Tractor speed

How much speed do I gain going from 15.5.38 to
18.4.38 on a 4020 synchro

You can look at the chart on this link, which is for radial tires. It shows a 15.5R38 circumference at 187" and 18.4R38 at 207" so you will gain between 10% and 11% in speed
Tire RCI Chart

I would guess about 3 mph in road gear. Maybe a bit more. 15.5 's were a low profile tire compared to the rest of the rear tire sizes.

You will gain about 2 MPH in road gear. You will also lose 5th as a work gear for heavy work. The stepped up speed makes it too fast for a lot of common work.

If you want a bigger tire,I would suggest 16.9x38. I put a set on my 706 when I added the turbo. The 15.5s wouldn't hold it.The 16.9s do the job nicely without being too big.

Been running 480/80/38 tires for ten years and love them but always wondered how much speed I gained with them they are .5 inch wider than 18.4.38 they are about bald now and I have a set of 18.4.38 23 degree Firestone?s . I run 4th gear plowing and fifth or 6th drilling and curing hay and spraying . Put one of the Firestone?s on the other day . It will run down the road 25 mph now . But I have no idea in field gears ⚙️ the only speedometer I can find won?t read below about 10 mph

Nothing like getting high centered plowing on those dinky 15.5.38s which yes has happened more than I want to remember . The 480:80:38 are a little wide for use on ice with no more ballast than I have but they sure pull in the dirt

You can check it with a GPS if you have one.

SV, your I-phone should be able to read GPS speed or you should be able to find a free app from the app store.

I found an app called DigiHUD in the Google store to use when I was driving a truck that only read in KM/H. It reads down to tenths of a mph and can be set for SAE or metric. Plus it can show a really large number that I can aee through my coke bottles. Can choose your choice of colors etc for easy day/night use.

I have no affiliation with the developer but I have had it for at least 5 years and it is awesome.

Carl

I just downloaded the digihud speedometer guess
we will see if It can read tractor speed

Per owner's manual the ground speeds shown are for 18.4-38 and 15.5-38 are 4% slower, 16.9-38 are 3% faster and 18.4-38 are 5.9% faster.

Should have said ground speeds shown are for 18.4-34 not 38.

Our 4010 was built with 15.5's, the factory tires were down to around 60% tread depth when we bought it. Neighbor ordered out the first side console 4020-D on 15.5's because he thought he might mount his picker on it. He started trading help with another neighbor and put the picker on his 3020G nfe. Neighbor with the new 4020 had new Firestone Deep Treads, still 15.5's mounted, even when he turbo-charged it the Deep Treads tied the tractor to the ground. The GY Power Torque tires were mounted on our 4010, never even made it to town.

BTO I worked for had two early 4020's an open station NFE, and wfe cab tractor, about 1969-'70 he traded both 4020's for side console 4020D-nfe and a 4320 with Stopler ROPS cab with heat & A/C. Later bought a used 4020-gas wfe, and later got a 4230 with turbo and ALL were on 18.4x34's.
Heard a lot of guys complain about putting 18.4x38's on tractors that had 18.4x34's, Where did my HP go?
The BTO had a F-145 5-14 plow, pulled it with every tractor I listed except the 4230, always in 5th gear, except the 4020 gas could only manage 4th. The 4320 just played with that plow, probably could have run 18.4x38's and still plowed in 5th. Or 5-16's.

Guy was luck, most of his ground only 1/2 to a mile away from our home farm but our's was hilly, or rolling. His all was flat, level, maybe a few little slopes in some fields. Amazing what a difference that made when plowing/didking. IH's with TA's ruled on hills. When we went from a 450 gas Farmall to a 4010-D with the 4020 kit on our 4 bottom equipment we picked up about 1/2 mph overall.

So only about a 1/4 mile an hour faster

(quoted from post at 14:51:43 10/07/18) So only about a 1/4 mile an hour faster

Click to expand...

Depends on whose figures you want to go by. JD Seller stated +2 mph which is about 15% increase in mph & Fordy20 stated 5.9% increase which would be close to to 1 mph increase. Either % will be more than 1/4 mph increase

Well, starting with the 18.4-34 it's -4% for 15.5-38 and +5.9% for 18.4-38 or a total of 9.9% difference. So 8th gear @ 2200 rpm with 18.4-34 shows 17.6mph less the 4% to get down to 15.5-38 or 16.9mph and add 9.9% to that gives 18.6mph or a difference of 1.7 mph. Page 12 of owner's manual SN 250,001 and up.