Except they are for BMX, and 7/8" 22.2mm Not 27,2.. anything thicker diameter will be custom So.. a Design and Material, specification TBA.

still suggest getting onto a beefier bigger frame... with a Level top tube .. perhaps Hire one built

Perhaps a cargo bike builder who works in thicker wall 4130 (many are used to light spec materials since people spend more to have it weigh less)

a post with a triangulated strut set, to transfer the bending load instead, as compression , straight down to the rear axle ..



I was just thinking of Dursley Pedersen bike a very triangulated old Design http://www.dursley-pedersen.net/
http://www.oldbike.eu/museum/wp-cont...n-1024x840.jpg