Roller wheel(s)

Brief comments on some existing designs for attaching a third wheel to a side-folded folding bicycle for easy rolling.

a) Adding a hinged or pivoted leg with a wheel at the end, allowing it to be lowered when folded and raised when riding. E.g. early model of Dahon folding bicycle.

Pros:

Does not affect the seatpost adjustment.

Easy maneuvering.

Cons:

Only on folding bicycles that come with it.

Significant extra weight.

Hinge and pivot performance tends to deteriorate.

Need to lower and raise the leg when folded and unfolded.

b) Replacing the seatpost with one that has another tube at the lowerend with a wheel fixed at the bottom. E.g. JSK Folded Bike Moving Caster Seatpost.

Pros:

Does not affect the seatpost adjustment.

Can be implemented on different folding bicycles

Does not need extra tasks to use it.

Easy maneuvering.

Cons:

Need to replace the existing seatpost.

Must match the seat tube dimensions.

Significant extra weight.

Significant lower clearance between wheel and floor when riding.

c) Mounting a wheel at the end of the seatpost. E.g. Qbicle folding bike roller.

Pros:

Little extra weight.

May not affect the seatpost adjustment.

Can be implemented on different folding bicycles.

May not need extra tasks to use it.

Cons:

Need to remove if end of seatpost goes into the seat tube for riding.

Need to roughly match the seatpost diameter.

Slightly lower clearance between wheel and floor when riding.

Need to align the wheel direction during each installation.

Difficult maneuvering.

d) Dahon D-Walker.

Pros and Cons: I think picture says a thousand words. I say it is over engineered but not much added value.
Correction: After having experiencing folding bikes with the N-fold design, I guess the above design is to help tackle the unbalance "problem" in N-fold design.

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From here, I came across these after I have come up with my version.

e) Another implementation, away from seat post/tube: The clip talks about the magnet but the wheel appeared in it.

f) Dahon Landing Gear
Only for certain Dahon frame that allow it to be mounted at the BB.

g) mo:Rack
A Singapore product.

h) "Imitation" of the Qbicle Folding Bike Roller

i) Another Japanese kinda over engineered version. This one has almost the same concept as my current version.

j) The best design I have come across so far. Easy installation, rotatable, no need to be removed, light, cheap!