Long Teng / Mondince aero frame FM126

[Leon1234]

I think they designed the frame on paper. The proper process would be to manufacture it, test it, make adjustments, and repeat until the product is fully developed. I think in this case, they designed it on paper, manufactured it, and then sold it straight away to the customer. I’ve learned never to be the first to buy again 😅

I am not 100% sure about that, as the frame is produced by long teng which is a reputable manufacturer it would surprise me a bit. Still the flex you are experiencing is weird. Have you send mondice the video regarding clarification? Maybe it is actually an issue with your frame as the other buyers in this forum have yet to report something similar.

[Lukas_W]

Hi, I’ve ordered the FM126 as well. It’s the first bike I’m building myself, and I could use some help with the headset. It came with four bearings, a compression ring, and a ring for cable routing. Can anyone tell me the correct order for installing these parts? I assumed I’d install one bearing at the bottom and one at the top, then place the compression ring on the top bearing, followed by the cable routing ring. However, that leaves a large gap at the top. It looks flush without the compression ring, but simply leaving a part out seems wrong to me.

[Lukas_W]

Okay, from what I gather, the compression ring here is actually a crown race. Can anyone tell me if I’ve installed it the right way round and whether it’s the new version or the old one?

[patliean1]

I wonder if all of this is similar to the viral "squeeze-gate" of the Tarmac SL7 downtube. Meaning yeah you can squeeze it. But that isn't an area or angle where torque/load (?) is distributed. Yeah I'm definitely not an engineer.

[Ludo]

The test seems to be relevant because you’re definitely applying similar forces when pedaling, is it relevant to safety or performance?!!

[BeR]

Okay, from what I gather, the compression ring here is actually a crown race. Can anyone tell me if I’ve installed it the right way round and whether it’s the new version or the old one?

It needs to flush the fork (it will do it when you preload with the top cap stem).


7 mm height bearing for lower.
8 mm height bearing for upper.

[Leon1234]

The test seems to be relevant because you’re definitely applying similar forces when pedaling, is it relevant to safety or performance?!!

Where you able to replicate the test with your own bike?

[Serge_K]

Lean the bike against the wall so that the rear wheel and the handlebars are supported. Then you can apply force to the bottom bracket. In my case, the rear wheel was supported by a doorframe that was close to the wall, and the handlebars were against the wall.

thanks, i tried to do the same, wheel (nor rear triangle) on door frame, bars on another door frame. I get lateral movement, but some of it is the tyres that are half deflated (it seems). What i do not get, is the gap between the seat stays and the rim almost disappearing. Is it a wheel thing, or a frame thing? Would you mind using the same wheels for the test? I feel like most of the play could actually be the wheel rather than the frame.
I guess ideally we'd apply pressure at the rear at the thru axle, not on the wheel. There was no easy way for me to apply pressure on the frame rather than the wheel.
Interesting shenanigans...

[glitch]

Any riding feedback yet?

And what was the frame weight on your builds?

Considering this frame to replace a 2019 SystemSix which - love the SystemSix but would like lower weight, 32 mm clearance and somewhat more compliance, therefore considering the UL version

[bigApple]

thanks, i tried to do the same, wheel (nor rear triangle) on door frame, bars on another door frame. I get lateral movement, but some of it is the tyres that are half deflated (it seems). What i do not get, is the gap between the seat stays and the rim almost disappearing. Is it a wheel thing, or a frame thing? Would you mind using the same wheels for the test? I feel like most of the play could actually be the wheel rather than the frame.
I guess ideally we'd apply pressure at the rear at the thru axle, not on the wheel. There was no easy way for me to apply pressure on the frame rather than the wheel.
Interesting shenanigans...

All right, then let’s get back to our highly scientific work. This time, I didn’t lean the rear wheel against the wall or the doorframe, but rather the frame’s axle itself. That means the rear wheel is essentially removed from the equation. Then I asked the Gemini AI how much the bottom bracket deforms relative to the ground. The result is that the bottom bracket of the FM126 shifts about twice as much in the horizontal direction.

[bigApple]

Any riding feedback yet?

And what was the frame weight on your builds?

Considering this frame to replace a 2019 SystemSix which - love the SystemSix but would like lower weight, 32 mm clearance and somewhat more compliance, therefore considering the UL version

Don't get me wrong. You can ride the bike, but because the bottom bracket area lacks stiffness, the frame just isn't responsive enough. I wouldn't race crits on it, for example. I am not a world tour sprinter, but my Sprint with 1000w+ does not feel good on this bike. At least I haven't noticed any disc rubbing so far. Since I ride 1x, I can't tell if it might be rubbing at the front derailleur.

[Lukas_W]

It needs to flush the fork (it will do it when you preload with the top cap stem).


7 mm height bearing for lower.
8 mm height bearing for upper.

When I turn the bolt on the stem cap, it just tightens the headset, right? The gap between the frame and the fork seems to stay the same, though. I’ve also been in touch with Jack again in the meantime, and he told me I should use a 6.5mm bearing at the bottom, which he’s sending me along with the new fork crown race.

[Lukas_W]

I hope that helps. The current gap is still quite large.

[BeR]

I hope that helps. The current gap is still quite large.

It seems that you have installed the crown race in the wrong side. Flip it.

[Lukas_W]

Thanks for the info. Jack also wrote to me saying I installed the cone incorrectly. However, the gap is almost just as big the other way around. I hope things improve with the new parts.