Having finished the complete resto of my D1 plunger my next plan is to build a C15 250cc based dirt bike style bike for road and green laning along the lines of the attached photo (not a C15!). How much of a complete C15 could I use and what would need to be replaced / modified please? Has anyone here done something similar?
That one is very modified including a lot of frame work.
You also see a lot which use the standard frame with the footrest hangers cut off and folding footrests welded on just below the swinging arm pivot.
Really it just depends how far you want to go.
If you're going to do serious off road work the later all-welded (rather than the swan neck frame) is a better bet.
Could I just point out a few of that bike's modifications...
Metal Profile front forks, with 21 inch front wheel.
275x21 front, and 4.00x18 rear trials tyres. ( IRC are best.) with security bolts.
Increased ride height at the rear, also maybe 60 tooth rear sprocket.
The engine internals could have been very modified; Trials Cam and compression ratio.
Wide ratio gears.
Legal Ball end levers, and trials wide handlebar, Trials number holder. Single Seat.
High level exhaust, Alloy Tank...
Maybe a few other bits as well.