LT245/70/R17 VS. P265/70/R17 for use on F150

[Fordiesel69]

I have never grasped the whole tire model gibberish but when I rolled over the 265 and put it next to the 245, the 265 looked like it was taller and was a larger diameter.

Now, why would a 2015 f150 use the 265, and the 2018 uses the 245? Is that to give the engine more power?

 

[Fordiesel69]

And can these be interchanged?

 

[dnewton3]

use tire calculator and the comparison tool

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245/75-17 and 265/70-17 have nearly identical diameters and are essentially interchangeable with no reason to alter the spedo calibration. (I upgraded to the shorter sidewall with wider pattern on my F250). AT 70mph, there would only be a .2mph difference between them.

But ...
245/70-17 and 265/70-17 will be significantly different and would require a spedo calibration change. At 70mph, there would be a 2.5mph difference between them.

 

[racer12306]

Tire Numbers broken down...

265 - The section width of the tire in millimeters. This is not the tread width, it's basically this width of the widest part of the time.

70 - This is the sidewall height in the form of a ratio, 70%. The sidewall will be 70% of the section width.

17 - Obviously the wheel diameter.

When you're calculating the height of a tire, use the calculator dnewton posted, but if you want to know the nuts and bolts....

265*.7 = 185.5mm

Times 2 (top and bottom) = 371mm

Convert to inches (divide by 25.4) = 14.61"

Add in the wheel diameter (+17) = 31.61" of total tire height.

 

[MNgopher]

Recognize that the F150 comes with multiple tire and wheel sizes - depends on the year, trim level, drivetrain, and ordered options.

Why a 2015 would come with one size and the 2018 another again depends on trim level, drivetrain, and ordered options.

(As an example, my 2106 F150 came from the factory with a tire that was an additional option above the base trim level and drivetrain.)

 

[MParr]

I have never grasped the whole tire model gibberish but when I rolled over the 265 and put it next to the 245, the 265 looked like it was taller and was a larger diameter.

Now, why would a 2015 f150 use the 265, and the 2018 uses the 245? Is that to give the engine more power?

The XL, XLT, Platinum have several different wheel and tire combinations from the factory.
Look at the placard on the driver’s side door post.
When there is a LT in front of the size, that is going to be a load range C or load range E tire. Those tires are generally for 3/4 ton or above. Like the F-250 and etc. Personally, I wouldn’t use an LT tire on a F-150.

 

[goingplacesanddoingstuff]

I have never grasped the whole tire model gibberish but when I rolled over the 265 and put it next to the 245, the 265 looked like it was taller and was a larger diameter.

Now, why would a 2015 f150 use the 265, and the 2018 uses the 245? Is that to give the engine more power?

70% of 245 is less than 70% of 265, so this makes sense. More likely is that different submodels spec different size tires, as already mentioned.

 

[dnewton3]

Now, why would a 2015 f150 use the 265, and the 2018 uses the 245? Is that to give the engine more power?

I'm going to presume you're not serious about the "power" question? Tires don't give "power" to anything. "Power" is defined as work per unit of time.

Tire size affects the thrust force at the road surface; the size affects the radius of the torque arm represented by the wheel/tire/axle relationship. Given that a fixed amount of torque comes at any single moment from the axle (drivetrain), then the larger the tire, the less thrust it can translate to the road surface.
T= F x D (torque is a product of the applied force multiplied by the vector distance relative to the axis of rotation)
When the product is a fixed value, then the two contributing elements are inversely proportional in relation.
If torque were the fixed value, then doubling the distance would halve the force.
So a larger tire actually produces less forward thrust (force) at the road surface, all other things being constant.

Road surface velocity is also affected by tire size, but in the opposite sense. Presuming enough torque is present to create sufficient minimum required thrust, then the relative road velocity will increase with an accompanying increase in the size of the tire.


Ya can't cheat the laws of physics!

 

[meep]

the 2018 models I'm aware of use a 265 - maybe a 265/65 or 265/70. Much wider than a 245. This is with the aluminum 18 wheel. It's possible that a special-order utility version might have 17" wheels and a 245 width tire.

 

[MNgopher]

Availible wheel sizes on the F150 in 2018 are 17", 18", 20", and 22".

In 2018 17" wheels come on XL and XLT trim trucks standard, but upgrading to sport or chrome or off road packages often bumps you to 18".

The 17" Wheel is also standard on the Raptor.

Note also in the table below that the 245's are also available on the heavy duty payload package or off road packages.

The whole grid of tire sizes and options as found in the Ford Brochure is:

In other words, the F150 comes with a huge variety of tire sizes and types.

In my case, I have the LT tires on an off road package (FX4) equipped truck, which got me Load Range C LT tires that have a weight rating near the P series tire, but with deeper, more aggressive tread. I've run one 1/2 of the OEM tires for 90,000 miles and still have decent tread. The other 1/2 had to be replaced due to a non repairable flat.

 

[Fordiesel69]

Was not joking about the power issue. I was serious. Let me explain what I am talking about.

What I failed to mention is my dads 2015 F150 came with a spare set of nice summer tires. When he brought it home it already had mounted awsome winter tires with 10/32 tread, and before I paid money to have them de-mounted and placed in storage, I removed the LT245/70/17 from my 2018 F-150 and installed his rims and tires P265/70/17. I took it for a test drive and could really feel an acceleration and power difference as they are "taller" tires.

When I put my factory rims and tires (LT245/70/17) back on, the acceleration and power was back to normal.

I dont think a speedo calibration would fix this. Would it? Becuase mine has the added towing package that his 2015 lacks, maybe that is why? Im not sure.....

 

[dumkid]

Was not joking about the power issue. I was serious. Let me explain what I am talking about.

What I failed to mention is my dads 2015 F150 came with a spare set of nice summer tires. When he brought it home it already had mounted awsome winter tires with 10/32 tread, and before I paid money to have them de-mounted and placed in storage, I removed the LT245/70/17 from my 2018 F-150 and installed his rims and tires P265/70/17. I took it for a test drive and could really feel an acceleration and power difference as they are "taller" tires.

When I put my factory rims and tires (LT245/70/17) back on, the acceleration and power was back to normal.

I dont think a speedo calibration would fix this. Would it? Becuase mine has the added towing package that his 2015 lacks, maybe that is why? Im not sure.....

sigh... the engine is making the same power it always has. speedo calibration will just correct your speedometer reading. the bigger tires effectively change the gear ratios of your truck. the bigger tires are making your truck work a little bit harder and that's the acceleration difference you feel.

 

[tiger862]

The only way different tire sizes give different seat of the pants feel, is the differential gearing. With taller tires the gear ratio might be 323 however if you have shorter tires gear ratio could be 273. So if you put 33 inch tires on 273 ratio it would be sluggish, however if 410 it feels more low end power. Tire size and gear ratio go hand in hand.

 

[goingplacesanddoingstuff]

sigh... the engine is making the same power it always has. speedo calibration will just correct your speedometer reading. the bigger tires effectively change the gear ratios of your truck. the bigger tires are making your truck work a little bit harder and that's the acceleration difference you feel.

You’re both correct. If you put it in a dyno and measure whp, it’ll measure lower. Saying larger wheels lower power is not inaccurate in this sense. They just reduce power by raising gear ratios.

 

[Fordiesel69]

So another thread bump.

Assuming I can get my speedo corrected, and with my axle gears being 3.73:1 , would using the larger diameter P265/70/17 over the factory LT245/70/17 give a light bump in fuel economy? Reason I ask, is most likely the engine will be operating at a very slightly less RPM for the given speed.

 

[XJRiver]

I've went up to 265's on a 2013 Silverado. The difference was a more comfortable ride and a higher load index number. The small alteration in speedometer accuracy didn't affect real world driving dynamics at all.