He'll pay attention to it closely if he wants his tires to wear properly and ride closest to stock.
A thicker, heavier constructed tire needs MORE air pressure to carry the same load? Um, no. This doesn't even jive with common sense, much less real world results.
Not many people here run the larger 35x12.50 and up sizes, but go over to a Jeep Wrangler forum and ask what those guys are running their tires at. NONE of them will tell you 40 psi or higher. Almost everyone is running 20-35 psi on the street with larger LT tires.
We have on many occasions seeked help from tire manufacturers and also tire distributors/vendors about the proper pressures to run in larger tires, and NEVER have they told us that a heavier duty tire or larger tire needs MORE air pressure. In fact it's just the opposite...larger tires hold more air. A higher volume of air requires less of it to hold the same load. This is science I know.. but science and common sense agree in this case.
There is so much wrong here its hard to know where to start!
1st he's not running 35" tires, he's running 32" tires, so lets leave that out of the discussion for now (I'll get back to it later). I'm not going to re-post and re-quote all of [MENTION=2798]JB.[/MENTION] 's information here, I'll give a quick summary. LT tires the exact same size as a corresponding P metric tires require more inflation pressure to carry the same load. That's not a theory, it's a fact - all of the tire manufacturer's will supply you with information on load - look at the load rating/inflation pressure's in [MENTION=2798]JB.[/MENTION] 's thread.
Yes LT tires are thicker and heavier than corresponding P metric tires - that means they will build up more heat for any given combination of load & inflation pressure. I haven't looked at every single load rating/inflation pressure chart for every size of LT tire - I have looked at them very carefully for the 265/70R17 sizes, and they all start at 35psi. 35 psi is the minimum inflation pressure required to achieve the stamped speed rating for LT tires in this size.
That's not to say that running an LT tire with a Q speed rating at 34 psi means its going to blow up at highway speeds, it just means that you are now operating outside of the engineered parameters of the tire and are cutting into the safety factors of the tire and its ability to dissipate heat at high speed. The faster you go and the lower the inflation pressure you go, the more likely you are to exceed the tires capability to dissipate heat and the more likely you are to have a failure. Because you are operating outside of the tire manufacturers guidelines you are purely guessing at this point.
DOT establishes minimum performance characteristics for tires based on their size, designation and speed rating. P Metric tires in 265/70R17 require a minimum inflation pressure of 26psi to meet in their speed rating. This inflation pressure is below the vehicles manufacturers recommendation, as Toyota is making recommendations based upon even wear, maximizing mileage and handling/braking characteristics. When you change from a P metric tire to a LT tire you have to start at the minimum inflation pressure (35psi in this case) and walk your pressure up from there seeking your optimum inflation pressure bases upon the aforementioned characteristics (handling/braking, mileage, wear).
There is no perfect right number - most seem happiest w/ LT tires inflated between 38-44psi in 265/70R17, but there is a wrong number - THAT'S ANY NUMBER OUTSIDE OF THE TIRE DESIGN PARAMETERS! Below 35psi is outside the design parameters for LT tires in this and it is potentially dangerous to operate LT tires in this size below this min pressure.
Back to the 35" LT tires - those aren't LT 265/70R17 tires and as such they have different design parameters. Referencing the Load Tables [MENTION=2798]JB.[/MENTION] was kind enough to link to:
http://www.toyotires.ca/sites/default/files/loadinflationtable.pdf
We can see that the minimum inflation pressure for LT 35x12.5 R17 tires is 25psi. I can easily see a tire manufacturer suggesting a light weight vehicle with comparatively large tires to run at the min. inflation pressure, so it's not surprising that Jeeps running this size are getting good performance on the street at 25-30psi. I could even see that some may run less than the min 25psi and get away with it because they probably are not running at high speeds for long periods of time, but it doesn't change the fact that they are operating outside of the tire manufactures engineered design parameters and they are "on their own" at that point.
Recommending tire pressures for someone running LT265/70R17E's based on previous experiences running LT35x12.5 R17 on a different vehicle is ignorant. And wrong!
David
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