this all explains why the cars today are so hopelessly undergeared on the original rims.
original cross ply tyres gave a decent final drive, but 12" radials available today dont.
early ford escorts with 12" wheels have the same problem, 4th gear feels like 3rd.

well i find running the smaller rims (13") with larger side walls that my car drives a little like a boat and sort of sways a little bit in the rear end and when your tearing through windy roads in the hills at 100k's thats not the best feeling. the 15's handle much better and offer less understeer, with my driving style. so im not saying that this is the way to go for everyone, its just what works for me.

Quote:I have drawn my info from the "Tyre & Rim Association Australia. Standards Manual."

These are the people who set the standards in cohorts with global regulatory bodies, & who manufacture tyres & rims.
I have assumed that they would know the diameters of various tyre sizes.

There are also a number of tyre size calculators available online, so a quick check there will help confirm the sizing.

The original sizes for the 1200 were ....
Standard/original fitment.
6.00x12x4 ply. diagonal ply [574mm, highway tread, Page S-03 of the 1988 book]
Optional fitment.
155SR12 [554mm, highway tread, page S-06]

My 1972 sales brochure lists only the 6.00x12 tyre but my 1973 owners manual lists both sizes in the 'recomended tyre inflation pressure' chart on page 31.
It clearly describes the radial as "optional"

If your Ute is moving around with the 13's then you're running on half flat tyres. I run mine up around the 30psi mark & don't have a problem, but then perhaps I drive a little more smoothly these days.

Besides, even girls are more fun when they have a little 'wiggle in their walk'
So are our cars.