Shifting ?

[Old smart]

Fred noted some data concerning speed, gearing and RPM. It is theoretical, as if the vehicle were being driven in a vacuum and with no driveline friction. What isn’t theoretical is if a real world outside force overcame wind resistance friction – like the inertia the vehicle provides when downshifting. As was said before, that can pull the engine into uncontrolled over-rev territory. So, Fred’s numbers for 6,000 RPM (I chose 6,000 as a high practical one might not want to exceed):

1st 2nd 3rd 4th
26.0 44.9 68.3 91.1

1st: Doesn’t really apply as the smart won’t downshift into first unless stopped.
2nd: You can first try to downshift from third to second at 45.
3rd: You can first try to downshift from fourth to third at 68. I can’t imagine why one would want to at that speed anyway.
4th: The smart will barely make 91.

If you are downshifting to give the car a little more temporary hussle, then look to do things that will bring in the lower gear at the engine’s peak torque RPM of 4,500. Again Fred’s numbers for 4,500:

1st 2nd 3rd 4th
19.5 33.7 51.2 68.3

1st: Still doesn’t apply.
2nd: Downshift from third to second at about 34. This if you really need to.
3rd: Downshift from fourth to third at about 50.
4th: Downshift from fifth to fourth at about 68. This might happen at times when merging, passing, or on a hilly highway.

This confirms jonnysan's conclusions. And, a tachometer is your friend.

[gotnobum]

I drive a car hauler in which I loaded every kind of car under the rainbow. This is the first car that I would recommend that you do NOT lift your foot off of the gas during a shift. If you keep a constant pressure on the pedal during the shift the computer de revs the car automatically for you then resumes to where you were at for continued acceleration. It has made for a much smoother shift.