Say Guys , Could one of you tell me if I changed the tire size on my truck if it would effect my fuel mileage ? I 'm running 225-75-16's on it now and at 110k's my tack is showing 2500 rpm's . I was just wondering if I went to a larger tire size to try and get my rpm's down a bit to get better mileage???? Is my thinking right or not ?Alan

4.10's with 33x12.5x16.5 or 235x75x16's will put you tach at 2350 going 70 MPH. i can't say you'll burn less fuel. It takes more energy to get them moving and to stop them, but on the highway they feel solid and roll well enough( i run mud tires).

Alan


What is on the sidewall of the tire isn't necessarily the true tire height as installed, I read an article in 4 Wheeling magazine last year talking about is a 31-33-35" really that tall, bottom line in the article was only way to know for sure is measure the installed height; and use that # to correct your speedo. Air pressure, rim width, tire profile width all played into true tire size.


Mpg and indicated speed can be affected by and change to the combo of tire & wheel. My factory spec by door sticker is 265/75R16 on 16x7x6.5 wheel I run same tire but on 16x8x5.5 wheels my indicated speed is 3-4 mph higher than what my GPS tells me I'm running I don't know how this equates to fuel as that throws the odometer off as well, biggest impact to my mpg is right foothttp://www.dieselplace.com/forum/smileys/HiHi.gif.

Two out of three of the ones I maintain are 5 mph lower than actaul. I've had more than one stop and the laser reading is always 5 mph higher than i thought I was going. I've adopted the habit of going 5 mph slower at all times now, but you can program in new tire sizes for speedo calibration.

I switched from 245/75/R16 to a 285/75/R16 and have noticed that my speedo is now off close to 10%(reads slower than I am actually going). But my mileage has improved slightly all around(although not much as I'm still only getting 15-16). I have 4.10 gears and before my rpm at 70 mph was around 2600, now it is are around 2300(actual speed not measured by speedo). I have noticed a slight decrease in power at highway speeds but still have enough power to go up a 6% grade at 65 mph without kicking out of OD.


I like it a lot better just because it doesn't feel like the engine is running so hard. Also the suspension is pretty stiff and the added sidewall has helped smooth out the ride some.

I read somewhere that the optimal RPM range for fuel economy with these engines is 1800-1900 rpm. So I think the closer you get to that the better mileage you should have. If you really want to get better mileage get axles with higher gear ratios.

My truck has 235-85-R16 tires (these are about the same height as 265-75-R16 tires) and 3:42 gears and if I am cruisin' around 60 mph I can get 27 mpg (imperial) thats about 23mpg for you american folks.

I agree that you have to measure your tires also because the calculated height is usually a bit taller. For a 265-75-R16 the calculated height is about: (26.5cm/2.54 x .75)x2 + (16") = 31.65 inches, measured is usually more like 31 inches.

check out this page to calculate your RPM given tire size

http://www.dalesplace.com/htm/information/rpm_calculator.htm

going with a larger tire will help mileage to a certain extent.


once you go to big, than it takes more fuel to turn them monsters.


i had 3.42 gears on my 95 1500, it was supposed to have 225/75/16's on it and i put 265/75/16's on it. my mileage went to sh*t around 10 or 11 from over 15.


usually one size bigger than stock is ok


but you have to keep in mind that when going with a bigger tire, your final gearing is changed. so with my 265's instead of 245's, my 3.73's are probably now closer to 3.42's. and my speedo is off as well. on my old truck it was off 7 mph at 60. just something you have to remember when driving.

My truck has 235-85-R16 tires (these are about the same height as 265-75-R16 tires) and 3:42 gears and if I am cruisin' around 60 mph I can get 27 mpg (imperial) thats about 23mpg for you american folks.



Actually that is closer to 21.6 mpg US.


An imperial gallon is about 5 US quarts.

Thanks guys , with the small amount of gain that I would get going to a larger tire size it really is not worth it . I'm getting 17.9 mpg around town so I think I'm going to be happy with that , Mite not get as good on the highway, just got to slow down abit . Right ! Thanks again Alan

17.9 around town is pretty darn good


i usually only get 15 drivin around town