Plowing speeds--read only if you love tractor trivia

If you are an armchair engineer (I confess I am), you might like to search the web with terms like "tractor plowing speeds." I found the complete text of an old IHC booklet on plowing (but no pictures). There are summaries of some modern research on plowing done at universities, but the academic jargon is about as understandable as some of the stuff written by computer programmers.
I have a copy of an article published in 1920 by Oliver Zimmerman (apparently of IHC) called "Tractor Plowing Speeds." It is fairly long and goes into a lot of different conditions, but one of the graphs clearly shows why steel-wheeled tractors could pull their "rated load" at about 3 mph, but not much faster. As speed increases (a straight line on the graph), plow draft rises faster than the speed (a curved line going upward on the graph).
A plow that takes 4.5 hp at 2 mph requires about 12 hp at 4 mph. At 4.5 mph, the plow needs almost 15 hp!!It is easy to see that if your tractor is rated at 10 drawbar horsepower (which might put out 14 or 15 maximum hp), it will run out of steam around 3.5 mph (plow requires almost 10 hp at that speed). Anybody who has ever worked with steel-wheels will remember that the lugs really rob the power, and that increasing speed takes a lot away from the drawbar hp. I remember very well that our 10-20 would pull through anything in second gear, but would pull almost nothing in third. An F-20 that I used to plow with sometimes had been converted to 36" rubber. It would plow in second at close to 4 mph (h.p. of the 10-20 and F-20 are close enough to make a reasonable comparison), sometimes in third (estimate 4.5 mph) and even in 4th (over 5 mph) in very light soil. If you are an avid reader of Nebraska tractor tests, you can see the loss of power to the wheels with steel-wheeled tractors (I'd put it at about 35% loss on average; this helps explain the old ratings like 10-20, with the higher number for belt hp). Today, four-wheel-drive tractors are probably putting around 85-90% of the engine power to the ground. I'm sure modern plow bottoms are shaped for the new speeds, too. In "my day," I believe the moldboards were actually designed to do a good job of turning over the soil at about 3 mph. In the old tractor brochures from the 20s and 30s, they often talked about "plowing speed," which was usually in the neighborhood of 3 mph.

An old friend told me of plowing a big field (well over 160 acres) in Idaho with another guy, two identical tractors. The tractor dealer showed up with the owner and a set of rubber tires. They stopped my friend and let the other guy keep moving. He and the dealer swapped the tires for the steel lugs and he kept plowing. He said he caught up with the other tractor before they finished the round and when he showed up first at the gate the owner paid for the tires and sent the dealer back to town for another set.

Sounds like a pretty good sales tactic.

Excellent information.

I've never "worked" a tractor with steel wheels (plowing, cultivating, etc), but have taken a few out for a spin. The one benefit that I've noticed about steel is in mud. The steel sinks to the bottom and still gets traction where rubber tires will load up with mud and spin.

One faction of Amish in our area does not allow tires with air in them. 20-30 years ago, I can remember seeing them with lug steel and today they bolt rubber tire tread on steel rims. I'm sure they don't have the traction of aired up tires because of no flex or cushion, but evidently the tread alone is better than lugs.

(quoted from post at 05:19:34 02/04/10) One faction of Amish in our area does not allow tires with air in them. 20-30 years ago, I can remember seeing them with lug steel and today they bolt rubber tire tread on steel rims. I'm sure they don't have the traction of aired up tires because of no flex or cushion, but evidently the tread alone is better than lugs.

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And you keep your teeth in your head! Up by Dorchester, WI the "cheater Amish" are running around with MFWA steel wheel tractors and steel/solid rubber tired skid loaders. I can't imagine what a steel wheel skid loader would be like. I hope it has an active seat!!!

have a look at this.
http://www.youtube.com/watch?v=4ArChT6MaBI

I remember as a boy growing up on an Arkansas cotton - soybean farm we always thought that you had to moldboard plow every year to prepare a good seedbed. We had two pretty much equal Farmall M's which pulled 3 bottom 14-inch little genius plows. We generally plowed in 3rd gear (Sometimes 4th in extremely light soil). One of the M's had rice and cane tires and the other had low tread tires. I remember in plowing together that the low tread tractor would plow at a little faster speed because it had less tire slippage than the tractor equipped with the rice and cane tires. Low tread tractor tires put more surface area to ground than rice and cane and were much more efficient in normal soil conditions. We would probably wear out two sets of rice and cane tires to one of the low tread tires due to tread wear.

LenNH,
Thanks for researching this plow speed info. I plowed in the 1950s with an F20, H Farmall, and SC Case, all pulling a 2-14" easily at about 3 mph. Also used a SM with 3-14". Back then, seemed like everyone plowed at that speed, regardless of tractors used. Plowing and other field work was basically done at nearly the speed as horses used to do just a few yrs before.

Then 50 yrs later I still have that same H and I bought a 2-16" #8 plow. After buying an operator's manual for the plow and setting up the tail wheel correctly (and an overhauled motor) the H can pull that plow quite easily in 3rd gear. (Tail wheel setting is very important on a trailer plow).

In 3rd gear the plowed soil turns over nice and "orderly". In lighter soils I've tried 4th gear and with throttle wide open that plow throws the soil over way too far and is not quality plowing.

But modern powerful newer (New to me is an 806) tractors all run plow speeds much faster and seems to me that those plows do a very nice job of turning the soil over at those higher speeds. And looking at the moldboards of old and new plows, it appears to me that the curvature is different. Plows today running at higher speeds do as good a job as our old plows did at lower speeds.

Regardless, just sitting here in the winter and thinking about plowing this Spring makes my pulse jump! I love plowing. Harry Truman once said "You do your best thinking while plowing".
LA in WI

LenNH,
Any chance you could post your plow research? Sure would like to see that.
LA in WI

Love the comments this brought.
I will see if I can scan this document and get it presentable enough so that anybody can read it. Maybe it will work best via e-mail. Will let you all know when I figure something out.
Comments about mud and steel wheels are probably right on. My grandfather grew potatoes, which go in pretty early. He had an F-12 on rubber, but it slipped too much in early plowing, so he bought another one on steel. My father had a steel-wheeled 10-20, which I plowed with for probably 10 years. The wheels on a 10-20 are 42" but the F-12 wheels are 54". This isn't very scientific, but I swear that the big wheels rode better--probably a shorter "fall" for the lugs coming down. I remember like it was this morning how the 10-20 rode on a gravel road. A real bone shaker. You could stay on it if you throttled way back in second, or maybe in first throttled up somewhat. On plowed ground or on sod, it wasn't bad at all, although you were aware of some slippage that occurred when the lug was pushing backward against the soil (a kind of little jerk, but not unpleasant). You are all probably aware that Allis-Chalmers tried out rubber tires in 1932 (I think this was the year) and found out that they wasted much less power than the steel wheels. Here is a little anecdote:
My father bought a new F-12 on those beautiful cast wheels in 1938. I began to drive it maybe the following year, when I was 8. I say "drive," when I really should stay "steer." I couldn't reach the pedals, but I was bound-bent-and-billy-be-damned (my father's favorite way of saying "determined") that I was going to drive. At first I would steer while pulling a wagon and hayloader. An adult would jump up on the drawbar and swing his leg over the axle to reach the clutch. Anyway, we plowed with double-bottomed 12" Little Genius, in second gear, AND we pulled the 7-foot IHC double-disk that my grandfather had bought for the 10-20. A neighbor once asked if he could use the F-12 for a day. When he returned it, he said he was amazed at how much power it had. He had had a steel-wheeled F-12 and thought it was pretty anemic.
I used to wish the F-12 was bigger and had more power (don't all kids?), but as I look back, I realize that it was quite a wonderful machine for its day. We used ours for at least 15 years without any repairs at all except to put in a new fuel-pump diaphragm (very common to all fuel pumps back in the 40s, before synthetic rubber entered the picture). The engine was of first quality, as was the rest of the machine. It could have used an extra gear for road use, but then it was designed for steel wheels in the first place. It was short and quite maneuverable, had a great many implements you could mount on it fairly easily (cultivators, a mower, even a corn picker, I believe), and it was fairly comfortable to ride on and drive (could have used a real platform, but then we never thought much about comfort back in those days). Today, I'd love to have one for chores. I'm no longer in a hurry and kinda enjoy just tootling along at half-throttle.

I have just scanned this very old article by Zimmerman, but the numbers are so small that I don't think they can be read on e-mail. I'll try something else, but it'll take a while: I'll summarize the article (fairly wordy) and see if I can blow up the graphs so they can be read.

It would be interesting to have a modern agricultural engineer study this article to see if there is any correspondence between ground speeds and greatly-increased horsepower needs as speeds go up. That was certainly the case with Zimmerman's research. For example, at 2 mph, a particular plow required 4.5 hp, but at twice the speed, it required almost three times the horsepower. Raising the speed to 4.5 mph added almost 2.5 hp to the requirement. This looks a lot like some of the laws of various forces in physics, in which (IF I remember this correctly) forces go up--or down--as the square of the change in speed. If you hit a brick wall in your car at 30 mph, there is X amount of force. If you double the speed, forces go up four times (2-squared). Hitting the same wall at 60 is going to be four times more unpleasant. What COULD be at work in the Zimmerman research is that the shape of the early plow moldboards is responsible for at least some of the extra resistance at higher speeds. Modern moldboards appear to be less curved and probably offer less resistance to soil being thrown back against it. I have never plowed with a "modern" plow, but I'd bet that it wouldn't turn over very well at 2 mph. Can anybody with experience second that?

I'm sorry to say that I'm not an engineer, so
please take my "observations" with any amount of salt necessary. I'd be glad to have input from anybody who can correct any of these armchair engineering notions.

My Dad had a welding shop in Aurora Il back in the 40's and he told me that the local Firestone dealer would take a set of wheels my Dad had cut down and welded rims onto out to farmer when he was in town on Sat. The dealer would remove the farmers steel wheels and install the rubber tired rims. He would keep the steel wheels and when the farmer gothome all he could do was use the tractor with the rubber tires. The dealer said He always made a sale once the farmer had used the rubber.

(quoted from post at 22:41:32 02/05/10)

This looks a lot like some of the laws of various forces in physics, in which (IF I remember this correctly) forces go up--or down--as the square of the change in speed.


What COULD be at work in the Zimmerman research is that the shape of the early plow moldboards is responsible for at least some of the extra resistance at higher speeds.

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You are correct in your assumptions. Draft force for tillage tools is a function of speed squared (In general). And horsepower then is a function of force multiplied by speed. I would encourage you to find ASAE standard D496.3 FEB2006 and D497.5 FEB2006. Go to asabe.org and try to search their publications. I would post a link, but I am afraid it won't work. I am at a university and sometimes the university logs into professional organization websites to allow me to view publications without me knowing it. Anyway, I said "in general" because a moldboard plow uses speed squared to determine draft but a chisel plow for example only uses speed multiplied by a machine specific parameter. It must be something in the nature of how the two different tillage tools fail the soil.

As far as moldboard shape: If you are interested in this stuff, you should purchase, Principles of Farm Machinery, 3rd edition by Kepner, Bainer, and Barger. The 3rd edition was published in 1978 and it is an ag engineering text book but it is a fairly easy read. You don't get bogged down in too much theory. What I like about the book is that it has tons of references to look up. You can pick the book up pretty cheap and it covers every piece of farm equipment. I read the whole book, it was so interesting.
Anyway, the book mentions research from 1959 that a high speed plow bottom needs to be taller, longer, more sharply twisted, and have less share angle. The plow bottom must at higher speeds produce the same amount of inversion and soil break-up as the older bottom at lower speeds.

Moldboard plow research was hot in the early 30's but unfortunately came to a stand still once the dust bowl hit. One interesting research article that I fould thanks to the above mentioned book was from 31 or 32 and compared draft of moldboard shapes in different soil types. One would assume that a heavy clay soil should turned over slowly and gently to create the least draft. But, the research found one particular stubble bottom beat the other general purpose and scotch bottoms in draft. I would only assume in that case, draft had less to do with the nature of the soil turning, and more to do with the soil friction against the moldboard. Interesting stuff. Most of that research is found in ASAE Transactions which should be found in a good land grant university library, or in an Ag Engineering building.

As far as steel wheel and rubber tire traction efficiency: There were research articles published in ASAE transactions in the 30's showing that rubber tires outperformed steel wheels without showing the how. One phenomena of tires and soil failure is that some slip has to occur to create the most draft force and the best traction efficiency. This creates the chicken and the egg problem: does draft create slip or does slip create draft? From what I have seen, steel wheels bite too well and don't allow any slip. That is my guess at how rubber outperforms steel wheels. There are probably other reasons.

Wow! This is great stuff!
As to steel wheels vs. rubber, I had always assumed that the v-shaped lugs would rob some power as they penetrated the soil (in effect, trying to lift the tractor). My engineering is confined to the armchair day-dreaming variety, so
I could be all wet in my theories. I used to
read the Nebraska tests when I had access to them at a state university library. They are marvels of concise information in tabular form. They even include the percentage of slip! The other day, I looked at an old photocopy of one of the tests, which showed the Farmall H with a slippage of 17% in first gear! Too much torque for the traction available with the narrow tires of the day, and possibly no weights/water added.
The DB horsepower was correspondingly lower than it was in the other gears, where there is less torque and less slip.
One of these days, I am going to try to look at a bunch of Nebraska tests of tractors on steel and rubber and see if I can come up with an average for power losses with both types of wheels. When I do, I'll post them here for the likes of us.
Thanks for making my day, as Clint Eastwood might have put it (I think he paralyzed the punks with his stare, so they never really made his day).