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Old 03-05-2016, 08:29 AM   #1
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New 10 ply tires help

My 2007 Chev suburban says to have 35lbs PSI for standard tires. I bought TOYA 10 plys for safety and the ride is not real good until it warms up the tires and they stop bouncing. But the gas mileage went out the door. Why such a change in gas mileage? The tires call for a much higher PSI that 35lbs that the dealer put in them. If I raise that up will my mileage get better and will the car computer go nuts because it is higher than it calls for.
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Old 03-05-2016, 08:38 AM   #2
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you need to run the pressure the tire says, or at least very close too it. Mileage will probably not go up, and the ride will be worse. Tires are much heavier and stiffer, but that's what's needed to handle towing safely. The tire sensors can be retrained I believe.
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Old 03-05-2016, 08:42 AM   #3
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You went from a P metric to a LT tire? Did you change wheels too? Those wheels on your 1500 Suburban likely do not have the raring to handle much more pressure than what the tire dealer put in them.
What size did you put on vs what was on it? That likely has fooled your lie o meter which I suspect your using for your fuel economy numbers.
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Old 03-05-2016, 08:45 AM   #4
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heavier tires will effect mileage. Lots more weight to get spinning. Even if size is the same.
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Old 03-05-2016, 08:48 AM   #5
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Quote:
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heavier tires will effect mileage. Lots more weight to get spinning. Even if size is the same.
Exactly! More rotational inertia.
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Old 03-05-2016, 05:48 PM   #6
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Yes. I switched my 2011 F150 to 10 ply and lost 3 litres per 100. But that are great for toeing. Much more sure footed
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Old 03-05-2016, 05:52 PM   #7
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Quote:
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The tires call for a much higher PSI that 35lbs that the dealer put in them.
Am I understanding correct that you are currently running 35 psi in a 10 ply rated tire?
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Old 03-05-2016, 06:37 PM   #8
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This article may help explain my question above. If you can verify my question above, we can go from there:

Tire Types: Tire Load Capacities & Pressure for Euro-metric, P-metric Tires

the main jist of which is this:

'Size-for-size, compared to P-metric tires, LT tires require higher air pressures to carry equivalent loads.'

We'll need to examine your derated OE P-Metric size that you took off your truck, and see what LT size you put on, to actually find out if the above applies to your scenario.
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Old 03-05-2016, 09:51 PM   #9
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Yes that's what the dealer put in them. He said to raise the pressure when pulling a TT. Didn't make sense to me......
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Old 03-05-2016, 09:57 PM   #10
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Yes that's what the dealer put in them. He said to raise the pressure when pulling a TT. Didn't make sense to me......
OK, we need to look into this further. If your truck is handy, can you open the driver side door, and look on the jamb (but it can be on the door itself). There should be a tag there that states the OE tire size and air pressure (front and rear). Can you note this along with the weights on the tag, and then also note the 10 ply tire you purchased, and the size of it.

I can get you the correct info from all of that.

Thanks.
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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:
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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.
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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