I don't see where anyone is using the tractor's drive train ratio in their calcs. Don't just rely upon printed factory tire sizes to establish the correct ratio and then use different profile wheels to boot. Presuming you can establish the actual factory rim dimensions and have the DTR then try using static load ratio (SLR) in lieu of Diameter or Rolling Circumference. I found all this stuff immensely aggravating and at least Titan provided a lot of specs to make sizing up easier.
Talk with a Kubota tech directly and seek their assistance. I found them wonderfully helpful.
Regards,
Clay
And there in lies the problem knightman and Wolfman pointed it out to you
correctly.
You CANNOT use any formula based on the radius diameter or using pi etc to get the correct and factual number that you need which is:
ROLLING CIRCUMFERENCE period. Each manufactures specifications are different though some or should I say most familiar OE name brand tires such as Firestone Goodyear and Titan are nearly identical and the reason that's the case as the tractor manufactures may have to switch brands for any number of reasons ( fire at factory strike raw material problem ) which may even include the price based on each suppliers contract bid etc. Rim size will change rolling circumference so that does add a grain of salt into the wound
process of buying replacement tires.
ROLLING CIRCUMFERENCE of a tire is the actual measured distance the tire travels in inches on a tractor when making one complete revolution. To further understand what this means think of this: mark the tire at the bottom 6 O'clock position and the driveway/road/garage floor then drive the tractor ahead with someone spotting you until the tire makes that revolution and comes back to the 6 O'clock position. Mark the surface as you did when you started then measure the distance in inches from start to finish and that answer is the Rolling Circumference of that tire. It will change with wear of course and the front and rears both do that at a slightly different rate. So the 2% allowance allowed really is to cover that as the fronts on a 4x4 tractor wear out faster than the rears.
I did not go back and figure out the answer you came up with that showed you at the 2% on those different sizes because I didn't go searching for nor did I know what brand of tires you were using for comparison. I also thought
that those numbers weren't from any manufactures specs but do know from
Wolfmans answer ( he's very good at this! ) that he 99% of the time did go out and research to come up with his answers.
I unlike most on here do sell tires for a living and have NEVER sold a single tire to anyone on the board yet because that's not why I'm here. I'm here to learn from others experiences that we collectively share and the results that we all hope for is to avoid making mistakes to save us all a bunch of money so we can continue to enjoy our toys WHOOPS! I meant to write tools! for many many years and use the money saved to add to the implements we can attach to them to make our lives easier or to do a much better job at what we do. I have learned a bunch saved a bunch and haven't had to learn it all by making the mistakes I avoided by others advice much I might add they did learn the hard way and posted it immediately so others wouldn't suffer the same bad education. If you buy the wrong tires based on false/faulty information one thing I can guarantee you is that it will be a very expensive mistake if it doesn't work out as planned AND after spending money to fix a broken tractor you'll be spending the money too to buy the correct tires that you should have bought in the first place.
$1000.00 difference in a set of 4 new tires is cheap in comparison to buying all new front differential parts..gears bearings differential carrier axles etc
plus the labor or at least your own time to change it all if you're capable to do it which lots of people are not. Oh and don't forget that extra $1000.00 will then be spent on top of it all.
Al