Ford Tractor Tire Sizing for the Elenco 4WD Front Wheel Assist
You need to know the ring and pinion ration on both the tractor rear end and the
Elenco font end.
The two tractors that I am working on are a 841 diesel and a 841 gas. How I
managed to get 2 tractors with exactly the same information I am not sure but
and very thankful for. Below is the information you will need to be sure you get
the tire size correct. If the tire size is not correct you will wear out tires, gears,
chains etc. before their time.
MY INFORMATION
Tractor Rear end
number of ring teeth
number of pinion teeth
43
6
Coupler Sprocket
Transfer case sprocket
number of teeth
number of teeth
19
17
Elenco front end
number of ring teeth
number of pinion teeth
44
9
43 divided by 6 equals 7.17
So the rear end ratio is
7.17:1
Here is the math
Tractor rear end
Coupler/Transfer case
19 divided by 17 equals 1.117
So the transfer case ratio is
1.117:1
Elenco Front end
44 divided 9 equals 4.889
So the front end ratio is
4.889:1
Because the transfer case causes a set up in revolutions you need to multiple
what is coming out of the rear end pinion by the ration coming out of the transfer
case to the drive shaft.
7.17 times 1.117 equals 8.00889 or 8.009
So the ratio when you combine the rear end to the transfer case you have 8.009:1
Now the front end pinion turns 4.889 times around to get one revolution of the
front end ring/axle/tire. So you divide 8.009 by 4.889 to see how many
revolutions of the front end ring you would get to the rear end ring.
8.009 divided by 4.889 equals 1.638
That is the number you need to size your front tires to your back tires. One
percent difference is ideal but no more than five percent difference front to
back tires.
Below is a general list of tires and their rolling circumference. Be sure to check
the rolling circumference of the brand you buy because Ag tires vary sometimes
2” in height which will change the rolling circumference.
REAR TIRES
12.4 x 24
12.4 x 28
13.6 x 24
13.6 x 28
14.9 x 24
14.9 x 28
16.9 x 24
16.9 x 28
136”
148”
143”
158”
148”
160”
156”
168”
+/- 1%
134.64/136.36
146.52/149.48
141.57/144.43
156.42/159.58
146.52/149.48
158.4/161.6
154.44/157.66
166.32/169.68
+/- 5%
129.2/142.8
140.6/155.4
135.85/150.15
150.1/165.9
140.6/155.4
152/168
148.2/163.8
159.6/176.4
FRONT TIRES
7 x 16
8 x 16
9.5 x 16
87”
91”
99”
87 times 1.638 equals 142.51”
91 times 1.638 equals 149.06”
99 times 1.638 equals 162.16”
So there you have it. Bill’s thought process to tire sizing but keep in mind if you
use tires that are worn down, under inflated on either the front or back then the
rolling circumference is going to change. If you use a different manufacturer other
than the one I used you need to verify the rolling circumference.