R4's on a ~3,500lb tractor with loader... What tire pressure are you running?

[LouNY]

Yes, I was referring to adjusting tire pressure to change the lead lag of the front to rear axles.
We try to keep a bit of lead in the front axle as they will turn much easier with less disturbance of the sod in hay fields,
also pulling up a hill the directional control is much better with a bit of lead in the front.
Our tractors have electrically engaged 4wd, when switched on when traveling straight on a high traction surface if the fronts are lagging you will feel the tractor actually slow a bit, then when turning it off it will jump ahead a bit. If it slows down when turning it off it may have to much lead. You can also observe the tire marks in dirt to determine if the fronts are leading or lagging. If leading the front tire tread marks will show as a spin type mark with the front pulling on the dirt where if its lagging you can see the tread marks are pushing towards the fronts.
With the smaller tires on the front of a tractor leading or lagging they will tend to wear a bit faster then the rears as they wear they will lose the lead they had as new to get that lead back that we desire we can increase the front tire pressure or decrease the pressure in the rears. It doesn't take a large pressure change to effect the lead ratio as it is the loaded tire radius that determines the amount of lead / lag. With the extreme variables in front and rear weights depending on the axle loads and how much the weights are changing with different drawbar or 3 point loads, the weight of liquid tanks on the front, adding or remove ballast for tillage or haying.
When comparing tire and trying to match them the loaded radius is the critical measurement as that will determine the loaded circumference. It only takes a couple pounds of air pressure change to effect the loaded radius.

To shorten this up if my tires look good with a decent footprint on the ground and good side hill stability but my desired lead isn't there I'll drop 2 psi in the rear and add 2 psi to the front and recheck to see if that was too much or not enough, as the fronts wear I'll have to lower the rear pressures to maintain the lead.

Lou

 

[art]

A lot of good information here already! the tires should have good contact across the tread surface. A typical compact with industrial tires should have the fronts with loader with near max inflation depending on use. the rears are often about ten pounds to achieve a full print on the ground. The lead lag ratios are adjusted to a degree with the air pressure but it can change with just a different brand of tire. Even within makes of tires you might go from a lead to a lag within a brand of tires! For what I've seen a lead of about 3% is about ideal! It will help with steering but not be to much and it should give an easy engagement and disengagement of the four wheel drive.

 

[Texasmark]

Yes, I was referring to adjusting tire pressure to change the lead lag of the front to rear axles.
We try to keep a bit of lead in the front axle as they will turn much easier with less disturbance of the sod in hay fields,
also pulling up a hill the directional control is much better with a bit of lead in the front.
Our tractors have electrically engaged 4wd, when switched on when traveling straight on a high traction surface if the fronts are lagging you will feel the tractor actually slow a bit, then when turning it off it will jump ahead a bit. If it slows down when turning it off it may have to much lead. You can also observe the tire marks in dirt to determine if the fronts are leading or lagging. If leading the front tire tread marks will show as a spin type mark with the front pulling on the dirt where if its lagging you can see the tread marks are pushing towards the fronts.
With the smaller tires on the front of a tractor leading or lagging they will tend to wear a bit faster then the rears as they wear they will lose the lead they had as new to get that lead back that we desire we can increase the front tire pressure or decrease the pressure in the rears. It doesn't take a large pressure change to effect the lead ratio as it is the loaded tire radius that determines the amount of lead / lag. With the extreme variables in front and rear weights depending on the axle loads and how much the weights are changing with different drawbar or 3 point loads, the weight of liquid tanks on the front, adding or remove ballast for tillage or haying.
When comparing tire and trying to match them the loaded radius is the critical measurement as that will determine the loaded circumference. It only takes a couple pounds of air pressure change to effect the loaded radius.

To shorten this up if my tires look good with a decent footprint on the ground and good side hill stability but my desired lead isn't there I'll drop 2 psi in the rear and add 2 psi to the front and recheck to see if that was too much or not enough, as the fronts wear I'll have to lower the rear pressures to maintain the lead.

Lou

Thanks. You just verified that front lead.....aka front axle is sharing more of the load, makes for better steering and I can understand that because since 2007 I have had my first 4wd vehicle and in turning corners with my tractors, having the 4wd engaged when turning corners is an obvious advantage for pulling you around a corner rather than the front axle being pushed (sideways) around the corner (if brake on that side not applied) as is the case with 2 wd machines.

Thanks.

 

[Texasmark]

A lot of good information here already! the tires should have good contact across the tread surface. A typical compact with industrial tires should have the fronts with loader with near max inflation depending on use. the rears are often about ten pounds to achieve a full print on the ground. The lead lag ratios are adjusted to a degree with the air pressure but it can change with just a different brand of tire. Even within makes of tires you might go from a lead to a lag within a brand of tires! For what I've seen a lead of about 3% is about ideal! It will help with steering but not be to much and it should give an easy engagement and disengagement of the four wheel drive.

Another way to tell if your gear train is not matched is to travel down a hard surface in 4wd with the steering centered and push in the clutch. If the tractor acts like you have the brakes depressed as compared to how it acts in 2wd, your ratio is mismatched.....did for me.

 

[ovrszd]

One way to tell if your gear train is not matched is to travel down a hard surface in 4wd with the steering centered and push in the clutch. If the tractor acts like you have the brakes depressed as compared to how it acts in 2wd, your ratio is mismatched.

It'll actually display that characteristic even if properly setup. The proper lead/lag will create this.

My Ford is currently equal. No lead/lag. Driving in a straight line on any surface, with no load, it acts no different if in 4wd or 2wd. This situation is currently happening because my rear tires are new and my fronts are 25% tread. I've adjusted air pressure as Lou described as far as I'm comfortable with to get to zero lead/lag. I'll just live with it until I buy new fronts.

 

[Texasmark]

Yes, I was referring to adjusting tire pressure to change the lead lag of the front to rear axles.
We try to keep a bit of lead in the front axle as they will turn much easier with less disturbance of the sod in hay fields,
also pulling up a hill the directional control is much better with a bit of lead in the front.
Our tractors have electrically engaged 4wd, when switched on when traveling straight on a high traction surface if the fronts are lagging you will feel the tractor actually slow a bit, then when turning it off it will jump ahead a bit. If it slows down when turning it off it may have to much lead. You can also observe the tire marks in dirt to determine if the fronts are leading or lagging. If leading the front tire tread marks will show as a spin type mark with the front pulling on the dirt where if its lagging you can see the tread marks are pushing towards the fronts.
With the smaller tires on the front of a tractor leading or lagging they will tend to wear a bit faster then the rears as they wear they will lose the lead they had as new to get that lead back that we desire we can increase the front tire pressure or decrease the pressure in the rears. It doesn't take a large pressure change to effect the lead ratio as it is the loaded tire radius that determines the amount of lead / lag. With the extreme variables in front and rear weights depending on the axle loads and how much the weights are changing with different drawbar or 3 point loads, the weight of liquid tanks on the front, adding or remove ballast for tillage or haying.
When comparing tire and trying to match them the loaded radius is the critical measurement as that will determine the loaded circumference. It only takes a couple pounds of air pressure change to effect the loaded radius.

To shorten this up if my tires look good with a decent footprint on the ground and good side hill stability but my desired lead isn't there I'll drop 2 psi in the rear and add 2 psi to the front and recheck to see if that was too much or not enough, as the fronts wear I'll have to lower the rear pressures to maintain the lead.

Lou

Site Administrator: If you catch this, you might consider making a Sticky out of it.....some great info that affects anybody with 4wd. Thanks

 

[ericm979]

Keep in mind that in turns the front tires take a longer path than the rears. The lead ratio is needed so the fronts are not too slow in turns. When they are the front end will push (understeer). Or in a slow moving tractor, the fronts will chew up the ground more in turns.

If you're like me and do more turning than straight driving you want more lead not less. If you mostly care about straight driving you might want less lead ratio.

 

[CADplans]

The front tires on my 4105 are so worn,, they are closer to turf tires than industrial,,, :laughing:

Interestingly, the ratio is VERY close to neutral, the 4WD can be shifted into, or out of 4WD with zero resistance at any distance, as long as you go straight.

The 4WD will develop resistance when I mow up a steep grade, or back up the grade,,
then, I have to reverse direction to get the 4WD to disengage,,
the same resistance occurs after a sharp turn,,

I seldom use 4WD when mowing,, except when I encounter a steep grade.

 

[ovrszd]

Yep. Your tractor was built with "lead". As the front tires got smaller in circumference you have lost that. Now you are at a neutral place. Same with my Ford as I described above.

This is what Lou was talking about in his excellent post about adjusting air to maintain the ratio he desires.