Rigid Or Suspension?
As the trike gets bigger(large car engined), you can use a rigid frame, but it`s  your vertebre you  are hurting.  Most big trikes have some sort of IRS(Independant Rear Suspension) like Jaguar or Ford in the UK.
Rigid frame for motorcycle engine.
Fabricated IRS to fit VMax
Pic provided by Stace from Trike owners and builders
Ford Independant Rear Suspension
Four link system developed by early hot-rodders
Detail of how track rods link to axle.
Four link system.
Outboard suspension ^
Trick inbord-mounted shocks.
CBR special.
One-off RoverV-8 frame. ^
Yamaha XS650 with
four link.
Cutting Edge trike with inbords again.
Honda Goldwing with Jaguar IRS.
Close up of Jaguar IRS.
Please excuse the spacing on this page, as however I tune it, it goes back to the right.