Greetings from Iowa!

[Harpo]

New member here, adding a Magic Pie 5 26" to a TerraTrike Rover along with rear derailleur, replacing 20" with SA internal 8sp.  I've got almost all the parts now, will be starting soon!

[Bikemad]

Hi Harpo andto the forum.

I'm curious as to why you would use a 26" MP5 instead of a 20" MP5.
I suspect that the original frame is capable of accepting the larger diameter rear wheel, but you will probably find that the width of tyre that you'll be able to use will be reduced as it will now be located in a narrower part of the chain stays.

The 20" MP5 is a solid cast wheel that would be much better at resisting the high lateral forces that it would be exposed to when cornering at speed on a non-tilting trike.
Also, being the same diameter as the original wheel it wouldn't decrease the castor angle on the steering by ~3° or raise the Centre of Gravity.

Alan
 

[Harpo]

My main reasons for selecting 26" vs 20" rear are better top end, a little better ride, and ease of usable ratios with stock chainwheel.  It's also the only Magic Pie 5 available with internal controller, another feature I wanted for clean installation. 

The Rover chassis will accept a 26" rear with no modifications.  I've run across quite a few on the internet who have done this, and Utah Trikes even offered a model built this way, the Rover X-5 (https://www.youtube.com/watch?v=RdBTSRkgeIE)  I also spoke directly with TerraTrike, they confirmed the change is often done, no issues reported.

With the stock 20" rear the Rover sits 3" low at the rear, so the 26" merely brings it level.  Overall caster change is minus ~4.3°, maybe a little bit twitchier but the adjustable tension steering should make it manageable.  The Golden Motor rim is a surprisingly good looking alloy 26x1.5x36H, so tire width remains 1.75.