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Old 09-21-2017, 03:31 PM
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Tire Air Pressure

I recently replaced my stock Michelins 275/65/20 with Nitto Terra Grappler G2's 295/65/20. A tad taller, wider, no raised white letters and
a little more aggressive. Both tires have max 80psi. The label on my driver side door jam(SCCL) reflects cold tire inflation: front 60 rear 65psi.
When I picked up my truck from dealer when new, dealer had Michelins at 75 front and rear.
The Terra Grapplers were installed at 65 front and rear. I have experienced some loss in mpg which was expected but maybe not as much as I'm seeing 1.5mpg +- . I guess what I'm getting at...why would dealer put pressure at 75psi when door specs and OM state 60 and 65psi ? Also, what are some of y'all (I'm from tx) running pressures at empty and not pulling ?
I'm looking to increase mine back up in increments, and see if I can find the sweet spot of ride comfort vs mileage.
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Old 09-21-2017, 03:45 PM
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My door specs are same as yours (60/65). Again, like your truck had, I have the OEM Michelin tires. I run 50/50 to improve ride, which it helped immensely. My MPG is good IMO at 13.5 around town and 17.5 hwy avoiding long running speeds above 70mph. I did have to FORScan my TPMS settings to avoid the nag light.
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Old 09-21-2017, 04:06 PM
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Personally I wouldn't put much thought into why the tire pressures were set at those levels by 2 different people. My experience is whenever I get tires installed or take delivery of a vehicle I always have to set the pressures to correct them. It's sad but you just cannot count on dealerships or tire install companies to get things like tire pressure correct unless you specifically ask for a certain pressure. Even torque on lug nuts should be specifically asked for. Otherwise they will just use their air tools and it becomes pretty random at what you get.
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Old 09-21-2017, 05:55 PM
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Because new vehicles can sit for such long periods dealerships over-inflate the tires to prevent flat spots.

The Grapplers will definitely negatively impact mileage compared to the Michelins.

You can run your tires to suit your loads but the only thing i can add is truck's sensor/computer can throw up the inflation warning light on the dash if you stray too far from 60 psi. The Forscan machine can adjust for this from what I have been told.
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Old 09-21-2017, 05:58 PM
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72 Front 70 rear 295 70 18 Michelins on 18X9 Methods
My door says 75 front 80 rear
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Old 09-21-2017, 07:27 PM
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It has been my experience with a few different Ford models (Excursions, Mustangs, Explorers and an F150) that the door jamb sticker-listed tire pressures are consistently too low. I think my F150 specified 35 PSI F & R, but I had to run them at 45 PSI to get even wear from the tires. The Excursions were run at 80 PSI and had no uneven wear. With the latest Explorer, I ran the specified 35 PSI and the outer edges began to wear prematurely ... running 40 now on replacement tires. Currently running 65 PSI F & R on the F250 20" Michelins and may bump them up to 70 (door spec recommends 60 F & 65 R).
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Old 09-21-2017, 09:58 PM
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What exactly is PSI?

The term PSI tells us more about tire pressure than just a simple number on the door sticker. It's pounds per square inch, right? We all know that.

But did you know that a tire at 50psi with a contact patch of 50 square inches is holding up exactly 2500lbs? 50x50=2500. If you use chalk or wet paint to measure the area of where the tire pushes down on the road, that's your contact patch. Imagine your truck parked on a huge piece of glass. You could literally measure your contact patches from underneath. Pounds per square inch.

I don't know offhand how many square inches your or my contact patch is...but I know that with a bigger, taller, fatter tire you can safely have a bigger contact patch with less pressure than a stock tire. You can run less PSI in a bigger tire and still support the same load. Because your contact patch is bigger. And square inches times pressure equals PSI.

Let's say you pump up that same tire to 100psi. What happens to your contact patch? It gets smaller. It has to be half of what it is at 50psi. That's the physics of the situation.

So, long story short, you can lower your air pressure if you go to bigger tires, and still safely support the same load (assuming we're talking about the same load range for all tires involved). And you'll get slightly better ride to boot, but you'll consume more fuel as the bigger tire flexes more and offers more air resistance.

John Cappa did a great writeup on all this years ago in Four Wheeler mag. He's gone solo now, but you can follow him on FB.

if you can find that old Four Wheeler article, it tells you exactly how to measure your contact patches for each wheel, and calculate optimum PSI based on the weight supported by each tire. It's not exactly the same left to right. When guys build wild 4x4 custom buggies, there is no tire sticker on the door frame.
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Old 09-22-2017, 07:52 AM
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I've found that 60 P.S.i. all the way around give me a decent ride as well as acceptable fuel economy. Aftermarket tires with aggressive tread will normally reduce the MPG just by the nature of the tread design. If the weigh differences were measured you would very likely find that the new tires are a little heavier that the OEM Michelin tires.
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Old 09-22-2017, 07:59 AM
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Quote:
Originally Posted by shortride View Post
I've found that 60 P.S.i. all the way around give me a decent ride as well as acceptable fuel economy. Aftermarket tires with aggressive tread will normally reduce the MPG just by the nature of the tread design. If the weigh differences were measured you would very likely find that the new tires are a little heavier that the OEM Michelin tires.
I agree with all of this. Yet I was shocked today to see the BFG KO2ís are 1 lb lighter than the stock/original equipment Michelinís. I would have guessed they would have been 3-5 lbs heavier due to their more off road/ rugged design.
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Old 09-22-2017, 10:07 AM
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Quote:
Originally Posted by Redrockerstl55 View Post
I agree with all of this. Yet I was shocked today to see the BFG KO2ís are 1 lb lighter than the stock/original equipment Michelinís. I would have guessed they would have been 3-5 lbs heavier due to their more off road/ rugged design.
I was going to buy them. They have a good reputation. But on their web site there are a lot of unhappy customers complaining about tread life as low as 20k miles. So I chose Nittos Grappler G2 tires which come a treadware warranty from Nitto.

Michelin owns BFG so the tech should be very good. But Michelin is also obsessed with green and other SJW causes. No thanks.
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Old 09-22-2017, 10:09 AM
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Quote:
Originally Posted by shortride View Post
SNIP
If the weigh differences were measured you would very likely find that the new tires are a little heavier that the OEM Michelin tires.
Keep your wheels in mind too. Metal is heavier than rubber. I went down to 18" wheels while going up to 37s, to help offset the weight gain of the overall pack.
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Old 09-22-2017, 10:32 AM
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Iíve been checking out the brand new Continental Terrain Contact A/T. I have always loved my Continentals.

These tires have received really strong initial reviews. Although they are more like the Michelinís...kinda designed for people who are 90% on road/10% off road.
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Old 09-22-2017, 01:07 PM
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I have the same tires, they air them up so the TPMS don't alarm. I've found that they ride best under 60 PSI - so I set them at 55 cold . The load rating of these tires is much higher too. I had to do a forscan mod to change the TPMS monitor to 55 PSI. They are heavy compared to the stockers. I kept the stockers for long road trips
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Old 09-22-2017, 06:22 PM
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Stupid question, but what do you do if the dealer put magical nitrogen in the tires? I realize that F1 cars might, I mean might benefit from nitrogen in their tires as there are temperature concerns at their MPH and G's. But my TPMS shows my tires are all over the map from the dealer. What do I do? Take it to the dealer for magical nitrogen or fire up my DeWalt compressor and just bring them all up to 50-60 psi range. Atmosphere is 70% N anyway. I always thought this nitrogen deal was a scam. I did not intend to hijack this thread, but it was about air pressure.
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Old 09-22-2017, 06:42 PM
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It's a scam if they charge $49.95. Tell 'em "All I need is the Air that I breathe" and not paying for boutique tire stuff or anybody's boat payment.
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