I’m sure one of the mags tried this a few years ago.
These are all the trail centres and riding bases in Wales according to MB wales
Mountain Bike Wales
Although this includes BPW and Antur. Neither are TCs in my book nor consider themselves as such – if you do add those you’ll need to be up to riding some serious terrain like the Pro Line at BPW. You’ll also need to make multiple runs of the same trail as they join different sections further down the trail.
So forgetting BPW and AS and DH trails, and discounting the MTB ‘bases’ (which is a shame because you miss Brechfa) you’re left with:
Afan Forest Park – maybe 2 days of riding, but it’ll be tough it’s 100k+ of riding with 3000m of climbing.
Coed Llandegla – 1, but you’ll be repeating a lot of trail to hit all the various options
Coed-y-Brenin 2 or 3? 150k and 3200m of climb.
Cwmcarn – 1 day and the Twrch is diverted down to an hours riding max.
Nant-yr-Arian 1 if you’re very fit, 2 if you’re not.
And – Coed Trallwm & Elan Valley, which really isn’t a trail centre by any real measure.
So that’s 9ish solid days of riding to cover the Welsh bit.