Tires: tire squirreliness and air pressure, uniroyal liberator, tramlining

Question
QUESTION: Thanks for your help.
I have a '91 Silverado, running 235-75R-15 tires. I recently bought a set of cheap WM Uniroyal Liberator A/T tires. I am fully aware of "getting what I pay for" , but I had no problems whatsoever w/ an earlier set for my S-10. I have two issues/questions:
1- The tires can be inflated up to 50psi. The door label suggests 35psi, front and rear. What pressure should I inflate my tires to?
2- These tires are a week old. They feel squirrely, meaning they don't seem to track straight. THey seem to give left and right when making even subtle turns w/ the steering wheel, as if the sidewall isn't holding up the weight of the truck sufficiently when underway. This drifting feels dangerous. I read on a previous answer that this relates to tramlining or groove wander, and  that I just have to live w/ it. Can manipulating the psi help this situation?


ANSWER: Tim,

Your vehicle came with P235/75R15's and you put on LT235/75R15.  These are different animals - so I recommend that people only replace "P"'s with "P"'s and "LT"'s with "LT"'s.

To get the same load carrying capacity, the LT's need to be inflated 15 psi more than the P's.

But is your issue about groove wander or not?  If it is, there is nothing in the pressure situation that will cure this.

---------- FOLLOW-UP ----------

QUESTION: Thanks for the quick reply.
The tires are marked P235/75R15 108S M+S Extra Load, not LTs.
I should have ordered my questions differently. The primary problem is the tracking/drift feel. I feel like I'm all over the road when holding the steering wheel straight and steady. (There is no alignment issue, so it isn't mechanical.) I brought the inflation levels into the picture,wondering if adjusting them would help any with that problem.
Also, I had seen you give advice in other inquiries that the psi on the door label is the suggested inflation level. Does that mean regardless of the tire's maximum psi rating?
I hope that clears my problem up.
Thanks
Tiom

Answer
Tim,

Opps!  I forgot about the possibility that the tire could be an Extra Load.

Your question:  "......... Also, I had seen you give advice in other inquiries that the psi on the door label is the suggested inflation level. Does that mean regardless of the tire's maximum psi rating?....."

Provided the tire size is the same (including the letters) the load carrying capacity is the same at a given pressure AND is independent of what the maximum pressure is on the sidewall.

Put another way:  You should only use the maximum pressure stamped on the sidewall as an indication that you are doing something wrong and not as a way to figure out what the proper pressure is supposed to be.

So back to your original inquiry:  Pressure will have very little effect on groove wander.  I guess the question I still have is:  Are the tires following the grooves in the pavement?  Or is that just the way it feels?

One thing I would really do - if you haven't already - is check the alignment.  You can get this feeling if there is excessive toe out.