Tire Size Conversion

[Bill <Y1TopBanana73@xxxxxxxxx>]

I'm trying to find info on how to convert modern tire sizes
(215/75/14) to the old sizes (D75-14). I ultimately want to figure out
what is the correct speedo gear is for my current setup.

The wife and I went to the Herr's Cruise Night in Nottingham, PA last
night w/ the Coronet and my Model T. I was trailering the T home and
driving no more than 55-60 mph. She was following me also supposedly
going 60 mph and fell back VERY quickly, so the speedo is most
definitely reading fast.

Anyone have any charts, websites, and or calculations they can provide
to point me in the right direction?

Thanks

Bill M
65 Coronet 500 'vert