F-20 high speed 4th

Hi all, Not the bolt on road gear, but the high speed 4th gear vs stanard tranny what is speed difference at top end? on F-20
Thanks oldiron29

Really depends on tire size. With 14.9 28 rears the factory hi speed 4th gear is about 10 mph with 13.6 36 its about 13mph. The low speed 4th gear is listed at 3.75 in the manual which is on steel I think. Rubber tires would probably get you about 4mph or so. Taller rubber maybe 5mph plus.

thanks rob 10 MPH is good enough for me.
Oldiron29

The original F-20 steel wheels were 40", but 36" rubber gave a larger-diameter wheel. Once, many years ago when I was an eager whippersnapper, I actually ran an F-20 on 36" tires next to an
F-12 (40" rubber). The F-20 was almost as fast in second as the F-12 in 3rd. I estimated at that time that 4th gear gave around 5 mph, maybe a little more with the engine at high idle. Recently, I saw a table that shows the effects of rubber tires on these tractors, and it turns out my guess was pretty close (just under 5 mph in 4th gear at governed load speed). Will look for this table among my papers, and will pass it on when I find it. One interesting thing that was immediately apparent to anybody who ever spent much time on steel-wheeled tractors is that steel wheels waste probably a third of the engine power, while rubber tires lose quite a bit less--maybe 15%, even less today with improved tires (I had about 10 years on 3 steel-wheeled tractors--an F-12, a 10-20 and an early Oliver Row-Crop). If you're an armchair engineer, you can dig out the Nebraska tests and
compare a number of tractors. What is absolutely wonderful is to find the same tractor tested on each type of wheel--there are a few (F-12 was on steel, F-14, as I remember, on rubber; the percentages of loss should be the same for either tractor). My original point is that with rubber tires, an F-20 would pull at nearly 4 mph (36" rubber, second gear) what it had originally pulled at 3 mph on steel; less power wasted meant the tractor could pull more. A neighbor had had a steel-wheeled F-12, which he thought pretty anemic. When he borrowed my father's F-12 on 40" rubber, he was amazed at what it would do.
We always pulled a 7-foot double-disc, which had
come with the '29 10-20 we had on the farm. The F-12 shouldn't have been able to handle that disc, but it did.