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Old 10-04-2011, 11:57 AM   #1
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What tire size?

I want to move from a P classification to an LT tire for the stronger sidewalls. I'm pulling a Flagstaff 829FKSS with a 2010 Ford F150 Supercab. It has the 255 rear end. Was wondering what tire size you all are using. I've considered the LT265/70/R17 but have been told I should stay with the LT245s. Any input will be greatly appreciated.
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Old 10-04-2011, 12:23 PM   #2
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What's OEM spec for your truck?

Keep in mind going too much larger than OEM spec will raise the truck higher into the air, and also might cause fender rub when locking the wheel from side to side.

Tires are a complicated mess of a subject, especially what PSI to run them at. I'm not really super familiar so I'll just start off this conversation and then back out to let the pros have at it.
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Old 10-04-2011, 01:18 PM   #3
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The truck came with P235/70/R17 tires, so I know the correct P series size. I just don't know which LT tires to use. I want the LT series for the stronger sidewalls. Maybe I should go with LT235s, but some have suggested I go with a larger tire, such as a LT245 or LT265. I thought maybe someone had already gone through this exercise.
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Old 10-04-2011, 01:39 PM   #4
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I would call your tire dealer and ask them for the correct conversion from p to lt . It would be in your best interest since it is there fortay .
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Old 10-04-2011, 01:54 PM   #5
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Quote:
Originally Posted by Chillbilly View Post
The truck came with P235/70/R17 tires, so I know the correct P series size. I just don't know which LT tires to use. I want the LT series for the stronger sidewalls. Maybe I should go with LT235s, but some have suggested I go with a larger tire, such as a LT245 or LT265. I thought maybe someone had already gone through this exercise.

What you want is 17" LT tires that have the same circumferences as your P metric tires otherwise your changing the rear end ratio and creating a speedometer error.

As you're towing you DO NOT want to increase the tire diameter/circumference as it will have the same effect as lowering (numerically) your rear end ratio. This would make acceleration and hill climbing worse.

Dave
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Old 10-04-2011, 02:30 PM   #6
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Chillbilly, keep us posted with what you find out. I want to do the same with my F150 when the time comes.
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Old 10-05-2011, 10:43 AM   #7
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Quote:
Originally Posted by Chillbilly View Post
The truck came with P235/70/R17 tires, so I know the correct P series size. I just don't know which LT tires to use. I want the LT series for the stronger sidewalls. Maybe I should go with LT235s, but some have suggested I go with a larger tire, such as a LT245 or LT265. I thought maybe someone had already gone through this exercise.
I agree with Dave entirely. What is the goal that you are trying to accomplish? A wider tire will not increase the towing capacity of your truck. And there are negatives. As Dave pointed out, you do not want to increase the circumference of your tire. It affects towing capacity, odometer, speedometer, handling characteristics; rolling friction, directional tracking on uneven surfaces, more pressure on steering components, . . . . So, you would need to go to a lower profile tire (eg 70 to 60) to compensate for a wider tire cross section. (70% of 235 is about the same sidewall height as 60% of 265)

Many people think that Bigger is Better whether it is tires, WD bars, springs, etc. That is often (perhaps mostly) not true. I would stick with the stock size tire. If you do go wider (eg. 235 to 265) you definitely need to go lower profile. But I think you might be disappointed.

By the way, I've changed cross section and aspect ratio for winter tires, racing, etc so I have quite a bit of first hand experience with this subject. Sometimes I've gone wider for racing and sometimes narrower for winter traction. Always, always I stick to the same overall diameter. IMO you should proceed cautiously and be aware of the ramifications of your choices. Good Luck!
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Old 10-05-2011, 11:32 PM   #8
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P.S. Going from P to LT in the same size tire shouldn't be an issue. LT load range C (50 psi) is probably plenty though. Ford F150 LT factory tires are Range C. Many tire dealers do not recommend Range E (80 psi) for 1/2 ton trucks. A major tire dealer here in MN refused to put Range E on my 1/2 ton truck. I know that some people swear that is the way to go though.
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Old 10-06-2011, 12:00 AM   #9
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Go to the OEM tire manufacturers web site and do some research. Look for the overall diameter of the tires you have. Now go to the manufacturers web site for the new tires you are considering and find a LT tire that has the same or nearly same diameter. that is the size you want to buy.
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Old 10-06-2011, 06:29 AM   #10
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Donn said it in a sentence. Go to tirerack.com and look at your OEM tire and then the tires in which you are interested. Go to the specifications tab. It will tell you diameter, revs/mile, etc. As Donn says, this is what you want to match. Or if you PM me with your email, I could also send you an Excel spreadsheet that calculates diameter. You enter cross section size, aspect ratio, and rim size. then it calculates for you. It is an easy way to compare tires.
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