Upgrading from 20" to 26" rear wheel on tandem trike

[Recumbent Ron]

My son and I are doing a multi day bike ride this summer and although we are within the total weight of the trike (TerraTrike Tandem Pro), we are not within the 175 pound weight limit for the rear 20" tire (Schwalbe Marathon Plus 20x1.75), where my son is the stoker. I would like to convert the tandem to accommodate a 26x2.00 Marathon Plus, which has a weight limit of 260 pounds, much more appropriate for his weight. TerraTrike used to make a dropout extension for the Tandem Pro, but contacting them I find it is no longer available. I am looking for suggestions, perhaps someone has done something similar on any recumbent they could share. Or better yet, does anyone have a set of those dropout extensions for sale?

Edited to add, and realize it may not matter, this tandem has a GRIN electric assist that I installed with a rear hub motor. It's not just the weight limit I am aiming for, but also performance. I have a 26" rear wheel on my single trike, with a GRIN set up, really enjoy the performance.

 

[amberwolf]

Some thoughts:

If the motor is in a smaller wheel now, a bigger one will have less torque, though potentially higher top speed (assuming a controller and battery capable of the power necessary to go that speed).

If you can get a dimensioned drawing of the extension you could have them made by one of the many prototyping places (or even hand cut and file them). Or a good photo, as close to direct side-on view, then you could draw it up yourself using other parts of the frame you already know the dimensions of directly.