Converting numeric to current tire sizes.
 

When I was fiddling around with my spare the other day, I realized it was OEM because it had "Made in Japan" on the sidewall, and then noticed it was significantly taller than my current set. So, I google and find that the tire rack has this nifty little chart. Unfortunately, it seems to be off, because according to it, the 700R14 OEM spare isn't as tall as the stockers on right now, but if you put it and one of the 195/75R14s next to each other there's a big difference. Even with less than 5lbs of air pressure, it was still way taller than all the others when mounted (and sagging).

Going off of a guess, I converted 14" (rim size) to mm and got that the diameter of the wheel/tire now was ~550mm. If I assume the diameter of the OEM full sized spare was 700mm, then things start making sense. And my gas longs start to really match up, when comparing my use of the odo previously to my current use of mapquest and "better" mileage. Hell, I'm going faster now and doing more heavy city, but my mileage has gone up by ~3mpg, hmmm... :rolleyes:

From years of ancient cars.....700 is also 7.00, an inch sized tire, not metric. While 195 75R14 is a modern tire close in size, it will still be wider and not as tall. Radial tires even such as 165 R15 are still at 80% in most cases.

Also most likely a bias ply tire, not sure what car this (guessing 1970s or an early truck if it is an OEM tire?) is on as you do not list it, but do not mix it with radialply tires.

82 Toyota pickup. Would it be o.k. for a spare, or should I just dismount it and hang it on my garage wall? In retrospect it's kinda dumb assuming the 700 meant mm. So, 7"=177mm, and the diameter is 177(2)+355.6 (14" rim)=709.6. Compared to the current diameter of 648.1, previous distances need to be adjusted by a factor of 1.095. Thanks for the help! :)

its a spare being used as a spare, i see nohtign wrong with that

heres an idea: for all of you who think a wider tire makes a significant mpg loss try this: get or borrow 4 spare tires or doughnuts as i liek to call em, drive around for a few tanks with them on as your wheels and tell me if theres any difference. (obviously dont go over 50 but why would you?)

ive had the stock rims and tires on my truck for half a year then i put my summer rims and tires on which are the exact same size just about 2-3" wider. ive seen no significant change in my mpg...so i dunno if it makes a huge difference or not and was wondering if someoen would be willing to go to the skinniest tire possible (thats why i say borrow or go to a junk yard and get 3 spares) and see if it changes your FE. id be kind of interested to see what the results are.

Well, to get (limp?) home maybe, but the problems of mixing tire sizes on a drive axel for any long period of time are known (increased diff wear) and the mix of bias/crossply and radials can cause handling problems.

I experienced this in the worst ever car for it, a Tatra 603, starting with terrible rear weight bias on top of a mix of fine Eastern European bias and radial tires!

An old tire would make cool wall art. I assume an ancient Bridgestone? I had a 380mm Michelin XAs for a few years as a display tire...

https://www.biesheuvel.nl/ENGINE/IMAG...orisch_xas.gif

Peakster recently tried this out, I think...