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I think you are mistaken about nomenclature - the 14-34 is a late 40's / early 50's designation - if you go back still further I believe it was the same as a 12.75-34 in the 30's. M.E. Miller tire has a pretty good dissertation on tire width but if you also can find an old Goodrich handbook from the 50's you will find it interesting history. You can also get current tire specifics from Goodyear Ag handbook or Firestone or Titan tire. The design rim width for a 1950s 14-34 was 14" - the tire width was measured on tread not sidewall cross section. A change was made in the late 50's or early 60's to measure sidewall cross section hence the same 14-34 tire is now designated 16.9-34. (see Miller, Titan, Goodyear, Firestone, et al). Same thing happened when a 6.70-15 became a 7.75-15 circa 1964 - same tire. Prior to about 1960, there were never 15.5 (or for that matter 13.9) size tires. In concert with one or more of the tractor manufacturers (JD I believe) the tire industry came out with a low profile tire that would give a better traction footprint to better suit the larger diameters on the row crops (mostly 13.9-36 on late 530's I believe and 15.5-38 initially on the larger JD Rowcrops but never on their standards). Thats why you don't find 15.5-34 or other 13.9 or 15.5 variations. The 15.5-38 caught on based on performance and for all practical purposes made the 14.9-38 obsolete still the 14.9 exists in other sizes as does the 13.6 (vs the 13.9-36). FYI a 15.5-38 is approx 2" shorter that a 14.9-38 (per Titan - one of the few manufacturers that has same tire in both sizes). The 14.9-38 shows 15.1" width on a 13" rim and a diameter of 63.8" and capacity of 3740 pounds for a 6 ply at 20 psi. The 15.5-38 in same tire shows 15.7" width on 14" rim and a diameter of 61.8" and capacity of 3520 pounds for a 6 ply at 20 psi. Kind of like the low profile car tires that started showing up beginning with the 57's and continuing today. The 15.5 and 13.9 variations were never available as OE on anything but row crops. The standards had the smaller diameter but wider tires to get load capacity that row crops did not need in that timeframe. FYI2 - the footprint is simply the load divided by the inflation pressure - the distinction is whether you want a long skinny footprint or a shorter wider variation, but all other things being equal, square inches will be same in theory. Getting back to your 14-34 question - a different Titan tire is listed in 16.9-34 at 17.8" width on a 15" wide rim (the trend toward wider rims continues) with a diameter of 63" and a capacity of 3960 pounds for a 6 ply at 18 psi. Goodyear shows their 16.9-34 at 429 mm (16.9") on a 15" rim but notes that loaded section width growth (at footprint) is 462 mm (18.2"). The corresponding 15.5-38 footprint growth is to 434 mm or 17.1". Best. Ed All above is for bias tires - note radials grow differently by design.
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