WREN vs Mastodon | Comparison

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

In the world of fat bike front suspension three forks generally come to mind. The Rockshox Bluto which was the first out of the gate, the Wren with its unique inverted design and more recent Manitou Mastodon. The RST Renegade and Lauf Carbonara are additional fat front squish options, however the Bluto, Wren and Mastodon tend to be top of mind.

While the Bluto owned the fat bike scene for several years, the Wren Inverted Fork and Manitou Mastodon appear to be jockeying for the best seat in the house.

Wren Inverted Fork 

Wren Sports first introduced their line of products to the cycling world at Interbike 2014 and their inverted fat bike fork was an instant hit. What makes the Wren different than traditional front suspension forks is that the stanchions slide UP into the sliders instead of down. Being reviewed is the Wren 110mm inverted fork with tapered tube and QR. 

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

According to the folks at Wren, the advantages of inverting their fork includes:
  • Having lighter stanchions on the bottom, the mass of moving parts is less so the fork will react more quickly.
  • Anchoring the stanchions into the stronger, larger upper tubes and crown making the overall chassis much stronger and stiffer.
  • Lowering the fulcrum point where the uppers join the stanchions decreases the leverage factor.
  • Positioning the seals downward keeps dirt and nasty stuff from getting pulled into the fork
  • A strong, stiff, quickly moving fork is especially important for fat bikes where the size and weight of the tires put increased pressure on the fork
Another feature of the Wren is the keyed stanchions that keep the fork running true and prevents the stanchions from twisting. The 43 mm uppers are channeled to accept brass keys that are attached to the oversized 36 mm stanchions. These keys align the stanchions in the uppers and are designed to shear should the fork take a big hit. This protects the channels and the fork from damage and the keys can be easily replaced.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

The Wren TwinAir system allows the fork to be plush or progressive by simply using a shock pump - no need to disassemble the fork to adjust spacers. The floating piston in the TwinAir system is infinitely adjustable and allows the spring rate to be fine tuned to match riding style and conditions. Adding air to the top of the left fork will give a plusher ride, while adding air to the bottom gives a more progressive feel.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Wren ATK Wren 110

The damper in the Wren is actually a sealed unit that uses a flexible bladder to keep the oil under pressure at all times. It is maintenance free, needs no servicing and has an adjustable compression lever on the top (with full lock out) and a rebound damper knob at the base. While an available option on previous models, the All-Weather Damper now comes standard on all forks. It has been field tested to a frigid -27 Fahrenheit (-33 Celsius).

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Wren ATK Wren 110

The Wren is available in two fat options – a 110 mm (adjustable to 100 mm, 90 mm and 80 mm) and 150 mm (adjustable to 140 mm, 130 mm and 120 mm). Both forks have an optional QR or bolt-on axle and a tapered steer tube with a strait tube as a special order. According to Wren both the 110 and the 150 are capable of running tires with max 774 mm diameter.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Wren ATK Wren 110

All Wren suspension forks come standard with carbon bash guards and clamps (to protect the lower stanchions), travel clips for adjusting travel only or travel and AC length and a brake hose/cable routing kit.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Wren ATK Wren 110

Manitou Mastodon

The Manitou Mastodon arrived on the scene in 2017 touting a list of specs and options to entice the everyday fatbiker. Mixing and matching different features gives the consumer access to a fat fork at different price points. The model being reviewed here is a Mastodon Pro EXT factory set to 100 mm.

Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Fat Bike Fork

According to Manitou

Mastodon is the real-world trail suspension for fatbikes. This fatbike fork delivers all-temperature performance, working equally well in winter or summer, soaking up chatter and big hits. Extended ride height versions fit up to 26×5.15” / 27.5×4.5” tires. Standard ride height versions fit up to 26×4” / 27.5×3.8” tires on the snow, or taking on shimmering hot sand like a pro. All-temperature performance born of frigid winter ride-testing. 34mm trail chassis is stiffer and steers more precisely than any other fatbike suspension fork.

Unlike the Wren, the Mastodon uses a more traditional approach to providing front squish with the upper (34 mm) stanchions sliding into the (42 mm) lowers. However, unlike many other forks, Manitou opted to place the fork’s arch on the inside of the fork - behind the high point of the tire - rather than on the outside.

Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Fat Bike Fork

Inside the Pro EXT you will find Dorado Air Spring w/IVA. According to Manitou the Dorado Air Spring is their lightest weight spring technology with an all aluminum construction. The IVA (Incremental Volume Adjust) allows riders to tune the fork by physically moving tuning spacers above or below the piston to adjust the piston volume.

Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Fat Bike Fork

On the right leg of the fork is MC2 Compression Damping which provides separate high-speed and low-speed adjustments. On the top of the tube, the black high-speed dial controls the unsprung bike over square edge bumps, while the red low-speed dial controls damping for sprung chassis movement. At the bottom of the tube is the TPC (Twin Piston Chamber) Rebound Damping. This blue knob controls the speed at which the wheel returns to the sag position after being compressed.

Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Fat Bike Fork

Keeping the fat wheel mounted to the fork is their 15mm Hexlock SL Thru Axle. Manitou states that the simplified hexagonal axle design gives it a lower weight.

Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Fat Bike Fork

As mentioned previously, the Mastodon is available in several different flavors.  The Mastodon STD (max tire diameter 758 mm) and Mastodon EXT (max tire diameter 796 mm) are both available in a Comp and Pro configuration. The Comp is adjustable between 80-140mm while the Pro is adjustable from 100-150mm. Generally, extended ride height (EXT) versions will clear a 5” (up to 26×5.15” / 27.5×4.5”) tire while the standard (STD) ride height versions fit a 4” (up to 26×4” / 27.5×3.8”) tire.

Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Fat Bike Fork

Digging Deeper

What is it going to cost if looking to add one of these beasts to your fattie? While a Mastodon may come stock on some OEM builds, looking at MSRP shows the Wren being a more economical option of the two.

  • Wren 110 $699.99 USD (January 12, 2021)
Both the Wren 110 and Mastodon Pro EXT 100 are impressive looking forks. I personally prefer the clean looking lines of the Wren with the carbon bash guards and the absence of the fork brace. Unless you have a super keen eye you may not physically notice that the Wren has considerably beefier stanchions (36 mm vs 34 mm) and “lowers” (43 mm vs 42 mm) than the Mastodon.


Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Wren Fat Bike Fork

The Mastodon has a wider opening between the forks than the Wren (159 mm vs 136 mm) and is also wider overall when measured at the crown (241 mm vs 235 mm). Once again, you may not be able to pick up on the physical size difference, but your downtube may with extreme bar angles.

Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Wren Fat Bike Fork

The Wren also enjoys 110 mm of travel in stock form while the Mastodon legs give a little less squish at 100 mm.

Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Wren Fat Bike Fork

Although both manufacturers make weight claims about their forks (Wren 2151 g vs Mastodon 2172 g), what really matters is the true weight when set up for installation – steer tube cut with star nut and crown race installed. The Wren weighs in at 2174g (23g over claimed) and the Mastodon at 2251g (79g over claimed). However, the Wren installed weight is 77g lighter than the Mastodon.

Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Wren Fat Bike Fork

The mechanics of installing the Wren and Mastodon are pretty much the same. The dedicated cable mounts for the brake cable on the Mastodon does take the guess work out of cable routing, however the Wren supplied cable guides do allow for a more customized mounting. I found that running 180 mm rotors with SRAM calipers required a 20 mm brake post spacer for the Wren, while the Mastodon did not.

Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Wren Fat Bike Fork

Both the Wren 110 and Mastodon Pro EXT have documentation detailing their setup. The Wren requires putting 50 psi in the top chamber and adjusting it to achieve a 22-27 mm sag. The Mastodon has a rider weight/psi chart on its leg providing a recommended PSI and requiring a sag between 15 – 25%.

Fatbike Republic Fat Bike Fatbike Newfoundland Mastodon Wren Fat Bike Fork

As noted previously, once the sag is set on the Wren adding air to the top chamber will give a plusher ride, while adding air to the bottom gives a more progressive feel. The damper side had an adjustable compression lever on the top (with full lock out) and a rebound damper knob at the base. The Mastodon has the TPC Rebound damper on the bottom of the fork with an adjustable high-speed and low-speed damping control up near the rider.

Wren Setup
Mastodon Pro Setup

When ordering your Wren you have a choice of two axles – bolt on and QR. The bolt on requires a pair of 8 mm hex keys to install and remove, while the QR has a convenient built-in lever. The Mastodon’s Hexlock SL requires one 6 mm hex to remove the rim.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

As fat bikes spend a good portion of their life in cold temperatures, it’s important for the fork not to freeze up when the temperatures dip. On the Wren’s web site they state their inverted fork, with the stock cold weather damper, has been field tested to -27 Fahrenheit (-33 Celsius). Over on the Manitou site it states the mastodon has “all-temperature performance born of frigid winter ride-testing”. The actual effective temperature range of the Mastodon could not be uncovered.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

With the availability of 26" and 27.5" fat rims, tire selection and fitment can seem rather complicated. To help the consumer both Wren and Mastodon have on-line guides to help determine what tire and rim combination will fit their fork. As mentioned previously, the Mastodon Pro EXT 100 can take a maximum tire width of 131mm and diameter of 796 mm. A handy tire chart on their site looks at the diameter of several popular fat bike tires on both 26” and 27.5” rims. Looking to the Wren, the maximum fork opening is 136 mm measured at the uppers with a max tire diameter of 774 mm.


Forks cannot run perfect forever and will need servicing at some point in time. I'm sure there are options to send the Wren and Mastodon "away" to get serviced, however both forks do have on-line support tutorials and information to assist in disassembly and servicing. The Mastodon has a 13 page guide while the Wren has a more succinct four page description coupled with videos. One thing worth reminding is that the Wren damper is a sealed unit that uses a flexible bladder to keep the oil under pressure at all times, while the Mastodon fork uses loose oil that requires draining and replacing.


Hands on 

Over the past three years I have placed considerable time on each fork in all types of conditions – from dry summer heat to frigid winter cold and most types of conditions in-between. I am not a fair weather rider, and while I do like bouncing around on mountain bike trails, my preference is to ride my fattie on less groomed trails in full exploration mode at speeds that sometimes may exceed a quick jog. These forks have graced the front ends of various hardtail fatties (both alloy and carbon) with a Wren spending time on a full suspension Trek Farley EX8.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

Once installed, both forks were pretty straight forward to set up with a slight nod to the Mastodon for simplicity. Adjusting the primary damper on both forks was a simple as turning the knob on the bottom of the fork – I generally select the middle position.

When fine tuning the forks I did find the Wren 110 to be infinitely more adjustable - adding air to the top of the fork does give a noticeable plusher ride while adding to the bottom does firm it up. I could actually feel the difference in the Wren’s characteristics by adding and removing air. And the Wren has a positive lockout for those rare times when front squish was not needed.


Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

The MC2 Compression Damping on the Mastodon is pretty convenient to adjust as it’s just there on top of the right fork leg. No need for a pump. I played with both the red (low speed) and black (high speed) dials after reviewing the spec sheet numerous times. I can honestly say that I could not find any noticeable difference in the Mastodon’s performance unless I put the dials in the extreme positions. Maybe it was my laid back non-aggressive riding style? In the end I just set both dials to the mid range and rode.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

If you have been around the fat bike world for any amount of time you know that tires rarely measure out exactly as stated on the sidewall. So when fitting a wheel and tire combination it’s very important to ensure that what you want to roll will actual fit the fork you choose to run. While playing with the Wren and Mastodon I rode both 26 x 80 and 27.5 x 80 rims on the forks with various tires.


The Mastodon and Wren both soaked up the nasty bumps, however my seat of the pants experience gives the nod to the Wren. The combination of the inverted nature of the fork, larger stanchions and infinite adjustability of the TwinAir system just made the fork seem smoother in the rough and not so rough terrain.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

And as mentioned previously, while the Mastodon did a good job of bump absorption, I was unable to feel any significant performance changes in the fork when adjusting the low and high speed compression unless in the extreme positions.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

Whether riding dirt or snow I was not able to physically feel that the Mastodon was 77g heavier than the carbon shod Wren. However, when the temperature dropped to extremely chilly conditions I did notice some lag in the Mastodon while the Wren still felt smooth. 

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

But when it came to removing the front wheel, the Mastodon Hexlock axle was easier and quicker to remove and install than the Wren’s removable axle.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

While I don’t remember ever bottoming out either of the forks, the Wren did offer an additional 10 mm of squish right out of the box.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

With the Wren’s 45 mm offset I did find that climbing required me to shift my weight a little more forward when comparing it to the Mastodon with its 51 mm offset. However, the Wren did make the descents feel a little more stable.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

While I have not performed any disassembly on a Mastodon, I did install an All-Weather Damper in an older Wren 110 and I felt the written instructions and video did a good job of walking me through the process without any specialty tools. Based on this experience I’m confident that I would attempt a full servicing when it’s warranted. I’m unsure if I would attempt the same with the Mastodon.

Fatbike Republic Fat Bike Fatbike Newfoundland Wren Inverted Fork Mastodon Wren VS Mastodon Fat Bike Fork

During my time riding both these fork I needed to contact both Wren and Manitou for technical advice and questions on their forks. There was a distinct difference in how my enquiries were handled. My experience with Wren was how I would expect customer service to be – consistently quick and accurate provided by a person who seemed to know what they were talking about. I cannot say I had the same experience regarding the Mastodon.

Final Thoughts

Both the Wren Inverted Fork and the Manitou Mastodon make riding fat bikes more comfortable and a heck of a lot more fun. 


However, I feel that the Wren’s infinite adjustability, beefier stanchions, lower price, excellent cold weather performance, serviceability and great dirt and snow mannerisms creep ahead of the Mastodon’s larger capacity, easier axle removal, and quicker set-up.

Which ever one you choose to grace the front end of your bike, it’s sure to improve your fat riding experience in the rough stuff.


RIDE FAT!





Comments

  1. I ride the Manitou and will keep it as i put my fat in my suv, i need to remove the front wheel frequently. So the Manitou was standard on my VLT1 but the Wren was in my target as soon as i knew for the removal. Great review. Thank you

    ReplyDelete
    Replies
    1. I do the same with my SUV for winter. The QR on the Wren is much easier to remove than the straight axle. And I keep a 3-way in my vehicle for Mastodon axle removal. :-)

      Delete
    2. You are very thorough. I wasn't aware of the Wren until I stumbled on your site as I looked for the best car/suv to carry my fat bike.

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