My concerns for a custom built super light weight frame would be durability and safety.
Locally i have noticed there are more guys who have had cracked light weight frames.
(Both road and Mtb frames)
It seems it comes to a sweet spot and then they simply get to brittle.
A numerous production of a certain size could and should have been tested,
but for full custom under 600 grams i would wonder if that is resonable?
I am dead sure that all these super light frames have rolling updates as fails for sure will come and we will
never hear about more than a fraction of them. No matter what brands we talk of here.
You ride an AX Lightness Vial EVO D frameset with a weight around 700 grams. And THM fork around 275 grams. So to you 700 grams means its durable and safe and won't crack. But 600 grams and its take your life in your hands? Where exactly is this sweet spot where the frame gets too brittle? Is 700 SAFE and 600 BRITTLE? 100 grams is 14% of a 700 gram frame. Significant? And what about forks? THM makes some that are 250 grams. Your 275 fork is pretty close. Seems to me forks take the brunt on any ride. They are directly impacted when you hit holes, cracks, rocks. The frame is cushioned from direct impacts because the fork receives the direct force! The fork is in the most danger. Why isn't everyone screaming about all the unsafe, dangerous, deadly lightweight forks?
I have never written that Ax is not in the zone i spoke of, have i?
I suggest most of these super thin wall frames are in the risk zone.
But if we keep to THM fork. I think you have never seen a THM fork close, have you?
I can say, the THM forks are internally threaded and does not use any standard headset expander.
The fork steer tube is way thicker than any other fork made from carbon.
You should know that most carbon forks fail in the steerer tube.
I think you missed my point?
Why do i even mention this?
Because i got some words from a few dealers mentioning fail rates of light weight frames.
Also from speaking to quite a few cyclists who have had head tubes, chainstays etc cracked just from cycling (no crashed involved).
(I do rather not point out specific brands)
I would deem all frames under 800 grames as exceptionally light weight.
My UP is by all means not light weight, but it is standing abuse which simply would rattle and crack such as my Ax.
However, this might be unfair comparison as Vial EVO D is a road bike and UP is a gravel bike (which has been through all sorts of terrain and some adventures involving crashes.
Only blemish on this, is from chain jumping off the 34 tooth chainring riding mtb tracks.
Frame and paint is almost to pretty inspite of all i've been taking this bike through.