Tractor tire sizes... Help please!

[tirediron]

Okay... the rims for my Super A are stamped on the inside "3.00-15" The tires that I took off were "4.00-15" (I believe), and the manual calls for "5.00-15". The question I have is: "If the 3.00/4.00/5.00 represents the tire width at the widest point, are all of these still going to fit onto the same rim, and what is the difference going to be? (Yes, I know, a basic question, but tire sizes are something I have never been able to wrap my head around - they make about as much sense as pipe sizes!)

[John G. Simpson]

3. 15 should be the rim size. 15 is the dia. and 3 is the rim width, where the tire bead rests. the 4.00/5.00 is not the tire width, but tire diameter. a 4.00x 15 is15+4+4= 23 in dia. new tires are measured differently. ( only god knows)
my book of nebraska tests show a 4.00 x 15 tires on the farmall a. mine has 5.00 x 15, so either one works.
hope this helps. thanks harry.
john

[Eric Best]

Rear tractor tires are an extreme example of this. Only in relatively recent times have rim widths even come close to the width (and width number) of the tire. For example, a 14" rim for a long time was generally used with a 16.9" tire. In the first days of tractor tires, most rear rims were 8.00" rims. The tires, regardless of diameter (cross section) fit on these rims because that was the inflated dimension at the bead used on almost all rear tractor tires. Note that a 16.9" rear tractor tire is no where near as tall as it is wide (cross section, again) and the 16.9" is, in fact, the width at the widest point, inflated. Miller Tire of Wauseon, Ohio gives a pretty good explanation of tire and rim sizes in his tire catalog.

Front tires work in a similar way. 7.50 x 20 runs on a 5.50 x 20 rim because 5.50 is the bead dimension and 7.50 is the nominal maximum inflated tire width. It would also be the diameter of the cross section only if it is a 100% profile tire. With car tires, for example, the profile is part of the string of numbers representing the size and indicates the ratio of the sidewall height to the maximum width. The smaller the profile number, the more squat (lower sidewall) the tire. The profile number doesn't affect the basic size number but will certainly affect the overall diameter of the tire.

Eric.

[tirediron]

Excellent, thanks guys. I don't suppose anyone knows of a chart that lists the ranges of tire sizes applicable to a given rim?

[John G. Simpson]

Tired.
my tire book is hiding, but a rule of thumb is 18.4 on a 16 in. rim. 14.6 on a 12 in. rim. about 2 to 3'' wider than rim
your 'a' would take 9'' 9.5" 10.0" on a 8" rim newer sizes 11.2 12.4
will fit a 8" rim don't know about radial tires.
i have seen some pretty big tires on skinny rims, but don't recommend it.
john

[tirediron]

Thanks!