Wasn't it you that mentioned the 'Rubber Ruler' that tire companies use
When I got the car, it had been set up for Autocross, and had 175/70 Yokos on +2 rims: they hit the front fenders on bumps and were awfully close in the rear. When I found that the Panasports with Nokians wouldn't fit, I went to a local tire store and bought a set of cheap, off-the-shelf NoName 155s so I could use the car. I think the tires were really intended for heavy cars like Pintos and the like, so they're oversize for 155s. They do help the gearing, and I'm not racing the car, so they're still in service.
I went out to the garage with a tape measure and have:
Lotus +2 K/O 5.5" w/ SR4 Steel Radial All Season P155/80R13 79S M&S - not kidding about "No Name"
Width 6-3/4" (Sidewall to Sidewall)
Circumference 71-1/8"
Panasport K/O 5.0" w/ Nokian RRT2 165/70R13 79T
Width 6-1/8" (Sidewall to Sidewall)
Circumference 69-1/2"
Backspace 4-3/8" (Sidewall of tire to hub face)
I had a Sprite wheel handy, so I measured that as well.
Street Minilite B/O 5.0" w/ Goodyear Eagle GT 175/70HR13
Width 7" (Sidewall to Sidewall)
Circumference 71-1/8"
The outside face of the +2 5.5" wheel is in exactly the same place as the Elan 4.5" wheel - all the added width is added to the inside. The Panasport is only 1/2" wider than the stock wheel, but that width is split between front and back, probably to clear the stock springs: I have small diameter springs, so my +2 wheels have plenty of room.