Gainful Grip with the Formula Mod MTB Coil Shock [Review]

If you're hungry for the fluid sensitivity and all day consistency of a coil shock, alongside a wide range of tunability, the Formula Mod might be your next great go-faster mountain bike upgrade.

Formula offered countless sneak peeks behind the curtain before releasing their new Mod coil shock for public purchase. It’s been tested by a variety of elite gravity racers and average riders alike, and we took a long look at it during a media event last spring. I have since tested the shock on three different Horst-link frames that have all played a little differently with its dynamic damping magic.

The Mod uses a high flow oil system with a 30mm internal piston to help maintain consistent performance no matter how long a descent may be. The external reservoir, or piggyback, uses a large volume bladder instead of the usual IFP to ease oil movement. All of this fluid-flow goodness is said to minimize friction in the system and improve small bump sensitivity.

In addition to these internal characteristics, the Mod offers a climb switch to firm up the pedaling platform, wide-ranging external rebound and compression adjustments, and three different Compression Tuning System (CTS) valves to suit different riders and trail types. Swapping the CTS valves is similar to sending your shock to a suspension guru for a custom tune, but with the Formula system you can do the work at home in the time it takes to drain a beer.

As a performance-focused brand, Formula tunes every shock to the specific bike it will be working with rather than selling a generic tune intended to suit most leverage curves. For the Jeffsy Base that meant they contacted the folks at YT Industries to discuss the bike’s suspension characteristics in detail. Once they were happy with the internal tune they shipped the 210 x 55mm standard-mount shock my way and I had it bolted to the bike in a matter of minutes.

I rode the Jeffsy for a few days with the recommended 400lb. spring to match my weight, then swapped in a 450lb. steel spiral to make the 150mm bike a little more bike park-friendly. Given the faster and rougher descents that I rode over the rest of the testing period, the stiffer spring stayed put and felt supportive throughout.

Swapping out the RockShox Deluxe Select damper on the alloy Jeffsy for a Formula Mod coil shock is hardly a fair comparison, as the lightweight air-sprung trail shock wasn’t up to the bike’s performance capabilities to begin with. Regardless, it made a massive improvement in the way the Jeffsy handles on long and rough descents, and improved adjustability and rear-tire grip tremendously. The simple stock air-shock heats up half way down any descent that’s longer than a few minutes, becoming hard and making for a harsh ride. With the Mod, the rear tire feels smooth and predictable even on descents that last over ten minutes. With that added consistent sensitivity, there’s no question that the coil shock made a massive improvement on that affordable trail bike.

The 400lb. spring is currently on the bike.

Swapping springs on the Mod is as quick and simple as the initial mounting process. Loosen the preload collar enough to slide the spring up the shock body about 8mm, then pull the C-clip off the bottom, remove the lower mounting hardware, and slide the spring off. Swap in the desired spring, replace the hardware and C-clip, and tighten it all back together by hand with the preload adjuster. The whole process takes about five minutes. Folks who love the speed and ease of air-sprung suspension might call foul on that spring swap duration, but five minutes seems reasonable for a modification that riders will make once or twice per year at most.

I tested different spring rates on both the Jeffsy and the Privateer 161, and with the 161 the two springs that worked best gave the bike two different personalities entirely. I started with the 450lb spring, adding very little compression, with the rebound a few clicks faster than the middle setting. With minimal sag, this spring gives the bike a super supported feel that’s perfect for fast park laps or all-out racing. It keeps the rear end high in its travel and allows me to run the fork nice and fast for a balanced and composed race tune.

Now that the bike parks are shuttered and awaiting their winter blankets, the 400lb. spring gives the 161 a smoother ride and slightly less aggressive stance that fits well with my local trails and the damp fall soil conditions. After adding a few clicks of compression, and speeding up the rebound by a click to make up for the lower spring pressure, the bike’s temperament is better suited to slower and more frolicsome trail riding. With the fork adjusted to fit, the Mod has been surprising me with gainful grip on wet roots and rocks.

I have managed to bottom the shock out a few times with this lighter spring, and the Mod bottom-out bumper keeps that last bit of travel feeling as smooth as any of the others I have used. There’s no harsh sound or jarring sensation. Instead, it gives a firmly gummy squish before the big return.

The most surprising ride I’ve had thus far with the Mod shock is on the Sunn Kern EN 29 that I’m currently testing. The shock was developed, in part, with feedback from the Sunn Enduro Team, and the frame and shock have been tuned accordingly. It’s no wonder they know where to scratch one another’s backs.

From the first few turns with the Kern EN 29 I could feel a unique style of grip and support that I haven’t experienced with another rear suspension pairing. When I push to compress the rear end into a roller or off the lip of a jump it gives back with as much or more energy. There’s a clear point of rebound combined with support that allows the pilot to pump like mad, making speed along the way. All of that smooth feedback and support is typically found in air-sprung shocks, and the partnership between Formula and Sunn bore a defined winner. Alongside that frisky goodness, the rear tire maintains the sort of traction we all love and expect with a coil. While I haven’t yet seen the leverage curve for the Kern, I am sure it’s correct for this shock. I’ll dive into that further in the full bike review.

You can also have a titanium-colored coil if Ultraviolet doesn’t fit your bike’s trail outfit.
Price€699 or $829
External adjustmentsLockout, 17 clicks compression, 17 clicks rebound, preload, 3 CTS valves
Spring options300-600lbs in 50lbs increments
Standard length/stroke options210 x 55, 52.5, 50, 47.5 or 230 x 65, 62.5, 60, 57.5
Trunion length/stroke options185 x 55, 52.5, 50, 47.5 or 205x 65 , 62.5, 60, 57.5
Spring colorsUltraviolet or titanium

I didn’t need to swap out the CTS valves in any of these bikes because the tunes were dialed and the medium compression valve worked well with my riding style. However, I did get a chance to change the valve just for kicks, and it is undoubtedly a task anyone can tackle. All you need is a shock pump, some basic tools, and this video.

Regarding other adjustments, the compression clicker moves through seventeen speeds that you will undeniably feel on the trail. None of that unsure “uh, I think it feels a little different” sensation after three clicks. Several friends rode my test bikes with the Mod mounted, and each of them mentioned surprise around how fast the shock is able to move. Since coil springs don’t ramp up at the end of the stroke, they also don’t rebound with added force. Riders who love the magical coil feel often like being able to speed the shock up to compensate for the naturally lighter rebound characteristics, and the Mod can definitely accommodate. Once I found the too fast point, the shock still had several clicks before it was fully open. The range of external adjustment on this damper should suit almost anyone’s preferences.

YT Jeffsy Base model with a Formula Mod shock and Selva S fork.

Final thoughts

These steel-spring-sprung dampers weigh more than their air counterparts, but with the Mod’s level of trail performance a few added grams are welcomed. If you’re hungry for the fluid sensitivity and all day consistency of a coil, alongside a wide range of tunability, the Mod might be your next great go-faster upgrade.

Mod coil shocks will sell for €699 or $829 at your local Formula dealer. Click over to the Formula site for additional information on the Mod coil shock.