4x4 lead/lag stress on drivetrain...what's the dif

MJB · Mar 3, 2003

Re: 4x4 lead/lag stress on drivetrain...what\'s the dif

My take on the lead versus lag drivetrain strain problem is this: In order to minimize the strain on the gear train the goal is to minimize the delta in ratio between the front and the rear axles. As a tractor turns the front wheels have to follow a longer path around the turn than the rear wheels. If a tractor is setup with the front wheels "leading" the rears, as the tractor enters a turn, since the front wheels have to travel a longer distance, their "lead" becomes less and less until at at some nominal radius of turn, the front and rear wheels would both be "in phase". As the tractor turns even sharper the front wheels will in effect begin to lag the rears. If you do this same experiment with at tractor that has the fronts "lagging" the rears when is is running in a straight line as the tractor begins to turn the lag ratio becomes larger and larger thus increasing the strain on the gear train. The bottom line is that the tractor has to have the fronts "lead" the rears in a straight line in order to minimize the delta in gear ratios under all operating conditions. Clear and mud? /forums/images/graemlins/wink.gif

Anonymous Poster · Mar 3, 2003

Re: 4x4 lead/lag stress on drivetrain...what\'s the dif

Interesting point MJB!

So far I see two good reasons why lead might cause less stress/strain on the driveline than lag, when the tractor is moving forward:

1.) Tractors can break into a "power hop" situation if there is a lag condition. This is the experience of tractor owners speaking here...not theory or a calculation. This has to be very stressful on the driveline.

2.) As MJB says, if you have lead, things only get better when you turn, as the mechanics appear to cause the front tires to "lead less" as the turn sharpens. If they were lagging when going straight, they would lag more in the turn, stressing the drivetrain increasingly.

Another benefit of front tires leading is, as pointed out above, that steering/control is negatively impacted by front tires that are lagging.

I am satisfied that for these reasons [and there may be others too] lagging front tires will, in the practical world we find our selves in, stress the 4x4 driveline more than leading tires will.

Thanks for all the input... /forums/images/graemlins/smile.gif Guess starting tonight I'll be able to sleep again. /forums/images/graemlins/grin.gif

Anonymous Poster · Mar 4, 2003

Re: 4x4 lead/lag stress on drivetrain...what\'s the dif

After starting this thread, I saw I could ask Firestone via email the same question. So I did, and here is the reply I received today.

I don't think they would mind me relaying their answer here...

<font color="blue">No amount of lag is acceptable to the tire...some lag is acceptable to the tractor...excessive lead or lag is not acceptable to the tractor. Confused ?

We recommend no lag and up to 5% lead as acceptable for tire wear. If lag occurs, it's like applying brakes to the front tires, it causes rapid tire wear.

The tractor transfer case will probably accept up to 5% lag...the tires won"t. </font>

Nice of them to take the time to reply... /forums/images/graemlins/smile.gif

gordon · Mar 5, 2003

Re: 4x4 lead/lag stress on drivetrain...what\'s the dif

Dang that sure didn't explain too much now did it.
/forums/images/graemlins/confused.gif

Gordon

Anonymous Poster · Mar 5, 2003

Re: 4x4 lead/lag stress on drivetrain...what\'s the dif

Hi,

After thinking about it, I concluded that the reason that they say lag is unacceptable, is because any amount of lag will cause rapid tire wear.

I think saying that the driveline could handle 5% lag is basically saying that 5% lead or 5% lag is about the same as far as stress on the driveline goes. That is the way I read it anyway.

At what point a severe power hop situation would would occur I have no idea.

Makes sense to me that a tire manufacturer would be addressing the question of relative tire speeds from the perspective of tire wear/damage.

My understanding of the lead/lag question has increased greatly thanks to everyone's input. Thanks!

Anonymous Poster · Mar 19, 2003

Re: 4x4 lead/lag stress on drivetrain...what\'s the dif

I happened upon this technical bulletin on the Firestone site. Note the '1% to 5%" range stated. Interesting that among all the stated actions, it doesn't link to the page noted in the original post.