I saw this Facebook post by Brompton Kitchen recently. They managed to fit an 11-25t cassette on a stock rear wheel set, wjth stock derailleur and stock tensioner.
It seems like they’re using a Ridea hanger for the tensioner, and another modification piece for the rear mech, to accommodate the largest rear cog. Any idea where to find these two pieces? With them, I don’t think it would be too difficult to replicate.
https://www.facebook.com/share/HVCBe7eTU9XTnYsC/?mibextid=WC7FNe
by mcorbei3