Long time lurker here. I'd like to thank the community for their great trove of information and provide some content back in the form of a review of a frame that I've seen very little about.
This review is less about Tantan and more about the frame. Tantan were fine to deal with, some small challenges and delays but nothing out of the ordinary. Ultimately, the correct frame arrived, in the right size, and painted to the correct specification (after a minor paint specification error was spotted in the QC pictures).
The FM629 belongs to a family of lightweight endurance/climbing geometry frames. The geometry and some of the design features are heavily inspired by the Cervelo R5.
There are 4 frames in the family, a non integrated and an integrated in both disc and rim. The non integrated has an IS42/IS52 headset and the cables pass through opening in the downtube. The integrated has an IS52/IS52 (we'll cover this a bit later in more detail as it's not quite to standard), with no opening in the downtube (or at least none on my frame), so you have to go through the top bearing.
I bought the rim brake version so can't comment on the disc brake version (particularly the tolerance or flatness of the flat mounts, nor the routing of these).
The FM629 as an integrated frame comes with a set of integrated bar/stem and headset/spacers. While I didn't use this bar and stem, due to being long reach (approx 85mm), in the hand it is good quality, and stiff. The headset is your standard Chinese affair, no name bearings and no seals. The spacers are aluminium, and satin finish so they might not match the frame and bars if you leave them unpainted
If you want to run another set of bars on this bike you can but you need to be aware of the non standard bearing seat depth. IS52/IS52 normally has an 8.7mm bearing seat depth upper and 7mm lower. This has a 6.5mm upper and 7.5mm lower.
The included headset lower has an increased flange thickness on the crown race and a taller bearing to compensate.
With the included headset the upper has a small frame gap. If you run a standard IS52/28.6 upper you'll get a significant gap and will need to modify or use a customised compression ring/spacer to reduce this gapping. I used a Deda ACR nylon spacer and shaved material off to make it fit.
This shallow bearing depth has an advantage though (particularly for rim brake) in that it means the brake cable doesn't need to make a "U bend" turn to head along the top tube to the rear brake.
In terms of build quality of the frame, I can't fault it. The interior of the frame is clean enough and while there was some evidence of wrinkling, there was no evidence of resin pooling or voids in the areas I inspected. There was quite a bit of fibrous material left in the steerer tube which I would assume to be the remains of the internal mould. I would rate the internal of the frame as equivalent to a mid range frame. Safe to ride, but not as clean as I've seen from Carbonda.
Tolerances seem fine out of the box. The frame is BB86. I had the frame reemed and faced, but out the box the dimensions were:
Shell Width 86.95-86.98 (overwidth by 0.45-0.48mm)
Left cup diameter 40.90 Horizontal 40.90 Vertical (undersized 0.08mm)
Right cup diameter 40.94 Horizontal 40.96 Vertical (undersized 0.02-0.04mm).
While I didn't weigh the frame pre build, weight built up is about average for 105 drivetrain and deep section carbon wheels is about 7.3kg with mount, pedals, and bottle cages. It's not a super lightweight frame, nor is it overly heavy. Thankfully this is Chinertown not Weight Weenies...
The frame is a climbing/endurance bike so has (for a small/medium) a slack seat tube of 73 degrees. This is less of an issue for larger sizes, and perhaps even an advantage! The frame has a straight seatpost included to counteract this. The seatpost is a standard round 27.2mm, with an integrated wedge which does a good job of retaining the seatpost. However, if you are running carbon rails (7x9mm) you'll need to find a longer bolt as the included 35mm bolt is too short for the threads to engage with the wider clamp width due to the thicker rails.
For people (like me) that need their seat far forward/are reach constrained you might want to consider this when sizing and potentially size down, otherwise expect to run the saddle towards the end of the rails.
Finally, the bike rides like a superbike (with a good set of wheels). It feels fast to accelerate, it holds speed well, but it doesn't offer the most compliant and soft ride if you have a very stiff wheelset.
The frame offers ample clearance for thicker rubber (28mm) to offset this.
Overall the frame is worth considering if you want a modern rim brake frame and prefer a more endurance geometry. I would probably advise you go down the FM609 route unless you're set on internal cable routing since fully integrated mechanical isn't an enjoyable job, especially with the non standard headset. The frame is set up for outers to be run the full length so make sure your front mech is suitable for this.
I can't really fault any aspect of it, but I think if you're going the disc brake route there's probably better options out there.
Bonus review: Ltwoo RX (2x12 speed groupset). Use this groupset for the shifters only and pair with Shimano R7000 or higher. The front mech does work but doesn't allow for outers to be run to it, nor does it have cable tension, so not suitable for this frame. The rear mech doesn't work nicely with the mech hanger on this frame (which is a sandwich style as used on a few Cannondale frames).
The hanger has a small tip, and the rear mech relies on a long b screw to get bigger cassettes to work, so the b screw will go past the tip due to the angles/alignment. This makes it impossible to set up. With an R7000 mech or anything with a shadow link it works perfectly. The 11 speed mech works perfectly with the 12 speed shifters so must have a compatible pull ratio.
The Ltwoo shifters can get jammed up if you try to shift them without cable in, and not return to the fully relaxed position. But this can be solved easily as the shift mechanism in these shifters are in a cassette which can be removed from the shifter body and then the springs and pawls coaxed back into the correct arrangement.
