RSD Mastodon fat bike suspension fork

Joined
Nov 27, 2015
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783
Location
S.E. Idaho USA
Anyone have any experiences with this fork, good, bad, or ugly? https://365cycles.com/index.php/manitou-mastodon-comp-fat-bike-fork-120mm-travel-15-x-150-mm-axle-tapered-matte-black-extended-version-fits-up-to-a.html?ff=1&fp=51076&gclid=CjwKCAiAx4fhBRB6EiwA3cV4KtDNqxWZ6TjwXzzL6JDgxUa5j2ziQn9Iie7YnRJq7wo_hIWJRSXkRhoCPhsQAvD_BwE

As an interesting side note, I see in the tail end, the last line of the blurb about it, it is mentioned that it "is designed for ebikes." My take on the fork is that it was NOT designed for ebikes, but what they mean is it would WORK on an ebike. The fork has gotten some major mention on e bike hating mtbr forums anyway....I think it's good marketing on the part of any company making any bike part, right at the tail end of the tech description, throw in: designed/will work, for e bikes.

As an example, check this video out, a promo for the fork, no ebikes involved but some incredible skills!

https://www.youtube.com/watch?v=HTGVC8X1_YY
 
I'd never seen a fork by "RSD" (though a google shows a lot of hits) but when I visited the link it says it's made by Manitou; I have an old worn Manitou I can't recall the name of, which other than the leakage of air from wear on teh seals, it worked well enough for me until I broke the dropout tips off testing a motor offground without any nuts on the axle. :( (which was stupid)


These are the specs / details off that page. Looks like its air-only, no hydraulic or spring damping. I guess that should make it easily adjustable in pressure on-road, and if it had a small leak you could even keep airing it up as you ride home, if you had to, assuming that like the old one I have here it has a schrader valve on the top of the leg.

It doesn't say if it uses one stanchion for compression and one for rebound, or if it's both in each leg. (AFAICR, mine is the former; I'd guess it would be better if it was the latter, but I still know little of decent suspension systems).

All-weather performance down to 0 degrees Fahrenheit
E-MTB Certified
120mm forks can be adjusted up to 140mm of travel
Compression Damping: Absolute
Extended fits up to 26x5.15" / 27.5x4.5" tires,
Rebound Damping: Adjustable TPC
Spring: ISO Air

Item Specifications
Color Matte Black
Weight 2430
Offset 51
Axle to Crown Length 550
Crown Race 40
Steerer Tube Length 251
Brake Type Post Mount 180
Wheel Size 26" Fat
Travel 120
Defined Color Black
Steerer Type Tapered
S.H.I.S. Stem Clamp Diameter 28.6
External Adjustments Low Speed Compression Damping
External Adjustments Rebound Damping
Positive Spring Air
Front Axle 15mm Thru x 150mm
Negative Spring Air
Stanchion Diameter 34
Lockout Switch None
Maximum Tire Width 131
Designed for ebike Yes

Stanchion Diameter 34
Steerer Tube Length (mm) 251
Steerer Type Tapered
Travel (mm) 120
Wheel Size 26" Fat
Manufacturer Product Number 19134020A502
Model Number 22617
Model ID 22617
Model Name Mastodon Comp
Make / Model Mastodon Comp

Tools Required
Torque wrench
3 way y-allen wrench (4, 5, 6mm)
Spoke wrench
15mm open end wrench

Bike Assembly & Adjustments
Install handlebars
Install seatpost and saddle
Install wheels
Pump up tires to correct pressure
True front and rear wheels
Adjust front and rear brakes
Adjust front and rear derailleurs
 
It is not from RSD. RSD is a bike manufacturer. Their suspension fatbikes are equipped with the Manitou Mastodon. It is good, but it is a fat bike fork. Not much competition in that category. The only other comparable is the Rock Shox Bluto. The Bluto is on the market for a few years already. The Mastodon is new, with better tuning. Yet, Rock Shox forks are more reliable, lower maintenance than Manitou, and the Bluto can be upgraded with their racing cartridge, making it better than the Mastodon. Both forks are air spring only, cartridge type.

It is not like one has many choices for fat bike suspension. Both are close to one another, single crown. The Mastodon has the clearance for 27.5. The Bluto is only 26, but quite lighter.
 
Interesting...... thanks for the name correction. One advantage of the Mastodon seems to be it's seals are better cold weather rated, right down to zero.

Another fatbike fork that has caught my eye, (but more then I want to spend, got to draw the line somewhere, mine is around $500.00) I'm considering all of these for my Soma Sandworm build:https://www.bikeman.com/bicycle-product-reviews/new-product-introductions/2974-carver-bikes-trans-fat-suspension-fat-bike-fork

This fork stuff reminds me of the action going on in the experimental aircraft world lately, my current plane had Super Cub style gear, with bungee chords taking the shock loads, the tried and true way to do this. But in addition it also has Fox air shocks to retard the rebound, helping avoid ballooning back into the air. Making a lousy pilot look good when landing. Especially useful when landing tight, off airport, as keeping the tires on the ground makes it easier to brake, ha ha. Some are going over to all shock suspension, no bungees at all, lot's of innovation going on. Old school bungees still have their place though, maybe I should build my own fork, not really!
 
craneplaneguy said:
maybe I should build my own fork, not really!
I've considered building my own fork for SB Cruiser; it'd use a rear triangle from a full-suspension bike, backwards, mounted to the steerer/crown off a junked steel fork. SInce the original shock from the FS bike was crap, I'd replace it with a better one I have from something else (but I'm not certain it will work directly; it might require some geometry modification of the triangle).

This style of suspension has been used on (racing?) motorcycles, so it does work. Just looks wierd and has other consequences that change stuff from a regular fork--but it can be lighter than a big oil-filled twin-stanchion fork would be for the same suspension, from the little I found at the time, so is probably why it was used.

Ideally I'd use a four-bar-link triangle for this, but don't have one that's suitable, and my skills are probably still not sufficient to build one from scratch. :)

I thought I had mockup pics in the SB Cruiser thread, but can't find htem so maybe I never did that and just thought about it. (lots of ideas, not enough time, hard to remember which ones I've ever actually done anything about. :oops: )
 
Don’t let BS sales pitch fool you. Single crown inverted fork is absolute fail waiting to happen. Inverted forks need to be double crown and even then, few of them DH double crown inverted forks are stiff enough.

Making your own fat bike fork?
One good, proven way to do that: Buy an old Marzocchi DH fork. Monster T is best for that purpose, or a Shiver DC if you prefer inverted forks. Then make (or order at a local machine shop) custom crowns to the width that you need. That is the way to have the real deal. Heavier of course, but any fat bike fork on the market is a cheap toy in comparison.

PS: Those forks are clearing 4 inch already, maybe not all 4 inch tire/rim combos, but some of them at least.
 
craneplaneguy said:
As an interesting side note, I see in the tail end, the last line of the blurb about it, it is mentioned that it "is designed for ebikes." My take on the fork is that it was NOT designed for ebikes, but what they mean is it would WORK on an ebike.

By the features, sounds like a decent fork; but not sure if those features are "designed for ebikes". I'm still getting a feel for riding an ebike on trails, but notice that most of my climbing is in the the saddle when I have a motor assisting me, so lockout or setting a platform may not be necessary. The fork I'm using currently doesn't have either, but will be building up my next bike to be purpose built toward offroad riding. I'm throwing on an old Fox Talas RLC and anticipate I'll only be needing the compression and rebound adjustments.
 
I think some marketing whiz kid just threw that "for e bikes" thing at the end just because....I got that impression anyway, that it was a mountain fatbike shock first and foremost, and oh yeah, it'd work on e bikes also! I read a lot of favorable reviews on it on mtbr forums FWIW. As more and more formally purist companies jump on the ebike bandwagon, I can see this type of marketing becoming more common!

My fat riding is mostly on very rocky and steep trails that no other bikes ride, like none, in the 3 years I've rode it. They all stay on the more normal bike trails in town, (which are awesome, but they are 15 miles away) these rocky trails are dirt bike/multi use, and right behind my house 1/4 mile away. I ride them slow because I don't want to die, more like a trials bike ride then anything. The big cushy tires are perfect for this trail. My current fattie has a basic Rock Shox, so I guess I feel the need to put something on this new ride other then a fixed fork.

I am also considering using a fatter tire in front, at least a 4.5 or maybe even a fiver. 4" in the rear is what I am told is the largest I can use on a Soma Worm. When the frame comes in I'll take my 4.5 off my current ride and see if it will work on the rear. I am also considering putting a larger tire and rim on the front of my Montague, 3" instead of 2". I have been spending too much time on the mtbr forums perhaps, but I see there is a good arguement for doing so, for trail riding anyway. Not so much for street riding I guess.
 
I think if a fork or frame was *really* "designed for ebikes" it'd have integrated clamping dropouts. :lol:

Or at least integrated torque arm mounts, and a high quality thick torque arm included, for each of the common axle sizes (so it fits the axle "perfectly").

But I haven't ever seen any of the stuff claimed to be "designed for ebikes" made this way, except for perhaps some of the frames of actual OEM ebikes (though I can't recall any by name ATM, I think I've seen pics of at least one here on ES of an OEM rear clamping dropout?).
 
amberwolf said:
I think if a fork or frame was *really* "designed for ebikes" it'd have integrated clamping dropouts. :lol:

Yup. That is the only fork that could be called ebike specific.

Not likely to happen soon. Common suspension forks can't be made to work properly with a motor in its wheel. It would have to be some kind of springer type, with double linkage. Kind of front swing arm.
 
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