Most modern rigid mtbs (including fat bikes) have suspension corrected forks and frame geo.

The frame is designed around a rigid fork that is longer than it needs to be so that a swap to an appropriate suspension fork will not screw up the geometry.

Lets be honest here, how much can you really compensate for a longer fork? Manufacturers end up needing to steepen the seat tube angle in order to make up for it. The entire geometry of the bike ends up changing somewhat in order to compensate. The head tube is typically left alone because the slacker angle can help with stability and the increased fork trail will make up for that anyways. Maybe the bottombracket is lower slightly since the longer fork can raise that up a bit. This sort of altered geometry can work well on singletrack, but its not ideal for most types of riding.

Moisture, you're right!

How much can you compensate? Completely.

When a company produces a rigid bike with suspension corrected geo, they spec it with a rigid fork that is roughly the same length as then intended suspension fork AT SAG..

This is well established, incredibly common, and widely accepted by people who understand bike geo.. I suggest Googling “suspension corrected geometry” and try to understand it before continuing here.

I have a carbon Trek Farley. Putting 100mm Mastodon on it really made the bike much more versatile, a go anywhere trail bike, and with. the 29x3.0 wheels it rips. If I only rode it in snow or beach or gravel, rigid would be fine. But I like that I can head off piste and deal with anything I encounter. I also like riding it when I go out with buddies on faster trail bikes that may be slower riders.

Yes, cabbage, I know what suspension correction is. 425mm fork designed to correct in length for 100mm suspension, etc.

My point is, that whether youre talking rigid or suspension, shorter forks tend to offer better handling and agility.

My other point is that rigid forks tend to offer better control and speed over most obstacles you may encounter.

There is so much wrong with this on so many levels I don’t even know how to start unpacking it.

But to address your first point: if you knew what a suspension corrected fork was, you never would have claimed that a suspension fork would screw up the frame’s geometry.

I’m going to try just walking away.

I see what you're saying. I think you may have slightly misinterpreted what I am trying to say.

You want the fork to be designed around the geometry of the frame, not the other way around. When manufacturers begin to tinker with angles and bottom bracket heights etc to make things work with a long ATC length fork, for whatever the reason maybe, they are in some ways compromising the handling of the bike, perhaps for some sort of benefits elsewhere.

This is a good thread topic. I want people to understand the differences in performance and why one may work better for you over the other without any bias. If someone thinks the suspension is better but never tried a rigid fork, i think their input is complete nonsense.

My point is, a bike designed around a 395mm atc fork will certainty handle better than one designed around something longer, suspension corrected or not.

You may be right, but that is because so much of you basic assumptions are so wrong it is hard to make heads or tails of your points. Like this one:
I have no idea where you got those numbers from or why you thing they necessarily go together. A rigid fat bike fork for 100mm suspension correction would be a lot longer than 425mm. I have no idea what you are even thinking here.

This is factually incorrect. It is just plain wrong. Frames and forks are designed TOGETHER. Or at least there is is a fork length in mind when the frame is designed. And here is what you seem to not understand: You can in fact design two frames with different length forks with identical geo and handeling. All you are changing is the head tube length... more specifically, where the bottom of the head tube is. This, in and of itself, in no way affects the angles or handling of the bike.

If you do not understand why this is true, then you don't understand bike geometry. You are simply wrong about this. You can either go and do some research on this, or keep repeating this false information.

Complete nonsense for the reason stated above. And is yet again proof that you do not understand what a suspension corrected fork (and the frame designed with it) is for and how it works.

Absolutely an untrue statement.

No. Rigid forks offer less control and speed because the fork/and bike get bounced all around the trail. Suspension allows the tires to stay planted to the ground for better control and speed over obstacles.

You'd do yourself a favor by not even commenting anymore on this thread since you have no clue what you are talking about.

Two things about some of the recent back-and-forth:

1. This thread is in the Fatbike forum and many of these comments seem to be more general MTB related comments. Not a bad conversation, but if you're talking generally about suspension or fatbike specific suspension, please make it clear.

2. This Toad is an old-head, I like rigid MTB (& bikes in general). But that said, I've rented suspended bikes from time-to-time, and I have a comparison (not apples-to-apples, but a comparison):

I'm lucky to live with somebody that LOVES the North Shore of O'ahu and loves me enough to let me play bikes while on vacations. The resort we go to has single-track trails and rental bikes. I've ridden this loop 19 times over 7 years: Turtle Bay Beginners Loop. Most years, I ride a rental full suspension MTB (see pic below); early this year (in The Before Times), I brought my Breezer gravel/adventure bike with me (see pic below). I use my Breezer for CX, single-track, but mostly for ultra-endurance rides. I know this bike very well and it's well equipped - my best lap with the Breezer was 4:08; with the rental MTB, I got 3:17 ... and that MTB has 6 times on this lap that are faster than my Breezer.

To be clear: drop-bars are not the right choice on single-track; the Breezer has a long wheel base, making tight corners more difficult; the MTB has more aggressive knobby tires; and so many other reasons that this is not an apple-to-apples comparison.

All that said, IMHO a full-suspension MTB is the right tool for the fastest laps on single-track trails. OTOH you can enjoy single-track trails on most bikes, so if you're not racing ... run what you brung & have fun!

My Breezer Pro Radar gravel/adventure bike:

https://cimg3.ibsrv.net/gimg/bikefor...5d45043f9d.jpg

One of the rental MTB:

https://cimg5.ibsrv.net/gimg/bikefor...d48cb5445b.jpg

For those that are interest: I brought the Breezer to do some adventure rides on the North Shore, but was a little limited - the hills above the resort are military property that normally sits unused and can be ridden on weekends, but during our stay they were doing exercises the whole time and I couldn't take the ride I was planning. (edit/afterthought) - the Breezer did bring home some Strava glory and was faster than the rental bikes, but only on the gravel road segments ... so IME the a gravel bike is faster than a MTB on gravel roads.

I am not sure what type of bike Moisture is thinking of, but the concepts I am talking about apply to Fat bikes as well as other MTBs, or for that matter any bikes that uses a suspension corrected rigid fork. There are good reasons for choosing a rigid fork over suspension on a Fat Bike, but suspension forks screwing up the geo and handling (as Moisture is suggesting) is not one of them (assuming the bike was designed for it, and you are using the appropriate length suspension fork).

I see a lot of valid points on both sides so i think I’ll just get a F/S Fatty and a rigid Fatty.May the best Fatty win............my heart.

how often does the average person come across singletrack challenging enough to call the need for suspension? 1%? Less?

If you like to have suspension on singletrack that isn't too challenging, you're simply using the extra shock absorption to tackle terrain instead of sheer riding skill. Nothing can replace rider skill when it comes to getting that front axle over obstacles yourself.

in terms of speed and agility, on gravel, pavement and most types of singletrack, you will never come close to a properly balanced rider using rigid.

more like 99%. More. This is nonsensical. I have rigid (gravel), hard tail (fat bike that used to be rigid now has Mastodon fork) and full suspension bikes (XC and enduro), and 100% of the single track I ride (and its a lot and varied) requires a suspension fork and I'd estimate that 80% of it is ridden faster on full suspension vice hard tail. 20% would be be really sketch/dangerous on a hard tail. Could it be ridden on a rigid. Sure, it's possible, like its possible to ride a fat bike in a criterium.

And the axle to crown distance on a fat bike, eg, Trek Farley is 531mm w/out sag correction (511mm with).

Better to remain silent and be thought a fool than to speak and remove all doubt...

What a strange way of looking at it. Why does rider skill matter? I don't ride because I can then tell others on the internet that I am a skilled rider. I ride because it's fun. And having a 120mm manitou mastodon makes riding my Ice Cream Truck a lot more fun because the fork allows for a lot more speed in the downhills as well as makes riding / climbing technical stuff easier. I got the mastodon, because my typical trails weren't fun with a rigid. But they were a lot of fun with a suspension fork. I did manage to ride the trails with a ridid fatbike so I suppose my rider skill was enough. But I also ended up hating the slow going and constant evaluating of ride lines, wheel lifts, bunny hops etc. I want to ride, not play 4d chess.

I do agree that one needs to evaluate the terrain one rides and choose the tools accordingly.
Where I live there's only trail riding. I used to think that typical mountain biking is riding technical single track, but then someone decided that's trail riding so I guess I'm a trail rider. What suprised me was that apparently XC happens on fire roads and easy singletrack. From my perspective that's gravel riding. And for gravel a fatbike is massive overkill and also a pretty slow choice.

So the tool I find to be best suited for the type of riding I do is a front suspended fatbike with 120mm travel. I tried 140mm travel, but that's just too much. Actually a full suspension fatbike would be even better, but I only have a front suspended one. I suppose that objectively for some trails a 29er hardtail would be better and for some a 140mm full suspension 27.5", but I only have space and energy for one mountain bike so the front suspended fatbike is that bike.

I’m definitely on board with the specific purposes thinking. Rigid Fat for slow sloppy rides, dual sus for the rest.

Since you’re only planning on needing the fat tires a few times a year, we’re it me, I’d just rent one on those days and put my money and garage space into a regular duallie.

RS 100% for me