From P series tire to LT series tire?

[cairopd1069]

2013 Ram 1500 Crew Cab 2WD 5.7 Hemi. This should generate a lot of responses! I wanted to take my 275 60 20 rear tires off of my factory chrome clad rims. Why? I bought a new travel trailer and was afraid the P series sidewalls might not be strong enough. My mechanic ordered some LT275 65 20 Nitto Crosstek tires for the rear. To the say the handling was erratic is an understatement!! When changing lanes or quick turns it felt like I was pulling a 50' trailer. I was scared to drive it back to the shop. The truck felt like it took the rear 3 to 5 seconds to respond. So, we ordered two more for the front, thinking maybe having LT on the back and P on the front might affect the handling. That did not work, it was worse. Does anyone have any idea what caused the handling to go to crap just because I changed the tires? Needless to say, we put the Goodyears back on.

 

[mjd91]

How much pressure did you have in them?

I have experienced a sort of "walk" with new tires before. They feel like they are swaying back and forth all over the place but stop after they got some miles on them.

 

[cairopd1069]

We first put 60, no change, then 80 (max psi) no change, then I hooked my 6400 lb trailer to see if the added weight would help, no change. The Dodge service manager drove it and he said "Whoa, this is not even safe to drive".

 

[smurfs_of_war]

Well, first off 80 is way too high. Past the safe point for a non LT rim like the OEM 20s. Even 60 is on the high side. looking at the crosstek, that's a pretty mild tread so it shouldn't be yanking you around. I would be curious of a few things:

1. You got a bad tire.
2. The lugs arent torqued
3. The wheel isn't flush

bad tire gets my antennae up immediately though. Inflate them to 55 and do a chalk test first, then look at them real closely. New tires are a bit squirmy until they "bake" a bit, but shouldn't be nearly as bad as you describe.

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[cairopd1069]

I have seen several people on the net mention the max air pressure for a wheel, where are you finding this info? Not disputing what you said, just would like to be able to research it in the future. If I dropped the air pressure down to 55, wouldn't i be defeating the purpose of having an LT tire to pull my Travel Trailer with? Wouldn't the sidewalls give? Thanks for the response.

 

[Csanders1992]

I run 42 in my 305/55/20s they are an lt. Also they are wearing very well so the pressure is right


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[smurfs_of_war]

I have seen several people on the net mention the max air pressure for a wheel, where are you finding this info? Not disputing what you said, just would like to be able to research it in the future. If I dropped the air pressure down to 55, wouldn't i be defeating the purpose of having an LT tire to pull my Travel Trailer with? Wouldn't the sidewalls give? Thanks for the response.

The information is based on the average responses I gathered when I researched it further. Called several shops, dealers, wheel and tire manufactuters. The general consensus is- a rim not rated for LT pressures will not handle the pressure of an LT tire. They can fracture under the constant pressure. They gave no safe number but a common one I heard was 65 max.

Doing some deeper digging on the net verified that info to an extent. The cast aluminum wheels for example would actually crack at the bead lip. Found that gem on a Ford forum. Also TPMS systems can fail as they are not rated for that on a truck that comes with OEM P tires. Unfortunately I can't find any SOLID proof online or stamped on tje wheels. Wish Ram would publish it. I just err on the side of caution. If wheel manufacturers are saying it's a bad idea, there must be a reason for it.

You would still see benefit from an LT tire at 55. The construction is heavier with stiffer sidewalls. You really notice a difference.

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[smurfs_of_war]

Added:

Here is an interesting read that implies the pressure rating is mainly due to the stems. Rubber vs. Steel. 65 and 100 respectively.

http://www.forestriverforums.com/forums/f12/tv-tire-pressure-27123.html

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[BoldAdventure]

Yes, rubber stems are rated much lower.

 

[TRCM]

One possibility is the road. I have had issues in the past with tread patterns like the crossteks (large circumferential grooves) on pavement that is grooved in the direction of travel instead of 90 deg to the direction of travel.

The circumferential grooves on the tire try to stay with the grooves in the road, and give you a floating squirrelly feeling, almost like the tires are way low on air, even thought they aren't.


I had to return some tires due to this, and had some with a different tread pattern (without the circumferential grooves) put on, and had no issues with the same vehicle on the same roads.