Tires Miss-matched Tires ratio Yanmar 336D (4WD)

[Dokholliday]

I have a friend who has a 336D Yanmar and somewhere down the line I have a suspicion the wheels / tires have been changed to sizes that are not compatible with the ratio between the front and back. I drove it las year and noticed it seems to be either overrunning or under-running in the front when in 4WD.
The size on the front is 8X16 (98 inch circumference)and on the back is 13.6 X 26 (156 inch circumference) The operators manual we have calls for 28 inch tires on the back. I told him to take a measurement of the circumference of the front and back tires and we would try and see if we couldn't do the math and get the right sizes to match BUT I can't find my IT shop manual (which are not to much on detail) and if I did I'm not sure that it would have the ratios listed.

Can anyone help with this quiz? I'm thinking there are 26 inch tires that will be tall enough and or of sufficient size to work so we don't have to buy new wheels. I have also been looking at the John Deere double alternative and the info I'm getting is that a 1050 JD is the same as the Yanmar 336D?

 

[284 International]

Post this in the Yanmar forum to know for sure, but according to Firestone's website the 12.4-28 is within an inch of rolling circumference to the 13.6-26. You should be well within the margins with just an inch of difference.

The fronts are supposed to overrun a little bit anyway. That doesn't mean you don't have mismatched tires in spite of all that. Try the Yanmar forum, there are some guys with 336Ds over there.

 

[Dokholliday]

I've done a little more investigating and it's suggested on one of the sites I've go to a suggestion for a 2% overrun of the front tires and on another that says that 1 to 5% overrun is within the limits. The site you've directed me to has a lot more cross reference than the one I found; hey and I appreciate the quick reply. Now I won't be second guessing.

I did find a post on this forum that gave the ratio between the front and back (now I can't find it 1.6??:1) but I'm not sure if my math worked out right because when I went to work the math out according to the measurements that my friend gave me I came out with a lot bigger tire on the back. But it started to make sense to me when I factored in the "ROLLING. CIRCUMFERENCE INDEX" as in loaded as it would be quiet a bit different from static dimensions and the radius from the center of hub to the ground. It all starts to make sense when I think about my own tractor (Yanmar 3810D with a front end loader and a three point hitch back hoe) that when I pick something up heave my ratio changes and can create a lot of stresses on the drive line because of the shorted distances from the center hub to the ground and tire wear etc. Sometimes I'm surprised that equipment can maintain so much in such stressful conditions; it gets mind boggling to think of those 90 degree gears and shafts and the torsion on them til of course I hear the big BANG.
Thanks again