Tire size? 4wd Lead/Lag

[1720DnTennessee]

I posted this in the Yanmar section yesterday but thought I would post here too for additional replys.

I was looking at tires on the net today and came across several posts regarding lead/lag for 4wd tractors. The PO of my tractor put 9.5 x 22 turf tires on the rear and 115/65/14 car tires on the front. The tractor originally came with 8.33 x 22 on the rear and 5 x 14 on the front.

I haven't performed the rolling test to check the current lead/lag. Now here in lies my question. With the rear tires being 9.5 x 22 what tire size should I purchase for the front in order to have the correct lead situation? From what I understand the only way to truly determine the lead/lag is by doing the rolling test. I don't want purchase front tires only hoping they will produce the correct lead.

I have a set of 5 x 14 ag tires for the front so I could purchase 8.3 x 22 ag's for the rear but the turf tires that are on the tractor are practically new Bridgestones.

What to do?

 

[Gary Fowler]

You are going to have to measure the circumference of both front and rear that you wish to put on. Front should lead by about 5-7%. The fronts usually wear down faster than the rears so a little over the 5% is OK with the 5% number being ideal from what I have read. You don't want the fronts being pushed by the rears so go over rather than under the 5% mark.

 

[1720DnTennessee]

You are going to have to measure the circumference of both front and rear that you wish to put on. Front should lead by about 5-7%. The fronts usually wear down faster than the rears so a little over the 5% is OK with the 5% number being ideal from what I have read. You don't want the fronts being pushed by the rears so go over rather than under the 5% mark.

Thanks Gary but what is the formula for determining the lead/lag based on tire circumference? The information I have seen from Firestone Ag is to count the number of revolutions of the front tires for every 10 revolutions of the rear times, once with the front wheels engaged and once not engaged. The difference in the number of revolutions of the front tires is used to calculate the lead/lag. How does this relate to the circumference of the tire?

 

[90cummins]

My 1720 Ford had turf tires and had a very large lead on the front tires, so much so it would bind up within a few feet on hard ground.
My advice is forget the formulas and test it on hard flat ground.
Determine whether there is lead or lag on the fronts then air up the tires that are lagging and/or air down the tires that are leading. Do this until the tractor will roll/drive without binding.
It's possible you can relieve minor binding with tire pressure adjustments.
In my case this was not possible, I needed a different size tire so I aired the rear tires up to max psi and dropped the front tire psi until there was no binding. At this point the front tires were almost flat.
I then measured from the ground to the center of the tire/axle to determine the circumference and went to the tire book to find the size that would get me as close as possible to the ideal size and then did the fine adjustment with tire pressure.
You can also mark the & floor and roll the tractor until the tire makes 1 full turn then measure the distance traveled to determine the tire diameter needed.
My tractor will now engage/disengage on pavement going straight with no binding.
Unfortunately the tractor manufactures don’t always get it right and sometimes not even close!
90cummins

 

[prs]

There is no set formula because not all front to rear gearing ratios are the same. But the procedure of measuring how many revs the front make per 10 rear revs will get you the ratio for your machine and that will let you find the circumference needed up front to match the rear. Rolling circumference is a bit off from "round" circumference, but since both tires are measured the same you will be very close. Then again, the bugaboo is that mounted inflated tires are larger than new tires unmounted; but still if measures are from same condition, you will be "close".

prs