Oliver 1855 mfd all the numbers for gear ratios, tires

I am re posting my question for my Oliver 1855 with MFD. I still want to work out the correct calculations for the % lead/ lag.

Here are all the numbers

When one side of the tractor is raised with the mfd engaged:
The driveshaft turns close to 29.50 times for 2 turns of the rear tire and
20 turns for 2 turns of the front tire (by the way the tag was wrong).
I could be off slightly if slack between gear teeth can make a difference.

When the rear tire is turned once, the front tire turns 1.4706 times (once around plus 8 of 17 tire lugs).
Or inversely 0.68 measured the other way.

Currently the front tires are BKT 14.9x25 with manufacturer RCI of 152.1
The rears are Goodyear 18.4x38 with a listed RCI of 207.

These are the tire sizes suggested in the operators manual for this tractor.
Unfortunately there were different ratios used and the manual does not specify which ratio their recommendations are for.

There seem to be different opinions on how to calculate the lead. By what I read the desired lead is 2 to 6%. To me it seems higher here.
I have posted before but never really got a really good answer. With all these numbers there should be people who can figure it out. Some good replies on this would be so helpful.

A little more info. we have a fork on the back and an Allied 790 loader on the front. Much of the time we carry 2 bales (one bale at each end). The manufacturer BKT recommends 22 to 30 psi with a max of 35 for their tires on the front. Because of the weight we have been running them at the max. For the back I think 20 to 25 psi is recommended and likely is 25 in ours, They also have about 40% of the lugs left . We probably should have less air in the front but I don't want to wreck the tires either, just replaced them. I could put 20.8 x 38s on the back but would rather not if my lead is okay as it is.
I hope I have given you enough information now!

The way we have done it is to count the revolutions on the front driveshaft versus the front tire, that will tell you what gears are in the front diff, then you can look at the chart in the manual. I'm not positive that you need to be checking anything on the rear tires, but others may have other ideas , just how we have done it.

If you go with the 20.8x38 on the rear I am pretty sure you will need 16.9x26 on the front and 18" rims on the back. Are your front tires wearing out to soon?

The previous front tires went bald after a some years but we did use it in 4 wd alot so I don't know if it is premature or not.

One sure fire way to check if the ratios are right is to park the tractor on a flat piece of hardtop,put it in 4WD with the engine off and roll it by hand and if it tightens up
and gets hard to impossible to push your ratios are off somehow.

I got some charts and finally found the specs for Goodyear dyna-torque II bias tires. The rolling circumference is actually 209" and the static loaded radius is 32.28". From my measurements it looks like the lead for the current tires is around 7%. If I switched to 20.8 rears it would be about 4.5%. Now I wonder if I can just leave as is for now. I have a pair of 20.8 on 18" rims I was planning to put on a white 2-155. I could put the 18.4s on it instead. Trouble is the paint would be the wrong color on all of them and the 20.8s would have been nice on the 2-155.

Mfwd ratio chart from the service manual.

page 2

It looks like it blew the image up too much posting to this forum. There in the parts and pieces galleries on this site also.

Will it work if you measure the circumference of the front and back tire and then figure the ratio?

Which shop manual is this? I have not seen this chart in mine. I wish your picture was clearer.

Well that throws a wrench into my calculations. When you use LR instead of RC it ends up different. RC does not equal 2*(pi)*LR for most tires. I found a simple lead-lag calculator using RC's at Titan https://www.titan-intl.com/en/resources/Lead-Lag-Calculator . The other thing is the manual above states that all 1855s had the 7/44 bevel gears in the rear which are supposed to give 29 driveshaft revs per 2 rear tire turns. I have counted the revolutions over and over but I always get 29.5. My 1855 is a 1974 sn 247-865-xxx, one of the later ones (it has the pump for the oil cooler in the transmission instead of on the engine like the earlier ones) Is there something I don't know?

Well that throws a wrench into my calculations. When you use LR instead of RC it ends up different. RC does not equal 2*(pi)*LR for most tires. I found a simple lead-lag calculator using RC's at Titan https://www.titan-intl.com/en/resources/Lead-Lag-Calculator . The other thing is the manual above states that all 1855s had the 7/44 bevel gears in the rear which are supposed to give 29 driveshaft revs per 2 rear tire turns. I have counted the revolutions over and over but I always get 29.5. My 1855 is a 1974 sn 247-865-xxx, one of the later ones (it has the pump for the oil cooler in the transmission instead of on the engine like the earlier ones). Is there something I don't know?