[SoonerStroker04]

Hello all, I am new to the site but have been the proud owner of several good powerstroke diesels. my current vehicle is an 04 6.0 cc 4x4, i have the 1704 tuner and usually keep it on the low setting, and most of my driving is all hwy around 65mph. My question that I have is I am wanting to put 20x9 wheels on with either a 285 or 295 AT tire and I was wondering if anyone has done this to their truck and what kind of mileage did they lose. i like getting around 16.5 mpg and dont know about losing a lot..sorry for the long post any input will be appreciated....

 

[SoonerStroker04]

Just realized this is not engine related......sorry

 

[lubeowner]

In my sig you will see a link to pictures of my truck. I have 22's and lose about 2 or 3 m.p.g when I put them on.

 

[POS]

I wanted to bump up to 18s and watch the mpg as well. Assistance is needed guys!

 

[ralphinnj]

Your mileage will go down in most cases. Some guys post that it stayed the same, but most factors suggest otherwise. Rolling resistance is higher, weight is higher, diameter is larger (meaning without gear changes, it is harder to generate acceleration with the same power input). I have 285's on 19.5.....lost at least 2 mpg.

RL

 

[04crew]

did you have the speedo corrected for the bigger tires? if you didnt, it will show a lose of mpg .

 

[ralphinnj]

[ QUOTE ]
did you have the speedo corrected for the bigger tires? if you didnt, it will show a lose of mpg .

[/ QUOTE ]

No, I have not made any corrections to the truck, but I can calculate the conversion and keep a spreadsheet that takes the odometer readings and converts them into actual miles. Then I take the actual gallons bought and calculate the true MPG. In my case, it goes something like this:

Conversion for bigger tires:

Old tires (235/85R16) were 31.7" tall (16" for the rim, then 2 times 85% of 235mm); New tires (285/70R19.5) are 35.3" tall. That means for every revolution, I actually travel 1.11 (35.3/31.7) times as far as the odometer said. So if it clocks 100 miles, I actually covered 111 miles. That's easy enough to correct for.

Conversion for gears:

Old gears were 4.10's and new ones are 4.88's. That corrects me in the other direction by 4.88/4.10 = 1.19.

So the net net (I think) is 1.11/1.19 = 0.93. That means for every mile shown on the odometer, I actually travel 0.93 miles.

I think the above is correct, but strangely, it does not match what I see on the road. I know that work is about 35 miles one way. I expected to see 35/0.93 = 37.5 miles on the odometer. In fact, I saw LESS than 35, something like 10% less. So something weird is going on. I also have a Detroit Locker in the rear, but I don't think that matters.

Anyone have an idea why I get what I get?

RL

 

[farmedition]

I hope I can help.
Take your odometer reading and multiply by 1.11.
Take the number you get then divide it by 1.19.
I am supposed to Graduate from GA Tech in about 12 months with a BS degree in Mechanical Eng. But you know what BS stands for and I have been wrong before.
If that doesn't work let me know and I sit down and go through it again but of the top my head this should work.
Thanks

 

[ralphinnj]

That's what I did (read above). The reason I am confused is that it does not jive. Some other factor is fubaring things that I don't understand.

RL

 

[TireFryerSS]

[ QUOTE ]
[ QUOTE ]
did you have the speedo corrected for the bigger tires? if you didnt, it will show a lose of mpg .

[/ QUOTE ]

No, I have not made any corrections to the truck, but I can calculate the conversion and keep a spreadsheet that takes the odometer readings and converts them into actual miles. Then I take the actual gallons bought and calculate the true MPG. In my case, it goes something like this:

Conversion for bigger tires:

Old tires (235/85R16) were 31.7" tall (16" for the rim, then 2 times 85% of 235mm); New tires (285/70R19.5) are 35.3" tall. That means for every revolution, I actually travel 1.11 (35.3/31.7) times as far as the odometer said. So if it clocks 100 miles, I actually covered 111 miles. That's easy enough to correct for.

Conversion for gears:

Old gears were 4.10's and new ones are 4.88's. That corrects me in the other direction by 4.88/4.10 = 1.19.

So the net net (I think) is 1.11/1.19 = 0.93. That means for every mile shown on the odometer, I actually travel 0.93 miles.

I think the above is correct, but strangely, it does not match what I see on the road. I know that work is about 35 miles one way. I expected to see 35/0.93 = 37.5 miles on the odometer. In fact, I saw LESS than 35, something like 10% less. So something weird is going on. I also have a Detroit Locker in the rear, but I don't think that matters.

Anyone have an idea why I get what I get?

RL

[/ QUOTE ]

Go measure your tires with them mounted on the truck. They are approximately 34.7" tall...not 35.3". That is where your mistake is.

 

[ralphinnj]

[ QUOTE ]
Go measure your tires with them mounted on the truck. They are approximately 34.7" tall...not 35.3". That is where your mistake is.

[/ QUOTE ]

Nice try, but that would make it worse! The smaller you make the tires (in the calculation), the lower the net ratio goes. I drive 35 or so miles to work (real miles) and the odometer shows LESS than 35 miles by 2-3 miles. If you are at a ratio less than stock, you should show high, not low.

I mean, with a 4.88 rear and 285/70R19.5's (which measure about 35 and an eighth (I measured the rear duallies since that is more accurate) with 100 psi), I should net out at 0.936 relative to my stock 4.10 gears and 235/85R16's. That means for every mile the odometer shows, I have actually only travelled 0.936 miles. Therefore, to go 35 real miles, my odometer should show 37.4 miles. I do not, I show like 32-33 miles. Something really weird is going on.

RL

 

[jdadamsjr]

R,
you're basing everything off the 35 miles to work...
are you SURE it's 35 miles...
how did you measure that /ubbthreads/images/graemlins/smile.gif

May be the fly in the ointment

night get on an interstate with the mile markers and run about 20 miles to see the indicated miles for your setup...

or get a gps to get an idea... /ubbthreads/images/graemlins/phoney.gif

 

[mikeym]

changing gears affects the odometer? the only way that should be so is if the meter is tied into the transmission? youre revolutions per mile is not changing, youre engine speed is just bumped up a notch by switching to lower gears. correct me if im wrong...