A few years ago I thought riding fat tires on dirt was silly, something that other people did, for various reasons that really made no sense to me.
3 surgeries later, with another being procrastinated, I have a different perspective on fat tires on dirt. Quite frankly they allow me to ride, period, when I otherwise might not due to pain or chronic ankle instability. Life moves pretty fast, apparently.
My intent here is not to provide an overview, as that sort of info is out and available through any number of outlets.
What I want to do is briefly mention a few of the other fat fork options I've tried the past few years, to give context to what Mastodon brings to the table.
First came the 'fork of many names' which is sold/marketed by many entities. It is an inverted design with a reasonable weight and cost, but sub-par stiffness and, to be direct, atrocious damping. If you want something to hold your wheel in place and go, occasionally, up and down, it will serve that purpose, but it won't feel very good doing either. I never owned one of these because the demo rides I did on others' bikes convinced me they weren't worth the money or frustration.
Next came RockShox Bluto. This fork is both light and relatively inexpensive, and there are a gazillion of them out there being ridden. I didn't enjoy Bluto because the chassis was anemic -- it was very easy to overdrive it pretty much constantly -- and because the damping was crude compared to almost every high-end damper in use today. The best thing I can say about Bluto is that he brought fat suspension to the masses, opening the door for improvement by whomever came next.
After punting on Bluto I bought a Wren fat fork. It was heavy. The damping didn't work below freezing temps -- the fork would literally freeze solid. There was a disconcerting amount of slop (not flex) in the keyed lowers, such that the wheel would flop and clunk when you changed direction quickly. When the damper wasn't frozen it felt crude, with a too-slow rebound circuit. There was considerable stiction in the system, possibly from the dual air spring, which never functioned as intended. Actually I'm not sure how it was intended to work, and my requests for an explanation from Wren were met with quick, friendly, and entirely confusing/conflicting answers. It sort of felt like they were learning as they went, and didn't always know how things were meant to work. I got it to function passably when temps were above 40*, but I never really enjoyed it.
The Fox 34 Boost+ came next. It was never designed nor intended to be run with fat tires, but for whatever reason it came with a freakish amount of clearance that allowed exactly that. Cost was on par with any other high-end fork, as were both stiffness and damping. I really liked everything about this fork, but wished for more tire clearance -- both to be able to run more meat, but also to have some wiggle room when rides occasionally got sloppy. Pretty minor niggles on an otherwise very, very good fork.
This is when Mastodon entered the equation, about 3 months ago.
Mastodon has massive tire clearance. Above is a 27.5 x 3.8" (nominal) Bontrager Hodag. Below is a Vee 2XL on a 105mm rim. Same fork in both pics -- plenty of clearance.
I actually rode Mastodon for ~10 days on my Meriwether fatbike -- above -- long enough to spend some time off piste with a number of wheels and tires, and to experiment with different amounts of travel. None of this was "exhaustive" testing -- I was just riding, learning, fiddling, and thinkering about where I'd most like to use what Mastodon brought to the table.
When just tooling along and smelling the lilies it was invisible -- a high compliment -- but the harder I pushed it the better it felt: zero noticeable chassis flex, a widely/easily adjustable damper, and a stictionless air spring. When I felt I had a handle on all of the above is when I decided to build a second Fatillac to compare Mastodon directly to the Fox 34 Boost+.
The bikes were literally identical in every way except for fork and color. I rode them back to back, same trails, for about ~2 months.
It bears repeating that I never constructed nor formulated any sort of objective "test" for either fork. My intent wasn't to prove that one was better, or ______ in any demonstrable way. I just rode them, noted differences, and thought about which I'd most want to have on my bike. No more complicated than just that.
I'd been riding the Fox with MRP's RAMP cartridge and loved that I could easily adjust air volume as a means for getting the fork to stand taller in it's travel in any given situation. RAMP doesn't do anything the stock volume adjusters can't, it just makes it easier to dial things in, and change things on the fly. I don't tend to fiddle too much with my suspension once I've dialed it in, so what RAMP did was to just make that process simpler. After dialing it in I never touched the RAMP dial again.
With Mastodon you have to pull the air cap and swap spacers around to change air volume. Not hard, not really a hassle, doable with basic tools, and no parts to lose or keep track of. Not as easy as RAMP, but just as effective. I pulled the air cap and swapped spacers a total of 3 times before I was happy with the end-stroke ramp and mid-stroke support.
I belabor the point about adjusting air volume because it's one of the few (admittedly minor, and RAMP is an aftermarket solution) differences in getting the Mastodon to feel as good as, maybe even better than, the Fox. The takeaway you should get is that the differences in these forks amount to a hill of beans once they are dialed in: Both feel great -- stiff, supple, capable, adjustable -- and I could happily ride either.
The only other difference then, comes down to the ability to run a wider range of tires in Mastodon, and for me that was the deciding factor in selling the orange bike with the Fox fork.
Some will want more detail than that -- and they should ask specific questions below!