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-   -   Michelin LT 275 20s to Replace Goodyear SRA 275 20s....Pressures? (http://www.airforums.com/forums/f463/michelin-lt-275-20s-to-replace-goodyear-sra-275-20s-pressures-125155.html)

interstateflyer 09-09-2014 06:12 PM

Michelin LT 275 20s to Replace Goodyear SRA 275 20s....Pressures?
 
My 2014 Dodge RAM 1500 5.7 Hemi just hit 20K miles and I'm considering replacing the OEM Goodyear SR-A P275/60 R20 Standard Load tires with Michelin M/S2 LT275/65 R20 LR Es.

The door jamb sticker says to inflate the tires to 39 psi. The Goodyear sidewall say 44 psi max. I've been inflating to 44 psi while towing.

I've run the Michelin LTs at or near the max of 80 psi indicated on their sidewall on trucks and trailers.

Should I completely disregard the 39 psi door jamb guideline and go somewhere nearer 80 psi on the Michelins?

Farmer Dan 09-09-2014 06:33 PM

I have the LR E Michelins on both trailers and my '10 F150. I run all of them at 80 PSI per my tire man. He's been in the industry for 35 yrs. He says flex at lower than max inflation will shorten tire life due to more heat. The F 150 had P tires when new and I had troubles so I bit the bullet at 16K mi on them and replaced with the Michelins. I now have 60K + miles on them and will trade the truck or replace them with probably 45% tread left.
Dan

CapriRacer 09-10-2014 06:31 AM

First, I am not a fan of replacing P type tires with LT type tires - and the reason will be clear in a moment.

In order to carry the same load a P275/60R20 does at 39 psi, an LT275/65R20 needs to use 47 psi.

Now since the vehicle's spring, shock damping, and sway bars were designed around a 39 psi tire spring rate, using 47 psi is going to not only cause a rough ride, but the vehicle will tend to overcompensate when encountering a bump, making the vehicle slightly less predictable, handling-wise.

BoldAdventure 09-10-2014 08:29 AM

That's fine, a lot of guys on the Ramforum have gone up to that size tire and all usually inflate to somewhere near 55psi. You can disregard the door jam. I myself plan on switching to that size shortly.

The Goopyears are a terrible tire, and anyone with a Ram who has driven on them knows they kind of suck when towing. I don't have a problem with them when not towing, but they are soft and tend to float.

msmcv51 09-10-2014 08:29 AM

Will rims designed to handle 47 psi be overstressed at 80 psi? :wally:

BoldAdventure 09-10-2014 08:33 AM

Quote:

Originally Posted by msmcv51 (Post 1508656)
Will rims designed to handle 47 psi be overstressed at 80 psi? :wally:

Depends on which rims. The Chrome clads I have are rated to 65psi max.

Wayward 09-10-2014 09:29 AM

I have not figured out any formula for this.

I always put larger and higher load rating tires on my trucks even adding spring leafs or small lifts to get as much tire as I can.

Here is what I do now....

- Ask the tire installer to inflate them 20% below the maximum pressure and take a short drive out of the shop.

- Look carefully at the initial wear pattern on the tread surface. When the tire is new it is fairly easy to see if the tires are touching closer to the "crown" or on the outside edges.

- I then go up or down 5 psi or so, as needed and recheck after another short trip

- After a few iterations it eventually gets close. After a few thousand miles they might show a bit of more permanent wear pattern and I make the final adjustment before rotating the tires.

Phoenix 09-10-2014 12:55 PM

We have a 2008 Tundra with 275/65x18 tires. OEM was BFGoodrich Rugged Trails, a "P" (passenger car) tire with max pressure = 44 psi. They had a soft ride, but were squishy when towing, even when inflated to 44 psi. Plus, they wore out quickly, even though our pickup isn't driven hard.

I replaced the BFGs with same size Michelin LTX M/S2, load range "E" LT tires. I now run 55 psi in the fronts so they wear more evenly, and 65 in the rears when towing (which is about 90% of the time). With the new tires and higher pressures, I don't think the ride is significantly harsher. However, there is a noticeable increase in road feel through the steering wheel; and handling is greatly improved.

It does ride a little more like a truck, and a little less like a passenger car; but it's still rides like a limo when compared to "Hal", our old, 1978, Chevy, 3/4-ton crewcab pickup.

I wouldn't run 80 psi. However, I think you'll find that your pickup will handle better, and your new Michelins will wear more evenly; if you use 44 psi as a minimum, and add a few psi in proportion to your load conditions in accordance with tire charts.

interstateflyer 09-10-2014 09:51 PM

How do you determine the max pressure for your wheels ?


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Wayward 09-10-2014 11:30 PM

Quote:

Originally Posted by interstateflyer (Post 1509034)
How do you determine the max pressure for your wheels ?

Should be stamped or cast on the inside of the rim.

I believe it is the max pressure to be used during mounting when stresses are high, not for normal driving inflation.

overlander63 09-11-2014 02:00 AM

Quote:

Originally Posted by Wayward (Post 1509066)
Should be stamped or cast on the inside of the rim.

I believe it is the max pressure to be used during mounting when stresses are high, not for normal driving inflation.

I am pretty sure that's not the case.
Every tire I've seen has a warning not to exceed 40 psi when mounting.
If a wheel has a max pressure stamped on it, that is the max pressure for operating.

Photobum 09-11-2014 03:41 AM

I run my Michelins at 65psi on my F-150, same as the trailer tires. No problems and having the ten plys makes me feel safer. I have 170M miles on my truck and am on my third set of tires. They wear much longer and better than the original OEM tires that I replaced at 350 miles.

CapriRacer 09-11-2014 04:41 AM

Quote:

Originally Posted by Wayward (Post 1509066)
Should be stamped or cast on the inside of the rim.......

There is no requirement that wheels have such stamping and many do not. So don't be surprised if you can't find a maximum pressure stamped anywhere on the wheel.

interstateflyer 09-11-2014 07:42 PM

Quote:

Originally Posted by CapriRacer (Post 1508624)
First, I am not a fan of replacing P type tires with LT type tires - and the reason will be clear in a moment.

In order to carry the same load a P275/60R20 does at 39 psi, an LT275/65R20 needs to use 47 psi.

Now since the vehicle's spring, shock damping, and sway bars were designed around a 39 psi tire spring rate, using 47 psi is going to not only cause a rough ride, but the vehicle will tend to overcompensate when encountering a bump, making the vehicle slightly less predictable, handling-wise.

Where can I read more about the negative impact of handling when using a stiffer tire with higher pressures?


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