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Old 03-05-2016, 11:33 PM   #11
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Okay here we go again. Forget the door sticker when changing from P metric tires to LT tires. Because this is a modification using this as a reference for air pressure is no longer applicable.
Check the sidewall on the tire for the max correct air pressure for the tire you are now installing or have installed. Lets say most 10 ply tires call for 85psi max. This is the pressure to set the tire when fully loaded or towing. Airing down to 65psi is about the lowest you want to go with a 10 ply tire when not loaded or towing. Bigger heavier tire will affect fuel mileage and ride when empty but really make a difference when loaded.
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Old 03-06-2016, 01:12 AM   #12
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I have a 2014 Suburban and I went from P rated to LT rated 10ply. The tire dealer had to reset the air pressure defaults to handle the higher pressure required for the LT tires. I run them at 65 cold. When towing, they go up to almost max rating of 80. When not, they stay under 70. I did not notice a mile/gal decrease.
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Old 03-06-2016, 06:56 AM   #13
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What size tires were on the truck, and what size tires went on?
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Old 03-06-2016, 08:03 AM   #14
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"3 liter per 100" doesn't help me much...

I'm considering this change myself in a month or two. Can anyone describe in MPG what sort of loss I might expect? I currently get 17.5mpg on my daily work commute.
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Old 03-06-2016, 09:45 AM   #15
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The tires are LT275/65R18 Toya's 550KPG 80PSI Cold
The yellow sticker says P265/65R18 S cold pressure says 220kPa, 32PSI Front and Rear
Spare P265/70R17 S 240 KPa, 35 PSI.
Not sure why I have a 17 inch spare? that's crazy.
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Old 03-06-2016, 09:50 AM   #16
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To be of any use to you the tires need to carry 80PSI. But sadly your wheels probably cannot handle that pressure. Lets face it,you got the wrong tires for your SUV. Dealer should never have sold them or installed them on your vehicle.
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Old 03-06-2016, 09:50 AM   #17
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I lost almost 3 miles per gallon but maybe due to tires being under inflated though. Going to raise pressure to see if it helps and will let you know if it effects the ride and mileage. Going LT was expensive almost twice the cost of conventional.
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Old 03-06-2016, 09:53 AM   #18
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Thanks bbcutright, I'll plug in the numbers and post a lot of additional information that may be of help to your situation. It may take me awhile to get it all typed up.

Did it have your OE weights on that tag too, that would save some time?

I'm wanting to see if it's around the 2135 lb mark per tire.
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Old 03-06-2016, 09:54 AM   #19
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Are you saying I need new rims also? Or just regular tires on these old rims. Am I at risk for tire failure running at 80 because of the rims?
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Old 03-06-2016, 09:56 AM   #20
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Quote:
Originally Posted by bbcutright View Post
The tires are LT275/65R18 Toya's 550KPG 80PSI Cold
The yellow sticker says P265/65R18 S cold pressure says 220kPa, 32PSI Front and Rear
Spare P265/70R17 S 240 KPa, 35 PSI.
Not sure why I have a 17 inch spare? that's crazy.
You went up a size with the new tires. They are a larger diameter. Your speedo is off. And, you've lowered the effective rear end gear ratio as well. The engine's going to work harder to pull your TT.
I roll on 20's and have an 18" spare - on a steel wheel. I'll bet you have aluminum wheels and a steel spare wheel too. It's cheaper to equip them that way.
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