The Shiny New AM831 Group Buy (A) Thread!

[cybrsrce]

What are everyone’s impressions of tire clearance? Is 2.4 on ~30mm internal rims about the real limit or might I be able to fit a 2.6? (Presumably fitting protective stickers to ward off any occasional rub.) I demoed a Hightower this summer and noticed tire clearance was crazy tight, just wondering if the 831 is similar that way. I live in a very rooty rocky area and would like maximum tire volume.

Clearance is tight with a 2.4 that actually measures 2.4 (61mm) and the last time I measured it there is only a 66mm opening where the 29" tire treads are.  I am also in a rocky/rooty area but the 2.4 is fine.  You might get more space with the 27.5 as it opens up a bit more.

Also, any thoughts on possible over-shocking or running offset bushings to raise the bike for an MX build? I like the idea of trying out a mullet setup but would want to bring the geometry as close to normal as possible. I don’t love super low BB heights on my usual trails, too many violent pedal strikes even with good technique. 

27.5x2.6 is probably going to be about an inch smaller than a 29x2.4, going to drop the BB by 10-15mm maybe?  You can try offset bushings to counter that.  I don't know that 5mm tire width and a little volume is worth it unless you're already set on MX.

With 29x2.6F, 29x2.4R, and 165mm cranks I only had two pedal strikes and one crank strike today!  MX would make the bike nearly unusable for me, ymmv.

[FlaMtnBkr]

+++ You can also buy a complete headset (110, Hellbender 70 or 40 models) with the appropriate measurements: IS42/28.6 (upper bearing size)  and IS52/40 (bottom bearing size).

Are you sure it's a IS42? I thought that was the "Italian" version that's less common? I'm currently using the supplied headset but was going to upgrade at some point and thought when I measured it was an IS41 but it's put together now.

[cybrsrce]

Are you sure it's a IS42? I thought that was the "Italian" version that's less common? I'm currently using the supplied headset but was going to upgrade at some point and thought when I measured it was an IS41 but it's put together now.

Supplied headset is a 41.8mm bearing which is a common size for ZS and EC, the Cane Creek IS42 bearing fit for me.

[Jal]

The bearing included with the Cane Creek IS42/28.6 upper headset is 41.8mm, exactly the same measurement as the headset bearing supplied with the frame:

[FlaMtnBkr]

I measured the frame and used info from Cane Creek when I thought it was an IS41. But it's been a while and I could have measured wrong.

The box the headset came in had no info on it and while I would like to think the wrong one couldn't have found its way, I don't think I'm that confident. That said, I have no idea if the wrong one could fit? It seems like the bottom surface with the angle is what mainly located the bearing and that there was some space between side of bearing and the frame. If that were the case then I would think similar sizes could possibly fit but I could be remembering that wrong as well.

Hopefully I'm wrong and wasting bandwidth, but since I measured and thought it was the IS41 I will make sure to triple check everything when I have it apart. The IS42 I'd definitely the "Italian" version and not the standard size so it's a bit strange to me to use that size and I guess I would rather sound like an idiot than say nothing if there is even a small chance of something being wrong...

[Deso]

Hey, Magura caliper at the back and apparently Shimano lever - is that a "Shigura" setup? Why a Shimano caliper in front then?

I've got a dual piston magura for the front too! But had the hose on order so just waiting for that to come in. Shigura's are cool so just a bit of an experiment,

[Jal]

I have measured the diameter of the hole for the bearing in my frame, and it is 42mm (hundredths above hundredths below, measuring from different points). I guess that the headsets for 42mm hole come with a 41.8mm bearing to allow some clearance and to fit with no pressure and allow a little space for the grease to serve as a seal. But, although I have never experienced it or seen anyone do it, I think putting a 41 bearing would leave too much space and could create play and noise issues, and perhaps spoil the bearing and its seat, but I'm not sure either. I would not try. What is certain is that the headset bearing included with the frame is 41.8mm, as the bearing provided by Cane Creek with its specific headset for 42mm bore

[scourge]

What torque specs are everyone using for the shock mounts?

[cybrsrce]

What torque specs are everyone using for the shock mounts?

I asked Eddy and didn't get an answer so I've been using 10nm.  Bolt checks before rides and nothing has been loose so far. 

[BSAM]

Yes, of course, BSAM.

Jal,  you are the man.  Thank you so much for taking your time to provide the links for us (Especially newbie like me).  Brought couple parts, then found out it won't fit => 

[BSAM]

I can confirm that the 29x2.6 would not work because it rubbed like crazy.  In fact, when I first attempted and spin the wheel on the bike stand. The tire took a layer of the pain off due to the rubbing friction. 

Clearance is tight with a 2.4 that actually measures 2.4 (61mm) and the last time I measured it there is only a 66mm opening where the 29" tire treads are.  I am also in a rocky/rooty area but the 2.4 is fine.  You might get more space with the 27.5 as it opens up a bit more.

27.5x2.6 is probably going to be about an inch smaller than a 29x2.4, going to drop the BB by 10-15mm maybe?  You can try offset bushings to counter that.  I don't know that 5mm tire width and a little volume is worth it unless you're already set on MX.

With 29x2.6F, 29x2.4R, and 165mm cranks I only had two pedal strikes and one crank strike today!  MX would make the bike nearly unusable for me, ymmv.

[FullCarbonAlchemist]

That’s good to know. There are a lot of things I like best about the 831 out of the options I have for an modern “enduro” 29er unbranded frame, but I’m still trying to decide if I can live with a 2.4. I run 27.5x35mm internal rimsx2.8 on my current enduro bike (2020 GT Force) and demoed a 2021 Hightower this summer that reminded me of both the good and bad things about typical skinny tires. I think I’d be much happier with 2.6s.

The Light Carbon FS947 is my other candidate and while not nearly as easy on the eyes (or the suspension kinematics, probably), it’s got the tire clearance and a few other things going for it:

*BSA threaded BB
*Takes the same 185x55 trunnion shock as my Force so I already have two shocks that fit it, probably the right tune too
*No questions about fork crown/knob clearance/needing a spacer
*$300-400 cheaper shipped (if I’m not able to get in on an 831 group buy; it might be weeks more before I have the money for a frame), plus saves me ~$500 on a shock

The seat post insertion depth on the 947 is a bit short, it’s ~400g heavier, and it probably has a higher center of gravity than the 831 so probably a little disadvantage on handling. But I feel like I’m losing the argument with myself to justify the 831…

Maybe I’ll build a 947 this winter and then an 831 in the spring when I’ve sold enough other bikes to help pay for it.

[darius72]

Alchemist,
Which price did you get on FS 947 to be 300$ cheaper than 831?
About other concerns, to me press fit BB is a pain the ass, but I think you can ask for BSA option on 831; about the fork now the issue is addressed, 3mm spacer (you barely see it once installed) and the problem is solved.
For the rear tyre I confirm that with 29x2.4" maxxis the clearance isn't great, it barely fits, but to my personal taste I don't feel the need for a wider tyre; also the frame is more a trail/enduro than a pure enduro, and personally I don't do big jumps or drops. 2.4" maxxis has a good volume.

[FullCarbonAlchemist]

I could be misremembering — this is the stuff I’m trying to think through before I commit to one or the other — but I believe a 947 from Light Carbon is $620+100 shipping, whereas an 831 from the Tideace store on eBay is about $1000.

Maybe I’ll get lucky and have the money in time for an 831 group buy; I’m a suspension geek/gearhead of many years and would rather have that efficient low slung VPP swingarm.

I can probably learn to live with a 2.4 rear and the other little compromises the 831 requires….but I also have severe arthritis and do quite a bit of jumps etc despite it so a little extra tire is always appealing. And I’m trying to hit the value sweet spot with this build — being able to reuse a DPX2 Factory shock I already have on the 947 is hard to say no to. One less thing I’d have to sell in order to fund the build.

Since I’d probably be getting a Large, is the whole crown race spacer thing even an issue for me?

[darius72]

I could be misremembering — this is the stuff I’m trying to think through before I commit to one or the other — but I believe a 947 from Light Carbon is $620+100 shipping, whereas an 831 from the Tideace store on eBay is about $1000.

Maybe I’ll get lucky and have the money in time for an 831 group buy; I’m a suspension geek/gearhead of many years and would rather have that efficient low slung VPP swingarm.
Since I’d probably be getting a Large, is the whole crown race spacer thing even an issue for me?

I don't remember exactly but I think I paid 850$ for the 831 painted and shipped without a group buy; just contact Joy or Eddy directly. Concerning the spacer depends on the combination frame size / fork model, but 90% you will need it; not a big deal to me, install and forget it. About tyre size and other options it goes to personal taste, and the use of the bike: the main questions is will you climb with your legs or with lifts? In case B you can have big tyres, heavy parts, spring shocks, etc. I am mostly in the case A, so I built the bike light