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2021 Giant Fathom 29 2
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The shell is 92mm wide. These are press fit. I measured mine the last time I had the cranks out. The spindle is about 114mm long (4.5"). I have zero idea where the 68/73 comes into play. Bottom bracket standards confuse the crap outta me. I posted earlier that my XTR 9120 cranks are too long to work in this bike, so I'm not sure what Shimano cranks would, or how to search for them. Obviously the BB needs to be changed for the 24mm spindle, but I'm not sure how to address spindle length. Hope this helps a bit!
I believe that the 68/73 ID is a width measurement of the frame at the bottom bracket. This indicates that you can use a BB for widths between 68-73 with or without spacers.
 

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I believe that the 68/73 ID is a width measurement of the frame at the bottom bracket. This indicates that you can use a BB for widths between 68-73 with or without spacers.
When I say shell, what I think I'm talking about is the frame :oops:! Maybe I'm using the wrong terms when talking about this stuff. The width of the frame appears to be 92mm at the bottom bracket. It's all too confusing. Wonder if Giant would just tell us what Shimano BB and cranks are compatible with this frame? That would make it a lot easier!
 

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When I say shell, what I think I'm talking about is the frame :oops:! Maybe I'm using the wrong terms when talking about this stuff. The width of the frame appears to be 92mm at the bottom bracket. It's all too confusing. Wonder if Giant would just tell us what Shimano BB and cranks are compatible with this frame? That would make it a lot easier!
Yes it would make it easier, I looked for a number for Giant and have not been able to find one. Only way to communicate with them is through email form what I have seen. If anyone has contact info, please share and I will call them.

From doing a bunch of googling last night it seems that the press fit bracket is 89.5/92 and the threaded bracket is 68/73. Not 100% on that but that is what I mostly saw.
 

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When I say shell, what I think I'm talking about is the frame :oops:! Maybe I'm using the wrong terms when talking about this stuff. The width of the frame appears to be 92mm at the bottom bracket. It's all too confusing. Wonder if Giant would just tell us what Shimano BB and cranks are compatible with this frame? That would make it a lot easier!
I have no idea about the proper terminology either! Just going by what I've read or watched.

This is a fairly informative video involving a bottom bracket and crank install.


He discusses the BB measurements and proper spacings around 2:20.
 

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I have no idea about the proper terminology either! Just going by what I've read or watched.

This is a fairly informative video involving a bottom bracket and crank install.


He discusses the BB measurements and proper spacings around 2:20.
Ah yes, I have seen that video a few times. It pretty much solidifies my thinking. Someone correct me if I m wrong. Threaded BB is 68/73 mostly for MTB and press fit BB is 89.5/92 mostly. If you notice, the threaded BB has bigger cups on the outside than do the press fit ones. I believe this is how you can use the same crank on both. The bigger outside cups on the threaded BB (which is 68/73) take up the extra length from the press fit shell which is usually 89.5/92. It appears that the Shimano XT-Mt8100-1 crank that I have on the way should fit with the BB-MT800-P BB that I have ordered. Fingers crossed.
 

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Ah yes, I have seen that video a few times. It pretty much solidifies my thinking. Someone correct me if I m wrong. Threaded BB is 68/73 mostly for MTB and press fit BB is 89.5/92 mostly. If you notice, the threaded BB has bigger cups on the outside than do the press fit ones. I believe this is how you can use the same crank on both. The bigger outside cups on the threaded BB (which is 68/73) take up the extra length from the press fit shell which is usually 89.5/92. It appears that the Shimano XT-Mt8100-1 crank that I have on the way should fit with the BB-MT800-P BB that I have ordered. Fingers crossed.
I'm anxious to hear if your BB and cranks work. Keep us posted!
 

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I've been following this thread for quite a while now and about two weeks ago I ended up buying a barely used Fathom 2 with just one ride on it as my first mountain bike.

So far my bike won't drop the chain unless I spin the crank backwards quickly by hand in the highest gear, so I'm planning on leaving the stock 0mm offset chainring on for now.

Right from the start the front end of my bike has made all kinds of racket if you hold the brake and compress the forks. I've been playing around with it here and there to try and figure out if the noise is really coming from the forks, and in my case it seems it's actually the brake pads in the front caliper rocking very slightly every time you cycle the fork. I figured that out after I flipped the bike upside down to put pressure directly on the forks without the brakes involved and the clicking/tapping wasn't there. The rocking of the pads in the caliper allows the front wheel to move a bit and for a while I did think it was play in the fork bushings.

I don't have a fix since I haven't had a chance to pull the caliper off to investigate it further yet, but hopefully this noise issue isn't actually a fork problem.
 

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This morning I realized the fathom has the same calipers/pads on the front and rear and I found out I can recreate the same noise by holding the rear brake and moving the rear tire back and forth by hand. You can get it to make the noise in the rear while sitting on the bike, but you get so much feedback through the bars that it just feels like a fork problem.

After work this evening I'm going to pull the calipers and pads and try lightly greasing some contact points to see if it tones down the noise.

I'm very curious to find out if anyone else with the fork noise has ruled out the caliper/pads being the real problem.
 

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Well, don't get your hopes up too much since it seems my noise problem was two things. The pad movement was absolutely causing a ton of noise and what felt like play in the forks and I got that mostly solved with some grease where the pistons touch the pad along with some small strips of tape on the ends of the pad backing to slightly tighten up the fit in the caliper. The bad is there is still a slight tapping noise coming from my fork, but it's nowhere near as loud and annoying as the brake issue was.
 

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So this SRAM sprocket will fit the paraxis cranks with no mods? Just bolts right up?

Yes, the Praxis cranks take any SRAM direct mount chainring. Just as a reminder, there's a Shimano Hyperglide specific tooth pattern, which, as I understand it, is necessary to realize all the benefits of the Hyperglide shifting as well as ensure drive-train reliability. SRAM chainrings don't use this tooth pattern unless specifically noted (like the Absolute Black Oval that I picked up). Some have reported that the master link just needs to be swapped to an Eagle link rather than the Shimano to make it work. Lots out there on the old interwebs about this, but I've only read a little of it. I'd rather just keep it all Hyperglide specific, but that's just me. I wanted Shimano Hyperglide for a reason! Just food for thought!
 

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I ran full Shimano on my last bike with a SRAM chainring and it seemed fine?!

On my fathom I now have a Shimano chain with a SRAM ring. Everything seems fine?!


Sent from my iPhone using Tapatalk
 

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I ran full Shimano on my last bike with a SRAM chainring and it seemed fine?!

On my fathom I now have a Shimano chain with a SRAM ring. Everything seems fine?!


Sent from my iPhone using Tapatalk
I don't doubt it at all! I'm only stating what I've read. Is it marketing? Possibly. Probably. I'm just saying I'd rather not take the chance if there's an alternative, which there is. Personal preference!
 

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Discussion Starter #395
Dumb question, is the bolt for the left crank reverse threaded? I got my offset Praxis chain ring and want to get it on...
 

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Discussion Starter #397 (Edited)
1912607
1912608
As 86runner has already stated, the 3mm offset makes the chain line much better! Even if your bike is not having issues, I’m not sure why you wouldn’t want to throw an offset chainring on it as I gotta think a better chain line means less wear.

What I am reading online is 52mm chain line for boost requiring 3mm offset chain rings so I guess Giant and / or Praxis screwed up? I have to say that Praxis was super easy to deal with and they didn’t hesitate one bit when I explained the situation and they shipped super fastI gotta think that confirms this is an issue. I just wish they had a 30t for me as I don’t want a 32t.

The clearance with this 32t is VERY TIGHT against the chainstay. It doesn’t touch but no way you can go above this tooth count with the offset.

Unfortunately for me, my chain is now way too tight with this 32t on the granny gear so I can’t even use it unless I replace the chain. :(. Since I have a 30t offset coming, I am going to just wait.

Now if only Giant would give details on the Crest fork issues. They could learn a thing or too from Praxis. This is my first Giant and honestly not sure I will ever buy a Giant again given their silence to date. I understand the challenges of what all bikes manufacturers are experiencing. All I want is some acknowledgment or clarity that they are even looking into this.

This drivetrain issue I think is resolved because of this thread and individual contributions, no thanks to Giant.
 

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View attachment 1912607 View attachment 1912608 As 86runner has already stated, the 3mm offset makes the chain line much better! Even if your bike is not having issues, I’m not sure why you wouldn’t want to throw an offset chainring on it as I gotta think a better chain line means less wear.

What I am reading online is 52mm chain line for boost requiring 3mm offset chain rings so I guess Giant and / or Praxis screwed up? I have to say that Praxis was super easy to deal with and they didn’t hesitate one bit when I explained the situation and they shipped super fastI gotta think that confirms this is an issue. I just wish they had a 30t for me as I don’t want a 32t.

The clearance with this 32t is VERY TIGHT against the chainstay. It doesn’t touch but no way you can go above this tooth count with the offset.

Unfortunately for me, my chain is now way too tight with this 32t on the granny gear so I can’t even use it unless I replace the chain. :(. Since I have a 30t offset coming, I am going to just wait.

Now if only Giant would give details on the Crest fork issues. They could learn a thing or too from Praxis. This is my first Giant and honestly not sure I will ever buy a Giant again given their silence to date. I understand the challenges of what all bikes manufacturers are experiencing. All I want is some acknowledgment or clarity that they are even looking into this.

This drivetrain issue I think is resolved because of this thread and individual contributions, no thanks to Giant.
Wow, yeah that's really tight! It's interesting that the oval has more clearance than that. The 30t oval is supposed to be 32t at the largest part of the oval, and 28t at the smallest. I would think it would be similar to these Praxis 32t rings, but just judging by your pics, that's quite a bit closer. I have the Praxis ring, but hadn't tried it. Did Praxis give you an eta on the 30t? They just told me end of February.
 

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Discussion Starter #399
Wow, yeah that's really tight! It's interesting that the oval has more clearance than that. The 30t oval is supposed to be 32t at the largest part of the oval, and 28t at the smallest. I would think it would be similar to these Praxis 32t rings, but just judging by your pics, that's quite a bit closer. I have the Praxis ring, but hadn't tried it. Did Praxis give you an eta on the 30t? They just told me end of February.
Praxis said no sooner than February but it could be a lot longer. I'm not sure they are going to send me the 30t, they didn't say. However, I appreciate they sent the 32t so quickly. I have the 30t Sram I think you linked coming, hopefully tomorrow. SRAM X-Sync 2 Eagle Steel Direct Mount Chainring 30T Boost 3mm Offset
 
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