Community Forums

w2drfg · 05-06-2014, 07:46 PM

The original tire size on my truck is 245 but the last owner put 285s on it. I am thinking that 265 will give better fuel economy and better pulling. Any suggestions?

caissiel · 05-07-2014, 05:44 AM

Larger tire have very little gain in capacity over the 245s, except the 285s.
Smaller tire have great advantage in fuel mileage and low end torque. I have larger tires on my truck and with 3% increase in diameter I feel it and need to run a bit faster.

w2drfg · 05-07-2014, 06:46 AM

So are you saying to go to 265 or stay with 285. Looking for more MPG

caissiel · 05-07-2014, 07:00 AM

If stock tires carry the load it will be best. 265 don't add much more but 285 does add more capacity. But do they realy fit on the rims properly.

SmokeyWren · 05-07-2014, 08:12 AM

Quote:

Originally Posted by ksmith

The original tire size on my truck is 245 but the last owner put 285s on it. I am thinking that 265 will give better fuel economy and better pulling. Any suggestions?

The math is simple, but you have to know the tire revolutions per mile (revs/mile) for each size tire you're looking at. You can get the revs/mile in the specs for that size tire at tirerack.com.

The difference in effective rear axle ratio, speedo error, odometer error, and trip meter error is the percentage difference in tire revs/mile.

Stock size was LT245/75R16 with 683 revs/mile.

LT285/75R16 have 630 revs/mile

683 minus 630 = 53. divided by 683 = 7.76%.

So assuming your axle ratio is 3.73, then your 3.73 axle ratio "feels like" 3.73 minus 7.76% = 3.44.

You cannot accurately compute MPG unless you first have the speedo calibrated to correct the speedo/odo/trip meters. With a calibrated speedo and the "longer legs" of the taller tires, then you should see a bit better MPG unloaded, but maybe even worse MPG when towing a heavy trailer.

Assuming your speedo was accurate with stock-size tires, and hasn't been recalibrated for the taller tires, then it will show about 65 MPH at a true 70 MPH. When your tripmeter shows 400 miles on a tank of fuel, you would have actually covered 431 miles.

If you put the speedo on 70 MPH, Officer Bob's radar will show that you're actually cruising at over 75 MPH.

LT265/75R16 tires have 668 revs/mile. You can do the math to see the effect on axle ratio and speedo/odo/trip meter error.

wandering1 · 05-07-2014, 08:38 AM

The sticker on the drivers side door jamb will tell you the tire size for the PU you have.

w2drfg · 05-07-2014, 11:32 AM

I like all that technical stuff and do appreciate all of it. I just thought there would be a lot of chevy 2500hd LBZ diesel owners that has already been through this tire size buying delima that could just tell their tire size and mpg. The diesel is going to pull this little 25ft trailer wherever i want to go but I just do not really like the big tires and the 245s look so small. So it looks like the 265 may be ok.

fvstringpicker · 05-07-2014, 05:23 PM

I changed from a 285 to a 265 on my 2007 duramax. Overall I'm happy but I didn't see a big improvement in mileage; maybe a mile per gallon.

SmokeyWren · 05-08-2014, 07:46 AM

Quote:

Originally Posted by ksmith

... I just do not really like the big tires and the 245s look so small. So it looks like the 265 may be ok.

Ford agrees with you.

Back when Ford still installed 16" tires on the F-250, LT265/75Rx16E BSW all-season tires were standard with Lariat trim, and were optional with XLT trim. Stock size with XL and XLT trim were LT235/85R16, which are identical diameter to the LT265/75R16, so viewed from the side the wheel wells were filled the same whether Lariat, XLT or XL trim.

Pikehunter · 05-08-2014, 09:27 AM

Quote:

Originally Posted by ksmith

The original tire size on my truck is 245 but the last owner put 285s on it. I am thinking that 265 will give better fuel economy and better pulling. Any suggestions?

In years gone by, thru trial/error I discovered the 265's are "D" tires and the 285's will rub. I eventually replaced mine with 235's which are "E" rated, carries the load better and gives you better mpg.

Now I have a more substantial rig that I don't worry about mileage as much as how much I can carry safely.

Pikehunter · 05-08-2014, 09:34 AM

Quote:

Originally Posted by wandering1

The sticker on the drivers side door jamb will tell you the tire size for the PU you have.

Not necessarily. It shows what OEM was when it was built, but not what is on the truck now. Just look at the tires themselves.

SmokeyWren · 05-08-2014, 10:52 AM

Quote:

Originally Posted by Pikehunter

In years gone by, thru trial/error I discovered the 265's are "D" tires ...

No, LT265/75R16 tires are available in load range E (Serv. Desc: 123/120) as well as D and C and P-Series. Ford F-250s around 2001 thru 2004 had LT265/75R16E tires as factory standard with Lariat trim and optional with other trim.

I just went to TireRack.com and searched on LT265/75R16, and they had 74 different tires that size. More than half of those tires were load range E (Serv. Desc: 123/120), including different treads by BFGoodrich, Bridgestone, Firestone, Dunlop, General, Goodyear, Hankook, Kumho, Michelin, Pirelli, Yokohama, and others.
http://www.tirerack.com/tires/TireSe...75&diameter=16

So if you cannot find a size LT265/75R16 tire in load range E, you're not trying very hard.

Pikehunter · 05-09-2014, 07:14 AM

Quote:

Originally Posted by SmokeyWren

So if you cannot find a size LT265/75R16 tire in load range E, you're not trying very hard.

Don't want to find a 265. Put the LT235/85R16 "E" tire on if you want better mileage.

SmokeyWren · 05-09-2014, 10:35 AM

Quote:

Originally Posted by Pikehunter

Don't want to find a 265. Put the LT235/85R16 "E" tire on if you want better mileage.

Quibbling, I know, but those two tires are exactly the same diameter (revs/mile), so MPG difference will probably not be enough to measure. The 265/75 is a bit wider than the 235/85, so in theory they should have more drag, but only a tiny bit more. So you will probably get "better mileage" with the narrower tires, but not enough better to measure.

I tried various tire sizes on my '99.5 F-250 PowerStroke and settled on LT235/85R16E for the last years I had that pickup. Because that size was available in a Michelin XPS, which is the best tire on the market, and bigger sizes were not (and still are not) available in the XPS. Not cheap, but worth it:
http://www.tirerack.com/tires/tires....XPSR&tab=Sizes