I can't find a 40% recommendation for ANY tire fill anyplace.
I sure would like to see a screenshot of that manual page.
Now wondering if the 40% is the recommended MIX of water & methanol to get to where it won't freeze.
That would leave 60% water to the 75% fill that the OP isn't figuring into his weight calculations.
I guess I did say found in my Kubota manual. And you are right, 40% is not in the Kubota manual, I was mistaken.
Kubota only mentions 75% as a MAXIUM fill. It does not make a preferred recommendation. Leaves that to the dealer.
The information below is from the salesman manual posted online by John Deere. You can read their Preferred recommendation just after the IMPORTANT below.
This posting can be found here:
Using liquid ballast in tires
I suspect that may be because of increased law suits regarding
ballast experienced in more recent years. Looks like the link is dated 2006, but I think the last update was stated as 2013. The very first statement clearly displays the JD concern about using liquid.
And I an not saying I agree with that. The benefits of that ballast (for me) clearly outweighs the down side and ride performance.
But regardless, I do not want excess weight above the axle.
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IMPORTANT:Liquid ballast is not preferred in rear tires. Liquid weight greatly increases tire stiffness at lower operating pressures and greatly reduces ride performance.
In some cases liquid will be needed in the front tires to achieve the correct weight splits with some implements for field operation and transporting.
CAUTION: Installing liquid ballast requires special equipment and training. See your John Deere dealer or tire service store.
IMPORTANT: Never fill any tire to more than 90% full. More solution could damage tire.
Use of water or calcium chloride solution can be used to provide economical ballast. A mixture of 3.5 lb. of calcium chloride per U.S. gal. (0.42 kg per liter) will not freeze solid above -50 F (-45 C). However, liquid ballast is not recommended because it results in harsh ride, difficulty in handling, spills if flats occur, and when used in rear tires can result in greater susceptibility to power hop.
CAUTION: Avoid possible injury due to losing control of tractor. Limit transport speed to 20 mph (32 km/h) when using liquid ballast.
Note:Use of alcohol as liquid ballast is not recommended. Calcium chloride solution is heavier and more economical.IMPORTANT: A maximum liquid fill of 40 percent is recommended in rear tires for better tractor performance instead of the previous recommendation of 75 percent fill. Fill tube-type or tubeless tires up to valve level (40 percent full) with valve (A) shown above, in the 4 o'clock position. When putting liquid in either front or rear tires, make sure both front tires have the same amount of liquid fill and/or all rear tires have the same amount of liquid fill. |
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REAR TIRE Liquid Weight Per Tire | | | | | | | | | | Tire Size | 40% Fill | 75% Fill | | | | | | | | 3.5 lb./gal. (kg) | 5.0 lb./gal. (kg) | 3.5 lb./gal. (kg) | 5.0 lb./gal. (kg) | | | | | | | 14.9R46 | 429 (195) | 462 (210) | 805 (365) | 867 (393) | 18.4-42 / 18.4R42 | 619 (281) | 661 (300) | 1160 (527) | 1240 (563) | 18.4R46 | 701 (318) | 747 (339) | 1314 (596) | 1400 (635) | 20.8-38 / 20.8R38 | 758 (344) | 811 (368) | 1421 (645) | 1521 (690) | 20.8R42 | 802 (364) | 853 (387) | 1503 (682) | 1600 (726) | 320/90R50 | 297 (134) | 320 (145) | 556 (252) | 600 (272) | 320/90R54 | 303 (138) | 320 (145) | 568 (258) | 600 (272) | 380/90R50 | 429 (195) | 455 (206) | 805 (365) | 854 (387) | 420/80R46 | 467 (212) | 498 (226) | 876 (397) | 934 (423) | 480/80R42 | 614 (278) | 654 (297) | 1148 (521) | 1227 (557) | 480/80R46 | 644 (292) | 690 (313) | 1207 (548) | 1294 (587) | 480/80R50 | 676 (307) | 725 (329) | 1267 (575) | 1360 (617) | 520/85R38 | 719 (326) | 768 (348) | 1349 (612) | 1440 (653) | 520/85R42 | 770 (349) | 818 (371) | 1444 (655) | 1534 (696) | 520/85R46 | 827 (375) | 882 (400) | 1551 (703) | 1654 (750) | 620/70R42 | 915 (415) | 974 (442) | 1716 (779) | 1827 (829) | 620/70R46 | 991 (450) | 1058 (477) | 1858 (843) | 1984 (895) | 650/85R38 | 1237 (561) | 1316 (597) | 2320 (1052) | 2467 (1119) | 710/70R38 | 1092 (495) | 1159 (526) | 2048 (929) | 2174 (986) | 710/70R42 | 1231 (558) | 1316 (597) | 2308 (1047) | 2467 (1119) | 800/70R38 | 1433 (650) | 1529 (694) | 2687 (1219) | 2867 (1301) |
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From Kubota Manual.
A Do not fill tires with water or solution more than 75% of
full capacity (to the valve stem level at 12 o'clock
position).
(A) Correct-75% Air compresses like a cushion
(B) Incorrect-100% Full Water can not be
compressed