment and focus that comes with downhill laps, or just the bulkier helmet, but I never found the shock to be particularly loud as the oil flowed through the circuits, like some riders have mentioned. The same goes for the plastic sleeve that protects the bottom out bumper, which remained quiet while battling the bomb holes. I did get questioned more than once about the noise levels. Rattling parts I can understand, but really, oil slurping shocks should be the least of your worries when you're bombing downhill tracks. And if that was noticeable, wouldn't that be an admirable trait?

Either way, this shock is built to race. There's a unique quality that was tricky to sum up. The tune is firmer than what I’d been used to and initially I thought I might have to back off the compression. On lap two, I realized I had to adjust my braking points. I was riding faster than before. Ultimately, the shock was offering more support and that allowed me to push the bike through rough sections without getting bent out of shape. You did have to hang on tighter though and brace for larger hits. We were moving. If you want forgiveness, there is enough range to back off the compression and ease up on attacking. When things got real muddy and slippery, I backed off the LCS to unlock additional grip.

Proof of this is where I found my happy place on the clickers; smack in the middle of the compression and very close on the rebound and HBC. Depending on the pace or conditions of the day, a few clicks here or there set the tone. Of course, the custom tune built for my weight and bike didn't hurt either. The only exception was the rebound which stayed between three or four clicks (out of ten) from closed. Moving up to a 550 spring might be a lot of return force for the damper to contender with. Dan had a similar takeaway with another shock that was specified as stock equipment in last year's test of the Supreme.

About those keyed adjusters... They sound like a PITA, but we're talking about downhill bikes here. Making changes each lap with tools at the trucks was a snap. The most crucial of all those knobs is the rebound dial, which can still be turned by hand in a pinch in the lift line.

Even on a bike with little progression towards bottom out, the Arma was the best of both worlds. The Supreme's leverage begins with a mild progression curve and then tapers off to a sloping line. Maybe it was the perfect pairing? It got me thinking, are linear bikes better when the rider is looking for predictability where they can ignore small roots and stay alert and strong for bottom outs? That lets the shock do its thing without erratic shaft speeds.

I’m still blown away by the ultra smooth transition from compression to rebound. There were absolutely no clunks or mechanical top outs from the Arma. DH track have enough bumps to worry about. You don’t need your shock adding more knocks. On one hand, it could feel like melted butter over polished roots and still have that support deep in the stroke to keep the bike from caving or my body from crumpling when you needed it. I pushed it to the best of my abilities through the high speed compressions of Mount Prevost and the filthy muck of the Cypress downhill tracks. Suppleness of coil and the bottom out resistance of air? Impossible you say? The Arma is freakin' close.



How Does It Compare?

Prior to installing the Arma, I spent the better part of the season onboard the Ohlins TTX22M, which is also hailed to be a phenomenal coil sprung shock. And it is. The Arma just squeezes out every ounce of damping in so many ways. 

First, the TTX has only three high speed compression settings. Less is more if you’re overwhelmed by options and feel the urge to wild twist knobs. Ohlins does keep things simple because those changes are quite noticeable - but too noticeable for my taste. I often toggled between the middle and closed HSC switch position for bike park speeds, mind you, it could be overbearing at times. On the low speed side of the compression, the effect was the opposite. It was barely on the radar.

There were also times at which a small amount of top-out was present on the Ohlins. I never felt this through chattery sections of trail, but on the occasional pre-hop, a small tap at the top of the stroke was there.

Don't get me wrong. The Ohlins also has that juicy, bump eating performance with a fluid change in shaft direction, but the Arma provides a wider tuning window with more influence from each turn of the dial. There's also a plain elastomer bottom out bumper on the Ohlins - nothing wrong with that, either, however EXT's HBC provides extra cushion that avoided any rude, mechanical bottom out punches. Most importantly, this aids in the bike settling slower as you reach the end of the travel.

You'll be reminded by all of these features when you click "add to cart" though. The Arma costs nearly $400 USD more at first glance, however that includes two lightweight springs. The Ohlins sells for $695 as just the damper and custom tunes are available through authorized service centers. Is it all worth it? Given the time versus performance demand of downhill bike shocks, I say go all in. They aren't disposable like rims or tires. With regular service, there's no reason why any quality damper couldn’t be used for more than one season or transferred from bike to bike, granted you may need to re-tune it depending on the leverage ratio.

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Pinkbike's Take

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Reviews and Tech Reviews Shocks Ext Ext Arma