why are my steer tires cupping?

Ya know I going going to say the exact same thing.

 

What brand/model of tire are you running? If you don't have a tire with decoupling grooves an OTR tire will usually get uneven wear on the shoulders.

Steer tires with solid shoulders are great fro P&D applications but not so good on long haul...

 

Well, in the end, I think we can all agree that road crown is ultimate root cause for outer shoulder wear on the right steer and every truck pulling to the right. Camber is not adjustable. You would change camber by bending the steer axle, this is no longer an accepted or recommended practice. If the camber is out of spec, some thing is wrong with your axle or spindle. Road crown is different all over. It is impossible to have a perfect "spec" for camber or caster because of this. Some roads are nearly flat, others are crowned big time, some highways have inverse road crown where the water drains in the middle. Anyway, when you have a truck that pulls to the right because of road crown the driver has to constantly pull back on steering to the left slightly to keep the truck straight. The right steer, outer shoulder gets the most stress applied to it all the time and will wear faster. Once the outer shoulder starts to show wear the tire is now cone shaped and will pull even harder to the right making the problem worse and worse. The only way to counter this is to induce a pull to left to even the pull to the right as best as possible. Cross caster is the only way to do this. Again, camber is not adjustable. Do not let anyone bend your axle, no manufacture recommends it! This isn't 1972! For trucks that pull to the right you need a good cross caster. Most trucks I see that have a moderate pull to the right have a cross caster less than -0.5 degrees. I think road crown here in Ontario is pretty much average. I set up my customers with a cross caster of ball-park -0.7 to -1.1 degrees. The cross caster will counter or cancel the pull caused from the road crown and you will get better wear. Ideally, you want about +0.2 degrees of camber on the left and -0.2 on the right to also help with road crown. Some axles are actually the opposite. The funny thing is, they are still in allowable tolerance, but the tires are angled to the right side of the road and so you can align that truck all day long and it will still pull to the right and wear tires. I find Eaton axles are the best with having the camber nearly perfect, Meritor axles are mediocre and Spicers are the worst - big time! Even with a good alignment, good tires and maintenance, some still have to rotate the steers side to side on occasion just to even out the wear.

 

Road crown and road surface are both high on the list. So is inflation pressure, small differences side to side mean unequal rolling resistance.

Here's how I explain how caster and camber work together. If you put a ball at the top of a hill it will roll down that hill. It will never roll up the hill. Caster and camber form a hill that slopes to the inside of that tire position. As the truck goes down the road those hills have to have an equal amount of force or they will turn in whatever direction it takes to equal out. In other words when you let go of the wheel the tires will turn in the direction needed to equal out those forces.

Or think of it this way. Remember the hill and ball? Imagine the two hills of the right and left wheels with a ball halfway down and a line between the balls. As long as the line is level the forces across the axle are equal. If one side is stronger than the other the tires will always turn in the weaker direction to force the weaker ball up the hill. When the forces are equal the line is level. What direction the truck is going is only secondary at that point. An alignment is used to make the wheels point straight ahead when those forces are equal.

Where you can really see the hill come to life is when an alignment is getting done. Remove the tierod and set the wheels on a set of turn plates. As the weight comes on the left turns right and the right turns left.

Bending the axle. Not good, don't do it. It's a great way to have an axle snap at a bad time.

 

need shocks, real shocks like King Shocks, and centramatics

 

OPPS Never mind this isn't supposed to be here

 

what does this have to do with tire cuppng? I dont have tire cupping, but I also have centramatics. the reason I ask is I never grease my 5th wheel. I use the slick disk. thank you.

 

TOO late it's here.

 

I was just going to say the same thing, word, for word.

 

I should add that type of road driven comes into play. Lots of flat interstate is easier to get higher miles out of because the forces on the axle are less. Higher crown 2 lanes will eat at the tires because the truck will think its turning right all the time.