Gots a Kubota 4x4 tractor that I wanna put new skins on. Original turf tires are 33 12.50 X 15, on the rear(33.8" rolling dia), 23 850 X12, on the front( 23.2" rolling dia). Hadda craigs list find hit me today, found same size fronts + 16" rear rims, fer $100, bout an hour from home, so I grabbed 'em. Here comes the questions. Found 9.5X16 R1's are 33.6 rolling diameter, at least on m.e miller's page... from the same source, 23 8.50X12's, in R4's (only ones I can find in the size) are 22.6" rolling dia. If I do the math that comes out to 1.45689 f-r ratio for original, and 1.48672 f-r for the new tires. question is, is what is the allowed variance in tire sizes, expressed as a percentage? Is there a general formula, for this? My gut says that .02983 won't make much slippage, except maybe on pavement, and since the gut's bigger than the brain, that's the way I would tend to go with this, unless somebody else has a better ideer
At least with larger MFWD tractors, they spec a 2-5% overdrive on the front axle. Probably close enough, but there should be a section of the owners manual covering tire selection.
I'd jack it up, rotate the driveshaft, and establish a ratio of front to back. Consider circumference, and do the math. Be concious that rear tires don't travel as far as front. As you corner, the rears take a shortcut across a circle. Drive a 4 x 4 pickup in circles on dry pavement, you'll see what I'm talking about. Always use 2 wheel drive when 4 isn't needed.
just run them, you are so close it wont matter
The tires will squat some as well so you can probably get even closer just by adjusting tire pressures a little.
Based on your calculations I don't see any reason it won't work. Taking into account all the info above I say gitter done!
Think about all the payloaders and MFWD tractors driving around with new tires on one end and bald on the other. Unless you drive lots of dry pavement in 4X4. I think you will be fine.
Even worse is a road truck with mismatched duals, will cause one to pull like steering is off to eating the side differential gears in lighter rear ends if kept that way for lengths of time. For dirt, off-road we never cared!!