a new version of hook may have become bigger, but i had 61t before, and then there was room for a little more.

now on the 69t bike i have taken away the hook, you may then instead use the hook disc of the (older) s1e, which catches the chain instead of the chainstay. it is mounted in the small pipe that sits halfway up the left front fork. i made a catch myself from some thick steel wire through that same hole, does the same job.

this pushes the limit, a too big chainwheel will then in folded state make contact with the right chainstay. 69t is no problem, and there is room for just a little more. but maybe not on a bike with widened rear triangle.

so why these monstrous chainwheels? because according to my experience 12t is the smallest usable cog. any substantial use of an 11t wears itself, the chain and the drivetrain in short time. and its draggy even when new. 12 is noticeably better, 13 and up perfect. i have 61/13 as the highest gear on my road bike, that cassette lasts for years, just renew the chain once in awhile.

@ OP: If I had a 69t B I would have to carry it instead of riding it . My legs do not want to cooperate at the moment...

Could you (maybe in a different thread) give us some pix of the 305 MTB Brompton mentioned with your bikes?

Edit: Googeling Kiffy Trike. That one is really cool! Should be posted in the Adaptive Cycling forum.

He already has in the thread "widest tires a Brompton can accept": https://www.bikeforums.net/folding-bi...-accept-2.html

yes, my 305 winter 'mtb-brommie' is seen posts no 24-30 in the thread about wide brompton tyres. as i wrote i really like the stock brompton tyres, but on a second bike wider tyres are handy in some situations.

more in the line of what is diskussed in this thread here about a wide rear triangle, a number of people have thus gone to custom forks and triangles to fit wider tyres or hubs. but my bikes are examples that it is sometimes possible to tweak either the bike or the tyres to make things work. but you need some experience with metal and pipes not to crack things. in case of the 305s i sanded away the outside part of the outer knobs to make it fit in the tight frame.

did the same to fit 3 inch bombolonis to my cube xc 29er, resulting in a full-suss 29 plus. such bikes are hard to find, have heard of just one or two models.

badmother, havent tweaked the kiffy trike yet, but its a great laugh wherever i go. plans are to make it more of a cargo bike with a large folding front rack. more gears are also wished for, might put in a schlumpf for a start.

Ahh, thank you. I have not been reading all threads recently. Did not know that tread has turned into such interesting discussions