He obviously meant the 3T Extrema, but there are tons of other gravel bikes with >50mm clearance. Among the cheaper frames, Peak Torque managed to fit 2.35" Hans Dampf front and Racing Ralph rear on his Yoeleo G21.
The 3T Extrema uses Sram dub wide. More of a one-off frame. Maybe a similar frame could be made by Chinese manufacturers, but it's basically introducing a whole new bike category between gravel and mountain bike. Buying parts would be frustrating since "gravel crankset" and the thousands of results, don't fit.
The Yoeleo G21 only clears 53mm tires and has interference issues between chainrings and the frame, leading to buyer frustration. I did a quick search for Peak Torque, good channel, and when he tried to fit his crankset on and it didn't fit, he called the frame "dogshit". Yes he came around to liking it, after getting it to work.
Gravel bikes are based on road bikes, so 700c tires will max out around 50mm. There's a whole question whether we should all support more one-offs like Sram Dub Wide, to give us more preceisely what we want, or stick to established standards.
It's an interesting discussion because rather than Sram Dub Wide, mountain bikes are just a bit wider than gravel, so are a good component set, and actually cheaper than gravel parts. So what we want is mtb frames to adopt a more traditional triangle shape and rider position used by gravel bikes. Which is what the Salsa Cutthroat does, and a lot of steel touring bikes too.
While that is nice, for most gravel bikes, manufacturers have been keeping gravel bikes frames oriented to gravel bike parts, on the basis that they both fall under 'road' category. Paved road and gravel road. But also, sticking to road standards is sneaky as parts cost more and make more profit. For example, the invention of GRX. Or how gravel bikes don't use post mount brakes, when they worked fine. But requiring new 'gravel and road' flat mount, allows Shimano and others to use the exact same parts but charge more money, for a smaller niche market. More profit, for awhile, until the Aliexpress companies catch up and make parts that are just as good for less money.
That said, I could have been more polite, true @serge_K. Sorry. If you want to run wide tires, get one of these frames that clear 50mm, and fit a set of 650b wheels. Then pay attention to tire size and research some wider tires in the 2.2-2.4" range that are a bit taller than wide, and you're good to go. The bikes look awesome configured this way too.
