Original 240 tire diameter

[Martzedcars]

yup.. sidewall is percentage of width. in mm .. And 175/80/14 is the same tire as a 175/R14   When the percentage is 80% thats a standard tyre height and leave the 80 away. Every other percentage is noted in the middle number.

 

225/50/R16  is a tyre 225 mm width, height is 50% of 225  = 112,5 mm  and the tyre is for a 16 inch rim..  (front tyre of a nissan 300zxtt)

225/R16  is Always a 80% height of 225 tyre, and for a 16 inch rim.. (a tyre for example on a Mercedes sprinter..?)

[Captain Obvious]

11 hours ago, JSM said:

So the side wall size is always represented in % not mm?  

Yes, As far back as I can remember. It's never been straight up measurement, it's always been ratio (as in "aspect ratio").

Even back with the alpha-numeric identified bias ply tires they did that. I think the first tires I ever bought were D78-14's. That meant they were "D wide" having a sidewall that was 78% as high as the width. Now, as far as exactly what the "D" meant...? All I can tell you for sure is that a "D" made by a tire manufacturer was guaranteed to be wider than a "C" from the same company and narrower than an "E" from the same company. I don't think standardizations between manufacturers was as predictable as it is today. One company's "D" could be different than another company's "D"

But in any event, here's two things you could easily hear back then:

1) I need new tires for my Fiat to replace my bald Michelin 155/75/13's.

2) My buddy just put M50s on the back of his Polara. They were so wide he had to put fender flares on it just so it would pass inspection!

Edited April 12, 2018 by Captain Obvious
Can't count

[Captain Obvious]

And while looking at the wheel section of the FSM's I turned up a mistake. This is an excerpt from the 72 manual, but this same mistake got copied all the way forward through 77. Looks like they finally fixed it in 78.

Dyslexic style typo on the wheel offset number: