The lead/ lag is the distance that your tires cover while traveling.
There is a gear ratio between the front and rear axles to compensate for the different tire sizes front to rear.
There is a lot of information and a really large amount of disinformation out and about.
Whoopee do, it's been terminologied to death
AND if we want to use the proper "tractor" terminology, the OP has a MFWD tractor, NOT a 4WD, as 4WD's have the same size tires all around.
SR
Complete and utter bull, drive is determined by the number of axles receiving power not how they perform once the torque is applied, both wheels will always receive the same amount of torque.
Last time I checked, at least on tractors... it's not 4 wheel drive but Front Wheel Assist. and if you don't have front axle locker, it's never 4wd anyway as only ONE front wheel will drive.
It is possible depending upon the loading and the traction available, it rarely happens unless the vehicle in question is operated extensively on high traction surfaces ( pavement/concrete while heavily loaded and in 4wd)
Additionally, the incorrect 'Lead-lag' ratio will eventually destroy the front end components from excessive load.
Your lead/lag is determined by the gearing in your tractor. It is hopefully just a bit of lead from the front tires while in 4wd. Meaning the front tires are covering just a bit more ground travel then the rears at the same time.
There are a few ways to determine how much you are leading/lagging.
1) with your tractor in 4wd on a level smooth surface, preferably not paved
Mark the rear tire and the ground in the center of the ground contact area of the tire, also mark the front tire and ground.
Now drive the tractor in a straight line at least one complete revolution of the rear tire and countthe number of revolutions of your front tire. While one revolution of the rear will work more are better.
2) now look carefully at the tire tread marks in the ground,
you should be able to see if the front tires are being pushed by the rears from how the tread marking is disturbed from perfect.
Is the dirt scoffed to the front of the tread impressions; lagging.
Or does it look like the front tire was trying to spin is the dirt pulled to the rear of the front tire tread marks; leading
3) Now vary your tire pressure and repeat until you see the fronts are just leading the rears.
The main factor under your control in requards to lead/lag is the loaded radius ( or loaded circumference) of your tires.
The unloaded, unmounted tire height is almost useless information, the unmounted unloaded tire diameter is also useless.
The loaded radius from the axle centerline to the ground is the most important measurement and the one that is the most varied by the air pressure you run and load on the tires.
AS an alternative drive the tractor in 2wd to a starting, engage 4wd and drive in a straight line, stop and attempt to disengage 4wd back to 2wd and see how much your tractor jumps and in which direction.
If it jumps forward the front tires were quite likely lagging, if it jumps rearward they were likely leading.
Depending on the method used then start varying the tire pressure.
If you feel the fronts are leading too much, lower the front tire air pressure or increase the rear tire pressure. Then repeat too see if the scuffing or jumping is better or worse. If better determine if those tire pressures will work in your application.
Go to your tire manufactures website and find the pressure to weight loading chart for your tires. Then determine the loading of each pair of tires. Air pressure above the required amount for the load being carried results in less traction, faster wear and decreased ride comfort. Air pressure below the required amount will result in excessive sidewall flexing and possibly tearing.
None of those pressures will likely be in your owners manual and they will not be on the tire sidewall. The number on the sidewall will be the maximum pressure the tire is desighned for to be able to carry the maximum load the tire is rated for.
Another method if you have a front end loader on your tractor is to drive straight in 4wd, stop and lower your loader to raise the front tires off the ground while holding the brakes and see what the front tires do. If they turn forward as the weight is removed they were lagging if rearward they were leading, again vary your air pressure and repeat till you achieve a slight leading condition.
My preference is to drive in dirt that will take a tire tread mark and observe the leading and trailing edges of the tread marks to determine which tire is being pulled or pushed.
Unfortunately the correct tire pressure to achieve the correct lead will change with every different load applied to the tractor,
an empty bucket loader compared to a full bucket. An empty three point hitch compared to a heavy load carried and used while supported and off the ground. A heavy drawbar load from a trailed implement. So the best is a comprimise that works for you most common loading or most critical one.
When I can engage and disengage 4wd with minimal felt effect it's good.
While driving you can play around with the 4wd, if engaging it seems to slow your tractor down you are likely lagging, if it feels like your tractor speeds up when engaged it is likely leading.
One thing not discussed here yet is trying to determine the gear ratio between the front and rear axles.
In 2wd mark the center of the tire and the ground for the rear wheel and the front wheel, drive forward a few revolutions, count the number of front wheel revolutions to the number of rear wheel revolutions this will give you the actual ratio of front to rear which could be compared to the manufactures specified gear ratio if known. If the tire loaded radius are the ones the manufacture used when determining the gear ration you would be close to the mechanical gear ratio. Depending on the designed lead percentage.
