JD750 4WD Tire Size question

[pmsmechanic]

Like I say I don't remember the explanation that made sense to me. Both of you made an argument that makes sense on the surface but is wrong. A taller tire is slower, not faster. Again I don't know why but that's the way it works. My 25x8.5x14 tires have considerably more slippage in 4x4 then the 26x12x12 tires.

 

[rScotty]

With respect, I think you should go back and read what Lou and I wrote and then think about it.

It's polite of you to say that we "made an argument that makes sense on the surface", but that's doesn't help with mechanical things. Gearing and gear ratios isn't like sports or beer tasting where there can be different opinions on what works best. Gearng is mechanical; it doesn't have the luxury of opinions. It either works how it works, or not at all.

Mostly I find when all is said and done that the difference in mechanical explanations is in how things are defined rather than in how they work. That may be the case here. The "slippage" that Lou and I are talking about is a loss of traction between the tire and the ground when a tire skids due to torsional stress or "windup" in the gear train driving the front axle. The windup is caused by a front/rear drive ratio mismatch, and it will happen equally when driving straight ahead or when turning.

Side slipping on turns is different & can be due to several other things. That happens for lots of reasons. But adding the peculiar slippage due to a ratio mismatch will make the slipping while turning more noticible.

Bottom line is I don't care what you believe. I was just trying to get you to minimize the chances of a repair bill.

rScotty

 

[pmsmechanic]

Bottom line is I don't care what you believe. I was just trying to get you to minimize the chances of a repair bill.

rScotty

It's not what I believe that counts in this case, it's what I've observed. And since the tires now have less slippage in 4x4 that would be less strain on the drive train. It's been 19 years and 3000 hours.

 

[LouNY]

If it has worked that long the replacement tires where very close to the same loaded height regardless of the labeled size. Different brands and even different series of the same brand can have very different loaded radius.
Regardless of what you think you have "observed" a taller tire will have more lead then a shorter one. Possibly your original tire was lagging a bit and the taller if taller tire corrected that. It can be difficult to tell if a tire is leading or lagging and it often is not correct from the factory. Tire brands or series are changed during production as price and availability change. One of the tractors on the farm 18-20 years ago required 3 sets of tire swaps before they got the lead lag corrected on a brand new tractor. Engaging the 4wd would make the tractor slow down, disengaging and she would jump ahead. Took them 3 swaps before it was corrected.