Here is the speed quoted by IH in an original brochure for H and M tractors that I have had since the forties:
1st gear (at 1650 rpm full load): 2-5/8 mph (2.625 mph)
Special low-speed: 1-5/8 mph (1.625 mph)
Reverse: 3 mph
Reverse, special low-speed 1-7/8 mph
(1.79 mph)The IH brochure quotes regular gear speeds at 1650 rpm as
2-5/8 (2.625), 3-1/2 (3.5), 4-1/4 (4.25), 5-3/8 (5.375) and 15-5/8 (15.625).
Tire sizes are not given, but I believe the usual factory equipment on the H was 9.00-38.
Better traction comes with wider tires, and most people re-equipped with wider rubber when the original set got old. The no-load speed for H is 1815 rpm, which is 1.1 times the full-load speed of 1650. If you multiply the regular gear speeds by 1.1, you get
2.89, 3.85, 4.68, 5.9 and 17.2. Can't put these new numbers back into fractions. Never was much good at them. Everything from here on is palaver of no use to anybody, so you can skip it and not miss anything. I just like to think back to happy times when I was surrounded by tractors and had lots of things to do with them. I was a kind of armchair engineer as a kid, and used to devour the brochures like the one I'm quoting here. IH offered not only the low-low first, but also a 7-mph fourth speed. Neither was available on steel wheels. It is not hard to know why. I spent a good 10 years riding steel-wheeled tractors and 1) you can't bear to ride on them over about 4 mph, and that only in very soft soil, like after disking 2) the steel wheels waste so much power that the tractors won't do any useful work much above 4 mph. The high-speed fourth would have been a wonderful thing to have back in the 40s. Regular fourth is too slow for hauling loads very far (bales, grain, etc.). Even to get just over 5 mph, you had to have the engine roaring wide-open. Fifth gear is just too fast on gravel roads, and it won't pull much of anything with the engine throttled back (not enough torque). I remember vividly that big gap between regular fourth and fifth. I think IH saw an easy (and probably somewhat cheaper) way to put in a road gear--just put a dog-clutch on the sliding fourth gear and mate with the clutch shaft. A solution made by people who hadn't had much experience in the field, I'd guess. I always admired the way a tractor that came from the factory on steel had "only four speeds," but could be "converted" to five speeds. During WWII, rubber was in very short supply, and a lot of tractors were sold on steel. After the war, most were converted to rubber. The change from 4 to 5 speeds involved about 30 seconds with a ratchet and socket wrench on a little bolt that went down through the top of the gearbox and simply blocked the shift rail from moving forward into fifth. A few turns of the bolt and voila! you got a road gear. This bolt is short on a factory-equipped 5-speed, and cannot block fifth gear even when screwed all the way down. I wonder if dealers sometimes offered to make this conversion without explaining that any apple-tree mechanic could do it in a jiffy. John Deere and Oliver had a better idea as to the higher gears: fifth gear somewhere in the neighborhood of 7-8 mph, and sixth somewhere around 10-12. Even the little Farmall A made a better hauler than the H on the dirt roads I remember, because its "road speed" was about 10, and you could throttle back a little, get good torque and tootle along at maybe 7-8 mph with no problem.
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